Merge m3a: brokerd's decision path (M3a)

Tasks 01 to 22, the review, and task 23 (the review fixes, with a second,
independent review of them). The one conflict, docs/implementer-lessons.md,
had the same T18 and T19 on both sides; m3a's T20 to T22 follow them.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

AGENTS.md

@@ -69,6 +69,10 @@ These come from defects found in review. The evidence is in `docs/implementer-le
 - A rule about one path applies to every path that does the same thing, including early returns
   and error paths the task did not walk through.
 - A file that exists but cannot be read is an error. Only a missing file may count as absent.
+- A file your own program can create before it writes anything must load like an empty one. Test
+  the state a crash leaves behind, not only the states you write on purpose.
+- When two programs must agree about a set of things (which files are a log, which names are ids),
+  one of them deciding alone is a bug. Write the case that walks both.
 
 ## The gate
 

Cargo.lock

@@ -7,6 +7,9 @@ name = "brokerd"
 version = "0.1.0"
 dependencies = [
  "proto",
+ "serde",
+ "serde_json",
+ "toml",
 ]
 
 [[package]]

Makefile

@@ -6,10 +6,14 @@ gate:
 	cargo fmt --all --check
 	cargo clippy --workspace --all-targets --locked --offline -- -D warnings
 	cargo test --workspace --locked --offline
+	cargo build --workspace --locked --offline
+	BOXMAKER_BROKERD=$(CURDIR)/target/debug/brokerd \
+		cargo test -p loopd --test end_to_end --locked --offline -- --ignored
 	cargo deny --offline check bans licenses sources
 	sh scripts/check-lines.sh
 	sh scripts/check-crate-deps.sh
 	sh scripts/check-dep-docs.sh
+	sh scripts/check-runbook.sh
 	sh scripts/test-gate-scripts.sh
 	@echo "gate: ok"
 

crates/brokerd/Cargo.toml

@@ -10,3 +10,6 @@ workspace = true
 
 [dependencies]
 proto.workspace = true
+serde.workspace = true
+serde_json.workspace = true
+toml.workspace = true

crates/brokerd/src/admin.rs

@@ -0,0 +1,129 @@
+//! One `admin.sock` connection: list, approve, refuse, check the grants; and expiry, which answers
+//! an approval the same way. Whoever takes an entry out of the table answers it.
+
+use std::os::unix::net::UnixStream;
+
+use crate::approvals::Entry;
+use crate::broker::{Broker, forbid, read_request, send};
+use crate::grants;
+use crate::ledger::{Answer, Answered};
+use proto::{
+    ApprovalList, Approve, ApproveResult, DecisionRecord, DenyReason, Empty, ErrorCode,
+    GrantsReport, Message, Refuse, Timestamp, WireError,
+};
+
+/// The Approval record's `by` for answers through admin.sock.
+pub const BY: &str = "bxctl";
+/// The refusal `bxctl` sees when the ledger could not record it.
+pub const REFUSAL_INTERNAL: &str =
+    "the refusal could not be recorded; the call is denied; see docs/runbook.md#audit-unavailable";
+
+/// Whoever takes an entry out of the table answers it: the ledger records the answer, then the
+/// verdict goes to the waiting thread, and only then is the record returned.
+pub fn answer(broker: &Broker, entry: Entry, answer: Answer, now: Timestamp) -> DecisionRecord {
+    // 1. The grants as they are now: an approval decides again with them.
+    let grants = broker.grants();
+
+    // 2. Record the answer; the ledger writes the Approval record and returns the verdict and
+    //    outcome together, or the audit-unavailable denial when it could not record.
+    let Entry { info, ask, reply } = entry;
+    let Answered { verdict, outcome } =
+        broker
+            .ledger()
+            .answer(ask, info.approval, answer, &grants, now);
+
+    // 3. The record is written either way; if the waiting thread is gone, there is nothing else to do.
+    if reply.send(verdict).is_err() {
+        broker.log(&format!(
+            "brokerd: approval {} was answered after its requester had gone",
+            info.approval
+        ));
+    }
+
+    // 4. The outcome the caller reports to bxctl.
+    outcome
+}
+
+/// Answer every approval whose time has run out, the same way an owner's refusal would.
+pub fn expire_due(broker: &Broker, now: Timestamp) -> usize {
+    let entries = broker.table().take_expired(now);
+    let count = entries.len();
+    for entry in entries {
+        answer(broker, entry, Answer::Expired, now);
+    }
+    count
+}
+
+/// Serve one `admin.sock` connection from bxctl: one request, one final answer.
+pub fn handle(mut stream: UnixStream, broker: &Broker) {
+    // 1. The peer is gone before it speaks, or its frame is malformed: answer and return.
+    let Some(envelope) = read_request(&mut stream) else {
+        return;
+    };
+    let id = envelope.id;
+    let msg = envelope.msg;
+    let now = Timestamp::now();
+
+    // 2. By message kind. `take` is the only way in: no one looks at an entry and removes it later.
+    let response = match msg {
+        Message::Approvals(_) => Message::ApprovalList(ApprovalList {
+            items: broker.table().list(),
+        }),
+        Message::Approve(Approve { approval }) => match broker.table().take(approval) {
+            None => Message::Error(WireError {
+                code: ErrorCode::NoSuchApproval,
+                detail: format!("approval {approval} is not pending"),
+            }),
+            Some(entry) => {
+                let outcome = answer(
+                    broker,
+                    entry,
+                    Answer::Approved {
+                        by: Some(BY.to_string()),
+                    },
+                    now,
+                );
+                Message::ApproveResult(ApproveResult { outcome })
+            }
+        },
+        Message::Refuse(Refuse { approval, reason }) => match broker.table().take(approval) {
+            None => Message::Error(WireError {
+                code: ErrorCode::NoSuchApproval,
+                detail: format!("approval {approval} is not pending"),
+            }),
+            Some(entry) => match answer(
+                broker,
+                entry,
+                Answer::Refused {
+                    by: Some(BY.to_string()),
+                    reason,
+                },
+                now,
+            ) {
+                DecisionRecord::Denied {
+                    reason: DenyReason::ApprovalRefused,
+                } => Message::Ok(Empty {}),
+                // The refusal could not be recorded: bxctl gets an Internal, the waiting call a denial.
+                _ => Message::Error(WireError {
+                    code: ErrorCode::Internal,
+                    detail: REFUSAL_INTERNAL.to_string(),
+                }),
+            },
+        },
+        // bxctl grants check shows the problems itself and must not use up the print-once of the broker.
+        Message::CheckGrants(_) => {
+            let problems = match grants::load(&broker.cfg().paths.grants) {
+                Ok(_) => Vec::new(),
+                Err(problems) => problems,
+            };
+            Message::GrantsReport(GrantsReport { problems })
+        }
+        other => {
+            forbid(broker, &mut stream, id, &other, "admin.sock");
+            return;
+        }
+    };
+
+    // 3. The final frame; a failed send is ignored.
+    let _ = send(&mut stream, id, true, response);
+}

crates/brokerd/src/approvals.rs

@@ -0,0 +1,76 @@
+//! The pending-approval table: whoever takes an entry out answers it, and everyone else finds it
+//! gone. In memory only.
+
+use crate::policy::{Ask, Decision};
+use proto::{DenyReason, PendingApproval, Timestamp};
+use std::collections::BTreeMap;
+use std::sync::mpsc::{Receiver, Sender, channel};
+use std::sync::{Mutex, MutexGuard};
+
+/// What the waiting thread is told. Boxed: clippy's `large_enum_variant` rejects it unboxed.
+#[derive(Debug)]
+pub enum Verdict {
+    Run(Box<Decision>),
+    Denied(DenyReason),
+}
+
+#[derive(Debug)]
+pub struct Entry {
+    pub info: PendingApproval,
+    pub ask: Ask,
+    pub reply: Sender<Verdict>,
+}
+
+#[derive(Debug, Default)]
+pub struct Table {
+    entries: Mutex<BTreeMap<u64, Entry>>,
+}
+
+impl Table {
+    pub fn new() -> Table {
+        Table {
+            entries: Mutex::new(BTreeMap::new()),
+        }
+    }
+
+    fn lock(&self) -> MutexGuard<'_, BTreeMap<u64, Entry>> {
+        self.entries
+            .lock()
+            .unwrap_or_else(|poisoned| poisoned.into_inner())
+    }
+
+    pub fn insert(&self, info: PendingApproval, ask: Ask) -> Receiver<Verdict> {
+        let (sender, receiver) = channel();
+        self.lock().insert(
+            info.approval,
+            Entry {
+                info,
+                ask,
+                reply: sender,
+            },
+        );
+        receiver
+    }
+
+    pub fn take(&self, id: u64) -> Option<Entry> {
+        self.lock().remove(&id)
+    }
+
+    pub fn take_expired(&self, now: Timestamp) -> Vec<Entry> {
+        // One lock: taking it once per id would let an approve slip in between.
+        let mut entries = self.lock();
+        let ids: Vec<u64> = entries
+            .values()
+            .filter(|entry| now >= entry.info.expires)
+            .map(|entry| entry.info.approval)
+            .collect();
+        ids.iter().filter_map(|id| entries.remove(id)).collect()
+    }
+
+    pub fn list(&self) -> Vec<PendingApproval> {
+        self.lock()
+            .values()
+            .map(|entry| entry.info.clone())
+            .collect()
+    }
+}

crates/brokerd/src/args.rs

@@ -0,0 +1,354 @@
+//! Tool arguments and the form checks for paths, hosts and URLs.
+//!
+//! `parse` turns the model's argument string into a typed value; the free functions say whether a
+//! path, a host or a URL is well formed. The module is pure: no I/O, no clock. Everything it reads
+//! was written by the model, so it is treated as hostile.
+
+use serde::{Deserialize, Serialize};
+use std::fmt;
+
+/// Maximum length, in bytes, of a path.
+pub const MAX_PATH: usize = 4096;
+/// Maximum length, in bytes, of a URL.
+pub const MAX_URL: usize = 2048;
+
+/// The four tools the broker can dispatch to.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ToolName {
+    ReadFile,
+    WriteFile,
+    Shell,
+    HttpFetch,
+}
+
+impl ToolName {
+    /// The four tools, in the order listed in the interface.
+    pub const ALL: [ToolName; 4] = [
+        ToolName::ReadFile,
+        ToolName::WriteFile,
+        ToolName::Shell,
+        ToolName::HttpFetch,
+    ];
+
+    /// Parse a tool name as written by the model.
+    pub fn parse(name: &str) -> Option<ToolName> {
+        match name {
+            "read_file" => Some(ToolName::ReadFile),
+            "write_file" => Some(ToolName::WriteFile),
+            "shell" => Some(ToolName::Shell),
+            "http_fetch" => Some(ToolName::HttpFetch),
+            _ => None,
+        }
+    }
+
+    /// The name as written by the model.
+    pub fn as_str(self) -> &'static str {
+        match self {
+            ToolName::ReadFile => "read_file",
+            ToolName::WriteFile => "write_file",
+            ToolName::Shell => "shell",
+            ToolName::HttpFetch => "http_fetch",
+        }
+    }
+}
+
+/// A parsed set of tool arguments, one variant per tool.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum ToolArgs {
+    ReadFile {
+        path: String,
+    },
+    WriteFile {
+        path: String,
+        content: String,
+    },
+    Shell {
+        command: String,
+        cwd: Option<String>,
+    },
+    HttpFetch {
+        url: String,
+        host: String,
+    },
+}
+
+impl ToolArgs {
+    /// The tool these arguments belong to.
+    pub fn tool(&self) -> ToolName {
+        match self {
+            ToolArgs::ReadFile { .. } => ToolName::ReadFile,
+            ToolArgs::WriteFile { .. } => ToolName::WriteFile,
+            ToolArgs::Shell { .. } => ToolName::Shell,
+            ToolArgs::HttpFetch { .. } => ToolName::HttpFetch,
+        }
+    }
+
+    /// The arguments written out again, so two spellings of one value look the same.
+    ///
+    /// Fields come out in the table's order, an absent `cwd` is left out, and `host` is never
+    /// written because it is not an argument. A serialization failure yields `"{}"`.
+    pub fn canonical_json(&self) -> String {
+        match self {
+            ToolArgs::ReadFile { path } => {
+                let value = ReadFileArgs { path: path.clone() };
+                serde_json::to_string(&value).unwrap_or_else(|_| "{}".to_string())
+            }
+            ToolArgs::WriteFile { path, content } => {
+                let value = WriteFileArgs {
+                    path: path.clone(),
+                    content: content.clone(),
+                };
+                serde_json::to_string(&value).unwrap_or_else(|_| "{}".to_string())
+            }
+            ToolArgs::Shell { command, cwd } => {
+                let value = ShellArgs {
+                    command: command.clone(),
+                    cwd: cwd.clone(),
+                };
+                serde_json::to_string(&value).unwrap_or_else(|_| "{}".to_string())
+            }
+            ToolArgs::HttpFetch { url, .. } => {
+                let value = HttpFetchArgs { url: url.clone() };
+                serde_json::to_string(&value).unwrap_or_else(|_| "{}".to_string())
+            }
+        }
+    }
+}
+
+/// Why `parse` refused a set of arguments.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum ArgsError {
+    /// The arguments were not the right shape for the tool.
+    Shape(String),
+    /// A path was not well formed.
+    Path(String),
+    /// A URL gave no valid host.
+    Url(String),
+}
+
+impl fmt::Display for ArgsError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            ArgsError::Shape(text) => write!(f, "invalid argument shape: {text}"),
+            ArgsError::Path(text) => write!(f, "invalid path: {text}"),
+            ArgsError::Url(text) => write!(f, "invalid url: {text}"),
+        }
+    }
+}
+
+impl std::error::Error for ArgsError {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        None
+    }
+}
+
+/// The argument shape for one tool, decoded then re-serialised.
+#[derive(Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
+struct ReadFileArgs {
+    path: String,
+}
+
+#[derive(Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
+struct WriteFileArgs {
+    path: String,
+    content: String,
+}
+
+#[derive(Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
+struct ShellArgs {
+    command: String,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    cwd: Option<String>,
+}
+
+#[derive(Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
+struct HttpFetchArgs {
+    url: String,
+}
+
+/// Decode `arguments` for `tool` into a typed value.
+pub fn parse(tool: ToolName, arguments: &str) -> Result<ToolArgs, ArgsError> {
+    match tool {
+        ToolName::ReadFile => {
+            let value: ReadFileArgs = match serde_json::from_str(arguments) {
+                Ok(value) => value,
+                Err(error) => return Err(ArgsError::Shape(error.to_string())),
+            };
+            if !valid_path(&value.path) {
+                return Err(ArgsError::Path(value.path));
+            }
+            Ok(ToolArgs::ReadFile { path: value.path })
+        }
+        ToolName::WriteFile => {
+            let value: WriteFileArgs = match serde_json::from_str(arguments) {
+                Ok(value) => value,
+                Err(error) => return Err(ArgsError::Shape(error.to_string())),
+            };
+            if !valid_path(&value.path) {
+                return Err(ArgsError::Path(value.path));
+            }
+            Ok(ToolArgs::WriteFile {
+                path: value.path,
+                content: value.content,
+            })
+        }
+        ToolName::Shell => {
+            let value: ShellArgs = match serde_json::from_str(arguments) {
+                Ok(value) => value,
+                Err(error) => return Err(ArgsError::Shape(error.to_string())),
+            };
+            if let Some(cwd) = &value.cwd
+                && !valid_path(cwd)
+            {
+                return Err(ArgsError::Path(cwd.clone()));
+            }
+            Ok(ToolArgs::Shell {
+                command: value.command,
+                cwd: value.cwd,
+            })
+        }
+        ToolName::HttpFetch => {
+            let value: HttpFetchArgs = match serde_json::from_str(arguments) {
+                Ok(value) => value,
+                Err(error) => return Err(ArgsError::Shape(error.to_string())),
+            };
+            let host = match url_host(&value.url) {
+                Some(host) => host.to_string(),
+                None => return Err(ArgsError::Url(value.url)),
+            };
+            Ok(ToolArgs::HttpFetch {
+                url: value.url,
+                host,
+            })
+        }
+    }
+}
+
+/// A path is well formed if it is at most `MAX_PATH` bytes, has no NUL, starts with `/`, and every
+/// component is a whole, non-dot name. The root `/` alone is valid.
+pub fn valid_path(path: &str) -> bool {
+    if !(1..=MAX_PATH).contains(&path.len()) || path.contains('\0') {
+        return false;
+    }
+    let rest = match path.strip_prefix('/') {
+        Some(rest) => rest,
+        None => return false,
+    };
+    if rest.is_empty() {
+        return true;
+    }
+    for component in rest.split('/') {
+        if component.is_empty() || component == "." || component == ".." {
+            return false;
+        }
+    }
+    true
+}
+
+/// Is `path` inside `grant_path`, by whole components rather than by bytes?
+pub fn inside(grant_path: &str, path: &str) -> bool {
+    match path.strip_prefix(grant_path) {
+        Some(rest) => rest.is_empty() || rest.starts_with('/') || grant_path == "/",
+        None => false,
+    }
+}
+
+/// A host label is 1 to 63 bytes of `a-z`, `0-9` or `-`, and neither starts nor ends with `-`.
+fn valid_label(label: &str) -> bool {
+    if !(1..=63).contains(&label.len()) {
+        return false;
+    }
+    let bytes = label.as_bytes();
+    if bytes.iter().next() == Some(&b'-') || bytes.iter().last() == Some(&b'-') {
+        return false;
+    }
+    bytes
+        .iter()
+        .all(|&byte| matches!(byte, b'a'..=b'z' | b'0'..=b'9' | b'-'))
+}
+
+/// A host is 1 to 253 bytes of dot-separated labels, each a whole non-dot name, and the last label
+/// starts with a letter. That last rule keeps out every spelling of an IPv4 address.
+pub fn valid_host(host: &str) -> bool {
+    if !(1..=253).contains(&host.len()) {
+        return false;
+    }
+    let labels: Vec<&str> = host.split('.').collect();
+    if labels.len() < 2 {
+        return false;
+    }
+    for label in &labels {
+        if !valid_label(label) {
+            return false;
+        }
+    }
+    match labels.iter().last() {
+        Some(last) => matches!(last.bytes().next(), Some(byte) if byte.is_ascii_lowercase()),
+        None => false,
+    }
+}
+
+/// A host, or `*.` followed by a host. Nothing else.
+pub fn valid_host_pattern(pattern: &str) -> bool {
+    match pattern.strip_prefix("*.") {
+        Some(base) => valid_host(base),
+        None => valid_host(pattern),
+    }
+}
+
+/// Does `pattern` match `host`? Without `*.` the strings must be equal; with `*.base` the host must
+/// end in `.base` with something before the dot.
+pub fn host_matches(pattern: &str, host: &str) -> bool {
+    let base = match pattern.strip_prefix("*.") {
+        Some(base) => base,
+        None => return pattern == host,
+    };
+    match host.strip_suffix(base) {
+        Some(before) => match before.strip_suffix('.') {
+            Some(prefix) => !prefix.is_empty(),
+            None => false,
+        },
+        None => false,
+    }
+}
+
+/// A character that may appear in a host name.
+fn host_char(c: char) -> bool {
+    matches!(c, 'a'..='z' | '0'..='9' | '.' | '-')
+}
+
+/// The host of a URL, if the URL is well formed. See the task's `url_host` rules for the order.
+pub fn url_host(url: &str) -> Option<&str> {
+    if url.len() > MAX_URL {
+        return None;
+    }
+    let without_scheme = url.strip_prefix("https://")?;
+    // Uppercase is not allowed anywhere in a valid URL, so the host is read as written.
+    let end = match without_scheme.find(|c: char| !host_char(c)) {
+        Some(end) => end,
+        None => without_scheme.len(),
+    };
+    let (host, rest) = without_scheme.split_at_checked(end)?;
+    if !valid_host(host) {
+        return None;
+    }
+    // A trailing `:443` is allowed; any other port, or anything else, must be the end or a path.
+    let after = match rest.strip_prefix(":443") {
+        Some(after) => after,
+        None => rest,
+    };
+    let remainder = if after.is_empty() {
+        after
+    } else {
+        after.strip_prefix('/')?
+    };
+    if remainder.bytes().all(|byte| (0x21..=0x7e).contains(&byte)) {
+        Some(host)
+    } else {
+        None
+    }
+}

crates/brokerd/src/audit.rs

@@ -0,0 +1,421 @@
+//! The audit writer: a hash-chained log of decisions, approvals and results, one JSON record per
+//! line. The chain is the log's integrity: every record carries the hash of the line before it, so
+//! any change is seen. Opening the log verifies it (a short check for an ordinary start, the whole
+//! log when a break is to be accepted), recovers a torn tail, or accepts a break in an older file
+//! when told to, and only then hands back a writer that appends the next record.
+
+use std::fs::{self, TryLockError};
+use std::io;
+use std::io::Write;
+use std::os::unix::fs::{DirBuilderExt, OpenOptionsExt};
+use std::path::{Path, PathBuf};
+
+use proto::{
+    AuditEvent, AuditRecord, ChainFailure, ChainReport, ChainVerifier, Hash32, Timestamp,
+    is_audit_log_name, sha256,
+};
+
+/// The notice appended to the log when a torn final line is recovered, as the RUNBOOK entry names.
+pub const RECOVERED_NOTICE: &str =
+    "audit: recovered a torn final line\nsee docs/runbook.md#audit-recovered";
+
+/// Where the owner looks when the audit log cannot be read, written or locked.
+const RUNBOOK_UNAVAILABLE: &str = "see docs/runbook.md#audit-unavailable";
+/// The RUNBOOK entry a second writer points to.
+const RUNBOOK_ALREADY_RUNNING: &str = "see docs/runbook.md#brokerd-already-running";
+/// The RUNBOOK entry a broken chain points to.
+const RUNBOOK_BROKEN: &str = "see docs/runbook.md#audit-chain-broken";
+
+/// Why opening or writing the audit log can fail.
+#[derive(Debug)]
+pub enum AuditError {
+    /// The log is already locked by another running brokerd.
+    Locked,
+    /// A record in the log does not chain: the log is damaged.
+    Broken(Box<ChainFailure>),
+    /// Asked to accept a break, but the log verifies: there is none.
+    NothingToAccept,
+    /// The log could not be read, written or locked.
+    Io { what: String, source: io::Error },
+    /// A write failed; the writer has stopped and must be restarted.
+    Stopped,
+}
+
+impl std::fmt::Display for AuditError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            AuditError::Locked => {
+                write!(f, "brokerd is already running\n{RUNBOOK_ALREADY_RUNNING}")
+            }
+            AuditError::Broken(failure) => write!(
+                f,
+                "{}:{}: {}\n{RUNBOOK_BROKEN}",
+                failure.file, failure.line, failure.what
+            ),
+            AuditError::NothingToAccept => {
+                write!(f, "nothing to accept: the audit log verifies")
+            }
+            AuditError::Io { what, source } => {
+                write!(f, "audit: {what}: {source}\n{RUNBOOK_UNAVAILABLE}")
+            }
+            AuditError::Stopped => write!(
+                f,
+                "audit: an earlier write failed; restart brokerd\n{RUNBOOK_UNAVAILABLE}"
+            ),
+        }
+    }
+}
+
+impl std::error::Error for AuditError {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        match self {
+            AuditError::Io { source, .. } => Some(source),
+            _ => None,
+        }
+    }
+}
+
+impl From<io::Error> for AuditError {
+    fn from(err: io::Error) -> Self {
+        AuditError::Io {
+            what: "audit log".to_string(),
+            source: err,
+        }
+    }
+}
+
+/// The log file name for a record's time: the day of the timestamp, `.jsonl`.
+fn day_name(time: Timestamp) -> String {
+    let when = time.to_rfc3339();
+    format!("{}.jsonl", &when[..10])
+}
+
+/// An I/O error as an audit error, the path in what.
+fn io(what: &str, path: impl AsRef<Path>, source: io::Error) -> AuditError {
+    let path = path.as_ref();
+    AuditError::Io {
+        what: format!("{what} {}", path.display()),
+        source,
+    }
+}
+
+/// The bytes after the last newline, once one trailing newline is removed. None if nothing is left.
+fn last_line(bytes: &[u8]) -> Option<&[u8]> {
+    let bytes = match bytes.last() {
+        Some(b'\n') => &bytes[..bytes.len() - 1],
+        _ => bytes,
+    };
+    let line = match bytes.iter().rposition(|b| *b == b'\n') {
+        Some(pos) => &bytes[pos + 1..],
+        None => bytes,
+    };
+    if line.is_empty() { None } else { Some(line) }
+}
+
+/// Every log file in `dir`, by name. An unreadable directory or entry is an I/O error.
+fn log_files(dir: &Path) -> Result<Vec<String>, AuditError> {
+    let mut names: Vec<String> = Vec::new();
+    let mut entries = fs::read_dir(dir).map_err(|e| io("read audit log", dir, e))?;
+    loop {
+        let entry = match entries.next() {
+            Some(entry) => entry,
+            None => break,
+        };
+        let entry = entry.map_err(|e| io("read audit log", dir, e))?;
+        let name = entry.file_name();
+        let name = name.to_string_lossy();
+        if is_audit_log_name(&name) {
+            names.push(name.into_owned());
+        }
+    }
+    names.sort();
+    Ok(names)
+}
+
+/// Verify the whole log, from the first record.
+pub fn verify_dir(dir: &Path) -> Result<ChainReport, AuditError> {
+    let files = log_files(dir)?;
+    let mut verifier = ChainVerifier::new();
+    for file in files {
+        let path = dir.join(&file);
+        let bytes = fs::read(&path).map_err(|e| io("read audit log", &path, e))?;
+        verifier.feed(&file, &bytes);
+    }
+    Ok(verifier.finish())
+}
+
+/// Verify the latest file only, resuming from the last line of the file before it, when that line
+/// is a record. Otherwise the whole log is verified.
+fn short_check(dir: &Path) -> Result<ChainReport, AuditError> {
+    let files = log_files(dir)?;
+    let (Some(latest), Some(before)) = (files.last(), files.iter().rev().nth(1)) else {
+        return verify_dir(dir);
+    };
+    let path_before = dir.join(before);
+    let bytes = fs::read(&path_before).map_err(|e| io("read audit log", &path_before, e))?;
+    let line = match last_line(&bytes) {
+        Some(line) => line,
+        None => return verify_dir(dir),
+    };
+    let record: AuditRecord = match serde_json::from_slice(line) {
+        Ok(record) => record,
+        Err(_) => return verify_dir(dir),
+    };
+    let next_seq = match record.seq.checked_add(1) {
+        Some(seq) => seq,
+        None => return verify_dir(dir),
+    };
+    let prev = match sha256(line) {
+        Ok(hash) => hash,
+        Err(_) => return verify_dir(dir),
+    };
+    let mut verifier = ChainVerifier::resume(next_seq, prev);
+    let path_latest = dir.join(latest);
+    let latest_bytes = fs::read(&path_latest).map_err(|e| io("read audit log", &path_latest, e))?;
+    verifier.feed(latest, &latest_bytes);
+    Ok(verifier.finish())
+}
+
+/// The hash of the last line of the file before the latest, or zero if there is no such file or
+/// it has no line.
+fn tail_of_file_before_latest(dir: &Path) -> Result<Hash32, AuditError> {
+    let files = log_files(dir)?;
+    let Some(before) = files.iter().rev().nth(1) else {
+        return Ok(Hash32::ZERO);
+    };
+    let path = dir.join(before);
+    let bytes = fs::read(&path).map_err(|e| io("read audit log", &path, e))?;
+    match last_line(&bytes) {
+        Some(line) => Ok(sha256(line).map_err(io::Error::other)?),
+        None => Ok(Hash32::ZERO),
+    }
+}
+
+/// End the last line of the log with a newline, in the file that holds it: the last log file that
+/// is not empty. A torn line is always there, even when an empty later file exists, and it must be
+/// ended in place, or the next record would join it on one line.
+fn end_last_line(dir: &Path) -> Result<(), AuditError> {
+    for name in log_files(dir)?.iter().rev() {
+        let path = dir.join(name);
+        let bytes = fs::read(&path).map_err(|e| io("read audit log", &path, e))?;
+        match bytes.last() {
+            None => continue,
+            Some(b'\n') => return Ok(()),
+            Some(_) => {
+                let mut file = fs::OpenOptions::new()
+                    .append(true)
+                    .open(&path)
+                    .map_err(|e| io("open audit log", &path, e))?;
+                file.write_all(b"\n").map_err(io::Error::other)?;
+                file.sync_all().map_err(io::Error::other)?;
+                return Ok(());
+            }
+        }
+    }
+    Ok(())
+}
+
+/// Append one record: serialise it, open the target file, write the line, and return the seq and
+/// the hash of the line it wrote. A fresh file is created mode 0600 and the directory synced.
+fn write_record(
+    dir: &Path,
+    target: &str,
+    seq: u64,
+    prev: Hash32,
+    event: AuditEvent,
+    time: Timestamp,
+) -> Result<(u64, Hash32), AuditError> {
+    let record = AuditRecord {
+        seq,
+        time,
+        prev,
+        event,
+    };
+    let json = serde_json::to_string(&record).map_err(io::Error::other)?;
+    let path = dir.join(target);
+    let mut file = fs::OpenOptions::new()
+        .append(true)
+        .create(true)
+        .mode(0o600)
+        .open(&path)
+        .map_err(|e| io("open audit log", &path, e))?;
+    file.write_all(json.as_bytes()).map_err(io::Error::other)?;
+    file.write_all(b"\n").map_err(io::Error::other)?;
+    file.sync_all().map_err(io::Error::other)?;
+    fs::File::open(dir).map_err(io::Error::other)?.sync_all()?;
+    let hash = sha256(json.as_bytes()).map_err(io::Error::other)?;
+    Ok((seq, hash))
+}
+
+/// The last record's file name: today's, or the latest if that is already current.
+fn target_for(latest: &Option<String>, time: Timestamp) -> String {
+    let candidate = day_name(time);
+    match latest {
+        Some(current) if candidate <= *current => current.clone(),
+        _ => candidate,
+    }
+}
+
+/// A held directory lock: the open `.lock` file, released when it drops. Kept in the `Writer` so
+/// the lock lasts as long as the writer; `fs::File` is not `Debug`, so this wraps it.
+struct Lock(fs::File);
+
+impl std::fmt::Debug for Lock {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_tuple("Lock").field(&"open").finish()
+    }
+}
+
+/// The audit log's writer. Holds the directory lock for its whole life, so a second writer is
+/// refused.
+#[derive(Debug)]
+pub struct Writer {
+    /// Held, never read: closing the file is what releases the lock. The file itself stays.
+    _lock: Lock,
+    path: PathBuf,
+    latest: Option<String>,
+    prev: Hash32,
+    next_seq: u64,
+    stopped: bool,
+}
+
+impl Writer {
+    /// Open the log at `dir`: create it, lock it, verify it, and recover or accept as needed.
+    pub fn open(dir: &Path, accept_break: bool) -> Result<Opened, AuditError> {
+        // 1. The directory, mode 0700. Create it if missing; if it already exists, that is fine.
+        if let Err(e) = fs::DirBuilder::new().mode(0o700).create(dir)
+            && e.kind() != io::ErrorKind::AlreadyExists
+        {
+            return Err(io("create audit log", dir, e));
+        }
+
+        // 2. The lock, mode 0600: try_lock refuses a second writer while this one lives.
+        let lock = Lock(
+            fs::OpenOptions::new()
+                .write(true)
+                .create(true)
+                .truncate(false)
+                .mode(0o600)
+                .open(dir.join(".lock"))
+                .map_err(|e| io("open audit lock", dir.join(".lock"), e))?,
+        );
+        match lock.0.try_lock() {
+            Ok(()) => (),
+            Err(TryLockError::WouldBlock) => return Err(AuditError::Locked),
+            Err(TryLockError::Error(e)) => return Err(io("open audit lock", dir.join(".lock"), e)),
+        }
+
+        // 3. Verify the log.
+        let report = if accept_break {
+            verify_dir(dir)?
+        } else {
+            short_check(dir)?
+        };
+
+        // The latest log file before any recovery or break, for the target of either.
+        let latest = log_files(dir)
+            .ok()
+            .and_then(|files| files.into_iter().last());
+        let now = Timestamp::now();
+        let recovered = report.torn_tail.is_some();
+
+        // 4-9. A broken chain, nothing to accept, or a torn tail: write the recovery record, if any,
+        // and set the chain state for the next append.
+        let (prev, next_seq) = if let Some(failure) = report.failure.as_ref() {
+            if !accept_break {
+                return Err(AuditError::Broken(Box::new(failure.clone())));
+            }
+            if failure.tail_torn {
+                end_last_line(dir)?;
+            }
+            let (seq, hash) = write_record(
+                dir,
+                latest.as_deref().unwrap_or(&day_name(now)),
+                failure.break_seq,
+                failure.break_prev,
+                AuditEvent::AcceptedBreak {
+                    file: failure.file.clone(),
+                    line: failure.line,
+                    last_good: failure.last_good,
+                },
+                now,
+            )?;
+            (hash, seq.checked_add(1).unwrap_or(report.next_seq))
+        } else if accept_break {
+            return Err(AuditError::NothingToAccept);
+        } else if let Some(torn) = report.torn_tail.as_ref() {
+            if !torn.has_newline {
+                end_last_line(dir)?;
+            }
+            let (seq, hash) = write_record(
+                dir,
+                latest.as_deref().unwrap_or(&day_name(now)),
+                torn.recovery_seq,
+                torn.recovery_prev,
+                AuditEvent::Recovery {
+                    torn_bytes: torn.bytes,
+                    torn_sha256: torn.sha256,
+                },
+                now,
+            )?;
+            (hash, seq.checked_add(1).unwrap_or(report.next_seq))
+        } else {
+            // No record verified: the chain goes on from the last line of the file before the
+            // latest, or starts at zero when there is none (a log whose only file is empty).
+            let prev = match report.head {
+                Some(head) => head,
+                None => tail_of_file_before_latest(dir)?,
+            };
+            (prev, report.next_seq)
+        };
+
+        // 10. Hand back the writer.
+        Ok(Opened {
+            writer: Writer {
+                _lock: lock,
+                path: dir.to_path_buf(),
+                latest,
+                prev,
+                next_seq,
+                stopped: false,
+            },
+            recovered,
+            accepted: report.failure.map(Box::new),
+        })
+    }
+
+    /// Append a record at `time`, in the right day's file. The seq it writes is returned.
+    pub fn append(&mut self, time: Timestamp, event: AuditEvent) -> Result<u64, AuditError> {
+        if self.stopped {
+            return Err(AuditError::Stopped);
+        }
+        let target = target_for(&self.latest, time);
+        let (seq, hash) =
+            match write_record(&self.path, &target, self.next_seq, self.prev, event, time) {
+                Ok(r) => r,
+                Err(e) => {
+                    self.stopped = true;
+                    return Err(e);
+                }
+            };
+        self.prev = hash;
+        self.next_seq = seq.checked_add(1).unwrap_or(self.next_seq);
+        if self.latest.as_deref() != Some(target.as_str()) {
+            self.latest = Some(target);
+        }
+        Ok(seq)
+    }
+
+    /// The seq the next append writes.
+    pub fn next_seq(&self) -> u64 {
+        self.next_seq
+    }
+}
+
+/// What `open` hands back: the writer plus what it recovered or accepted.
+#[derive(Debug)]
+pub struct Opened {
+    pub writer: Writer,
+    pub recovered: bool,
+    pub accepted: Option<Box<ChainFailure>>,
+}

crates/brokerd/src/broker.rs

@@ -0,0 +1,313 @@
+//! Serving one `broker.sock` connection: decide, record, run if allowed, record the result, and
+//! answer with one final frame carrying the request's id. An `ask` call first sends one pending
+//! frame and waits for whoever takes the table entry to send the verdict. Every record goes
+//! through the ledger.
+
+use std::io::Read;
+use std::os::unix::net::UnixStream;
+use std::sync::Mutex;
+use std::sync::mpsc::RecvTimeoutError;
+use std::time::Duration;
+
+use proto::{
+    DenyReason, Envelope, ErrorCode, FrameError, Message, PROTOCOL_VERSION, PendingApproval,
+    Timestamp, ToolResponse, WireError, read_frame, write_frame,
+};
+
+use crate::approvals::{Table, Verdict};
+use crate::config::Config;
+use crate::grants;
+use crate::ledger::{Call, Decided, Grants, Ledger};
+use crate::policy::{Ask, SessionState};
+use crate::runner;
+use crate::runner::Runtime;
+
+/// The failure message sent when a peer leaves at the last look, after the table entry is taken.
+pub const GONE: &str = "the requester went away";
+
+/// A line printer: one line per call, owned by the broker.
+pub type Log = Box<dyn Fn(&str) + Send + Sync>;
+
+/// The only role that holds authority: one runtime, the ledger, the approval table, and the grants
+/// the owner can re-read.
+pub struct Broker {
+    cfg: Config,
+    ledger: Ledger,
+    table: Table,
+    runtime: Box<dyn Runtime>,
+    log: Log,
+    printed: Mutex<Option<Vec<proto::GrantProblem>>>,
+}
+
+impl Broker {
+    pub fn new(cfg: Config, ledger: Ledger, runtime: Box<dyn Runtime>, log: Log) -> Broker {
+        Broker {
+            cfg,
+            ledger,
+            table: Table::new(),
+            runtime,
+            log,
+            printed: Mutex::new(None),
+        }
+    }
+
+    pub fn cfg(&self) -> &Config {
+        &self.cfg
+    }
+
+    pub fn ledger(&self) -> &Ledger {
+        &self.ledger
+    }
+
+    pub fn table(&self) -> &Table {
+        &self.table
+    }
+
+    pub fn log(&self, line: &str) {
+        (self.log)(line)
+    }
+
+    /// The owner's grants, printed once per distinct set of problems.
+    pub fn grants(&self) -> Grants {
+        match grants::load(&self.cfg.paths.grants) {
+            Ok(set) => {
+                let mut printed = self.printed.lock().unwrap_or_else(|p| p.into_inner());
+                *printed = None;
+                Ok(set)
+            }
+            Err(problems) => {
+                let mut printed = self.printed.lock().unwrap_or_else(|p| p.into_inner());
+                if printed.as_deref() != Some(problems.as_slice()) {
+                    self.log(grants::render(&problems).trim_end());
+                }
+                *printed = Some(problems.clone());
+                Err(problems)
+            }
+        }
+    }
+}
+
+/// The snake_case wire name of a message: all fourteen kinds, none with a leading underscore.
+pub fn kind(msg: &Message) -> &'static str {
+    match msg {
+        Message::ToolRequest(_) => "tool_request",
+        Message::ToolResponse(_) => "tool_response",
+        Message::Error(_) => "error",
+        Message::Turn(_) => "turn",
+        Message::TurnEvent(_) => "turn_event",
+        Message::TurnDone(_) => "turn_done",
+        Message::Approvals(_) => "approvals",
+        Message::ApprovalList(_) => "approval_list",
+        Message::Approve(_) => "approve",
+        Message::ApproveResult(_) => "approve_result",
+        Message::Refuse(_) => "refuse",
+        Message::Ok(_) => "ok",
+        Message::CheckGrants(_) => "check_grants",
+        Message::GrantsReport(_) => "grants_report",
+    }
+}
+
+/// One frame on the wire: the version, the request's id, whether it is the last, and the message.
+/// True when the frame reached the peer.
+pub fn send(stream: &mut UnixStream, id: u64, last: bool, msg: Message) -> bool {
+    let env = Envelope {
+        v: PROTOCOL_VERSION,
+        id,
+        r#final: last,
+        msg,
+    };
+    write_frame(stream, &env).is_ok()
+}
+
+/// The next frame, or `None` when the peer is gone. A malformed frame is answered with an error
+/// frame and then `None`.
+pub fn read_request(stream: &mut UnixStream) -> Option<Envelope> {
+    match read_frame(stream) {
+        Ok(env) => Some(env),
+        Err(FrameError::Closed) => None,
+        Err(frame_error) => {
+            let code = match &frame_error {
+                FrameError::BadVersion(_) => ErrorCode::BadVersion,
+                FrameError::Json(_) => ErrorCode::BadMessage,
+                _ => ErrorCode::BadFrame,
+            };
+            let _ = send(
+                stream,
+                0,
+                true,
+                Message::Error(WireError {
+                    code,
+                    detail: frame_error.to_string(),
+                }),
+            );
+            None
+        }
+    }
+}
+
+/// Refuse a message that does not belong on this socket: log it, then answer with `Forbidden`.
+pub fn forbid(broker: &Broker, stream: &mut UnixStream, id: u64, msg: &Message, socket: &str) {
+    let kind_name = kind(msg);
+    broker.log(&format!(
+        "brokerd: refused the message kind {kind_name} on {socket}\nsee docs/runbook.md#socket-forbidden"
+    ));
+    let _ = send(
+        stream,
+        id,
+        true,
+        Message::Error(WireError {
+            code: ErrorCode::Forbidden,
+            detail: format!("{kind_name} is not accepted on {socket}"),
+        }),
+    );
+}
+
+/// Whether the peer is still there: it sends nothing more and never half-closes, so a byte would
+/// break the protocol and a timeout means it is waiting.
+pub fn alive(stream: &UnixStream) -> bool {
+    let mut stream = stream;
+    if stream
+        .set_read_timeout(Some(Duration::from_millis(10)))
+        .is_err()
+    {
+        return false;
+    }
+    let mut byte = [0u8; 1];
+    match stream.read(&mut byte) {
+        Ok(_) => false,
+        Err(e)
+            if e.kind() == std::io::ErrorKind::WouldBlock
+                || e.kind() == std::io::ErrorKind::TimedOut =>
+        {
+            true
+        }
+        Err(_) => false,
+    }
+}
+
+/// Answer one call: decide, and either answer it or wait for an approval.
+pub fn handle(mut stream: UnixStream, broker: &Broker) {
+    let Some(envelope) = read_request(&mut stream) else {
+        return; // 1. the peer is gone before it speaks
+    };
+    let id = envelope.id;
+    let msg = envelope.msg;
+    let Message::ToolRequest(request) = msg else {
+        forbid(broker, &mut stream, id, &msg, "broker.sock"); // 2. not a tool request
+        return;
+    };
+
+    let now = Timestamp::now();
+    let grants = broker.grants();
+    let answer = match broker.ledger().decide(request, &grants, now) {
+        Decided::Denied(reason) => Some(ToolResponse::Denied { reason }), // 3a. denied
+        Decided::Allowed { decision, seq } => Some(run(broker, decision, seq)), // 3b. allowed
+        Decided::Ask { ask, seq, state } => {
+            pending(&mut stream, broker, id, ask, seq, state, now) // 3c. ask
+        }
+    };
+    if let Some(answer) = answer {
+        let _ = send(&mut stream, id, true, Message::ToolResponse(answer)); // 4. the final frame
+    }
+}
+
+/// Run an allowed call and record its result.
+fn run(broker: &Broker, decision: crate::policy::Decision, seq: u64) -> ToolResponse {
+    let call = Call::of(&decision, seq);
+    let response = runner::run(decision, broker.runtime.as_ref());
+    broker.ledger().finish(&call, response, Timestamp::now())
+}
+
+/// The `ask` path: send one pending frame, wait for the verdict, then answer. `None` means send
+/// nothing more: the requester left while it was pending.
+fn pending(
+    stream: &mut UnixStream,
+    broker: &Broker,
+    id: u64,
+    ask: Ask,
+    seq: u64,
+    state: SessionState,
+    now: Timestamp,
+) -> Option<ToolResponse> {
+    // 1. The expiry: now plus the ttl, or the grant's own expiry if that is earlier.
+    let ttl = broker.cfg().approvals.ttl_ms;
+    let by_ttl = match Timestamp::from_unix_millis(now.unix_millis().saturating_add(ttl)) {
+        Ok(expires) => expires,
+        Err(_) => Timestamp::MAX,
+    };
+    let expires = match ask.expires() {
+        Some(expiry) if expiry < by_ttl => expiry,
+        _ => by_ttl,
+    };
+
+    // 2. Record the pending call in the table.
+    let info = PendingApproval {
+        approval: seq,
+        session: ask.request().session.clone(),
+        call: ask.request().call,
+        tool: ask.request().tool.clone(),
+        arguments: ask.args().canonical_json(),
+        grant: ask.grant().to_string(),
+        taint: state.taint,
+        created: now,
+        expires,
+    };
+    let verdict = broker.table().insert(info, ask);
+
+    // 3. Show the caller the pending call. If the frame does not reach the peer, the entry is
+    // still ours to take; if it is gone, someone is already answering it.
+    if !send(
+        stream,
+        id,
+        false,
+        Message::ToolResponse(ToolResponse::PendingApproval {
+            approval: seq,
+            expires,
+        }),
+    ) && broker.table().take(seq).is_some()
+    {
+        return None; // 3. the peer left before the frame went out
+    }
+
+    // 4. Wait for the verdict, or for the peer to leave.
+    let outcome = loop {
+        match verdict.recv_timeout(Duration::from_secs(1)) {
+            Ok(verdict) => break Ok(verdict),
+            Err(RecvTimeoutError::Timeout) => {
+                if alive(stream) {
+                    continue;
+                }
+                match broker.table().take(seq) {
+                    Some(_) => return None, // 4. the peer left while we waited
+                    None => match verdict.recv() {
+                        Ok(verdict) => break Ok(verdict),
+                        Err(_) => break Err(DenyReason::AuditUnavailable),
+                    },
+                }
+            }
+            Err(RecvTimeoutError::Disconnected) => break Err(DenyReason::AuditUnavailable), // 4. the taker dropped it unanswered
+        }
+    };
+
+    // 5. Answer from the verdict.
+    match outcome {
+        Ok(verdict) => match verdict {
+            Verdict::Denied(reason) => Some(ToolResponse::Denied { reason }),
+            Verdict::Run(decision) => {
+                let decision = *decision;
+                if !alive(stream) {
+                    let _ = broker.ledger().finish(
+                        &Call::of(&decision, seq),
+                        ToolResponse::Failed {
+                            message: GONE.to_string(),
+                        },
+                        Timestamp::now(), // now, not when it was decided: records keep time order
+                    );
+                    return None; // 5. the peer left at the last look; nothing ran
+                }
+                Some(run(broker, decision, seq))
+            }
+        },
+        Err(reason) => Some(ToolResponse::Denied { reason }),
+    }
+}

crates/brokerd/src/config.rs

@@ -0,0 +1,124 @@
+//! `brokerd` configuration: read `brokerd.toml` into a typed `Config`.
+//!
+//! This is our own format, so unknown keys are errors in every table: a
+//! misspelt key that silently fell back to its default would be a setting the
+//! owner believes is set and is not.
+
+use serde::Deserialize;
+use std::path::{Path, PathBuf};
+
+#[derive(Debug, Clone, PartialEq, Eq, Deserialize)]
+#[serde(deny_unknown_fields, default)]
+pub struct Paths {
+    pub home: PathBuf,
+    pub grants: PathBuf,
+}
+
+impl Default for Paths {
+    fn default() -> Self {
+        Self {
+            home: std::env::var_os("BOXMAKER_HOME")
+                .map(PathBuf::from)
+                .unwrap_or_else(|| PathBuf::from("/var/lib/boxmaker")),
+            grants: PathBuf::from("/etc/boxmaker/grants"),
+        }
+    }
+}
+
+/// An empty path means "the default under `home`".
+#[derive(Debug, Clone, PartialEq, Eq, Deserialize, Default)]
+#[serde(deny_unknown_fields, default)]
+pub struct Sockets {
+    pub broker: PathBuf,
+    pub admin: PathBuf,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Deserialize)]
+#[serde(deny_unknown_fields, default)]
+pub struct Approvals {
+    pub ttl_ms: u64,
+}
+
+impl Default for Approvals {
+    fn default() -> Self {
+        Self { ttl_ms: 900_000 }
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Deserialize, Default)]
+#[serde(deny_unknown_fields)]
+pub struct Config {
+    #[serde(default)]
+    pub paths: Paths,
+    #[serde(default)]
+    pub sockets: Sockets,
+    #[serde(default)]
+    pub approvals: Approvals,
+}
+
+/// The longest an approval may wait: a day, the longest `loopd` waits after a pending frame.
+pub const MAX_TTL_MS: u64 = 86_400_000;
+
+#[derive(Debug)]
+pub enum ConfigError {
+    Read(PathBuf, std::io::Error),
+    Parse(PathBuf, toml::de::Error),
+    /// The file parses, but a value is outside what brokerd accepts.
+    Invalid(PathBuf, String),
+}
+
+impl std::fmt::Display for ConfigError {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        match self {
+            ConfigError::Read(path, err) => write!(f, "{}: {err}", path.display()),
+            ConfigError::Parse(path, err) => write!(f, "{}: {err}", path.display()),
+            ConfigError::Invalid(path, why) => write!(f, "{}: {why}", path.display()),
+        }
+    }
+}
+
+impl std::error::Error for ConfigError {}
+
+impl Config {
+    pub fn parse(text: &str) -> Result<Config, toml::de::Error> {
+        toml::from_str(text)
+    }
+    pub fn load(path: &Path) -> Result<Config, ConfigError> {
+        let text =
+            std::fs::read_to_string(path).map_err(|e| ConfigError::Read(path.to_path_buf(), e))?;
+        let config: Config =
+            toml::from_str(&text).map_err(|e| ConfigError::Parse(path.to_path_buf(), e))?;
+        // `loopd` waits at most a day after a pending frame, so a longer approval would be given up
+        // by the caller while `bxctl approvals` still listed it.
+        if !(1..=MAX_TTL_MS).contains(&config.approvals.ttl_ms) {
+            return Err(ConfigError::Invalid(
+                path.to_path_buf(),
+                format!(
+                    "[approvals] ttl_ms is {}; it must be from 1 to {MAX_TTL_MS} (a day)",
+                    config.approvals.ttl_ms
+                ),
+            ));
+        }
+        Ok(config)
+    }
+    pub fn broker_socket(&self) -> PathBuf {
+        if self.sockets.broker.as_os_str().is_empty() {
+            self.paths.home.join("run/loop-broker/broker.sock")
+        } else {
+            self.sockets.broker.clone()
+        }
+    }
+    pub fn admin_socket(&self) -> PathBuf {
+        if self.sockets.admin.as_os_str().is_empty() {
+            self.paths.home.join("run/owner-broker/admin.sock")
+        } else {
+            self.sockets.admin.clone()
+        }
+    }
+    pub fn audit_dir(&self) -> PathBuf {
+        self.paths.home.join("audit")
+    }
+    pub fn state_dir(&self) -> PathBuf {
+        self.paths.home.join("broker/sessions")
+    }
+}

crates/brokerd/src/grants.rs

@@ -0,0 +1,373 @@
+//! Loading the owner's grant files into a `GrantSet`, failing closed.
+//!
+//! A mistyped `deny` grant that was skipped would silently become an allow wherever another grant
+//! matches, so if any file is invalid the whole set is invalid. `load` therefore returns either a
+//! complete valid set or the full list of problems, never a partial one, and reports every problem
+//! in every file rather than only the first.
+
+use std::path::Path;
+
+use crate::args::{ToolName, valid_host_pattern, valid_path};
+use proto::{DataClass, Grant, GrantProblem, Mode, sha256};
+
+/// Where the owner reads the rules behind a rejected set.
+pub const RUNBOOK: &str = "see docs/runbook.md#grants-invalid";
+
+/// A grant read from one file: the id (the file stem), the parsed grant, and the file's hash.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct LoadedGrant {
+    pub id: String, // the file stem
+    pub grant: proto::Grant,
+    pub sha256: proto::Hash32, // of the file's bytes as read
+}
+
+/// A set that passed every rule, in id order. Its field is private: `from_grants` and `load` are
+/// the only ways to make one that is not empty.
+#[derive(Debug, Clone, PartialEq, Eq, Default)]
+pub struct GrantSet {
+    grants: Vec<LoadedGrant>,
+}
+
+impl GrantSet {
+    /// Build a set, checking every grant and refusing the whole set if any grant is invalid.
+    pub fn from_grants(grants: Vec<LoadedGrant>) -> Result<GrantSet, Vec<GrantProblem>> {
+        let mut grants = grants;
+        grants.sort_by(|a, b| a.id.cmp(&b.id));
+
+        let mut problems: Vec<GrantProblem> = Vec::new();
+        let mut seen: Vec<String> = Vec::new();
+        for grant in &grants {
+            if seen.iter().any(|id| id == &grant.id) {
+                push(
+                    &mut problems,
+                    format!("{}.toml", grant.id),
+                    None,
+                    "two grants have this id",
+                );
+            }
+            seen.push(grant.id.clone());
+            check_grant(grant, &mut problems);
+        }
+
+        if problems.is_empty() {
+            Ok(GrantSet { grants })
+        } else {
+            Err(problems)
+        }
+    }
+
+    /// The grants in id order.
+    pub fn grants(&self) -> &[LoadedGrant] {
+        &self.grants
+    }
+}
+
+/// A file name is a valid grant id when it is 1 to 64 characters of `a-z`, `0-9` and `-`.
+pub fn valid_id(id: &str) -> bool {
+    if !(1..=64).contains(&id.len()) {
+        return false;
+    }
+    id.bytes()
+        .all(|b| matches!(b, b'a'..=b'z' | b'0'..=b'9' | b'-'))
+}
+
+/// Read every `*.toml` in `dir` into a `GrantSet`, or report every problem found.
+pub fn load(dir: &Path) -> Result<GrantSet, Vec<GrantProblem>> {
+    // Step 1: the directory itself must be readable. A missing directory is not an empty set.
+    let entries = match std::fs::read_dir(dir) {
+        Ok(entries) => entries,
+        Err(error) => {
+            return Err(vec![GrantProblem {
+                file: dir.to_string_lossy().to_string(),
+                line: None,
+                problem: format!("the grants directory cannot be read: {}", error),
+            }]);
+        }
+    };
+
+    // Step 2: collect and sort the file names, so problems come out in the same order every time.
+    let mut names: Vec<String> = Vec::new();
+    for entry in entries {
+        match entry {
+            Ok(entry) => names.push(entry.file_name().to_string_lossy().to_string()),
+            Err(error) => {
+                // An entry that cannot be read is the same problem as the directory.
+                return Err(vec![GrantProblem {
+                    file: dir.to_string_lossy().to_string(),
+                    line: None,
+                    problem: format!("the grants directory cannot be read: {}", error),
+                }]);
+            }
+        }
+    }
+    names.sort();
+
+    // Steps 3-7: read each file, keeping the valid grants and recording every other problem.
+    let mut kept: Vec<LoadedGrant> = Vec::new();
+    let mut problems: Vec<GrantProblem> = Vec::new();
+    for name in &names {
+        if !name.ends_with(".toml") {
+            continue;
+        }
+        let id = &name[..name.len() - ".toml".len()];
+        let path = dir.join(name);
+
+        let bytes = match std::fs::read(&path) {
+            Ok(bytes) => bytes,
+            Err(error) => {
+                // Never treat an unreadable file as absent.
+                problems.push(GrantProblem {
+                    file: name.clone(),
+                    line: None,
+                    problem: format!("cannot be read: {}", error),
+                });
+                continue;
+            }
+        };
+
+        let text = match std::str::from_utf8(&bytes) {
+            Ok(text) => text,
+            Err(_) => {
+                problems.push(GrantProblem {
+                    file: name.clone(),
+                    line: None,
+                    problem: "is not UTF-8".to_string(),
+                });
+                continue;
+            }
+        };
+
+        match toml::from_str::<Grant>(text) {
+            Ok(grant) => {
+                let sha256 = match sha256(&bytes) {
+                    Ok(sha256) => sha256,
+                    Err(error) => {
+                        problems.push(GrantProblem {
+                            file: name.clone(),
+                            line: None,
+                            problem: error.to_string(),
+                        });
+                        continue;
+                    }
+                };
+                kept.push(LoadedGrant {
+                    id: id.to_string(),
+                    grant,
+                    sha256,
+                });
+            }
+            Err(error) => {
+                problems.push(GrantProblem {
+                    file: name.clone(),
+                    line: Some(span_line(text, &error)),
+                    problem: error.message().to_string(),
+                });
+            }
+        }
+    }
+
+    // Step 8: even when the steps above found problems, still check the valid grants so the owner
+    // sees everything at once. Return Err if anything at all was reported.
+    let mut all = problems;
+    let set = match GrantSet::from_grants(kept) {
+        Ok(set) => Some(set),
+        Err(value_problems) => {
+            all.extend(value_problems);
+            None
+        }
+    };
+    all.sort_by(|a, b| a.file.cmp(&b.file));
+    match set {
+        Some(set) => {
+            if all.is_empty() {
+                Ok(set)
+            } else {
+                Err(all)
+            }
+        }
+        None => Err(all),
+    }
+}
+
+/// The 1-based line of a parse error's start: the number of newlines before it, plus one.
+fn span_line(text: &str, error: &toml::de::Error) -> u64 {
+    match error.span() {
+        Some(range) => {
+            let before = match text.get(..range.start) {
+                Some(before) => before,
+                None => text,
+            };
+            let newlines = before.bytes().filter(|&b| b == b'\n').count();
+            u64::try_from(newlines).map_or(u64::MAX, |n| n.saturating_add(1))
+        }
+        None => 1,
+    }
+}
+
+/// Check one grant and push every problem it has. `file` is `"<id>.toml"`, `line` is `None`.
+fn check_grant(grant: &LoadedGrant, problems: &mut Vec<GrantProblem>) {
+    let id = &grant.id;
+    let inner = &grant.grant;
+    let file = format!("{}.toml", id);
+
+    // Rule 2: the id must be a valid grant id.
+    if !valid_id(id) {
+        push(
+            problems,
+            file.clone(),
+            None,
+            "the file name is not a valid grant id",
+        );
+    }
+
+    // Rule 3: the tool must be one of the four; an unknown tool skips rule 6 but not the others.
+    match ToolName::parse(&grant.grant.tool) {
+        None => push(
+            problems,
+            file.clone(),
+            None,
+            "unknown tool; only read_file, write_file, shell and http_fetch",
+        ),
+        Some(tool) => check_tool_constraints(tool, &file, inner, problems),
+    }
+
+    // Rule 4: secrets are not supported until M4.
+    if inner.secret.is_some() {
+        push(
+            problems,
+            file.clone(),
+            None,
+            "secrets are not supported until M4",
+        );
+    }
+    // Rule 5: patterns are not supported.
+    if !inner.constraints.patterns.is_empty() {
+        push(problems, file.clone(), None, "patterns are not supported");
+    }
+    // Rule 7: no path may be the whole file system or an invalid absolute path.
+    for path in &inner.constraints.paths {
+        if path == "/" {
+            push(
+                problems,
+                file.clone(),
+                None,
+                "a grant of the whole file system is not supported",
+            );
+        } else if !valid_path(path) {
+            push(
+                problems,
+                file.clone(),
+                None,
+                format!("{:?} is not a valid absolute path", path),
+            );
+        }
+    }
+    // Rule 8: every host must be a valid host pattern.
+    for host in &inner.constraints.hosts {
+        if !valid_host_pattern(host) {
+            push(
+                problems,
+                file.clone(),
+                None,
+                format!("{:?} is not a valid host pattern", host),
+            );
+        }
+    }
+    // Rule 9: a deny grant must apply at every taint.
+    if inner.mode == Mode::Deny && inner.max_taint != DataClass::Secret {
+        push(
+            problems,
+            file,
+            None,
+            "a deny grant must apply at every taint",
+        );
+    }
+}
+
+/// Rule 6: the per-tool checks on paths and hosts. `file` is `"<id>.toml"`.
+fn check_tool_constraints(
+    tool: ToolName,
+    file: &str,
+    grant: &Grant,
+    problems: &mut Vec<GrantProblem>,
+) {
+    let tool = tool.as_str();
+    match tool {
+        "read_file" | "write_file" => {
+            if grant.constraints.paths.is_empty() {
+                push(
+                    problems,
+                    file.to_string(),
+                    None,
+                    format!("{} needs at least one path", tool),
+                );
+            }
+            if !grant.constraints.hosts.is_empty() {
+                push(
+                    problems,
+                    file.to_string(),
+                    None,
+                    format!("{} does not take hosts", tool),
+                );
+            }
+        }
+        "shell" if !grant.constraints.hosts.is_empty() => {
+            push(
+                problems,
+                file.to_string(),
+                None,
+                format!("{} does not take hosts", tool),
+            );
+        }
+        "http_fetch" => {
+            if grant.constraints.hosts.is_empty() {
+                push(
+                    problems,
+                    file.to_string(),
+                    None,
+                    "http_fetch needs at least one host",
+                );
+            }
+            if !grant.constraints.paths.is_empty() {
+                push(
+                    problems,
+                    file.to_string(),
+                    None,
+                    "http_fetch does not take paths",
+                );
+            }
+        }
+        _ => {}
+    }
+}
+
+/// One line per problem, then `RUNBOOK` on its own line; every line ends with `\n`.
+pub fn render(problems: &[GrantProblem]) -> String {
+    let mut out = String::new();
+    for problem in problems {
+        match problem.line {
+            Some(line) => {
+                out.push_str(&format!("{}:{}: {}\n", problem.file, line, problem.problem));
+            }
+            None => {
+                out.push_str(&format!("{}: {}\n", problem.file, problem.problem));
+            }
+        }
+    }
+    out.push_str(RUNBOOK);
+    out.push('\n');
+    out
+}
+
+fn push(
+    problems: &mut Vec<GrantProblem>,
+    file: String,
+    line: Option<u64>,
+    problem: impl Into<String>,
+) {
+    problems.push(GrantProblem {
+        file,
+        line,
+        problem: problem.into(),
+    });
+}

crates/brokerd/src/ledger.rs

@@ -0,0 +1,499 @@
+//! The ledger: the audit writer and every session's state behind one lock, with the three steps
+//! that hold it. Without the one lock, two results for one session could each read `private` and
+//! the second write would put the taint back down; after any failed append or panic while the lock was held, the ledger refuses every later step, and only the next start's check puts a partial line on disk right.
+
+use std::sync::{Mutex, MutexGuard};
+
+use proto::{
+    ApprovalAnswer, AuditEvent, CallId, DataClass, DecisionRecord, DenyReason, GrantProblem, Mode,
+    SessionId, Timestamp, ToolRequest, ToolResponse,
+};
+
+use crate::approvals::Verdict;
+use crate::audit::{AuditError, Writer};
+use crate::grants::GrantSet;
+use crate::policy::{Ask, Denial, Label, SessionState};
+use crate::state::StateStore;
+
+/// The message `finish` returns when the raised taint and the record are not both on disk.
+pub const NOT_RECORDED: &str = "the result could not be recorded";
+/// After a panic while the lock was held: every call is denied until brokerd is restarted.
+pub const POISONED: &str = "brokerd: a thread panicked while holding the ledger; every call is denied until brokerd is restarted\nsee docs/runbook.md#audit-unavailable";
+/// After a failed append: every call is denied until brokerd is restarted.
+pub const STOPPED: &str = "brokerd: an earlier audit write failed; every call is denied until brokerd is restarted\nsee docs/runbook.md#audit-unavailable";
+
+/// What `grants::load` returns: a valid set, or the list of problems that made it invalid.
+pub type Grants = Result<GrantSet, Vec<GrantProblem>>;
+
+/// The audit writer behind one lock, so a step that fails to record refuses every later step.
+pub trait AuditSink: Send {
+    fn append(&mut self, time: Timestamp, event: AuditEvent) -> Result<u64, AuditError>;
+}
+
+impl AuditSink for Writer {
+    fn append(&mut self, time: Timestamp, event: AuditEvent) -> Result<u64, AuditError> {
+        Writer::append(self, time, event)
+    }
+}
+
+/// A call the broker is finishing: the session, the call, the decision it was approved under, and
+/// the label the result carries.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Call {
+    pub session: SessionId,
+    pub call: CallId,
+    pub decision: u64,
+    pub label: Label,
+}
+
+impl Call {
+    /// The call and label of an approved decision, with the seq it was approved under.
+    pub fn of(decision: &crate::policy::Decision, seq: u64) -> Call {
+        let request = decision.request();
+        Call {
+            session: request.session.clone(),
+            call: request.call,
+            decision: seq,
+            label: decision.label(),
+        }
+    }
+}
+
+/// How a call was decided.
+#[derive(Debug)]
+pub enum Decided {
+    Allowed {
+        decision: crate::policy::Decision,
+        seq: u64,
+    },
+    Ask {
+        ask: Ask,
+        seq: u64,
+        state: SessionState,
+    },
+    Denied(DenyReason),
+}
+
+/// The value a decided call carries past the record, or the denial reason when there is none.
+enum RecordPayload {
+    Allowed(crate::policy::Decision),
+    Ask(Ask),
+    Denial(Denial),
+    Simple(DenyReason),
+}
+
+/// An owner's answer to a pending call.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Answer {
+    Approved {
+        by: Option<String>,
+    },
+    Refused {
+        by: Option<String>,
+        reason: Option<String>,
+    },
+    Expired,
+}
+
+/// What an approval leaves: the verdict (run or deny) and the record written.
+#[derive(Debug)]
+pub struct Answered {
+    pub verdict: Verdict,
+    pub outcome: DecisionRecord,
+}
+
+struct Inner {
+    audit: Box<dyn AuditSink>,
+    state: StateStore,
+    stopped: bool,
+}
+
+/// The audit writer and every session's state behind one lock.
+pub struct Ledger {
+    inner: Mutex<Inner>,
+    log: Box<dyn Fn(&str) + Send + Sync>,
+}
+
+impl Ledger {
+    /// A ledger over the audit writer, the session store, and a sink for its notices.
+    pub fn new(
+        audit: Box<dyn AuditSink>,
+        state: StateStore,
+        log: Box<dyn Fn(&str) + Send + Sync>,
+    ) -> Ledger {
+        Ledger {
+            inner: Mutex::new(Inner {
+                audit,
+                state,
+                stopped: false,
+            }),
+            log,
+        }
+    }
+
+    /// The lock, `None` when the step cannot proceed: poisoned → `POISONED`, stopped → `STOPPED`.
+    fn lock(&self) -> Option<MutexGuard<'_, Inner>> {
+        let guard = match self.inner.lock() {
+            Ok(guard) => guard,
+            Err(_) => {
+                (self.log)(POISONED);
+                return None;
+            }
+        };
+        if guard.stopped {
+            (self.log)(STOPPED);
+            return None;
+        }
+        Some(guard)
+    }
+
+    /// Read a session's state, logging and returning "unknown" when it cannot be read.
+    fn state_read(
+        &self,
+        guard: &MutexGuard<Inner>,
+        session: &SessionId,
+    ) -> Result<SessionState, ()> {
+        match guard.state.read(session) {
+            Ok(state) => Ok(state),
+            Err(e) => {
+                (self.log)(&format!("brokerd: {e}"));
+                Err(())
+            }
+        }
+    }
+
+    /// Append a record, stopping the ledger on failure and logging why. `Ok(seq)` or `Err`.
+    fn append(
+        &self,
+        guard: &mut MutexGuard<Inner>,
+        now: Timestamp,
+        event: AuditEvent,
+    ) -> Result<u64, ()> {
+        match guard.audit.append(now, event) {
+            Ok(seq) => Ok(seq),
+            Err(e) => {
+                guard.stopped = true;
+                (self.log)(&format!("brokerd: {e}"));
+                Err(())
+            }
+        }
+    }
+
+    /// The refusal `finish` returns when the result could not be recorded.
+    fn not_recorded() -> ToolResponse {
+        ToolResponse::Failed {
+            message: NOT_RECORDED.to_string(),
+        }
+    }
+
+    /// The answer when the audit is unavailable: deny the verdict and record the denial.
+    fn audit_unavailable() -> Answered {
+        Answered {
+            verdict: Verdict::Denied(DenyReason::AuditUnavailable),
+            outcome: DecisionRecord::Denied {
+                reason: DenyReason::AuditUnavailable,
+            },
+        }
+    }
+
+    /// A denial verdict and its matching record, for one reason.
+    fn denied(reason: DenyReason) -> (Verdict, DecisionRecord) {
+        (Verdict::Denied(reason), DecisionRecord::Denied { reason })
+    }
+
+    /// The outcome of an approved re-decision: the named grant's mode, else allowed.
+    fn outcome_for(&self, decision: &crate::policy::Decision, grants: &Grants) -> DecisionRecord {
+        let mode = match grants {
+            Ok(set) => set
+                .grants()
+                .iter()
+                .find(|g| g.id == decision.grant())
+                .map(|g| g.grant.mode),
+            Err(_) => None,
+        };
+        match mode {
+            Some(Mode::Ask) => DecisionRecord::Ask {},
+            _ => DecisionRecord::Allowed {},
+        }
+    }
+
+    /// Decide and record a call.
+    pub fn decide(&self, request: ToolRequest, grants: &Grants, now: Timestamp) -> Decided {
+        let session = request.session.clone();
+        let call = request.call;
+        let tool = request.tool.clone();
+        let arguments = request.arguments.clone();
+
+        // 1. Lock fails → denied, nothing written.
+        let mut guard = match self.lock() {
+            Some(guard) => guard,
+            None => return Decided::Denied(DenyReason::AuditUnavailable),
+        };
+
+        // 2. Read the state, keeping the Result. The recorded state is "unknown" when unreadable.
+        let state = self.state_read(&guard, &session);
+        let recorded = match &state {
+            Ok(state) => *state,
+            Err(()) => SessionState {
+                taint: DataClass::Secret,
+                untrusted: true,
+            },
+        };
+
+        // 3. The outcome, first that applies.
+        let (outcome, grant, grant_sha256, payload) = match grants {
+            Err(_) => (
+                DecisionRecord::Denied {
+                    reason: DenyReason::GrantsInvalid,
+                },
+                None,
+                None,
+                RecordPayload::Simple(DenyReason::GrantsInvalid),
+            ),
+            Ok(set) => match state {
+                Err(()) => (
+                    DecisionRecord::Denied {
+                        reason: DenyReason::StateUnreadable,
+                    },
+                    None,
+                    None,
+                    RecordPayload::Simple(DenyReason::StateUnreadable),
+                ),
+                Ok(state) => match crate::policy::decide(request, set, state, now) {
+                    crate::policy::Outcome::Allowed(decision) => (
+                        DecisionRecord::Allowed {},
+                        Some(decision.grant().to_string()),
+                        Some(decision.grant_sha256()),
+                        RecordPayload::Allowed(decision),
+                    ),
+                    crate::policy::Outcome::Ask(ask) => (
+                        DecisionRecord::Ask {},
+                        Some(ask.grant().to_string()),
+                        Some(ask.grant_sha256()),
+                        RecordPayload::Ask(ask),
+                    ),
+                    crate::policy::Outcome::Denied(denial) => (
+                        DecisionRecord::Denied {
+                            reason: denial.reason,
+                        },
+                        denial.grant.clone(),
+                        denial.grant_sha256,
+                        RecordPayload::Denial(denial),
+                    ),
+                },
+            },
+        };
+
+        // 4. Write the record, then return the verdict.
+        let event = AuditEvent::Decision {
+            session,
+            call,
+            tool,
+            arguments,
+            outcome,
+            grant,
+            grant_sha256,
+            taint: recorded.taint,
+            untrusted: recorded.untrusted,
+        };
+        match self.append(&mut guard, now, event) {
+            Ok(seq) => match payload {
+                RecordPayload::Simple(reason) => Decided::Denied(reason),
+                RecordPayload::Allowed(decision) => Decided::Allowed { decision, seq },
+                RecordPayload::Ask(ask) => Decided::Ask {
+                    ask,
+                    seq,
+                    state: recorded,
+                },
+                RecordPayload::Denial(denial) => Decided::Denied(denial.reason),
+            },
+            Err(()) => Decided::Denied(DenyReason::AuditUnavailable),
+        }
+    }
+
+    /// Re-decide an approval and record it.
+    pub fn answer(
+        &self,
+        ask: Ask,
+        decision: u64,
+        answer: Answer,
+        grants: &Grants,
+        now: Timestamp,
+    ) -> Answered {
+        // 1. Lock fails → step fails.
+        let mut guard = match self.lock() {
+            Some(guard) => guard,
+            None => return Self::audit_unavailable(),
+        };
+
+        // 2. Read the state of the ask's session.
+        let session = ask.request().session.clone();
+        let call = ask.request().call;
+        let state = self.state_read(&guard, &session);
+        let recorded = match &state {
+            Ok(state) => *state,
+            Err(()) => SessionState {
+                taint: DataClass::Secret,
+                untrusted: true,
+            },
+        };
+
+        // 3. The answer and its fields.
+        let (answer, by, reason) = match &answer {
+            Answer::Approved { by } => (ApprovalAnswer::Approved, by.clone(), None),
+            Answer::Refused { by, reason } => (ApprovalAnswer::Refused, by.clone(), reason.clone()),
+            Answer::Expired => (ApprovalAnswer::Expired, None, None),
+        };
+
+        // 4. The re-decision (approved only); every other answer is a denial.
+        let redecide = match (answer, grants) {
+            (ApprovalAnswer::Approved, Ok(set)) => match &state {
+                Ok(state) => crate::policy::redecide(ask, set, *state, now),
+                Err(()) => Err(Denial::new(DenyReason::StateUnreadable)),
+            },
+            _ => Err(Denial::new(DenyReason::GrantsInvalid)),
+        };
+
+        // 5. The grant fields, then the verdict and outcome together.
+        let (grant, grant_sha256) = match &redecide {
+            Ok(decision) => (
+                Some(decision.grant().to_string()),
+                Some(decision.grant_sha256()),
+            ),
+            Err(_) => (None, None),
+        };
+        let (verdict, outcome) = match (answer, redecide) {
+            (ApprovalAnswer::Approved, Ok(decision)) => {
+                let outcome = self.outcome_for(&decision, grants);
+                (Verdict::Run(Box::new(decision)), outcome)
+            }
+            (ApprovalAnswer::Approved, Err(denial)) => Self::denied(denial.reason),
+            (ApprovalAnswer::Refused, _) => Self::denied(DenyReason::ApprovalRefused),
+            (ApprovalAnswer::Expired, _) => Self::denied(DenyReason::ApprovalExpired),
+        };
+
+        // 6. Record the approval, or step fails.
+        match self.append(
+            &mut guard,
+            now,
+            AuditEvent::Approval {
+                session,
+                call,
+                decision,
+                answer,
+                by,
+                post: None,
+                reason,
+                outcome: outcome.clone(),
+                grant,
+                grant_sha256,
+                taint: recorded.taint,
+                untrusted: recorded.untrusted,
+            },
+        ) {
+            Ok(_) => Answered { verdict, outcome },
+            Err(()) => Self::audit_unavailable(),
+        }
+    }
+
+    /// Raise the state, hash the response, and record a result, or stop the ledger on failure.
+    fn record_result(
+        &self,
+        guard: &mut MutexGuard<'_, Inner>,
+        call: &Call,
+        now: Timestamp,
+        status: proto::ResultStatus,
+        taint_after: DataClass,
+        response: &ToolResponse,
+    ) -> ToolResponse {
+        let (sha256, bytes) = match response {
+            ToolResponse::Result { content, .. } => match proto::sha256(content.as_bytes()) {
+                Ok(sha) => (sha, u64::try_from(content.len()).unwrap_or(u64::MAX)),
+                Err(_) => return Self::not_recorded(),
+            },
+            ToolResponse::Failed { message } => match proto::sha256(message.as_bytes()) {
+                Ok(sha) => (sha, u64::try_from(message.len()).unwrap_or(u64::MAX)),
+                Err(_) => return Self::not_recorded(),
+            },
+            _ => return Self::not_recorded(),
+        };
+        let (class, untrusted, truncated) = match response {
+            ToolResponse::Result {
+                class,
+                untrusted,
+                truncated,
+                ..
+            } => (*class, *untrusted, *truncated),
+            ToolResponse::Failed { .. } => (call.label.class, call.label.untrusted, false),
+            _ => return Self::not_recorded(),
+        };
+        let event = AuditEvent::Result {
+            session: call.session.clone(),
+            call: call.call,
+            decision: call.decision,
+            status,
+            class,
+            untrusted,
+            truncated,
+            bytes,
+            sha256,
+            taint_after,
+        };
+        match self.append(guard, now, event) {
+            Ok(_) => response.clone(),
+            Err(()) => Self::not_recorded(),
+        }
+    }
+
+    /// Raise the state and record a result.
+    pub fn finish(&self, call: &Call, response: ToolResponse, now: Timestamp) -> ToolResponse {
+        // 1. Lock fails → cannot record.
+        let mut guard = match self.lock() {
+            Some(guard) => guard,
+            None => return Self::not_recorded(),
+        };
+
+        match &response {
+            // 3. A result raises the state, then is recorded.
+            ToolResponse::Result { .. } => {
+                let raised = match self.state_read(&guard, &call.session) {
+                    Ok(state) => match guard.state.raise(&call.session, state, call.label) {
+                        Ok(raised) => raised,
+                        Err(e) => {
+                            (self.log)(&format!("brokerd: {e}"));
+                            return Self::not_recorded();
+                        }
+                    },
+                    Err(()) => return Self::not_recorded(),
+                };
+                self.record_result(
+                    &mut guard,
+                    call,
+                    now,
+                    proto::ResultStatus::Result,
+                    raised.taint,
+                    &response,
+                )
+            }
+            // 4. A failure changes no state, recorded by its message.
+            ToolResponse::Failed { .. } => {
+                let taint_after = match self.state_read(&guard, &call.session) {
+                    Ok(state) => state.taint,
+                    Err(()) => DataClass::Secret,
+                };
+                self.record_result(
+                    &mut guard,
+                    call,
+                    now,
+                    proto::ResultStatus::Failed,
+                    taint_after,
+                    &response,
+                )
+            }
+            // 5. The runner never returns these; nothing to record.
+            ToolResponse::Denied { .. } | ToolResponse::PendingApproval { .. } => {
+                Self::not_recorded()
+            }
+        }
+    }
+}

crates/brokerd/src/lib.rs

@@ -1,4 +1,14 @@
 //! The broker: the only role that holds authority.
 
+pub mod admin;
+pub mod approvals;
+pub mod args;
+pub mod audit;
+pub mod broker;
+pub mod config;
+pub mod grants;
+pub mod ledger;
 pub mod policy;
 pub mod runner;
+pub mod serve;
+pub mod state;

crates/brokerd/src/main.rs

@@ -1,4 +1,131 @@
-fn main() {
+//! `brokerd`: the broker role. `serve` takes the audit lock, binds both sockets, and serves.
-    eprintln!("brokerd: not implemented until M3");
+
-    std::process::exit(2);
+use std::ffi::OsString;
+use std::path::PathBuf;
+use std::process::ExitCode;
+use std::sync::Arc;
+
+use brokerd::audit::{AuditError, RECOVERED_NOTICE};
+use brokerd::config::Config;
+use brokerd::runner::Refusing;
+use brokerd::serve::{self, ServeError};
+
+const USAGE: &str = "usage: brokerd serve --config <path> [--accept-break]";
+/// Where the owner looks when brokerd cannot start: its config, a directory or a socket.
+const START_FAILED: &str = "see docs/runbook.md#brokerd-start-failed";
+/// Where the owner looks when brokerd stops serving after it started.
+const LISTENER_LOST: &str = "see docs/runbook.md#brokerd-listener-lost";
+
+fn main() -> ExitCode {
+    // The first argument must be `serve`.
+    // `args_os`: a path need not be UTF-8, and `args` would panic on one that is not.
+    let mut args = std::env::args_os().skip(1);
+    match args.next() {
+        Some(command) if command == "serve" => {}
+        _ => return usage(),
+    }
+
+    // `--config <path>` exactly once and `--accept-break` at most once, in any order.
+    let (config_path, accept_break) = match parse_serve(args) {
+        Ok(pair) => pair,
+        Err(()) => return usage(),
+    };
+
+    // Read the config before touching the filesystem: a bad config must make nothing.
+    let cfg = match Config::load(&config_path) {
+        Ok(cfg) => cfg,
+        Err(e) => {
+            eprintln!("brokerd: {e}\n{START_FAILED}");
+            return ExitCode::from(1);
+        }
+    };
+
+    // Keep the socket paths for the serving notice, before `cfg` is moved into `start`.
+    let broker_path = cfg.broker_socket();
+    let admin_path = cfg.admin_socket();
+
+    let started = match serve::start(
+        cfg,
+        accept_break,
+        Box::new(Refusing),
+        Arc::new(|line: &str| eprintln!("{line}")),
+    ) {
+        Ok(started) => started,
+        Err(ServeError::Audit(e @ AuditError::NothingToAccept)) => {
+            eprintln!("brokerd: {e}");
+            return ExitCode::from(2);
+        }
+        // The audit errors carry their own entry; the rest are this one.
+        Err(ServeError::Audit(e)) => {
+            eprintln!("brokerd: {e}");
+            return ExitCode::from(1);
+        }
+        Err(e) => {
+            eprintln!("brokerd: {e}\n{START_FAILED}");
+            return ExitCode::from(1);
+        }
+    };
+
+    if started.recovered {
+        eprintln!("{RECOVERED_NOTICE}");
+    }
+    if let Some(failure) = &started.accepted {
+        eprintln!(
+            "audit: accepted the break at {}:{}: {}",
+            failure.file, failure.line, failure.what
+        );
+    }
+    eprintln!(
+        "brokerd: serving tools on {} and approvals on {}",
+        broker_path.display(),
+        admin_path.display()
+    );
+
+    match started.run() {
+        Ok(()) => ExitCode::SUCCESS,
+        Err(e) => {
+            eprintln!("brokerd: stopped serving: {e}\n{LISTENER_LOST}");
+            ExitCode::from(1)
+        }
+    }
+}
+
+/// The argument list was not `serve --config <path> [--accept-break]`.
+fn usage() -> ExitCode {
+    eprintln!("{USAGE}");
+    ExitCode::from(2)
+}
+
+/// The `--config` and `--accept-break` flags after `serve`, or `Err(())` for a bad list.
+/// Flags are compared as `OsStr`, so one that is not UTF-8 is simply unknown; the path is kept as
+/// given.
+fn parse_serve<I: Iterator<Item = OsString>>(mut args: I) -> Result<(PathBuf, bool), ()> {
+    let mut config: Option<OsString> = None;
+    let mut accept_break = false;
+    loop {
+        match args.next() {
+            None => {
+                return match config {
+                    Some(path) => Ok((PathBuf::from(path), accept_break)),
+                    None => Err(()),
+                };
+            }
+            Some(arg) if arg == "--config" => match args.next() {
+                Some(path) => {
+                    if config.is_some() {
+                        return Err(());
+                    }
+                    config = Some(path);
+                }
+                None => return Err(()),
+            },
+            Some(arg) if arg == "--accept-break" => {
+                if accept_break {
+                    return Err(());
+                }
+                accept_break = true;
+            }
+            Some(_) => return Err(()),
+        }
+    }
 }

crates/brokerd/src/policy.rs

@@ -1,95 +1,498 @@
-//! Policy decisions. `Decision` can only be constructed in this module.
+//! Policy decisions. `decide` answers a tool call against the grants, the session's state and the
+//! time it is given; `redecide` is the only thing that turns an approval back into a `Decision`.
+//! Both are pure: they do no I/O and read no clock.
 //!
-//! Code outside this module cannot build a `Decision` with a struct literal, because its fields
+//! A `Decision` can only be built here, in `decide` and `redecide`: its fields are private, and no
-//! are private:
+//! constructor is exposed.
 //!
 //! ```compile_fail
 //! let request = proto::ToolRequest {
 //!     session: proto::SessionId::new("s1").unwrap(),
 //!     call: proto::CallId(1),
-//!     tool: "read_file".to_string(),
+//!     tool: "shell".to_string(),
-//!     arguments: "{}".to_string(),
+//!     arguments: r#"{"command":"ls"}"#.to_string(),
 //! };
-//! let _ = brokerd::policy::Decision { request, grant: "g".to_string() };
+//! let args = brokerd::args::parse(brokerd::args::ToolName::Shell, &request.arguments).unwrap();
+//! let _ = brokerd::policy::Decision { request, args, matched: todo!() };
 //! ```
 //!
-//! Nor with the constructor, because it is private to this module:
+//! Nor with a constructor that needs `Clone`:
+//!
+//! ```compile_fail
+//! fn needs_clone<T: Clone>() {}
+//! needs_clone::<brokerd::policy::Decision>();
+//! ```
+//!
+//! Nor one that needs to be decoded:
+//!
+//! ```compile_fail
+//! fn needs_decoding<T: serde::de::DeserializeOwned>() {}
+//! needs_decoding::<brokerd::policy::Decision>();
+//! ```
+//!
+//! The same three hold for `Ask`.
 //!
 //! ```compile_fail
 //! let request = proto::ToolRequest {
 //!     session: proto::SessionId::new("s1").unwrap(),
 //!     call: proto::CallId(1),
-//!     tool: "read_file".to_string(),
+//!     tool: "shell".to_string(),
-//!     arguments: "{}".to_string(),
+//!     arguments: r#"{"command":"ls"}"#.to_string(),
 //! };
-//! let _ = brokerd::policy::Decision::new(request, "g".to_string());
+//! let args = brokerd::args::parse(brokerd::args::ToolName::Shell, &request.arguments).unwrap();
+//! let _ = brokerd::policy::Ask { request, args, matched: todo!() };
 //! ```
 //!
-//! The same setup compiles when it goes through `decide`, which proves the two examples above
+//! ```compile_fail
-//! fail because of `Decision` and not because of a mistake in the setup:
+//! fn needs_clone<T: Clone>() {}
+//! needs_clone::<brokerd::policy::Ask>();
+//! ```
+//!
+//! ```compile_fail
+//! fn needs_decoding<T: serde::de::DeserializeOwned>() {}
+//! needs_decoding::<brokerd::policy::Ask>();
+//! ```
+//!
+//! The next example shows they fail because of `Decision` and `Ask`,
+//! not because of the setup: the very same request goes through `decide`, which succeeds and, with
+//! no grants, is denied with `NoGrant`.
 //!
 //! ```
+//! fn needs_clone<T: Clone>() {}
+//! fn needs_decoding<T: serde::de::DeserializeOwned>() {}
+//! needs_clone::<proto::ToolRequest>();
+//! needs_decoding::<proto::ToolRequest>();
 //! let request = proto::ToolRequest {
 //!     session: proto::SessionId::new("s1").unwrap(),
 //!     call: proto::CallId(1),
-//!     tool: "read_file".to_string(),
+//!     tool: "shell".to_string(),
-//!     arguments: "{}".to_string(),
+//!     arguments: r#"{"command":"ls"}"#.to_string(),
 //! };
-//! assert_eq!(brokerd::policy::decide(request).unwrap_err(), proto::DenyReason::NoGrant);
+//! let now = proto::Timestamp::from_unix_millis(0).unwrap();
+//! match brokerd::policy::decide(
+//!     request,
+//!     &brokerd::grants::GrantSet::default(),
+//!     brokerd::policy::SessionState::default(),
+//!     now,
+//! ) {
+//!     brokerd::policy::Outcome::Denied(denial) => {
+//!         assert_eq!(denial.reason, proto::DenyReason::NoGrant);
+//!     }
+//!     other => panic!("expected a denial, got {other:?}"),
+//! }
 //! ```
 
-use proto::{DenyReason, ToolRequest};
+use crate::args::{self, ToolArgs, ToolName, host_matches, inside};
+use crate::grants::GrantSet;
+use proto::{DataClass, DenyReason, Grant, Hash32, Mode, Timestamp, ToolRequest};
 
+/// The session's taint, and whether its results are untrusted. Only `taint` shapes a decision.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct SessionState {
+    pub taint: DataClass,
+    pub untrusted: bool,
+}
+
+impl Default for SessionState {
+    fn default() -> Self {
+        SessionState {
+            taint: DataClass::Private,
+            untrusted: false,
+        }
+    }
+}
+
+/// How a result is labelled: its data class and whether it is untrusted.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct Label {
+    pub class: DataClass,
+    pub untrusted: bool,
+}
+
+/// Why a call was denied, and (for a deny grant) which one denied it.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Denial {
+    pub reason: DenyReason,
+    /// `Some` only for `DeniedByGrant`: the deny grant's id.
+    pub grant: Option<String>,
+    /// `Some` only for `DeniedByGrant`: the deny grant's file hash.
+    pub grant_sha256: Option<Hash32>,
+}
+
+impl Denial {
+    pub fn new(reason: DenyReason) -> Denial {
+        Denial {
+            reason,
+            grant: None,
+            grant_sha256: None,
+        }
+    }
+}
+
+/// The winning grant and what it matched: the paths and hosts the runner mounts, and the expiry
+/// and label the caller reads.
+#[derive(Debug)]
+struct Matched {
+    grant: String,
+    grant_sha256: Hash32,
+    matched_path: Option<String>,
+    paths: Vec<String>,
+    hosts: Vec<String>,
+    expires: Option<Timestamp>,
+    label: Label,
+}
+
+/// A call the broker has decided to run: built only in this module, read by the runner.
 #[derive(Debug)]
 pub struct Decision {
     request: ToolRequest,
-    grant: String,
+    args: ToolArgs,
+    matched: Matched,
+}
+
+/// A call the broker left for the owner: built only in this module, re-decided by `redecide`.
+#[derive(Debug)]
+pub struct Ask {
+    request: ToolRequest,
+    args: ToolArgs,
+    matched: Matched,
 }
 
 impl Decision {
-    #[cfg_attr(not(test), expect(dead_code, reason = "grant matching arrives in M3"))]
-    fn new(request: ToolRequest, grant: String) -> Self {
-        Decision { request, grant }
-    }
-
     pub fn request(&self) -> &ToolRequest {
         &self.request
     }
-
+    pub fn args(&self) -> &ToolArgs {
+        &self.args
+    }
     pub fn grant(&self) -> &str {
-        &self.grant
+        &self.matched.grant
+    }
+    pub fn grant_sha256(&self) -> Hash32 {
+        self.matched.grant_sha256
+    }
+    pub fn matched_path(&self) -> Option<&str> {
+        self.matched.matched_path.as_deref()
+    }
+    pub fn paths(&self) -> &[String] {
+        &self.matched.paths
+    }
+    pub fn hosts(&self) -> &[String] {
+        &self.matched.hosts
+    }
+    pub fn expires(&self) -> Option<Timestamp> {
+        self.matched.expires
+    }
+    pub fn label(&self) -> Label {
+        self.matched.label
     }
 }
 
-/// Until M3 there are no grants, so every request is denied with DenyReason::NoGrant.
+impl Ask {
-pub fn decide(request: ToolRequest) -> Result<Decision, DenyReason> {
+    pub fn request(&self) -> &ToolRequest {
-    let _ = request;
+        &self.request
-    Err(DenyReason::NoGrant)
+    }
+    pub fn args(&self) -> &ToolArgs {
+        &self.args
+    }
+    pub fn grant(&self) -> &str {
+        &self.matched.grant
+    }
+    pub fn grant_sha256(&self) -> Hash32 {
+        self.matched.grant_sha256
+    }
+    pub fn matched_path(&self) -> Option<&str> {
+        self.matched.matched_path.as_deref()
+    }
+    pub fn paths(&self) -> &[String] {
+        &self.matched.paths
+    }
+    pub fn hosts(&self) -> &[String] {
+        &self.matched.hosts
+    }
+    pub fn expires(&self) -> Option<Timestamp> {
+        self.matched.expires
+    }
+    pub fn label(&self) -> Label {
+        self.matched.label
+    }
 }
 
-#[cfg(test)]
+/// The result of deciding a call: run it, ask, or deny it.
-mod tests {
+#[derive(Debug)]
-    use super::*;
+pub enum Outcome {
-    use proto::{CallId, SessionId};
+    Allowed(Decision),
+    Ask(Ask),
+    Denied(Denial),
+}
 
-    fn request() -> ToolRequest {
+pub fn decide(
-        ToolRequest {
+    request: ToolRequest,
-            session: SessionId::new("s1").unwrap(),
+    grants: &GrantSet,
-            call: CallId(1),
+    state: SessionState,
-            tool: "read_file".to_string(),
+    now: Timestamp,
-            arguments: "{}".to_string(),
+) -> Outcome {
+    // 1. An unknown tool is denied before its arguments are even parsed.
+    let Some(tool) = ToolName::parse(&request.tool) else {
+        return Outcome::Denied(Denial::new(DenyReason::NoGrant));
+    };
+    // 2. Malformed arguments are refused before matching, whatever the grants say.
+    let Ok(args) = args::parse(tool, &request.arguments) else {
+        return Outcome::Denied(Denial::new(DenyReason::InvalidArguments));
+    };
+
+    let MatchResult {
+        left,
+        expired,
+        tainted,
+    } = match_grants(&args, grants, state, now);
+
+    // 3. No grant left: the reason is whatever the ruled-out grants reminded us of.
+    let Some(winner) = winner(&left) else {
+        let reason = match (expired, tainted) {
+            (true, _) => DenyReason::GrantExpired,
+            (_, true) => DenyReason::TaintTooHigh,
+            (_, _) => DenyReason::NoGrant,
+        };
+        return Outcome::Denied(Denial::new(reason));
+    };
+
+    // 4. The label is over every grant left, not the winner alone.
+    let matched = build_matched(&left, &winner);
+
+    match winner.mode {
+        Mode::Deny => Outcome::Denied(Denial {
+            reason: DenyReason::DeniedByGrant,
+            grant: Some(winner.id.clone()),
+            grant_sha256: Some(winner.grant_sha256),
+        }),
+        Mode::Ask => Outcome::Ask(Ask {
+            request,
+            args,
+            matched,
+        }),
+        Mode::Auto => Outcome::Allowed(Decision {
+            request,
+            args,
+            matched,
+        }),
+    }
+}
+
+pub fn redecide(
+    ask: Ask,
+    grants: &GrantSet,
+    state: SessionState,
+    now: Timestamp,
+) -> Result<Decision, Denial> {
+    let MatchResult {
+        left,
+        expired,
+        tainted,
+    } = match_grants(ask.args(), grants, state, now);
+
+    let Some(winner) = winner(&left) else {
+        let reason = match (expired, tainted) {
+            (true, _) => DenyReason::GrantExpired,
+            (_, true) => DenyReason::TaintTooHigh,
+            (_, _) => DenyReason::NoGrant,
+        };
+        return Err(Denial::new(reason));
+    };
+
+    let matched = build_matched(&left, &winner);
+
+    match winner.mode {
+        Mode::Deny => Err(Denial {
+            reason: DenyReason::DeniedByGrant,
+            grant: Some(winner.id.clone()),
+            grant_sha256: Some(winner.grant_sha256),
+        }),
+        Mode::Ask | Mode::Auto => Ok(Decision {
+            request: ask.request().clone(),
+            args: ask.args().clone(),
+            matched,
+        }),
+    }
+}
+
+/// The grants left after matching, and the two flags that pick the denial reason when none are
+/// left.
+struct MatchResult {
+    left: Vec<Candidate>,
+    expired: bool,
+    tainted: bool,
+}
+
+#[derive(Clone)]
+struct Candidate {
+    id: String,
+    grant_sha256: Hash32,
+    mode: Mode,
+    matched_path: Option<String>,
+    paths: Vec<String>,
+    hosts: Vec<String>,
+    expires: Option<Timestamp>,
+    result_class: DataClass,
+    untrusted: bool,
+}
+
+/// Match a call against every grant, in id order, keeping the ones that still stand.
+fn match_grants(
+    args: &ToolArgs,
+    grants: &GrantSet,
+    state: SessionState,
+    now: Timestamp,
+) -> MatchResult {
+    let mut left: Vec<Candidate> = Vec::new();
+    let mut expired = false;
+    let mut tainted = false;
+
+    for loaded in grants.grants() {
+        // M1: only grants for this tool play a part.
+        if loaded.grant.tool != args.tool().as_str() {
+            continue;
+        }
+        // M2: does this grant cover the arguments, and with which path (if any)?
+        let Some(matched_path) = covers(args, &loaded.grant) else {
+            continue;
+        };
+
+        // M3: a grant that would match but is past its expiry or beyond the session's taint does
+        // not stand. Remember each reason, so the denial can name the right one.
+        let expired_at = loaded.grant.expires.is_some_and(|at| now >= at);
+        let too_tainted = state.taint > loaded.grant.max_taint;
+        if expired_at && !too_tainted {
+            expired = true;
+        }
+        if too_tainted && !expired_at {
+            tainted = true;
+        }
+        if !expired_at && !too_tainted {
+            left.push(Candidate {
+                id: loaded.id.clone(),
+                grant_sha256: loaded.sha256,
+                mode: loaded.grant.mode,
+                matched_path,
+                paths: loaded.grant.constraints.paths.clone(),
+                hosts: loaded.grant.constraints.hosts.clone(),
+                expires: loaded.grant.expires,
+                result_class: loaded.grant.result_class,
+                untrusted: loaded.grant.untrusted,
+            });
         }
     }
 
-    #[test]
+    MatchResult {
-    fn no_grants_means_deny() {
+        left,
-        assert_eq!(decide(request()).unwrap_err(), DenyReason::NoGrant);
+        expired,
-    }
+        tainted,
-
-    #[test]
-    fn decision_exposes_request_and_grant() {
-        let d = Decision::new(request(), "g1".to_string());
-        assert_eq!(d.request().tool, "read_file");
-        assert_eq!(d.grant(), "g1");
     }
 }
+
+/// Whether the grant covers the call, and the longest of its paths that holds the call. `None`
+/// means the grant does not cover the call at all.
+fn covers(args: &ToolArgs, grant: &Grant) -> Option<Option<String>> {
+    match args {
+        ToolArgs::ReadFile { path } => best_path(grant, path, true),
+        ToolArgs::WriteFile { path, .. } => best_path(grant, path, false),
+        ToolArgs::Shell { cwd: None, .. } => {
+            if grant.constraints.paths.is_empty() {
+                Some(None)
+            } else {
+                None
+            }
+        }
+        ToolArgs::Shell { cwd: Some(cwd), .. } => best_path(grant, cwd, true),
+        ToolArgs::HttpFetch { host, .. } => {
+            if grant
+                .constraints
+                .hosts
+                .iter()
+                .any(|pattern| host_matches(pattern, host))
+            {
+                Some(None)
+            } else {
+                None
+            }
+        }
+    }
+}
+
+/// The longest granted path `p` such that `inside(p, target)`. For writes, a path equal to the
+/// argument does not count.
+fn best_path(grant: &Grant, target: &str, itself_counts: bool) -> Option<Option<String>> {
+    let mut best: Option<String> = None;
+    for candidate in &grant.constraints.paths {
+        if !inside(candidate, target) {
+            continue;
+        }
+        if !itself_counts && candidate == target {
+            continue;
+        }
+        if best
+            .as_ref()
+            .is_none_or(|found| candidate.len() > found.len())
+        {
+            best = Some(candidate.clone());
+        }
+    }
+    // `None` means no path holds, so the grant does not cover the call; a held path becomes
+    // `Some(Some(p))` so `covers` can tell it apart from a covered call with no path.
+    best.map(Some)
+}
+
+/// Build the winning grant's `Matched`, with the label over every standing grant.
+fn build_matched(left: &[Candidate], winner: &Candidate) -> Matched {
+    Matched {
+        grant: winner.id.clone(),
+        grant_sha256: winner.grant_sha256,
+        matched_path: winner.matched_path.clone(),
+        paths: winner.paths.clone(),
+        hosts: winner.hosts.clone(),
+        expires: winner.expires,
+        label: combined_label(left),
+    }
+}
+
+/// The most restrictive standing grant, then the longest matched path, then the lowest id.
+fn winner(candidates: &[Candidate]) -> Option<Candidate> {
+    for &mode in [Mode::Deny, Mode::Ask, Mode::Auto].iter() {
+        let mut best: Option<&Candidate> = None;
+        for candidate in candidates.iter().filter(|c| c.mode == mode) {
+            best = Some(match best {
+                Some(found) if !better(candidate, found) => found,
+                _ => candidate,
+            });
+        }
+        if let Some(found) = best {
+            return Some(found.clone());
+        }
+    }
+    None
+}
+
+/// Is `a` a better winner than `b`: a longer matched path, or the same path and a lower id.
+fn better(a: &Candidate, b: &Candidate) -> bool {
+    let (la, lb) = (
+        a.matched_path.as_ref().map_or(0, String::len),
+        b.matched_path.as_ref().map_or(0, String::len),
+    );
+    match la.cmp(&lb) {
+        std::cmp::Ordering::Greater => true,
+        std::cmp::Ordering::Less => false,
+        std::cmp::Ordering::Equal => a.id < b.id,
+    }
+}
+
+/// The label over every standing grant: the highest data class, and untrusted if any says so.
+fn combined_label(candidates: &[Candidate]) -> Label {
+    let mut class = DataClass::Public;
+    for candidate in candidates {
+        if candidate.result_class > class {
+            class = candidate.result_class;
+        }
+    }
+    let untrusted = candidates.iter().any(|c| c.untrusted);
+    Label { class, untrusted }
+}

crates/brokerd/src/runner.rs

@@ -1,12 +1,138 @@
-//! Tool runner stub. Real tool execution arrives in M3.
+//! The runner seam: an allowed call becomes a `RunSpec` and is handed to a `Runtime`.
+//!
+//! A `RunSpec` can only be built here, from a `Decision`, so a runtime never sees a call policy
+//! did not allow.
+//!
+//! ```compile_fail
+//! let _ = brokerd::runner::RunSpec {
+//!     tool: brokerd::args::ToolName::Shell,
+//!     arguments: todo!(),
+//!     mounts: Vec::new(),
+//!     egress: None,
+//! };
+//! ```
+//!
+//! ```
+//! fn tool_of(spec: &brokerd::runner::RunSpec) -> brokerd::args::ToolName {
+//!     spec.tool()
+//! }
+//! ```
 
+use crate::args::{ToolArgs, ToolName};
 use crate::policy::Decision;
 use proto::ToolResponse;
 
-/// Takes the Decision by value, so one decision cannot run a tool twice.
+/// A directory mounted for one call: a path and whether the runtime may write to it.
-pub fn run(decision: Decision) -> ToolResponse {
+#[derive(Debug, Clone, PartialEq, Eq)]
-    let _ = decision;
+pub struct Mount {
-    ToolResponse::Failed {
+    pub path: String,
-        message: "no tool runner until M3".to_string(),
+    pub writable: bool,
+}
+
+/// What one call was turned into before it reached a `Runtime`: the tool, its arguments, the
+/// directories mounted and the hosts it may reach. Built only here, from a `Decision`.
+#[derive(Debug)]
+pub struct RunSpec {
+    tool: ToolName,
+    arguments: ToolArgs,
+    mounts: Vec<Mount>,
+    egress: Option<Vec<String>>,
+}
+
+impl RunSpec {
+    pub fn tool(&self) -> ToolName {
+        self.tool
+    }
+    pub fn arguments(&self) -> &ToolArgs {
+        &self.arguments
+    }
+    pub fn mounts(&self) -> &[Mount] {
+        &self.mounts
+    }
+    pub fn egress(&self) -> Option<&[String]> {
+        self.egress.as_deref()
+    }
+}
+
+/// A `Runtime`'s answer to one call. Its text reaches the model as a `failed` result labelled
+/// public and trusted, so a runtime may only put a fixed sentence in it.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum RunError {
+    Failed(String),
+    Unavailable(String),
+}
+
+/// What a `Runtime` produced for one call.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct RunOutput {
+    pub content: String,
+    pub truncated: bool,
+}
+
+/// Runs one call. `Send + Sync` so one `Runtime` can serve several brokers at once.
+pub trait Runtime: Send + Sync {
+    fn run(&self, spec: &RunSpec) -> Result<RunOutput, RunError>;
+}
+
+/// The production runtime for M3a. It runs nothing; every call is `Unavailable`.
+pub struct Refusing;
+
+impl Runtime for Refusing {
+    fn run(&self, _spec: &RunSpec) -> Result<RunOutput, RunError> {
+        Err(RunError::Unavailable(REFUSING.to_string()))
+    }
+}
+
+/// The sentence `Refusing` puts in every `Unavailable`: fixed, because it reaches the model.
+pub const REFUSING: &str = "the runner arrives in M3b";
+
+/// Turn an allowed call into a `RunSpec`, run it, and answer. A `RunError`'s text reaches the
+/// model unchanged, so a runtime may only put a fixed sentence in it.
+pub fn run(decision: Decision, runtime: &dyn Runtime) -> proto::ToolResponse {
+    let label = decision.label();
+    let args = decision.args();
+    let (mounts, egress) = match args {
+        ToolArgs::ReadFile { .. } => (matched_mount(decision.matched_path(), false), None),
+        ToolArgs::WriteFile { .. } => (matched_mount(decision.matched_path(), true), None),
+        ToolArgs::Shell { .. } => (
+            decision
+                .paths()
+                .iter()
+                .map(|path| Mount {
+                    path: path.clone(),
+                    writable: true,
+                })
+                .collect(),
+            None,
+        ),
+        ToolArgs::HttpFetch { .. } => (Vec::new(), Some(decision.hosts().to_vec())),
+    };
+    let spec = RunSpec {
+        tool: args.tool(),
+        arguments: args.clone(),
+        mounts,
+        egress,
+    };
+    match runtime.run(&spec) {
+        Ok(output) => ToolResponse::Result {
+            content: output.content,
+            class: label.class,
+            untrusted: label.untrusted,
+            truncated: output.truncated,
+        },
+        Err(RunError::Failed(message) | RunError::Unavailable(message)) => {
+            ToolResponse::Failed { message }
+        }
+    }
+}
+
+/// The matched path as one mount, or none when the call matched no path.
+fn matched_mount(path: Option<&str>, writable: bool) -> Vec<Mount> {
+    match path {
+        Some(at) => vec![Mount {
+            path: at.to_string(),
+            writable,
+        }],
+        None => Vec::new(),
     }
 }

crates/brokerd/src/serve.rs

@@ -0,0 +1,266 @@
+//! `brokerd serve`: bring the broker up, listen on both sockets, and keep it running.
+
+use std::fs::{DirBuilder, Permissions};
+use std::io;
+use std::os::unix::fs::{DirBuilderExt, PermissionsExt};
+use std::os::unix::net::{UnixListener, UnixStream};
+use std::path::{Path, PathBuf};
+use std::sync::Arc;
+use std::sync::mpsc;
+use std::time::Duration;
+
+use crate::admin;
+use crate::audit::{AuditError, Writer};
+use crate::broker::{self, Broker};
+use crate::config::Config;
+use crate::ledger::Ledger;
+use crate::runner::Runtime;
+use crate::state::StateStore;
+use proto::{ChainFailure, Timestamp};
+
+/// A failure while `brokerd serve` is starting up.
+#[derive(Debug)]
+pub enum ServeError {
+    /// The audit chain would not open. Displayed as the audit error's own text.
+    Audit(AuditError),
+    /// A directory could not be prepared, or made private.
+    Dir(PathBuf, io::Error),
+    /// A socket could not be bound, or made private.
+    Socket(PathBuf, io::Error),
+}
+
+impl std::fmt::Display for ServeError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            ServeError::Audit(e) => write!(f, "{e}"),
+            ServeError::Dir(path, e) => write!(f, "cannot prepare {}: {e}", path.display()),
+            ServeError::Socket(path, e) => write!(f, "cannot listen on {}: {e}", path.display()),
+        }
+    }
+}
+
+impl std::error::Error for ServeError {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        match self {
+            ServeError::Audit(e) => Some(e),
+            ServeError::Dir(_, e) | ServeError::Socket(_, e) => Some(e),
+        }
+    }
+}
+
+/// The result of `start`: a running broker with both sockets open.
+pub struct Started {
+    pub broker: Arc<Broker>,
+    pub recovered: bool,
+    pub accepted: Option<ChainFailure>,
+    tools: UnixListener,
+    admin: UnixListener,
+}
+
+/// Start the broker: open the audit chain, bind both sockets, and build the ledger and broker.
+pub fn start(
+    cfg: Config,
+    accept_break: bool,
+    runtime: Box<dyn Runtime>,
+    log: Arc<dyn Fn(&str) + Send + Sync>,
+) -> Result<Started, ServeError> {
+    // The audit lock comes first: if the chain will not open, no directory or socket is made.
+    let opened = Writer::open(&cfg.audit_dir(), accept_break).map_err(ServeError::Audit)?;
+
+    // Both sockets, in the order the task gives.
+    let tools = listen(&cfg.broker_socket())?;
+    let admin = listen(&cfg.admin_socket())?;
+
+    // The ledger and broker share the one log, each through its own box.
+    let log1: Box<dyn Fn(&str) + Send + Sync> = {
+        let log = Arc::clone(&log);
+        Box::new(move |line: &str| log(line))
+    };
+    let ledger = Ledger::new(
+        Box::new(opened.writer),
+        StateStore::new(&cfg.state_dir()),
+        log1,
+    );
+    let log2: Box<dyn Fn(&str) + Send + Sync> = {
+        let log = Arc::clone(&log);
+        Box::new(move |line: &str| log(line))
+    };
+    let broker = Broker::new(cfg, ledger, runtime, log2);
+
+    Ok(Started {
+        broker: Arc::new(broker),
+        recovered: opened.recovered,
+        accepted: opened.accepted.map(|b| *b),
+        tools,
+        admin,
+    })
+}
+
+/// Bind one socket: prepare its directory at 0700, make it private, remove any stale
+/// socket, bind, then make the socket itself private at 0600.
+fn listen(socket: &Path) -> Result<UnixListener, ServeError> {
+    // A socket needs a directory of its own: step 2 makes that directory 0700, which must never
+    // be `/` or a shared directory reached through a symbolic link.
+    let dir = match socket.parent() {
+        Some(parent) if parent.parent().is_some() && !parent.as_os_str().is_empty() => {
+            parent.to_path_buf()
+        }
+        _ => {
+            return Err(ServeError::Dir(
+                PathBuf::from(socket),
+                io::Error::other("a socket needs a directory of its own, not / or none"),
+            ));
+        }
+    };
+
+    // 1. The directory, at 0700.
+    DirBuilder::new()
+        .recursive(true)
+        .mode(0o700)
+        .create(&dir)
+        .map_err(|e| ServeError::Dir(dir.clone(), e))?;
+    // `set_permissions` follows a symbolic link, so a link would make the directory it points to
+    // private instead: refuse it.
+    let kind = std::fs::symlink_metadata(&dir)
+        .map_err(|e| ServeError::Dir(dir.clone(), e))?
+        .file_type();
+    if !kind.is_dir() {
+        return Err(ServeError::Dir(
+            dir,
+            io::Error::other(
+                "is a symbolic link or not a directory; brokerd will not change its mode",
+            ),
+        ));
+    }
+    // 2. Make it private, always, even when it was already there at 0755.
+    std::fs::set_permissions(&dir, Permissions::from_mode(0o700))
+        .map_err(|e| ServeError::Dir(dir.clone(), e))?;
+
+    // 3. A stale socket is removed; a missing one is fine.
+    match std::fs::remove_file(socket) {
+        Ok(()) => {}
+        Err(e) if e.kind() == io::ErrorKind::NotFound => {}
+        Err(e) => return Err(ServeError::Socket(socket.to_path_buf(), e)),
+    }
+
+    // 4. Bind, then 5. make the socket private.
+    let listener =
+        UnixListener::bind(socket).map_err(|e| ServeError::Socket(PathBuf::from(socket), e))?;
+    std::fs::set_permissions(socket, Permissions::from_mode(0o600))
+        .map_err(|e| ServeError::Socket(PathBuf::from(socket), e))?;
+    Ok(listener)
+}
+
+/// Which handler the accept thread runs for each accepted stream.
+#[derive(Copy, Clone)]
+enum Which {
+    Tools,
+    Admin,
+}
+
+/// Run the broker: start the expiry thread, one accept thread per socket, then wait for the
+/// first listener error.
+impl Started {
+    pub fn run(self) -> io::Result<()> {
+        let Started {
+            broker,
+            tools,
+            admin,
+            ..
+        } = self;
+
+        // The expiry thread: once a second, expire the approvals whose time has run out.
+        // `Builder` rather than `spawn`, which panics when the system refuses a thread.
+        {
+            let broker = Arc::clone(&broker);
+            std::thread::Builder::new()
+                .name("expiry".to_string())
+                .spawn(move || {
+                    loop {
+                        std::thread::sleep(Duration::from_secs(1));
+                        admin::expire_due(&broker, Timestamp::now());
+                    }
+                })?;
+        }
+
+        // One accept thread per socket, each with its own clone of the broker.
+        let (tx, rx) = mpsc::channel::<io::Error>();
+
+        accept_loop(tools, Arc::clone(&broker), tx.clone(), Which::Tools)?;
+        accept_loop(admin, Arc::clone(&broker), tx, Which::Admin)?;
+
+        // The first listener error stops the daemon.
+        match rx.recv() {
+            Ok(e) => Err(e),
+            Err(_) => Err(io::Error::other("a listener thread ended")),
+        }
+    }
+}
+
+/// Accept streams from one listener forever, starting a handler thread per stream. When the
+/// system is out of file descriptors or memory, the listener pauses and tries again instead of
+/// stopping: otherwise a peer holding many idle connections could stop the daemon, and the other
+/// socket with it. Any other error stops the daemon through `tx`.
+fn accept_loop(
+    listener: UnixListener,
+    broker: Arc<Broker>,
+    tx: mpsc::Sender<io::Error>,
+    which: Which,
+) -> io::Result<()> {
+    let name = match which {
+        Which::Tools => "accept-broker",
+        Which::Admin => "accept-admin",
+    };
+    std::thread::Builder::new()
+        .name(name.to_string())
+        .spawn(move || {
+            let mut reported = false;
+            for stream in listener.incoming() {
+                match stream {
+                    Ok(stream) => {
+                        reported = false;
+                        serve_one(stream, &broker, which);
+                    }
+                    Err(e) if out_of_resources(&e) => {
+                        if !reported {
+                            broker.log(&format!(
+                                "brokerd: cannot accept on {name} for now, retrying: {e}\nsee docs/runbook.md#brokerd-listener-lost"
+                            ));
+                            reported = true;
+                        }
+                        std::thread::sleep(Duration::from_millis(200));
+                    }
+                    Err(e) => {
+                        // Once `run` has returned, nobody receives; dropping this is correct.
+                        let _ = tx.send(e);
+                        return;
+                    }
+                }
+            }
+        })?;
+    Ok(())
+}
+
+/// Hand one stream to its own thread. If the system refuses the thread, the stream is closed, which
+/// the peer sees as the broker being unavailable, and the refusal is printed.
+fn serve_one(stream: UnixStream, broker: &Arc<Broker>, which: Which) {
+    let for_thread = Arc::clone(broker);
+    let started = std::thread::Builder::new().spawn(move || match which {
+        Which::Tools => broker::handle(stream, &for_thread),
+        Which::Admin => admin::handle(stream, &for_thread),
+    });
+    if let Err(e) = started {
+        broker.log(&format!(
+            "brokerd: cannot start a thread for a connection, so it was closed: {e}\nsee docs/runbook.md#brokerd-listener-lost"
+        ));
+    }
+}
+
+/// Errors from `accept` that mean "not now" rather than "never": out of file descriptors
+/// (`EMFILE`, `ENFILE`, the same numbers on Linux and macOS) or out of memory. `accept` already
+/// retries `EINTR` itself.
+fn out_of_resources(e: &io::Error) -> bool {
+    const ENFILE: i32 = 23;
+    const EMFILE: i32 = 24;
+    matches!(e.raw_os_error(), Some(ENFILE | EMFILE)) || e.kind() == io::ErrorKind::OutOfMemory
+}

crates/brokerd/src/state.rs

@@ -0,0 +1,149 @@
+//! Where the broker keeps what it knows about a session: one JSON line per session in
+//! `<dir>/<id>.json`. A read that fails is an error, never "a new session". Neither value ever
+//! goes down: `raise` only ever raises, and it writes atomically so a crash leaves the old file.
+//!
+//! The file's format is private (`StateFile`), so `SessionState` stays free of serde.
+
+use crate::policy::{Label, SessionState};
+use proto::{DataClass, SessionId};
+use serde::{Deserialize, Serialize};
+use std::fs;
+use std::io::{self, Write};
+use std::os::unix::fs::{DirBuilderExt, OpenOptionsExt};
+use std::path::{Path, PathBuf};
+
+/// Where the owner looks when a session's state file cannot be read or written.
+pub const RUNBOOK: &str = "see docs/runbook.md#broker-state-damaged";
+
+/// A state file that exists but cannot be read, or a write that could not reach disk.
+#[derive(Debug)]
+pub enum StateError {
+    /// The file exists and cannot be read, or is not a state.
+    Unreadable(PathBuf, String),
+    /// The new state could not be put on disk.
+    Write(PathBuf, io::Error),
+}
+
+impl std::fmt::Display for StateError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            StateError::Unreadable(path, detail) => write!(
+                f,
+                "cannot read the session state {}: {}; {}",
+                path.display(),
+                detail,
+                RUNBOOK
+            ),
+            StateError::Write(path, err) => write!(
+                f,
+                "cannot write the session state {}: {}; {}",
+                path.display(),
+                err,
+                RUNBOOK
+            ),
+        }
+    }
+}
+
+impl std::error::Error for StateError {}
+
+/// The directory that holds one `<id>.json` per session.
+#[derive(Debug, Clone)]
+pub struct StateStore {
+    dir: PathBuf,
+}
+
+impl StateStore {
+    /// A store for `dir`. This does not touch the disk.
+    pub fn new(dir: &Path) -> StateStore {
+        StateStore {
+            dir: dir.to_path_buf(),
+        }
+    }
+
+    /// The path of the file for this session: `<dir>/<id>.json`.
+    pub fn path(&self, session: &SessionId) -> PathBuf {
+        self.dir.join(format!("{}.json", session.as_str()))
+    }
+
+    /// The session's current state. A missing file is a fresh session; anything else that cannot
+    /// be read is an error.
+    pub fn read(&self, session: &SessionId) -> Result<SessionState, StateError> {
+        let path = self.path(session);
+        let text = match fs::read_to_string(&path) {
+            Ok(text) => text,
+            Err(err) if err.kind() == io::ErrorKind::NotFound => return Ok(SessionState::default()),
+            Err(err) => return Err(StateError::Unreadable(path, err.to_string())),
+        };
+        let file = match serde_json::from_str::<StateFile>(&text) {
+            Ok(file) => file,
+            Err(err) => return Err(StateError::Unreadable(path, err.to_string())),
+        };
+        if file.taint == DataClass::Public {
+            return Err(StateError::Unreadable(
+                path,
+                "a session's taint is never below private".to_string(),
+            ));
+        }
+        Ok(SessionState {
+            taint: file.taint,
+            untrusted: file.untrusted,
+        })
+    }
+
+    /// The raised state and whether its results are untrusted. It trusts `current`, never reads the
+    /// file again, and always writes, so the file exists from the first result on.
+    pub fn raise(
+        &self,
+        session: &SessionId,
+        current: SessionState,
+        label: Label,
+    ) -> Result<SessionState, StateError> {
+        let next = SessionState {
+            taint: current.taint.max(label.class).max(DataClass::Private),
+            untrusted: current.untrusted || label.untrusted,
+        };
+        let path = self.path(session);
+        if let Err(err) = Self::persist(&self.dir, &path, next.taint, next.untrusted) {
+            return Err(StateError::Write(path, err));
+        }
+        Ok(next)
+    }
+
+    /// Write the new state to `<path>` atomically, in six steps. Any failure maps to an `io` error
+    /// the caller turns into `Write`; an error leaves the old file untouched.
+    fn persist(dir: &Path, path: &Path, taint: DataClass, untrusted: bool) -> io::Result<()> {
+        // 1. The directory and any missing parents, mode 0700.
+        fs::DirBuilder::new()
+            .recursive(true)
+            .mode(0o700)
+            .create(dir)?;
+        // 2. Serialise and append the final newline.
+        let json =
+            serde_json::to_string(&StateFile { taint, untrusted }).map_err(io::Error::other)?;
+        let bytes = format!("{json}\n");
+        // 3. A fresh temporary file; `truncate` replaces a leftover one.
+        let tmp = path.with_extension("json.tmp");
+        let mut file = fs::OpenOptions::new()
+            .write(true)
+            .create(true)
+            .truncate(true)
+            .mode(0o600)
+            .open(&tmp)?;
+        // 4. Write it and force it to disk.
+        file.write_all(bytes.as_bytes())?;
+        file.sync_all()?;
+        // 5. Swap it into place.
+        fs::rename(&tmp, path)?;
+        // 6. Pin the rename itself to disk.
+        fs::File::open(dir)?.sync_all()
+    }
+}
+
+/// One line on disk: the taint and the untrusted flag.
+#[derive(Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
+struct StateFile {
+    taint: DataClass,
+    untrusted: bool,
+}

crates/brokerd/tests/admin.rs

@@ -0,0 +1,385 @@
+//! One `admin.sock` connection: list, approve, refuse, check the grants; and expiry, which
+//! answers an approval the same way. Do not edit.
+
+#[path = "support/client.rs"]
+mod client;
+#[path = "support/rig.rs"]
+mod rig;
+#[path = "support/runtime.rs"]
+mod runtime;
+#[path = "support/sink.rs"]
+mod sink;
+#[path = "support/tmp.rs"]
+mod tmp;
+
+use std::os::unix::net::UnixStream;
+use std::sync::{Arc, Barrier};
+use std::time::{Duration, Instant};
+
+use brokerd::admin;
+use brokerd::broker::{self, Broker};
+use brokerd::policy::Label;
+use client::{Serve, next, open};
+use proto::{
+    ApprovalAnswer, Approve, AuditEvent, DataClass, DecisionRecord, DenyReason, Empty, ErrorCode,
+    Message, Refuse, SessionId, Timestamp, ToolResponse,
+};
+use rig::{Rig, grant_text, request};
+use runtime::Recording;
+
+fn ask_notes(rig: &Rig) {
+    rig.grant(
+        "notes",
+        &grant_text("read_file", "ask", "", "paths = [\"/n\"]"),
+    );
+}
+
+/// Sends a call that waits for approval; returns its connection once the pending frame is read.
+fn pending(broker: &Arc<Broker>, call: u64, arguments: &str) -> (UnixStream, u64) {
+    let req = request("s1", call, "read_file", arguments);
+    let mut stream = open(broker, broker::handle, call, Message::ToolRequest(req));
+    match next(&mut stream).msg {
+        Message::ToolResponse(ToolResponse::PendingApproval { approval, .. }) => (stream, approval),
+        other => panic!("{other:?}"),
+    }
+}
+
+/// One admin request; returns the answer's message after checking its id and `final`.
+fn admin(broker: &Arc<Broker>, msg: Message) -> Message {
+    let mut stream = open(broker, admin::handle, 5, msg);
+    let env = next(&mut stream);
+    assert_eq!((env.id, env.r#final), (5, true), "{env:?}");
+    env.msg
+}
+
+fn approve(broker: &Arc<Broker>, approval: u64) -> Message {
+    admin(broker, Message::Approve(Approve { approval }))
+}
+
+fn refuse(broker: &Arc<Broker>, approval: u64, reason: Option<&str>) -> Message {
+    let reason = reason.map(str::to_string);
+    admin(broker, Message::Refuse(Refuse { approval, reason }))
+}
+
+fn final_answer(stream: &mut UnixStream) -> ToolResponse {
+    match next(stream).msg {
+        Message::ToolResponse(r) => r,
+        other => panic!("{other:?}"),
+    }
+}
+
+fn outcome(msg: Message) -> DecisionRecord {
+    match msg {
+        Message::ApproveResult(r) => r.outcome,
+        other => panic!("{other:?}"),
+    }
+}
+
+fn error_code(msg: &Message) -> Option<ErrorCode> {
+    match msg {
+        Message::Error(e) => Some(e.code),
+        _ => None,
+    }
+}
+
+fn denied(reason: DenyReason) -> ToolResponse {
+    ToolResponse::Denied { reason }
+}
+
+#[test]
+fn approvals_lists_the_arguments_as_policy_parsed_them() {
+    let rig = Rig::new("admin-list");
+    ask_notes(&rig);
+    let broker = rig.broker(&Recording::answering("x"));
+    assert!(matches!(
+        admin(&broker, Message::Approvals(Empty {})),
+        Message::ApprovalList(list) if list.items.is_empty()
+    ));
+    // A backslash-u escape of `/` is `/` in JSON; the owner sees the one spelling policy matched.
+    let escaped = format!(r#"{{"path":"{}n{}a"}}"#, "\\u002f", "\\u002f");
+    assert!(
+        escaped.contains("u002f"),
+        "the escape must survive: {escaped}"
+    );
+    let (_stream, approval) = pending(&broker, 1, &escaped);
+    match admin(&broker, Message::Approvals(Empty {})) {
+        Message::ApprovalList(list) => {
+            assert_eq!(list.items.len(), 1);
+            assert_eq!(list.items[0].approval, approval);
+            assert_eq!(list.items[0].arguments, r#"{"path":"/n/a"}"#);
+            assert_eq!(list.items[0].grant, "notes");
+        }
+        other => panic!("{other:?}"),
+    }
+    // The audit log keeps the raw string.
+    match &rig.events()[0] {
+        AuditEvent::Decision { arguments, .. } => assert_eq!(arguments, &escaped),
+        other => panic!("{other:?}"),
+    }
+}
+
+#[test]
+fn approve_runs_the_call_and_answers_with_the_re_decision() {
+    let rig = Rig::new("admin-approve");
+    ask_notes(&rig);
+    let rt = Recording::answering("the notes");
+    let broker = rig.broker(&rt);
+    let (mut stream, approval) = pending(&broker, 1, r#"{"path":"/n/a"}"#);
+    assert_eq!(outcome(approve(&broker, approval)), DecisionRecord::Ask {});
+    assert!(matches!(
+        final_answer(&mut stream),
+        ToolResponse::Result { .. }
+    ));
+    assert_eq!(rt.count(), 1);
+    match &rig.events()[1] {
+        AuditEvent::Approval { answer, by, .. } => {
+            assert_eq!(*answer, ApprovalAnswer::Approved);
+            assert_eq!(by.as_deref(), Some("bxctl"));
+        }
+        other => panic!("{other:?}"),
+    }
+}
+
+#[test]
+fn refuse_denies_the_call_and_records_the_reason() {
+    let rig = Rig::new("admin-refuse");
+    ask_notes(&rig);
+    let rt = Recording::answering("x");
+    let broker = rig.broker(&rt);
+    let (mut stream, approval) = pending(&broker, 1, r#"{"path":"/n/a"}"#);
+    assert!(matches!(
+        refuse(&broker, approval, Some("not today")),
+        Message::Ok(Empty {})
+    ));
+    assert_eq!(
+        final_answer(&mut stream),
+        denied(DenyReason::ApprovalRefused)
+    );
+    assert_eq!(rt.count(), 0);
+    match &rig.events()[1] {
+        AuditEvent::Approval { answer, reason, .. } => {
+            assert_eq!(*answer, ApprovalAnswer::Refused);
+            assert_eq!(reason.as_deref(), Some("not today"));
+        }
+        other => panic!("{other:?}"),
+    }
+}
+
+#[test]
+fn an_unknown_or_answered_id_is_no_such_approval() {
+    let rig = Rig::new("admin-unknown");
+    ask_notes(&rig);
+    let broker = rig.broker(&Recording::answering("x"));
+    assert_eq!(
+        error_code(&approve(&broker, 41)),
+        Some(ErrorCode::NoSuchApproval)
+    );
+    assert_eq!(
+        error_code(&refuse(&broker, 41, None)),
+        Some(ErrorCode::NoSuchApproval)
+    );
+    let (_stream, approval) = pending(&broker, 1, r#"{"path":"/n/a"}"#);
+    refuse(&broker, approval, None);
+    assert_eq!(
+        error_code(&approve(&broker, approval)),
+        Some(ErrorCode::NoSuchApproval)
+    );
+    assert_eq!(rig.events().len(), 2, "one decision, one approval");
+}
+
+#[test]
+fn approve_and_refuse_at_once_give_exactly_one_answer() {
+    let rig = Rig::new("admin-race");
+    ask_notes(&rig);
+    let broker = rig.broker(&Recording::answering("x"));
+    for round in 0..100u64 {
+        let (mut stream, approval) = pending(&broker, round, r#"{"path":"/n/a"}"#);
+        let start = Arc::new(Barrier::new(2));
+        let racers: Vec<_> = [true, false]
+            .into_iter()
+            .map(|approving| {
+                let (broker, start) = (Arc::clone(&broker), Arc::clone(&start));
+                std::thread::spawn(move || {
+                    start.wait();
+                    if approving {
+                        approve(&broker, approval)
+                    } else {
+                        refuse(&broker, approval, None)
+                    }
+                })
+            })
+            .collect();
+        let answers: Vec<Message> = racers.into_iter().map(|r| r.join().unwrap()).collect();
+        let losers = answers
+            .iter()
+            .filter(|m| error_code(m) == Some(ErrorCode::NoSuchApproval))
+            .count();
+        assert_eq!(losers, 1, "round {round}: {answers:?}");
+        final_answer(&mut stream);
+        let approvals = rig
+            .events()
+            .iter()
+            .filter(|e| matches!(e, AuditEvent::Approval { decision, .. } if *decision == approval))
+            .count();
+        assert_eq!(approvals, 1, "round {round}");
+    }
+}
+
+#[test]
+fn approve_after_the_grant_file_is_removed_is_denied() {
+    let rig = Rig::new("admin-removed");
+    ask_notes(&rig);
+    let rt = Recording::answering("x");
+    let broker = rig.broker(&rt);
+    let (mut stream, approval) = pending(&broker, 1, r#"{"path":"/n/a"}"#);
+    rig.remove_grant("notes");
+    let reason = DenyReason::NoGrant;
+    assert_eq!(
+        outcome(approve(&broker, approval)),
+        DecisionRecord::Denied { reason }
+    );
+    assert_eq!(final_answer(&mut stream), denied(reason));
+    assert_eq!(rt.count(), 0);
+}
+
+#[test]
+fn approve_after_the_taint_rose_past_the_grant_is_denied() {
+    let rig = Rig::new("admin-taint");
+    let text = grant_text("read_file", "ask", "", "paths = [\"/n\"]")
+        .replace("max_taint = \"secret\"", "max_taint = \"private\"");
+    rig.grant("notes", &text);
+    let rt = Recording::answering("x");
+    let broker = rig.broker(&rt);
+    let (mut stream, approval) = pending(&broker, 1, r#"{"path":"/n/a"}"#);
+    let s1 = SessionId::new("s1").unwrap();
+    let secret = Label {
+        class: DataClass::Secret,
+        untrusted: false,
+    };
+    rig.state()
+        .raise(&s1, rig.state().read(&s1).unwrap(), secret)
+        .unwrap();
+    let reason = DenyReason::TaintTooHigh;
+    assert_eq!(
+        outcome(approve(&broker, approval)),
+        DecisionRecord::Denied { reason }
+    );
+    assert_eq!(final_answer(&mut stream), denied(reason));
+    assert_eq!(rt.count(), 0);
+}
+
+#[test]
+fn an_approval_that_cannot_be_recorded_is_denied_on_both_sides() {
+    let rig = Rig::new("admin-norecord");
+    ask_notes(&rig);
+    let rt = Recording::answering("x");
+    let broker = rig.broker(&rt);
+    let (mut stream, approval) = pending(&broker, 1, r#"{"path":"/n/a"}"#);
+    rig.switch.fail(true);
+    let reason = DenyReason::AuditUnavailable;
+    assert_eq!(
+        outcome(approve(&broker, approval)),
+        DecisionRecord::Denied { reason }
+    );
+    assert_eq!(final_answer(&mut stream), denied(reason));
+    assert_eq!(rt.count(), 0);
+}
+
+#[test]
+fn a_refusal_that_cannot_be_recorded_is_an_error_for_bxctl() {
+    let rig = Rig::new("admin-norefuse");
+    ask_notes(&rig);
+    let broker = rig.broker(&Recording::answering("x"));
+    let (mut stream, approval) = pending(&broker, 1, r#"{"path":"/n/a"}"#);
+    rig.switch.fail(true);
+    match refuse(&broker, approval, None) {
+        Message::Error(e) => {
+            assert_eq!(e.code, ErrorCode::Internal);
+            assert!(
+                e.detail.ends_with("see docs/runbook.md#audit-unavailable"),
+                "{}",
+                e.detail
+            );
+        }
+        other => panic!("{other:?}"),
+    }
+    assert_eq!(
+        final_answer(&mut stream),
+        denied(DenyReason::AuditUnavailable)
+    );
+}
+
+#[test]
+fn expiry_denies_an_approval_nobody_answered() {
+    let rig = Rig::with_ttl("admin-expire", 100);
+    ask_notes(&rig);
+    let rt = Recording::answering("x");
+    let broker = rig.broker(&rt);
+    let (mut stream, _) = pending(&broker, 1, r#"{"path":"/n/a"}"#);
+    let until = Instant::now() + Duration::from_secs(10);
+    while admin::expire_due(&broker, Timestamp::now()) == 0 {
+        assert!(Instant::now() < until, "never expired");
+        std::thread::sleep(Duration::from_millis(20));
+    }
+    assert_eq!(
+        final_answer(&mut stream),
+        denied(DenyReason::ApprovalExpired)
+    );
+    match &rig.events()[1] {
+        AuditEvent::Approval { answer, by, .. } => {
+            assert_eq!((*answer, by.as_deref()), (ApprovalAnswer::Expired, None));
+        }
+        other => panic!("{other:?}"),
+    }
+    assert_eq!(rt.count(), 0);
+}
+
+#[test]
+fn check_grants_reports_every_problem_or_none() {
+    let rig = Rig::new("admin-grants");
+    ask_notes(&rig);
+    let broker = rig.broker(&Recording::answering("x"));
+    match admin(&broker, Message::CheckGrants(Empty {})) {
+        Message::GrantsReport(r) => assert!(r.problems.is_empty(), "{r:?}"),
+        other => panic!("{other:?}"),
+    }
+    rig.grant("bad", "tool = \"read_file\"\nmdoe = \"auto\"\n");
+    rig.grant(
+        "Worse",
+        &grant_text("read_file", "ask", "", "paths = [\"/n\"]"),
+    );
+    match admin(&broker, Message::CheckGrants(Empty {})) {
+        Message::GrantsReport(r) => {
+            let files: Vec<&str> = r.problems.iter().map(|p| p.file.as_str()).collect();
+            assert!(files.contains(&"bad.toml"), "{r:?}");
+            assert!(files.contains(&"Worse.toml"), "{r:?}");
+        }
+        other => panic!("{other:?}"),
+    }
+}
+
+#[test]
+fn every_other_kind_on_admin_sock_is_forbidden() {
+    let rig = Rig::new("admin-forbidden");
+    let broker = rig.broker(&Recording::answering("x"));
+    let req = request("s1", 1, "read_file", r#"{"path":"/n/a"}"#);
+    for msg in [
+        Message::ToolRequest(req),
+        Message::Ok(Empty {}),
+        Message::ToolResponse(denied(DenyReason::NoGrant)),
+    ] {
+        assert_eq!(error_code(&admin(&broker, msg)), Some(ErrorCode::Forbidden));
+    }
+    let lines = rig.lines.with("on admin.sock");
+    assert_eq!(lines.len(), 3, "{:?}", rig.lines.all());
+    assert!(lines[0].contains("tool_request"), "{}", lines[0]);
+    assert!(
+        lines
+            .iter()
+            .all(|l| l.ends_with("see docs/runbook.md#socket-forbidden"))
+    );
+    assert!(
+        rig.events().is_empty(),
+        "a refused tool request decides nothing"
+    );
+}

crates/brokerd/tests/approvals.rs

@@ -0,0 +1,159 @@
+//! The pending-approval table: whoever takes an entry answers it, and everyone else finds it
+//! gone. Do not edit.
+
+#[path = "support/build.rs"]
+mod build;
+
+use std::sync::{Arc, Barrier};
+
+use brokerd::approvals::{Table, Verdict};
+use brokerd::policy::{Ask, Outcome, SessionState, decide};
+use build::{grant, now, read, set, ts};
+use proto::{CallId, DataClass, DenyReason, Mode, PendingApproval, SessionId, Timestamp};
+
+fn ask() -> Ask {
+    let grants = set(vec![grant("n", "read_file", Mode::Ask).paths(&["/n"])]);
+    match decide(read("/n/a"), &grants, SessionState::default(), now()) {
+        Outcome::Ask(ask) => ask,
+        other => panic!("the test's call does not ask: {other:?}"),
+    }
+}
+
+fn info(approval: u64, expires: &str) -> PendingApproval {
+    PendingApproval {
+        approval,
+        session: SessionId::new("s1").unwrap(),
+        call: CallId(approval + 100),
+        tool: "read_file".to_string(),
+        arguments: r#"{"path":"/n/a"}"#.to_string(),
+        grant: "n".to_string(),
+        taint: DataClass::Private,
+        created: now(),
+        expires: ts(expires),
+    }
+}
+
+const LATER: &str = "2026-09-18T12:15:00.000Z";
+
+#[test]
+fn a_new_table_is_empty_and_lists_in_id_order() {
+    let table = Table::new();
+    assert_eq!(table.list(), []);
+    let _a = table.insert(info(7, LATER), ask());
+    let _b = table.insert(info(3, LATER), ask());
+    assert_eq!(table.list(), [info(3, LATER), info(7, LATER)]);
+}
+
+#[test]
+fn an_entry_can_be_taken_once() {
+    let table = Table::new();
+    let _rx = table.insert(info(5, LATER), ask());
+    let entry = table.take(5).expect("the entry is there");
+    assert_eq!(entry.info, info(5, LATER));
+    assert_eq!(entry.ask.grant(), "n");
+    assert!(table.take(5).is_none(), "taken twice");
+    assert_eq!(table.list(), []);
+}
+
+#[test]
+fn an_id_never_added_is_not_there() {
+    let table = Table::new();
+    let _rx = table.insert(info(5, LATER), ask());
+    assert!(table.take(6).is_none());
+    assert_eq!(table.list().len(), 1);
+}
+
+#[test]
+fn the_verdict_goes_to_the_waiting_side() {
+    let table = Table::new();
+    let rx = table.insert(info(5, LATER), ask());
+    let entry = table.take(5).unwrap();
+    entry
+        .reply
+        .send(Verdict::Denied(DenyReason::ApprovalRefused))
+        .unwrap();
+    match rx.recv().unwrap() {
+        Verdict::Denied(reason) => assert_eq!(reason, DenyReason::ApprovalRefused),
+        Verdict::Run(_) => panic!("the verdict changed on the way"),
+    }
+}
+
+#[test]
+fn an_entry_expires_at_its_expiry_and_not_before() {
+    let table = Table::new();
+    let _a = table.insert(info(9, "2026-09-18T12:00:01.000Z"), ask());
+    let _b = table.insert(info(2, "2026-09-18T12:00:00.500Z"), ask());
+    let _c = table.insert(info(4, LATER), ask());
+
+    let before = ts("2026-09-18T12:00:00.499Z");
+    assert!(table.take_expired(before).is_empty());
+
+    // Exactly at `expires` is expired.
+    let at = ts("2026-09-18T12:00:00.500Z");
+    let due: Vec<u64> = table
+        .take_expired(at)
+        .iter()
+        .map(|e| e.info.approval)
+        .collect();
+    assert_eq!(due, [2]);
+
+    let after = ts("2026-09-18T13:00:00.000Z");
+    let due: Vec<u64> = table
+        .take_expired(after)
+        .iter()
+        .map(|e| e.info.approval)
+        .collect();
+    assert_eq!(due, [4, 9], "in id order");
+    assert_eq!(table.list(), []);
+    assert!(table.take_expired(Timestamp::MAX).is_empty());
+}
+
+#[test]
+fn two_takers_at_once_one_gets_it() {
+    for round in 0..100 {
+        let table = Arc::new(Table::new());
+        let _rx = table.insert(info(1, LATER), ask());
+        let start = Arc::new(Barrier::new(2));
+        let takers: Vec<_> = (0..2)
+            .map(|_| {
+                let table = Arc::clone(&table);
+                let start = Arc::clone(&start);
+                std::thread::spawn(move || {
+                    start.wait();
+                    table.take(1).is_some()
+                })
+            })
+            .collect();
+        let got: Vec<bool> = takers.into_iter().map(|t| t.join().unwrap()).collect();
+        assert_eq!(
+            got.iter().filter(|g| **g).count(),
+            1,
+            "round {round}: {got:?}"
+        );
+    }
+}
+
+#[test]
+fn a_taker_and_the_expiry_at_once_one_gets_it() {
+    for round in 0..100 {
+        let table = Arc::new(Table::new());
+        let _rx = table.insert(info(1, "2026-09-18T12:00:00.000Z"), ask());
+        let start = Arc::new(Barrier::new(2));
+        let t = {
+            let (table, start) = (Arc::clone(&table), Arc::clone(&start));
+            std::thread::spawn(move || {
+                start.wait();
+                usize::from(table.take(1).is_some())
+            })
+        };
+        let e = {
+            let (table, start) = (Arc::clone(&table), Arc::clone(&start));
+            std::thread::spawn(move || {
+                start.wait();
+                table.take_expired(now()).len()
+            })
+        };
+        let total = t.join().unwrap() + e.join().unwrap();
+        assert_eq!(total, 1, "round {round}");
+    }
+}

crates/brokerd/tests/args.rs

@@ -0,0 +1,428 @@
+//! Tests for tool arguments: their shape, and the form of paths, hosts and URLs. Do not edit.
+//!
+//! Every row of the "Paths" and "Hosts" tables in the M3a spec is a case here.
+
+use brokerd::args::{
+    ArgsError, MAX_PATH, MAX_URL, ToolArgs, ToolName, host_matches, inside, parse, url_host,
+    valid_host, valid_host_pattern, valid_path,
+};
+
+#[test]
+fn the_four_tool_names() {
+    let names = ["read_file", "write_file", "shell", "http_fetch"];
+    for (tool, name) in ToolName::ALL.into_iter().zip(names) {
+        assert_eq!(tool.as_str(), name);
+        assert_eq!(ToolName::parse(name), Some(tool));
+    }
+    for other in [
+        "",
+        "echo",
+        "clock",
+        "call_tool",
+        "Read_File",
+        "read_file ",
+        "readfile",
+    ] {
+        assert_eq!(ToolName::parse(other), None, "{other:?}");
+    }
+}
+
+#[test]
+fn valid_paths() {
+    let longest = format!("/{}", "a".repeat(MAX_PATH - 1));
+    assert_eq!(longest.len(), MAX_PATH);
+    for path in [
+        "/",
+        "/etc",
+        "/home/kyle/notes/a.md",
+        "/home/kyle/notes",
+        "/with space/and\ttab",
+        "/dots.in.names/..hidden/...",
+        "/unicode/\u{e9}t\u{e9}",
+        longest.as_str(),
+    ] {
+        assert!(valid_path(path), "{path:?} should be valid");
+    }
+}
+
+#[test]
+fn invalid_paths() {
+    let too_long = format!("/{}", "a".repeat(MAX_PATH));
+    assert_eq!(too_long.len(), MAX_PATH + 1);
+    for path in [
+        "",
+        "notes/a.md",
+        "./notes",
+        "~/notes",
+        "/home/kyle/notes/../.ssh/id",
+        "/home/kyle//notes/./a.md",
+        "/home//kyle",
+        "/home/./kyle",
+        "/home/kyle/",
+        "/home/kyle/..",
+        "/..",
+        "/.",
+        "//",
+        "/nul\0byte",
+        too_long.as_str(),
+    ] {
+        assert!(!valid_path(path), "{path:?} should be invalid");
+    }
+}
+
+/// The table in the spec, row by row, for the rows about form and containment.
+#[test]
+fn inside_is_by_whole_components() {
+    let grant = "/home/kyle/notes";
+    assert!(inside(grant, "/home/kyle/notes/a.md"));
+    assert!(inside(grant, "/home/kyle/notes"));
+    assert!(inside(grant, "/home/kyle/notes/deep/er/b.md"));
+    assert!(!inside(grant, "/home/kyle/notes2/a.md"));
+    assert!(!inside(grant, "/home/kyle/note"));
+    assert!(!inside(grant, "/home/kyle"));
+    assert!(!inside(grant, "/"));
+    assert!(!inside(grant, "/other/home/kyle/notes/a.md"));
+    // A grant of the root is refused when grants are loaded, but the function is still right.
+    assert!(inside("/", "/etc/passwd"));
+    assert!(inside("/", "/"));
+}
+
+#[test]
+fn valid_hosts_and_patterns() {
+    let label63 = "a".repeat(63);
+    let long = format!("{label63}.{label63}.{label63}.{}.com", "b".repeat(57));
+    assert_eq!(long.len(), 253);
+    for host in [
+        "example.com",
+        "www.example.com",
+        "a.b.example.com",
+        "xn--bcher-kva.example",
+        "1password.com",
+        "3.example.org",
+        "a-b.c-d.io",
+        long.as_str(),
+    ] {
+        assert!(valid_host(host), "{host:?} should be a valid host");
+        assert!(
+            valid_host_pattern(host),
+            "{host:?} should be a valid pattern"
+        );
+        let wild = format!("*.{host}");
+        assert!(!valid_host(&wild), "{wild:?} is a pattern, not a host");
+    }
+    assert!(valid_host_pattern("*.example.com"));
+    assert!(valid_host_pattern("*.a.b.example.com"));
+}
+
+#[test]
+fn invalid_hosts_and_patterns() {
+    let label64 = format!("{}.com", "a".repeat(64));
+    let too_long = format!("{}.com", ["a".repeat(63).as_str(); 4].join("."));
+    assert!(too_long.len() > 253);
+    for host in [
+        "",
+        "localhost",
+        "com",
+        "Example.com",
+        "example.COM",
+        "example.com.",
+        ".example.com",
+        "example..com",
+        "-example.com",
+        "example-.com",
+        "exa_mple.com",
+        "example.com:443",
+        "example.com/path",
+        "user@example.com",
+        "exa mple.com",
+        "[::1]",
+        "::1",
+        // Every spelling of an IPv4 address: the last label does not start with a letter.
+        "127.0.0.1",
+        "127.1",
+        "10.0.0.0x1",
+        "1.2.3.4",
+        "example.123",
+        "b\u{fc}cher.example",
+        label64.as_str(),
+        too_long.as_str(),
+    ] {
+        assert!(!valid_host(host), "{host:?} should not be a valid host");
+        assert!(
+            !valid_host_pattern(host),
+            "{host:?} should not be a valid pattern"
+        );
+    }
+    for pattern in [
+        "*",
+        "*.",
+        "*.com",
+        "*example.com",
+        "www.*.com",
+        "*.*.example.com",
+        "**.example.com",
+        "*.Example.com",
+        "*.127.0.0.1",
+    ] {
+        assert!(!valid_host_pattern(pattern), "{pattern:?}");
+    }
+}
+
+/// The host table in the spec, row by row.
+#[test]
+fn host_matching() {
+    assert!(host_matches("example.com", "example.com"));
+    assert!(!host_matches("example.com", "www.example.com"));
+    assert!(host_matches("*.example.com", "www.example.com"));
+    assert!(host_matches("*.example.com", "a.b.example.com"));
+    assert!(!host_matches("*.example.com", "example.com"));
+    // A suffix is not enough: the match is by whole labels.
+    assert!(!host_matches("*.example.com", "badexample.com"));
+    assert!(!host_matches("*.example.com", "www.example.com.evil.org"));
+    assert!(!host_matches("example.com", "example.com.evil.org"));
+    assert!(!host_matches("*.example.com", ".example.com"));
+}
+
+#[test]
+fn valid_urls_and_their_hosts() {
+    let base = "https://example.com/";
+    let longest = format!("{base}{}", "a".repeat(MAX_URL - base.len()));
+    assert_eq!(longest.len(), MAX_URL);
+    for (url, host) in [
+        ("https://example.com", "example.com"),
+        ("https://example.com/", "example.com"),
+        ("https://example.com:443", "example.com"),
+        ("https://example.com:443/", "example.com"),
+        ("https://www.example.com/a/b.html", "www.example.com"),
+        ("https://example.com/search?q=a+b&x=%20#frag", "example.com"),
+        ("https://example.com/@user", "example.com"),
+        ("https://example.com/a:8080/b", "example.com"),
+        ("https://example.com/https://other.org/", "example.com"),
+        ("https://example.com/back\\slash", "example.com"),
+        (longest.as_str(), "example.com"),
+    ] {
+        assert_eq!(url_host(url), Some(host), "{url}");
+    }
+}
+
+#[test]
+fn invalid_urls() {
+    let base = "https://example.com/";
+    let too_long = format!("{base}{}", "a".repeat(MAX_URL - base.len() + 1));
+    assert_eq!(too_long.len(), MAX_URL + 1);
+    for url in [
+        "",
+        "example.com",
+        "http://example.com/",
+        "HTTPS://example.com/",
+        "https:/example.com/",
+        "https://",
+        "https:///path",
+        "ftp://example.com/",
+        "file:///etc/passwd",
+        // userinfo
+        "https://user@example.com/",
+        "https://user:pw@example.com/",
+        "https://example.com@evil.org/",
+        // ports
+        "https://example.com:8443/",
+        "https://example.com:80/",
+        "https://example.com:/",
+        "https://example.com:443x/",
+        "https://example.com:4433/",
+        "https://example.com:443:443/",
+        // what follows the host must be the end, `:443` or `/`
+        "https://example.com?q=1",
+        "https://example.com#frag",
+        "https://example.com\\@evil.org/",
+        // hosts that are not host names
+        "https://localhost/",
+        "https://127.0.0.1/",
+        "https://127.1/",
+        "https://[::1]/",
+        "https://Example.com/",
+        "https://example.com./",
+        "https://b\u{fc}cher.example/",
+        // the rest must be printable ASCII with no space
+        "https://example.com/a b",
+        "https://example.com/a\tb",
+        "https://example.com/a\nb",
+        "https://example.com/caf\u{e9}",
+        "https://example.com/\u{7f}",
+        " https://example.com/",
+        "https://example.com/ ",
+        too_long.as_str(),
+    ] {
+        assert_eq!(url_host(url), None, "{url:?} should be invalid");
+    }
+}
+
+#[test]
+fn each_tool_parses_its_own_arguments() {
+    assert_eq!(
+        parse(ToolName::ReadFile, r#"{"path":"/home/kyle/notes/a.md"}"#),
+        Ok(ToolArgs::ReadFile {
+            path: "/home/kyle/notes/a.md".to_string()
+        })
+    );
+    assert_eq!(
+        parse(
+            ToolName::WriteFile,
+            r#"{"path":"/home/kyle/notes/a.md","content":"line\n"}"#
+        ),
+        Ok(ToolArgs::WriteFile {
+            path: "/home/kyle/notes/a.md".to_string(),
+            content: "line\n".to_string()
+        })
+    );
+    assert_eq!(
+        parse(ToolName::Shell, r#"{"command":"ls -l"}"#),
+        Ok(ToolArgs::Shell {
+            command: "ls -l".to_string(),
+            cwd: None
+        })
+    );
+    assert_eq!(
+        parse(ToolName::Shell, r#"{"command":"ls","cwd":"/home/kyle"}"#),
+        Ok(ToolArgs::Shell {
+            command: "ls".to_string(),
+            cwd: Some("/home/kyle".to_string())
+        })
+    );
+    assert_eq!(
+        parse(
+            ToolName::HttpFetch,
+            r#"{"url":"https://www.example.com/a"}"#
+        ),
+        Ok(ToolArgs::HttpFetch {
+            url: "https://www.example.com/a".to_string(),
+            host: "www.example.com".to_string()
+        })
+    );
+    // Field order and white space in the request do not matter.
+    assert_eq!(
+        parse(
+            ToolName::WriteFile,
+            " { \"content\" : \"x\" , \"path\" : \"/a/b\" } "
+        ),
+        Ok(ToolArgs::WriteFile {
+            path: "/a/b".to_string(),
+            content: "x".to_string()
+        })
+    );
+    // `command` and `content` are not inspected.
+    assert!(parse(ToolName::Shell, r#"{"command":""}"#).is_ok());
+    assert!(parse(ToolName::Shell, r#"{"command":"rm -rf / ; ../../x"}"#).is_ok());
+    assert!(parse(ToolName::WriteFile, r#"{"path":"/a/b","content":""}"#).is_ok());
+}
+
+#[test]
+fn arguments_of_the_wrong_shape_are_refused() {
+    let cases: [(ToolName, &str); 17] = [
+        (ToolName::ReadFile, ""),
+        (ToolName::ReadFile, "null"),
+        (ToolName::ReadFile, "[]"),
+        (ToolName::ReadFile, r#""/etc/hosts""#),
+        (ToolName::ReadFile, "{}"),
+        (ToolName::ReadFile, r#"{"path":"/a","mode":"r"}"#),
+        (ToolName::ReadFile, r#"{"path":"/a","path":"/b"}"#),
+        (ToolName::ReadFile, r#"{"path":7}"#),
+        (ToolName::ReadFile, r#"{"path":null}"#),
+        (ToolName::ReadFile, r#"{"path":"/a"} trailing"#),
+        (ToolName::WriteFile, r#"{"path":"/a/b"}"#),
+        (ToolName::WriteFile, r#"{"content":"x"}"#),
+        (
+            ToolName::WriteFile,
+            r#"{"path":"/a/b","content":"x","append":true}"#,
+        ),
+        (ToolName::Shell, r#"{"cwd":"/a"}"#),
+        (ToolName::Shell, r#"{"command":"ls","cwd":"/a","env":{}}"#),
+        (ToolName::Shell, r#"{"command":["ls"]}"#),
+        (
+            ToolName::HttpFetch,
+            r#"{"url":"https://example.com/","method":"POST"}"#,
+        ),
+    ];
+    for (tool, text) in cases {
+        match parse(tool, text) {
+            Err(ArgsError::Shape(_)) => {}
+            other => panic!("{tool:?} {text:?}: expected a shape error, got {other:?}"),
+        }
+    }
+    // One tool's arguments do not fit another tool.
+    assert!(parse(ToolName::Shell, r#"{"path":"/a"}"#).is_err());
+    assert!(parse(ToolName::ReadFile, r#"{"url":"https://example.com/"}"#).is_err());
+}
+
+#[test]
+fn a_bad_path_or_url_is_refused_in_every_tool_that_takes_one() {
+    for bad in ["notes/a.md", "/home/kyle/notes/../.ssh/id", "/a//b", "/a/"] {
+        let quoted = serde_json::to_string(bad).unwrap();
+        let read = format!(r#"{{"path":{quoted}}}"#);
+        let write = format!(r#"{{"path":{quoted},"content":"x"}}"#);
+        let shell = format!(r#"{{"command":"ls","cwd":{quoted}}}"#);
+        assert_eq!(
+            parse(ToolName::ReadFile, &read),
+            Err(ArgsError::Path(bad.to_string()))
+        );
+        assert_eq!(
+            parse(ToolName::WriteFile, &write),
+            Err(ArgsError::Path(bad.to_string()))
+        );
+        assert_eq!(
+            parse(ToolName::Shell, &shell),
+            Err(ArgsError::Path(bad.to_string()))
+        );
+    }
+    assert_eq!(
+        parse(ToolName::HttpFetch, r#"{"url":"http://example.com/"}"#),
+        Err(ArgsError::Url("http://example.com/".to_string()))
+    );
+    // A NUL can only arrive as a JSON escape; it is refused once decoded.
+    let nul = format!("{{\"path\":\"/a{}u0000b\"}}", '\\');
+    assert!(matches!(
+        parse(ToolName::ReadFile, &nul),
+        Err(ArgsError::Path(_))
+    ));
+    // `cwd: null` is the same as no `cwd`.
+    assert_eq!(
+        parse(ToolName::Shell, r#"{"command":"ls","cwd":null}"#),
+        Ok(ToolArgs::Shell {
+            command: "ls".to_string(),
+            cwd: None
+        })
+    );
+}
+
+/// What the owner is shown is the parsed value written out again, so two spellings of one path
+/// look the same. The escape is built from pieces so that no tool rewrites it on the way here.
+#[test]
+fn canonical_json_shows_what_was_parsed() {
+    let escaped_slash = format!("{}u002f", '\\');
+    let sneaky = format!("{{ \"path\" : \"{escaped_slash}etc{escaped_slash}hosts\" }}");
+    assert!(sneaky.contains("u002fetc"));
+    let args = parse(ToolName::ReadFile, &sneaky).unwrap();
+    assert_eq!(
+        args,
+        ToolArgs::ReadFile {
+            path: "/etc/hosts".to_string()
+        }
+    );
+    assert_eq!(args.canonical_json(), r#"{"path":"/etc/hosts"}"#);
+
+    // Fields come out in the spec's order whatever order they came in.
+    let write = parse(ToolName::WriteFile, r#"{"content":"x\ny","path":"/a/b"}"#).unwrap();
+    assert_eq!(
+        write.canonical_json(),
+        r#"{"path":"/a/b","content":"x\ny"}"#
+    );
+    let shell = parse(ToolName::Shell, r#"{"cwd":"/a","command":"ls"}"#).unwrap();
+    assert_eq!(shell.canonical_json(), r#"{"command":"ls","cwd":"/a"}"#);
+    // An absent cwd is left out, and the host is never written: it is not an argument.
+    let bare = parse(ToolName::Shell, r#"{"command":"ls","cwd":null}"#).unwrap();
+    assert_eq!(bare.canonical_json(), r#"{"command":"ls"}"#);
+    let fetch = parse(ToolName::HttpFetch, r#"{"url":"https://example.com/a"}"#).unwrap();
+    assert_eq!(fetch.canonical_json(), r#"{"url":"https://example.com/a"}"#);
+    assert_eq!(fetch.tool(), ToolName::HttpFetch);
+    assert_eq!(write.tool(), ToolName::WriteFile);
+}

crates/brokerd/tests/audit.rs

@@ -0,0 +1,258 @@
+//! The audit writer: the chain it writes, the lock, rollover, and stopping after a failed
+//! write. Do not edit. Startup checks, recovery and accepted breaks are in `audit_startup.rs`.
+
+#[path = "support/audit_dir.rs"]
+mod audit_dir;
+
+use std::os::unix::fs::PermissionsExt;
+
+use audit_dir::{D1, D2, TempDir, denied, lines, ts};
+use brokerd::audit::{AuditError, RECOVERED_NOTICE, Writer, verify_dir};
+use proto::{AuditRecord, Hash32, sha256};
+
+fn mode(path: &std::path::Path) -> u32 {
+    std::fs::metadata(path).unwrap().permissions().mode() & 0o777
+}
+
+#[test]
+fn the_first_record_starts_the_chain() {
+    let dir = TempDir::unmade("first");
+    let opened = Writer::open(&dir.path, false).unwrap();
+    assert!(!opened.recovered);
+    assert!(opened.accepted.is_none());
+    let mut writer = opened.writer;
+    assert_eq!(writer.next_seq(), 0);
+
+    let seq = writer
+        .append(ts("2026-09-17T08:00:00.000Z"), denied(1))
+        .unwrap();
+    assert_eq!(seq, 0);
+    assert_eq!(writer.next_seq(), 1);
+
+    let text = std::fs::read_to_string(dir.path.join(D1)).unwrap();
+    assert!(text.ends_with('\n'), "a record is one line and its newline");
+    assert_eq!(text.lines().count(), 1);
+    let record: AuditRecord = serde_json::from_str(text.lines().next().unwrap()).unwrap();
+    assert_eq!((record.seq, record.prev), (0, Hash32::ZERO));
+    assert_eq!(record.time, ts("2026-09-17T08:00:00.000Z"));
+    assert_eq!(record.event, denied(1));
+
+    assert_eq!(mode(&dir.path), 0o700, "the directory open() made");
+    assert_eq!(mode(&dir.path.join(D1)), 0o600);
+}
+
+#[test]
+fn the_chain_runs_across_a_day_boundary() {
+    let dir = TempDir::unmade("days");
+    let mut writer = Writer::open(&dir.path, false).unwrap().writer;
+    let times = [
+        "2026-09-17T23:59:58.000Z",
+        "2026-09-17T23:59:59.999Z",
+        "2026-09-18T00:00:00.000Z",
+        "2026-09-18T00:00:01.000Z",
+    ];
+    for (i, time) in times.iter().enumerate() {
+        assert_eq!(writer.append(ts(time), denied(i as u64)).unwrap(), i as u64);
+    }
+    let (day1, day2) = (lines(&dir.path, D1), lines(&dir.path, D2));
+    assert_eq!((day1.len(), day2.len()), (2, 2));
+
+    // seq goes on across files, and the new file chains from the last line of the old one.
+    let first: AuditRecord = serde_json::from_str(&day2[0]).unwrap();
+    assert_eq!(first.seq, 2);
+    assert_eq!(first.prev, sha256(day1[1].as_bytes()).unwrap());
+
+    let report = verify_dir(&dir.path).unwrap();
+    assert_eq!(report.failure, None);
+    assert_eq!((report.records, report.next_seq), (4, 4));
+    assert!(report.clock_warnings.is_empty());
+}
+
+#[test]
+fn reopening_continues_the_chain() {
+    let dir = TempDir::unmade("reopen");
+    let mut writer = Writer::open(&dir.path, false).unwrap().writer;
+    writer
+        .append(ts("2026-09-17T08:00:00.000Z"), denied(1))
+        .unwrap();
+    writer
+        .append(ts("2026-09-17T08:00:01.000Z"), denied(2))
+        .unwrap();
+    drop(writer);
+
+    // One file: the whole of it is checked.
+    let mut writer = Writer::open(&dir.path, false).unwrap().writer;
+    assert_eq!(writer.next_seq(), 2);
+    assert_eq!(
+        writer
+            .append(ts("2026-09-18T08:00:00.000Z"), denied(3))
+            .unwrap(),
+        2
+    );
+    drop(writer);
+
+    // Two files: the latest is checked, resumed from the last line of the one before.
+    let mut writer = Writer::open(&dir.path, false).unwrap().writer;
+    assert_eq!(writer.next_seq(), 3);
+    assert_eq!(
+        writer
+            .append(ts("2026-09-18T08:00:01.000Z"), denied(4))
+            .unwrap(),
+        3
+    );
+    drop(writer);
+
+    let report = verify_dir(&dir.path).unwrap();
+    assert_eq!(report.failure, None);
+    assert_eq!(report.records, 4);
+}
+
+#[test]
+fn an_empty_latest_file_gets_the_next_record_as_its_first_line() {
+    let dir = TempDir::case("empty-latest", None);
+    let opened = Writer::open(&dir.path, false).unwrap();
+    assert!(!opened.recovered);
+    let mut writer = opened.writer;
+    assert_eq!(
+        writer
+            .append(ts("2026-09-18T08:00:00.000Z"), denied(9))
+            .unwrap(),
+        5
+    );
+
+    let day2 = lines(&dir.path, D2);
+    assert_eq!(day2.len(), 1);
+    let record: AuditRecord = serde_json::from_str(&day2[0]).unwrap();
+    assert_eq!(
+        record.prev,
+        sha256(lines(&dir.path, D1)[4].as_bytes()).unwrap()
+    );
+    assert_eq!(verify_dir(&dir.path).unwrap().failure, None);
+}
+
+#[test]
+fn a_second_writer_is_refused() {
+    let dir = TempDir::unmade("lock");
+    let first = Writer::open(&dir.path, false).unwrap();
+    let error = Writer::open(&dir.path, false).unwrap_err();
+    assert!(matches!(error, AuditError::Locked), "{error}");
+    let text = error.to_string();
+    assert!(text.starts_with("brokerd is already running"), "{text}");
+    assert!(
+        text.ends_with("see docs/runbook.md#brokerd-already-running"),
+        "{text}"
+    );
+
+    // The lock goes when the writer goes, however that happens.
+    drop(first);
+    assert!(Writer::open(&dir.path, false).is_ok());
+}
+
+#[test]
+fn the_writer_never_goes_back_to_an_earlier_file() {
+    let dir = TempDir::unmade("clock");
+    let mut writer = Writer::open(&dir.path, false).unwrap().writer;
+    writer
+        .append(ts("2026-09-18T00:00:05.000Z"), denied(1))
+        .unwrap();
+    // The clock is stepped back over midnight.
+    writer
+        .append(ts("2026-09-17T23:59:50.000Z"), denied(2))
+        .unwrap();
+
+    assert!(
+        !dir.path.join(D1).exists(),
+        "a record went into an earlier file"
+    );
+    assert_eq!(lines(&dir.path, D2).len(), 2);
+    let report = verify_dir(&dir.path).unwrap();
+    assert_eq!(report.failure, None);
+    assert_eq!(report.clock_warnings.len(), 1);
+
+    // It holds across a restart too.
+    drop(writer);
+    let mut writer = Writer::open(&dir.path, false).unwrap().writer;
+    writer
+        .append(ts("2026-09-17T23:59:55.000Z"), denied(3))
+        .unwrap();
+    assert!(!dir.path.join(D1).exists());
+    assert_eq!(verify_dir(&dir.path).unwrap().failure, None);
+}
+
+#[test]
+fn files_that_are_not_log_files_are_ignored() {
+    let dir = TempDir::case("good", None);
+    std::fs::write(dir.path.join("notes.txt"), "not a log\n").unwrap();
+    std::fs::write(dir.path.join("2026-09-19.jsonl.bak"), "not a log\n").unwrap();
+    std::fs::write(dir.path.join("latest.jsonl"), "not a log\n").unwrap();
+    let mut writer = Writer::open(&dir.path, false).unwrap().writer;
+    assert_eq!(writer.next_seq(), 10);
+    writer
+        .append(ts("2026-09-18T10:00:00.000Z"), denied(9))
+        .unwrap();
+    assert_eq!(verify_dir(&dir.path).unwrap().records, 11);
+}
+
+/// After one failed write the writer writes nothing more, even when the cause has gone: part of
+/// a line may be on disk, and only the next start deals with that.
+#[test]
+fn a_failed_write_stops_the_writer() {
+    let dir = TempDir::unmade("sticky");
+    let mut writer = Writer::open(&dir.path, false).unwrap().writer;
+    writer
+        .append(ts("2026-09-17T08:00:00.000Z"), denied(1))
+        .unwrap();
+
+    // A new day needs a new file, and the directory no longer allows one.
+    std::fs::set_permissions(&dir.path, std::fs::Permissions::from_mode(0o500)).unwrap();
+    if std::fs::write(dir.path.join("probe"), "").is_ok() {
+        eprintln!("skipped: this user can write to a read-only directory (root?)");
+        std::fs::set_permissions(&dir.path, std::fs::Permissions::from_mode(0o700)).unwrap();
+        return;
+    }
+    let error = writer
+        .append(ts("2026-09-18T08:00:00.000Z"), denied(2))
+        .unwrap_err();
+    assert!(matches!(error, AuditError::Io { .. }), "{error}");
+    assert!(
+        error
+            .to_string()
+            .ends_with("see docs/runbook.md#audit-unavailable"),
+        "{error}"
+    );
+
+    std::fs::set_permissions(&dir.path, std::fs::Permissions::from_mode(0o700)).unwrap();
+    for time in ["2026-09-18T08:00:01.000Z", "2026-09-17T08:00:02.000Z"] {
+        let error = writer.append(ts(time), denied(3)).unwrap_err();
+        assert!(matches!(error, AuditError::Stopped), "{error}");
+        assert!(
+            error
+                .to_string()
+                .ends_with("see docs/runbook.md#audit-unavailable"),
+            "{error}"
+        );
+    }
+    assert_eq!(
+        lines(&dir.path, D1).len(),
+        1,
+        "a stopped writer wrote something"
+    );
+    assert!(!dir.path.join(D2).exists());
+
+    // A restart puts it right.
+    drop(writer);
+    let mut writer = Writer::open(&dir.path, false).unwrap().writer;
+    assert_eq!(
+        writer
+            .append(ts("2026-09-18T08:00:03.000Z"), denied(4))
+            .unwrap(),
+        1
+    );
+    assert_eq!(verify_dir(&dir.path).unwrap().failure, None);
+}
+
+#[test]
+fn the_recovered_notice_names_its_runbook_entry() {
+    assert!(RECOVERED_NOTICE.starts_with("audit: recovered a torn final line"));
+    assert!(RECOVERED_NOTICE.ends_with("see docs/runbook.md#audit-recovered"));
+}

crates/brokerd/tests/audit_edges.rs

@@ -0,0 +1,134 @@
+//! Audit writer edge cases found in the M3a review: a log with no complete record, a file whose
+//! name only looks like a log, and the lock file outliving the writer.
+
+#[path = "support/audit_dir.rs"]
+mod audit_dir;
+
+use audit_dir::{D1, D2, TempDir, denied, lines, ts};
+use brokerd::audit::{Writer, verify_dir};
+use proto::{AuditRecord, Hash32};
+
+/// A kill between creating the day's file and writing its first record leaves it empty. It must
+/// open like an empty log, not panic.
+#[test]
+fn one_zero_length_log_file_opens_as_an_empty_log() {
+    let dir = TempDir::unmade("zero-length");
+    std::fs::create_dir_all(&dir.path).unwrap();
+    std::fs::write(dir.path.join(D1), b"").unwrap();
+
+    let opened = Writer::open(&dir.path, false).unwrap();
+    assert!(!opened.recovered);
+    let mut writer = opened.writer;
+    assert_eq!(writer.next_seq(), 0);
+    writer
+        .append(ts("2026-09-17T08:00:00.000Z"), denied(1))
+        .unwrap();
+
+    let record: AuditRecord = serde_json::from_str(&lines(&dir.path, D1)[0]).unwrap();
+    assert_eq!((record.seq, record.prev), (0, Hash32::ZERO));
+    let report = verify_dir(&dir.path).unwrap();
+    assert_eq!(report.failure, None);
+    assert_eq!(report.records, 1);
+}
+
+/// The same crash, a day later: the older file holds records and the new one is empty.
+#[test]
+fn a_zero_length_file_after_records_continues_the_chain() {
+    let dir = TempDir::unmade("zero-length-later");
+    let mut writer = Writer::open(&dir.path, false).unwrap().writer;
+    writer
+        .append(ts("2026-09-17T08:00:00.000Z"), denied(1))
+        .unwrap();
+    drop(writer);
+    std::fs::write(dir.path.join(D2), b"").unwrap();
+
+    let mut writer = Writer::open(&dir.path, false).unwrap().writer;
+    assert_eq!(writer.next_seq(), 1);
+    writer
+        .append(ts("2026-09-18T08:00:00.000Z"), denied(2))
+        .unwrap();
+    let report = verify_dir(&dir.path).unwrap();
+    assert_eq!(report.failure, None);
+    assert_eq!(report.records, 2);
+}
+
+/// A crash part-way through the very first record: one file, one torn line, nothing else.
+#[test]
+fn a_single_torn_first_record_is_recovered() {
+    let dir = TempDir::unmade("torn-only");
+    std::fs::create_dir_all(&dir.path).unwrap();
+    std::fs::write(dir.path.join(D1), br#"{"seq":0,"time":"2026-09-17T08:"#).unwrap();
+
+    let opened = Writer::open(&dir.path, false).unwrap();
+    assert!(opened.recovered);
+    let report = verify_dir(&dir.path).unwrap();
+    assert_eq!(report.failure, None);
+    assert_eq!(report.recoveries.len(), 1);
+}
+
+/// `2026-0x-19.jsonl` is not a log file, for `brokerd` as for `bxctl audit verify`: it is neither
+/// verified nor written to, and the real log goes on in its own files.
+#[test]
+fn a_file_that_only_looks_like_a_log_is_not_part_of_it() {
+    let dir = TempDir::case("good", None);
+    let odd = dir.path.join("2026-0x-19.jsonl");
+    std::fs::write(&odd, b"not a record\n").unwrap();
+
+    let mut writer = Writer::open(&dir.path, false)
+        .expect("a stray file does not break the chain")
+        .writer;
+    writer
+        .append(ts("2026-09-18T09:00:00.000Z"), denied(9))
+        .unwrap();
+
+    assert_eq!(
+        std::fs::read(&odd).unwrap(),
+        b"not a record\n",
+        "never written"
+    );
+    let report = verify_dir(&dir.path).unwrap();
+    assert_eq!(report.failure, None);
+    assert_eq!(
+        report.records, 11,
+        "the ten fixture records and the new one"
+    );
+}
+
+/// The lock file is never removed: a `brokerd` holding the old file open could otherwise lock it
+/// while a new one creates and locks a fresh file, and both would write.
+#[test]
+fn the_lock_file_outlives_the_writer() {
+    let dir = TempDir::unmade("lock-stays");
+    let writer = Writer::open(&dir.path, false).unwrap().writer;
+    drop(writer);
+    assert!(dir.path.join(".lock").exists());
+    Writer::open(&dir.path, false).expect("the lock was released with the writer");
+}
+
+/// A torn last line in one file, then an empty later file (created, never written). The torn line
+/// is ended in its own file and the recovery goes on the chain after it, so the log verifies and
+/// the next start is an ordinary one. Found by the independent review of task 23.
+#[test]
+fn a_torn_line_before_an_empty_later_file_is_recovered_in_place() {
+    let dir = TempDir::unmade("torn-then-empty");
+    let mut writer = Writer::open(&dir.path, false).unwrap().writer;
+    writer
+        .append(ts("2026-09-17T08:00:00.000Z"), denied(1))
+        .unwrap();
+    drop(writer);
+    let mut d1 = std::fs::read(dir.path.join(D1)).unwrap();
+    d1.extend_from_slice(br#"{"seq":1,"time":"2026-09-17T09"#);
+    std::fs::write(dir.path.join(D1), &d1).unwrap();
+    std::fs::write(dir.path.join(D2), b"").unwrap();
+
+    let opened = Writer::open(&dir.path, false).unwrap();
+    assert!(opened.recovered);
+    drop(opened);
+    let report = verify_dir(&dir.path).unwrap();
+    assert_eq!(report.failure, None, "{:?}", report.failure);
+    assert_eq!(report.recoveries.len(), 1);
+    assert!(std::fs::read(dir.path.join(D1)).unwrap().ends_with(b"\n"));
+
+    let again = Writer::open(&dir.path, false).expect("the next start is an ordinary one");
+    assert!(!again.recovered);
+}

crates/brokerd/tests/audit_startup.rs

@@ -0,0 +1,300 @@
+//! What `Writer::open` does with the log it finds: refuse a broken chain, recover a torn tail,
+//! accept a break when told to. Do not edit. The fixture logs are in
+//! `crates/proto/tests/fixtures/audit/`; each test works on a copy.
+
+#[path = "support/audit_dir.rs"]
+mod audit_dir;
+
+use audit_dir::{D1, D2, TempDir, denied, lines, snapshot};
+use brokerd::audit::{AuditError, Writer, verify_dir};
+use proto::{AuditEvent, AuditRecord, Location, Timestamp};
+
+type Case = (
+    &'static str,
+    Option<&'static [&'static str]>,
+    &'static str,
+    u64,
+    &'static str,
+);
+
+fn at(file: &str, line: u64) -> Location {
+    Location {
+        file: file.to_string(),
+        line,
+    }
+}
+
+/// An ordinary start checks the latest file only, so each damaged file is copied alone: it is
+/// then the latest. Nothing may be written to a log that does not verify.
+#[test]
+fn a_broken_chain_refuses_to_start_and_writes_nothing() {
+    let parse = "does not parse as an audit record";
+    // (case, the files to copy, then the failure's file, line and text)
+    let cases: [Case; 9] = [
+        (
+            "changed-byte",
+            Some(&[D1]),
+            D1,
+            4,
+            "prev is not the hash of the line before",
+        ),
+        ("deleted-line", Some(&[D1]), D1, 3, "seq is 3, expected 2"),
+        ("swapped-lines", Some(&[D1]), D1, 2, "seq is 2, expected 1"),
+        ("seq-gap", None, D1, 3, "seq is 3, expected 2"),
+        ("cut-short", Some(&[D1]), D1, 3, parse),
+        // Both files: the latest does not chain from the last line of the one before.
+        (
+            "file-not-chained",
+            None,
+            D2,
+            1,
+            "does not chain from the last line of the file before",
+        ),
+        (
+            "break-without-failure",
+            None,
+            D2,
+            6,
+            "an accepted break with no failure before it",
+        ),
+        ("recovery-wrong-hash", None, D2, 6, parse),
+        ("torn-recovery", None, D2, 6, parse),
+    ];
+    for (case, only, file, line, what) in cases {
+        let dir = TempDir::case(case, only);
+        let before = snapshot(&dir.path);
+        let error = Writer::open(&dir.path, false)
+            .err()
+            .unwrap_or_else(|| panic!("{case}: started"));
+        let AuditError::Broken(failure) = &error else {
+            panic!("{case}: {error}");
+        };
+        assert_eq!(
+            (failure.file.as_str(), failure.line, failure.what.as_str()),
+            (file, line, what),
+            "{case}"
+        );
+        let text = error.to_string();
+        assert!(
+            text.starts_with(&format!("{file}:{line}: {what}")),
+            "{case}: {text}"
+        );
+        assert!(
+            text.ends_with("see docs/runbook.md#audit-chain-broken"),
+            "{case}: {text}"
+        );
+        assert_eq!(
+            snapshot(&dir.path),
+            before,
+            "{case}: the log was written to"
+        );
+    }
+}
+
+/// A torn tail is recovered: the torn bytes stay, a newline ends them if one is missing, and a
+/// `Recovery` record follows in the same file, whatever today's date is.
+#[test]
+fn a_torn_tail_is_recovered() {
+    // (case, the torn line's file and number, newline already there)
+    let cases = [
+        ("torn-tail", D2, 6, false),
+        ("torn-tail-complete-json", D2, 6, false),
+        ("torn-unparseable-newline", D2, 6, true),
+        ("torn-first-line", D2, 1, false),
+    ];
+    for (case, file, line, has_newline) in cases {
+        let dir = TempDir::case(case, None);
+        let before = snapshot(&dir.path);
+        let opened = Writer::open(&dir.path, false).unwrap_or_else(|e| panic!("{case}: {e}"));
+        assert!(opened.recovered, "{case}");
+        assert!(opened.accepted.is_none(), "{case}");
+
+        let after = snapshot(&dir.path);
+        assert_eq!(
+            after.len(),
+            before.len(),
+            "{case}: the Recovery went into a new file"
+        );
+        let (old, new) = (&before[file], &after[file]);
+        assert!(
+            new.starts_with(old),
+            "{case}: bytes already on disk were changed"
+        );
+        let added = &new[old.len()..];
+        // One newline to end the torn line if it had none, then one line.
+        let added = if has_newline {
+            added
+        } else {
+            added.strip_prefix(b"\n").expect(case)
+        };
+        assert_eq!(added.iter().filter(|b| **b == b'\n').count(), 1, "{case}");
+        let record: AuditRecord =
+            serde_json::from_slice(added.strip_suffix(b"\n").expect(case)).expect(case);
+        assert!(
+            matches!(record.event, AuditEvent::Recovery { .. }),
+            "{case}"
+        );
+
+        let report = verify_dir(&dir.path).unwrap();
+        assert_eq!(report.failure, None, "{case}");
+        assert_eq!(report.torn_tail, None, "{case}");
+        assert_eq!(report.recoveries, vec![at(file, line)], "{case}");
+
+        // The chain goes on from the Recovery, and the next start finds nothing to recover.
+        let mut writer = opened.writer;
+        assert_eq!(
+            writer.append(Timestamp::now(), denied(9)).unwrap(),
+            record.seq + 1,
+            "{case}"
+        );
+        drop(writer);
+        let opened = Writer::open(&dir.path, false).unwrap();
+        assert!(!opened.recovered, "{case}");
+        assert_eq!(verify_dir(&dir.path).unwrap().failure, None, "{case}");
+    }
+}
+
+/// Damage in an older file is not seen by an ordinary start. `bxctl audit verify` sees it, and
+/// `--accept-break` must too: it verifies the whole log.
+#[test]
+fn a_break_in_an_older_file_can_be_accepted() {
+    let dir = TempDir::case("changed-byte", None);
+    let before = snapshot(&dir.path);
+    drop(Writer::open(&dir.path, false).expect("the latest file verifies"));
+    assert_eq!(snapshot(&dir.path), before);
+    let failure = verify_dir(&dir.path).unwrap().failure.unwrap();
+    assert_eq!((failure.file.as_str(), failure.line), (D1, 4));
+
+    let opened = Writer::open(&dir.path, true).unwrap();
+    assert!(!opened.recovered);
+    assert_eq!(
+        opened.accepted.as_ref().map(|f| (f.file.as_str(), f.line)),
+        Some((D1, 4))
+    );
+    let after = snapshot(&dir.path);
+    assert_eq!(after[D1], before[D1], "nothing is repaired");
+    assert!(after[D2].starts_with(&before[D2]));
+    let last: AuditRecord = serde_json::from_str(lines(&dir.path, D2).last().unwrap()).unwrap();
+    assert_eq!(
+        last.event,
+        AuditEvent::AcceptedBreak {
+            file: D1.to_string(),
+            line: 4,
+            last_good: failure.last_good,
+        }
+    );
+    assert_eq!(
+        last.seq, 10,
+        "seq 3 for the failing line, and seven lines to the break"
+    );
+
+    let report = verify_dir(&dir.path).unwrap();
+    assert_eq!(report.failure, None);
+    assert_eq!(report.accepted_breaks, vec![at(D2, 6)]);
+
+    let mut writer = opened.writer;
+    assert_eq!(writer.append(Timestamp::now(), denied(9)).unwrap(), 11);
+    drop(writer);
+
+    // The next ordinary start resumes at the latest file and meets a break that names a file
+    // it has not read.
+    let mut writer = Writer::open(&dir.path, false).unwrap().writer;
+    assert_eq!(writer.append(Timestamp::now(), denied(10)).unwrap(), 12);
+    assert_eq!(verify_dir(&dir.path).unwrap().failure, None);
+}
+
+#[test]
+fn a_break_in_the_latest_file_can_be_accepted() {
+    // (case, failing line, seq of the break record)
+    for (case, line, seq) in [("recovery-wrong-hash", 6, 12), ("torn-recovery", 6, 12)] {
+        let dir = TempDir::case(case, None);
+        let before = snapshot(&dir.path);
+        let opened = Writer::open(&dir.path, true).unwrap_or_else(|e| panic!("{case}: {e}"));
+        assert_eq!(
+            opened.accepted.as_ref().map(|f| f.line),
+            Some(line),
+            "{case}"
+        );
+        let after = snapshot(&dir.path);
+        assert!(after[D2].starts_with(&before[D2]), "{case}");
+
+        // torn-recovery ends without a newline: the break record must start on its own line.
+        let all = lines(&dir.path, D2);
+        let last: AuditRecord = serde_json::from_str(all.last().unwrap()).expect(case);
+        assert!(
+            matches!(last.event, AuditEvent::AcceptedBreak { .. }),
+            "{case}"
+        );
+        assert_eq!(last.seq, seq, "{case}");
+        assert_eq!(all.len(), 8, "{case}");
+
+        let report = verify_dir(&dir.path).unwrap();
+        assert_eq!(report.failure, None, "{case}");
+        assert_eq!(report.accepted_breaks, vec![at(D2, 8)], "{case}");
+        drop(opened);
+        assert!(Writer::open(&dir.path, false).is_ok(), "{case}");
+    }
+}
+
+/// The short check is a shortcut and never the last word: when it cannot be made, or fails, the
+/// whole log is verified and that verdict stands. Here the last line of the older file is the
+/// damage, so there is nothing to resume from.
+#[test]
+fn an_accepted_break_at_the_end_of_an_older_file_does_not_stop_later_starts() {
+    let dir = TempDir::case("good", None);
+    let day1 = std::fs::read_to_string(dir.path.join(D1)).unwrap();
+    let cut = format!("{}\n", &day1[..day1.len() - 40]);
+    std::fs::write(dir.path.join(D1), cut).unwrap();
+
+    let error = Writer::open(&dir.path, false).unwrap_err();
+    let AuditError::Broken(failure) = &error else {
+        panic!("{error}");
+    };
+    assert_eq!((failure.file.as_str(), failure.line), (D1, 5));
+
+    drop(Writer::open(&dir.path, true).unwrap());
+    let mut writer = Writer::open(&dir.path, false)
+        .expect("the break was accepted")
+        .writer;
+    writer.append(Timestamp::now(), denied(9)).unwrap();
+    assert_eq!(verify_dir(&dir.path).unwrap().failure, None);
+}
+
+#[test]
+fn accept_break_with_nothing_to_accept_is_an_error() {
+    for case in ["good", "torn-tail"] {
+        let dir = TempDir::case(case, None);
+        let before = snapshot(&dir.path);
+        let error = Writer::open(&dir.path, true).unwrap_err();
+        assert!(
+            matches!(error, AuditError::NothingToAccept),
+            "{case}: {error}"
+        );
+        assert!(error.to_string().starts_with("nothing to accept"), "{case}");
+        assert_eq!(
+            snapshot(&dir.path),
+            before,
+            "{case}: the log was written to"
+        );
+    }
+}
+
+/// A second failure after an accepted break needs its own break.
+#[test]
+fn damage_after_a_break_is_a_new_failure() {
+    let dir = TempDir::case("accepted-break", None);
+    drop(Writer::open(&dir.path, false).expect("the fixture verifies"));
+    let mut text = std::fs::read_to_string(dir.path.join(D1)).unwrap();
+    text.push_str("{}\n{}\n");
+    std::fs::write(dir.path.join(D1), text).unwrap();
+
+    let error = Writer::open(&dir.path, false).unwrap_err();
+    let AuditError::Broken(failure) = &error else {
+        panic!("{error}");
+    };
+    assert_eq!((failure.file.as_str(), failure.line), (D1, 8));
+    drop(Writer::open(&dir.path, true).unwrap());
+    let report = verify_dir(&dir.path).unwrap();
+    assert_eq!(report.failure, None);
+    assert_eq!(report.accepted_breaks, vec![at(D1, 6), at(D1, 10)]);
+}

crates/brokerd/tests/broker.rs

@@ -0,0 +1,324 @@
+//! One `broker.sock` connection: decision, record, run, answer; and every way it fails closed.
+//! Do not edit.
+
+#[path = "support/client.rs"]
+mod client;
+#[path = "support/rig.rs"]
+mod rig;
+#[path = "support/runtime.rs"]
+mod runtime;
+#[path = "support/sink.rs"]
+mod sink;
+#[path = "support/tmp.rs"]
+mod tmp;
+
+use std::io::Write;
+use std::os::unix::fs::PermissionsExt;
+use std::os::unix::net::UnixStream;
+use std::sync::Arc;
+
+use brokerd::broker;
+use brokerd::ledger::NOT_RECORDED;
+use brokerd::runner::{REFUSING, RunError};
+use client::{Serve, call, next, open};
+use proto::{
+    ApprovalList, Approve, ApproveResult, AuditEvent, DataClass, DecisionRecord, DenyReason, Empty,
+    Envelope, ErrorCode, GrantsReport, Message, Refuse, ResultStatus, SessionId, ToolResponse,
+    Turn, TurnDone, TurnEvent, Usage, WireError,
+};
+use rig::{Rig, grant_text, request};
+use runtime::Recording;
+
+const NOTES: &str = r#"{"path":"/n/a"}"#;
+
+fn read_notes(call_id: u64) -> proto::ToolRequest {
+    request("s1", call_id, "read_file", NOTES)
+}
+
+fn only(frames: &[Envelope]) -> &ToolResponse {
+    assert_eq!(frames.len(), 1, "{frames:?}");
+    assert!(frames[0].r#final);
+    match &frames[0].msg {
+        Message::ToolResponse(r) => r,
+        other => panic!("{other:?}"),
+    }
+}
+
+fn denied(reason: DenyReason) -> ToolResponse {
+    ToolResponse::Denied { reason }
+}
+
+fn auto_notes(rig: &Rig, class: &str) {
+    let text = grant_text("read_file", "auto", "", "paths = [\"/n\"]").replace(
+        "result_class = \"private\"",
+        &format!("result_class = \"{class}\""),
+    );
+    rig.grant("notes", &text);
+}
+
+#[test]
+fn a_call_no_grant_allows_is_denied_and_recorded() {
+    let rig = Rig::new("broker-nogrant");
+    let rt = Recording::answering("x");
+    let broker = rig.broker(&rt);
+    let frames = call(&broker, read_notes(41));
+    assert_eq!(frames[0].id, 41, "the answer carries the request's id");
+    assert_eq!(only(&frames), &denied(DenyReason::NoGrant));
+    assert_eq!(rt.count(), 0);
+    match rig.events().as_slice() {
+        [AuditEvent::Decision { outcome, .. }] => assert_eq!(
+            *outcome,
+            DecisionRecord::Denied {
+                reason: DenyReason::NoGrant
+            }
+        ),
+        other => panic!("{other:?}"),
+    }
+}
+
+#[test]
+fn an_allowed_call_runs_and_its_result_raises_the_state() {
+    let rig = Rig::new("broker-allowed");
+    auto_notes(&rig, "secret");
+    let rt = Recording::answering("the notes");
+    let broker = rig.broker(&rt);
+    let frames = call(&broker, read_notes(7));
+    assert_eq!(
+        only(&frames),
+        &ToolResponse::Result {
+            content: "the notes".to_string(),
+            class: DataClass::Secret,
+            untrusted: false,
+            truncated: false,
+        }
+    );
+    assert_eq!(rt.count(), 1);
+    let events = rig.events();
+    assert!(matches!(
+        events.as_slice(),
+        [
+            AuditEvent::Decision { .. },
+            AuditEvent::Result {
+                decision: 0,
+                status: ResultStatus::Result,
+                taint_after: DataClass::Secret,
+                ..
+            }
+        ]
+    ));
+    let state = rig.state().read(&SessionId::new("s1").unwrap()).unwrap();
+    assert_eq!(state.taint, DataClass::Secret);
+}
+
+#[test]
+fn a_runtime_failure_is_passed_on_and_recorded_as_failed() {
+    let rig = Rig::new("broker-refusing");
+    auto_notes(&rig, "secret");
+    let rt = Recording::with(Err(RunError::Unavailable(REFUSING.to_string())));
+    let broker = rig.broker(&rt);
+    let frames = call(&broker, read_notes(1));
+    assert_eq!(
+        only(&frames),
+        &ToolResponse::Failed {
+            message: REFUSING.to_string()
+        }
+    );
+    match &rig.events()[1] {
+        AuditEvent::Result {
+            status,
+            taint_after,
+            ..
+        } => assert_eq!(
+            (*status, *taint_after),
+            (ResultStatus::Failed, DataClass::Private)
+        ),
+        other => panic!("{other:?}"),
+    }
+    assert!(!rig.state_file("s1").exists(), "a failure changes no state");
+}
+
+fn every_kind_but_tool_request() -> Vec<Message> {
+    let usage = Usage {
+        cache_n: 0,
+        prompt_n: 0,
+        predicted_n: 0,
+        reasoning_tokens: 0,
+        thinking_capped: false,
+    };
+    vec![
+        Message::ToolResponse(denied(DenyReason::NoGrant)),
+        Message::Error(WireError {
+            code: ErrorCode::Internal,
+            detail: String::new(),
+        }),
+        Message::Turn(Turn {
+            session: SessionId::new("s1").unwrap(),
+            content: String::new(),
+            resume: false,
+        }),
+        Message::TurnEvent(TurnEvent::Content {
+            text: String::new(),
+        }),
+        Message::TurnDone(TurnDone {
+            content: String::new(),
+            usage,
+        }),
+        Message::Approvals(Empty {}),
+        Message::ApprovalList(ApprovalList { items: Vec::new() }),
+        Message::Approve(Approve { approval: 0 }),
+        Message::ApproveResult(ApproveResult {
+            outcome: DecisionRecord::Allowed {},
+        }),
+        Message::Refuse(Refuse {
+            approval: 0,
+            reason: None,
+        }),
+        Message::Ok(Empty {}),
+        Message::CheckGrants(Empty {}),
+        Message::GrantsReport(GrantsReport {
+            problems: Vec::new(),
+        }),
+    ]
+}
+
+#[test]
+fn every_other_kind_on_broker_sock_is_forbidden() {
+    let rig = Rig::new("broker-forbidden");
+    let rt = Recording::answering("x");
+    let broker = rig.broker(&rt);
+    let kinds = every_kind_but_tool_request();
+    assert_eq!(kinds.len(), 13, "every Message variant but tool_request");
+    for (i, msg) in kinds.into_iter().enumerate() {
+        let id = 100 + i as u64;
+        let mut stream = open(&broker, broker::handle, id, msg);
+        let env = next(&mut stream);
+        assert_eq!((env.id, env.r#final), (id, true));
+        match env.msg {
+            Message::Error(e) => assert_eq!(e.code, ErrorCode::Forbidden),
+            other => panic!("{other:?}"),
+        }
+    }
+    let lines = rig.lines.with("broker.sock");
+    assert_eq!(lines.len(), 13, "{:?}", rig.lines.all());
+    for line in &lines {
+        assert!(
+            line.ends_with("\nsee docs/runbook.md#socket-forbidden"),
+            "{line}"
+        );
+    }
+    assert_eq!(rig.lines.with("kind approve on broker.sock").len(), 1);
+    assert!(
+        rig.events().is_empty(),
+        "nothing is recorded for a refused kind"
+    );
+}
+
+#[test]
+fn a_frame_that_is_not_json_is_answered_with_bad_message() {
+    let rig = Rig::new("broker-badframe");
+    let rt = Recording::answering("x");
+    let broker = rig.broker(&rt);
+    let (mut client, server) = UnixStream::pair().unwrap();
+    let b = Arc::clone(&broker);
+    std::thread::spawn(move || broker::handle(server, &b));
+    client.write_all(&3u32.to_be_bytes()).unwrap();
+    client.write_all(b"{{{").unwrap();
+    let env = next(&mut client);
+    assert_eq!((env.id, env.r#final), (0, true));
+    match env.msg {
+        Message::Error(e) => assert_eq!(e.code, ErrorCode::BadMessage),
+        other => panic!("{other:?}"),
+    }
+    assert!(rig.events().is_empty());
+}
+
+#[test]
+fn one_invalid_grant_file_denies_a_call_a_valid_file_would_allow() {
+    let rig = Rig::new("broker-invalid");
+    auto_notes(&rig, "private");
+    rig.grant("bad", "tool = \"read_file\"\nmdoe = \"auto\"\n");
+    let rt = Recording::answering("x");
+    let broker = rig.broker(&rt);
+    for id in [1, 2] {
+        let frames = call(&broker, read_notes(id));
+        assert_eq!(only(&frames), &denied(DenyReason::GrantsInvalid));
+    }
+    assert_eq!(rt.count(), 0);
+    // Printed once for the two calls, with the pointer.
+    let printed = rig.lines.with("bad.toml");
+    assert_eq!(printed.len(), 1, "{:?}", rig.lines.all());
+    assert!(
+        printed[0].ends_with("see docs/runbook.md#grants-invalid"),
+        "{}",
+        printed[0]
+    );
+    rig.remove_grant("bad");
+    let frames = call(&broker, read_notes(3));
+    assert!(matches!(only(&frames), ToolResponse::Result { .. }));
+    assert_eq!(rt.count(), 1);
+}
+
+#[test]
+fn a_damaged_session_state_is_state_unreadable() {
+    let rig = Rig::new("broker-state");
+    auto_notes(&rig, "private");
+    std::fs::create_dir_all(rig.cfg.state_dir()).unwrap();
+    std::fs::write(rig.state_file("s1"), "{\"taint\":\"loud\"}").unwrap();
+    let rt = Recording::answering("x");
+    let broker = rig.broker(&rt);
+    let frames = call(&broker, read_notes(1));
+    assert_eq!(only(&frames), &denied(DenyReason::StateUnreadable));
+    assert_eq!(rt.count(), 0);
+    let lines = rig.lines.with("s1.json");
+    assert!(
+        lines
+            .iter()
+            .any(|l| l.ends_with("see docs/runbook.md#broker-state-damaged")),
+        "{lines:?}"
+    );
+}
+
+#[test]
+fn a_failed_audit_write_runs_nothing_now_or_later() {
+    let rig = Rig::new("broker-audit");
+    auto_notes(&rig, "private");
+    let rt = Recording::answering("x");
+    let broker = rig.broker(&rt);
+    rig.switch.fail(true);
+    let frames = call(&broker, read_notes(1));
+    assert_eq!(only(&frames), &denied(DenyReason::AuditUnavailable));
+    rig.switch.fail(false);
+    let frames = call(&broker, read_notes(2));
+    assert_eq!(only(&frames), &denied(DenyReason::AuditUnavailable));
+    assert_eq!(rt.count(), 0);
+    assert!(
+        !rig.lines
+            .with("see docs/runbook.md#audit-unavailable")
+            .is_empty()
+    );
+}
+
+#[test]
+fn a_state_that_cannot_be_written_withholds_the_content() {
+    if tmp::running_as_root("a_state_that_cannot_be_written_withholds_the_content") {
+        return;
+    }
+    let rig = Rig::new("broker-ro");
+    auto_notes(&rig, "secret");
+    let dir = rig.cfg.state_dir();
+    std::fs::create_dir_all(&dir).unwrap();
+    std::fs::set_permissions(&dir, std::fs::Permissions::from_mode(0o500)).unwrap();
+    let rt = Recording::answering("the secret");
+    let broker = rig.broker(&rt);
+    let frames = call(&broker, read_notes(1));
+    std::fs::set_permissions(&dir, std::fs::Permissions::from_mode(0o700)).unwrap();
+    assert_eq!(
+        only(&frames),
+        &ToolResponse::Failed {
+            message: NOT_RECORDED.to_string()
+        }
+    );
+    assert_eq!(rt.count(), 1, "it ran; its content is what is withheld");
+    let text = format!("{frames:?}");
+    assert!(!text.contains("the secret"), "{text}");
+}

crates/brokerd/tests/broker_pending.rs

@@ -0,0 +1,230 @@
+//! A call an `ask` grant matched: the pending frame, the table entry, the wait, and a requester
+//! that goes away. The tests answer entries by hand, as `admin` will. Do not edit.
+
+#[path = "support/client.rs"]
+mod client;
+#[path = "support/rig.rs"]
+mod rig;
+#[path = "support/runtime.rs"]
+mod runtime;
+#[path = "support/sink.rs"]
+mod sink;
+#[path = "support/tmp.rs"]
+mod tmp;
+
+use std::os::unix::net::UnixStream;
+use std::sync::Arc;
+use std::time::{Duration, Instant};
+
+use brokerd::broker::{self, Broker, GONE};
+use brokerd::ledger::Answer;
+use client::{Serve, next, open};
+use proto::{
+    AuditEvent, DataClass, DecisionRecord, DenyReason, Message, ResultStatus, Timestamp,
+    ToolResponse,
+};
+use rig::{Rig, grant_text, request};
+use runtime::Recording;
+
+fn ask_notes(rig: &Rig, extra: &str) {
+    rig.grant(
+        "notes",
+        &grant_text("read_file", "ask", extra, "paths = [\"/n\"]"),
+    );
+}
+
+/// Sends a call and reads its pending frame. Returns the connection and the frame's values.
+fn start(broker: &Arc<Broker>, arguments: &str) -> (UnixStream, u64, Timestamp) {
+    let req = request("s1", 9, "read_file", arguments);
+    let mut stream = open(broker, broker::handle, 9, Message::ToolRequest(req));
+    let env = next(&mut stream);
+    assert_eq!((env.id, env.r#final), (9, false), "{env:?}");
+    match env.msg {
+        Message::ToolResponse(ToolResponse::PendingApproval { approval, expires }) => {
+            (stream, approval, expires)
+        }
+        other => panic!("{other:?}"),
+    }
+}
+
+/// What `admin` does for an entry it took: record the answer, send the verdict.
+fn answer_by_hand(broker: &Broker, id: u64, answer: Answer) -> DecisionRecord {
+    let entry = broker.table().take(id).expect("the entry is pending");
+    answer_entry(broker, entry, answer)
+}
+
+fn answer_entry(
+    broker: &Broker,
+    entry: brokerd::approvals::Entry,
+    answer: Answer,
+) -> DecisionRecord {
+    let grants = broker.grants();
+    let done = broker.ledger().answer(
+        entry.ask,
+        entry.info.approval,
+        answer,
+        &grants,
+        Timestamp::now(),
+    );
+    entry.reply.send(done.verdict).unwrap();
+    done.outcome
+}
+
+fn approved() -> Answer {
+    Answer::Approved {
+        by: Some("bxctl".to_string()),
+    }
+}
+
+fn final_answer(stream: &mut UnixStream) -> ToolResponse {
+    let env = next(stream);
+    assert!(env.r#final, "{env:?}");
+    match env.msg {
+        Message::ToolResponse(r) => r,
+        other => panic!("{other:?}"),
+    }
+}
+
+fn eventually(what: &str, mut done: impl FnMut() -> bool) {
+    let until = Instant::now() + Duration::from_secs(10);
+    while !done() {
+        assert!(Instant::now() < until, "never happened: {what}");
+        std::thread::sleep(Duration::from_millis(20));
+    }
+}
+
+#[test]
+fn an_ask_call_waits_is_listed_and_runs_when_approved() {
+    let rig = Rig::new("pending-approve");
+    ask_notes(&rig, "");
+    let rt = Recording::answering("the notes");
+    let broker = rig.broker(&rt);
+    let before = Timestamp::now();
+    // Spaced JSON: the table shows the arguments as policy parsed them, not as sent.
+    let (mut stream, approval, expires) = start(&broker, r#"{ "path" : "/n/a" }"#);
+    assert_eq!(approval, 0, "the approval id is the decision's seq");
+    let items = broker.table().list();
+    assert_eq!(items.len(), 1);
+    let item = &items[0];
+    assert_eq!(item.approval, 0);
+    assert_eq!((item.session.as_str(), item.call.0), ("s1", 9));
+    assert_eq!(item.tool, "read_file");
+    assert_eq!(item.arguments, r#"{"path":"/n/a"}"#);
+    assert_eq!(
+        (item.grant.as_str(), item.taint),
+        ("notes", DataClass::Private)
+    );
+    assert!(item.created >= before);
+    assert_eq!(item.expires, expires);
+    assert_eq!(
+        expires.unix_millis() - item.created.unix_millis(),
+        900_000,
+        "now plus ttl_ms"
+    );
+    assert_eq!(rt.count(), 0, "nothing runs while it waits");
+
+    assert_eq!(
+        answer_by_hand(&broker, 0, approved()),
+        DecisionRecord::Ask {}
+    );
+    assert!(matches!(
+        final_answer(&mut stream),
+        ToolResponse::Result { .. }
+    ));
+    assert_eq!(rt.count(), 1);
+    let events = rig.events();
+    assert!(
+        matches!(
+            events.as_slice(),
+            [
+                AuditEvent::Decision { .. },
+                AuditEvent::Approval { decision: 0, .. },
+                AuditEvent::Result { decision: 0, .. }
+            ]
+        ),
+        "{events:?}"
+    );
+}
+
+#[test]
+fn the_expiry_is_the_grants_when_that_is_earlier() {
+    let rig = Rig::new("pending-grant-expiry");
+    let soon = Timestamp::from_unix_millis(Timestamp::now().unix_millis() + 60_000).unwrap();
+    ask_notes(&rig, &format!("expires = \"{}\"", soon.to_rfc3339()));
+    let rt = Recording::answering("x");
+    let broker = rig.broker(&rt);
+    let (_stream, _, expires) = start(&broker, r#"{"path":"/n/a"}"#);
+    assert_eq!(expires, soon);
+}
+
+#[test]
+fn a_denied_verdict_reaches_the_requester_and_nothing_runs() {
+    let rig = Rig::new("pending-refuse");
+    ask_notes(&rig, "");
+    let rt = Recording::answering("x");
+    let broker = rig.broker(&rt);
+    let (mut stream, approval, _) = start(&broker, r#"{"path":"/n/a"}"#);
+    let refused = Answer::Refused {
+        by: Some("bxctl".to_string()),
+        reason: None,
+    };
+    answer_by_hand(&broker, approval, refused);
+    assert_eq!(
+        final_answer(&mut stream),
+        ToolResponse::Denied {
+            reason: DenyReason::ApprovalRefused
+        }
+    );
+    assert_eq!(rt.count(), 0);
+}
+
+#[test]
+fn a_requester_that_leaves_takes_its_own_entry_and_nothing_is_written() {
+    let rig = Rig::new("pending-leave");
+    ask_notes(&rig, "");
+    let rt = Recording::answering("x");
+    let broker = rig.broker(&rt);
+    let (stream, _, _) = start(&broker, r#"{"path":"/n/a"}"#);
+    drop(stream);
+    // The waiting thread looks at its connection every second.
+    eventually("the entry is removed", || broker.table().list().is_empty());
+    std::thread::sleep(Duration::from_millis(200));
+    assert_eq!(rig.events().len(), 1, "only the decision");
+    let report = brokerd::audit::verify_dir(&rig.cfg.audit_dir()).unwrap();
+    assert_eq!(report.abandoned, [0]);
+    assert!(report.failure.is_none());
+    assert_eq!(rt.count(), 0);
+}
+
+#[test]
+fn a_requester_gone_at_the_last_look_runs_nothing_and_closes_the_call() {
+    let rig = Rig::new("pending-lastlook");
+    ask_notes(&rig, "");
+    let rt = Recording::answering("x");
+    let broker = rig.broker(&rt);
+    let (stream, approval, _) = start(&broker, r#"{"path":"/n/a"}"#);
+    // Take the entry first, so the waiting thread cannot take it back when it sees the
+    // connection gone; then approve.
+    let entry = broker.table().take(approval).unwrap();
+    drop(stream);
+    answer_entry(&broker, entry, approved());
+    eventually("the call is closed", || rig.events().len() == 3);
+    match &rig.events()[2] {
+        AuditEvent::Result {
+            status,
+            decision,
+            sha256,
+            bytes,
+            ..
+        } => {
+            assert_eq!((*status, *decision), (ResultStatus::Failed, 0));
+            assert_eq!(*sha256, proto::sha256(GONE.as_bytes()).unwrap());
+            assert_eq!(*bytes, GONE.len() as u64);
+        }
+        other => panic!("{other:?}"),
+    }
+    assert_eq!(GONE, "the requester went away");
+    assert_eq!(rt.count(), 0);
+    let report = brokerd::audit::verify_dir(&rig.cfg.audit_dir()).unwrap();
+    assert!(report.unfinished.is_empty() && report.abandoned.is_empty());
+}

crates/brokerd/tests/broker_sequence.rs

@@ -0,0 +1,238 @@
+//! Properties over sequences of calls, through `broker::handle` with many threads at once:
+//! the log verifies and no `seq` repeats; taint never goes down; every `Result` follows the
+//! record that let its call run; the runtime sees a call only after `allowed` or an approval.
+//! Do not edit.
+
+#[path = "support/client.rs"]
+mod client;
+#[path = "support/rig.rs"]
+mod rig;
+#[path = "support/runtime.rs"]
+mod runtime;
+#[path = "support/sink.rs"]
+mod sink;
+#[path = "support/tmp.rs"]
+mod tmp;
+
+use std::collections::BTreeMap;
+use std::sync::Arc;
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::time::Duration;
+
+use brokerd::ledger::Answer;
+use client::{Serve, call};
+use proto::{
+    AuditEvent, AuditRecord, CallId, DataClass, DecisionRecord, Message, SessionId, Timestamp,
+    ToolResponse,
+};
+use rig::{Rig, grant_text, request};
+use runtime::Recording;
+
+fn grants(rig: &Rig) {
+    let with = |class: &str, max: &str| {
+        grant_text("read_file", "auto", "", "")
+            .replace(
+                "result_class = \"private\"",
+                &format!("result_class = \"{class}\""),
+            )
+            .replace("max_taint = \"secret\"", &format!("max_taint = \"{max}\""))
+    };
+    rig.grant("notes", &(with("private", "secret") + "paths = [\"/n\"]\n"));
+    rig.grant("keys", &(with("secret", "secret") + "paths = [\"/k\"]\n"));
+    // Stops applying once a session has read a secret.
+    rig.grant(
+        "public",
+        &(with("public", "private") + "paths = [\"/p\"]\n"),
+    );
+    rig.grant(
+        "never",
+        &grant_text("read_file", "deny", "", "paths = [\"/d\"]"),
+    );
+    rig.grant(
+        "asked",
+        &grant_text("read_file", "ask", "", "paths = [\"/a\"]"),
+    );
+}
+
+/// Which call ran on what authority: (session, call) of every Decision that allowed and every
+/// Approval whose re-decision let the call run, keyed by the decision's seq.
+fn check_sequence(records: &[AuditRecord]) -> usize {
+    let mut may_run: BTreeMap<u64, (SessionId, CallId)> = BTreeMap::new();
+    let mut taint: BTreeMap<String, DataClass> = BTreeMap::new();
+    let mut results = 0;
+    for (i, r) in records.iter().enumerate() {
+        assert_eq!(r.seq, i as u64, "no seq repeats or skips");
+        match &r.event {
+            AuditEvent::Decision {
+                session,
+                call,
+                outcome: DecisionRecord::Allowed {},
+                ..
+            } => {
+                may_run.insert(r.seq, (session.clone(), *call));
+            }
+            AuditEvent::Approval {
+                session,
+                call,
+                decision,
+                outcome: DecisionRecord::Allowed {} | DecisionRecord::Ask {},
+                ..
+            } => {
+                may_run.insert(*decision, (session.clone(), *call));
+            }
+            AuditEvent::Result {
+                session,
+                call,
+                decision,
+                taint_after,
+                ..
+            } => {
+                results += 1;
+                let allowed = may_run.remove(decision);
+                assert_eq!(
+                    allowed,
+                    Some((session.clone(), *call)),
+                    "seq {}: a Result with no record letting its call run",
+                    r.seq
+                );
+                let before = taint.insert(session.as_str().to_string(), *taint_after);
+                assert!(
+                    before.is_none_or(|b| b <= *taint_after),
+                    "seq {}: taint went down",
+                    r.seq
+                );
+            }
+            _ => {}
+        }
+    }
+    assert!(
+        may_run.is_empty(),
+        "calls allowed but never finished: {may_run:?}"
+    );
+    results
+}
+
+#[test]
+fn eight_threads_two_sessions_fifty_calls_each() {
+    let rig = Rig::new("sequence-many");
+    grants(&rig);
+    let rt = Recording::answering("content");
+    let broker = rig.broker(&rt);
+    let paths = ["/n/x", "/k/x", "/p/x", "/d/x", "/none/x"];
+    let threads: Vec<_> = (0..8u64)
+        .map(|t| {
+            let broker = Arc::clone(&broker);
+            std::thread::spawn(move || {
+                let session = if t % 2 == 0 { "s-even" } else { "s-odd" };
+                for i in 0..50u64 {
+                    let path = paths[((t + i) % 5) as usize];
+                    let args = format!(r#"{{"path":"{path}"}}"#);
+                    let req = request(session, t * 1000 + i, "read_file", &args);
+                    let frames = call(&broker, req);
+                    assert_eq!(frames.len(), 1);
+                }
+            })
+        })
+        .collect();
+    for t in threads {
+        t.join().unwrap();
+    }
+    let report = brokerd::audit::verify_dir(&rig.cfg.audit_dir()).unwrap();
+    assert!(report.failure.is_none(), "{:?}", report.failure);
+    assert!(report.unfinished.is_empty());
+    let records = rig.records();
+    let decisions = records
+        .iter()
+        .filter(|r| matches!(r.event, AuditEvent::Decision { .. }))
+        .count();
+    assert_eq!(decisions, 400);
+    let results = check_sequence(&records);
+    assert_eq!(
+        rt.count(),
+        results,
+        "the runtime saw exactly the allowed calls"
+    );
+    assert!(results > 0 && results < 400);
+    // Both sessions read a secret.
+    for s in ["s-even", "s-odd"] {
+        let state = rig.state().read(&SessionId::new(s).unwrap()).unwrap();
+        assert_eq!(state.taint, DataClass::Secret);
+    }
+}
+
+#[test]
+fn approved_and_refused_calls_run_only_after_an_approval() {
+    let rig = Rig::new("sequence-ask");
+    grants(&rig);
+    let rt = Recording::answering("content");
+    let broker = rig.broker(&rt);
+    // An owner who approves even ids and refuses odd ones, as fast as they appear.
+    let stop = Arc::new(AtomicBool::new(false));
+    let owner = {
+        let (broker, stop) = (Arc::clone(&broker), Arc::clone(&stop));
+        std::thread::spawn(move || {
+            while !stop.load(Ordering::SeqCst) {
+                for item in broker.table().list() {
+                    let Some(entry) = broker.table().take(item.approval) else {
+                        continue;
+                    };
+                    let answer = if item.approval % 2 == 0 {
+                        Answer::Approved { by: None }
+                    } else {
+                        Answer::Refused {
+                            by: None,
+                            reason: None,
+                        }
+                    };
+                    let grants = broker.grants();
+                    let done = broker.ledger().answer(
+                        entry.ask,
+                        item.approval,
+                        answer,
+                        &grants,
+                        Timestamp::now(),
+                    );
+                    entry.reply.send(done.verdict).unwrap();
+                }
+                std::thread::sleep(Duration::from_millis(2));
+            }
+        })
+    };
+    let threads: Vec<_> = (0..4u64)
+        .map(|t| {
+            let broker = Arc::clone(&broker);
+            std::thread::spawn(move || {
+                for i in 0..10u64 {
+                    let path = if i % 2 == 0 { "/a/x" } else { "/n/x" };
+                    let args = format!(r#"{{"path":"{path}"}}"#);
+                    let frames = call(&broker, request("s1", t * 100 + i, "read_file", &args));
+                    let last = frames.last().unwrap();
+                    assert!(
+                        matches!(
+                            &last.msg,
+                            Message::ToolResponse(
+                                ToolResponse::Result { .. } | ToolResponse::Denied { .. }
+                            )
+                        ),
+                        "{last:?}"
+                    );
+                }
+            })
+        })
+        .collect();
+    for t in threads {
+        t.join().unwrap();
+    }
+    stop.store(true, Ordering::SeqCst);
+    owner.join().unwrap();
+    let records = rig.records();
+    let approvals = records
+        .iter()
+        .filter(|r| matches!(r.event, AuditEvent::Approval { .. }))
+        .count();
+    assert_eq!(approvals, 20, "one Approval for each of the twenty asks");
+    let results = check_sequence(&records);
+    assert_eq!(rt.count(), results);
+    let report = brokerd::audit::verify_dir(&rig.cfg.audit_dir()).unwrap();
+    assert!(report.failure.is_none() && report.abandoned.is_empty());
+}

crates/brokerd/tests/config.rs

@@ -0,0 +1,118 @@
+//! Tests for `brokerd`'s configuration. Do not edit: these define the required behaviour.
+
+use brokerd::config::{Approvals, Config, ConfigError, Sockets};
+use std::path::{Path, PathBuf};
+
+fn fixture(name: &str) -> PathBuf {
+    Path::new(env!("CARGO_MANIFEST_DIR"))
+        .join("tests/fixtures/config")
+        .join(name)
+}
+
+/// What `home` must default to in this process. The test does not set the variable: changing the
+/// environment of a running test binary would race with the other tests.
+fn default_home() -> PathBuf {
+    std::env::var_os("BOXMAKER_HOME")
+        .map(PathBuf::from)
+        .unwrap_or_else(|| PathBuf::from("/var/lib/boxmaker"))
+}
+
+#[test]
+fn an_empty_file_gets_every_default() {
+    let c = Config::load(&fixture("empty.toml")).unwrap();
+    assert_eq!(c.paths.home, default_home());
+    assert_eq!(c.paths.grants, PathBuf::from("/etc/boxmaker/grants"));
+    assert_eq!(c.sockets, Sockets::default());
+    assert_eq!(c.approvals, Approvals { ttl_ms: 900_000 });
+    assert_eq!(Approvals::default(), Approvals { ttl_ms: 900_000 });
+    assert_eq!(c, Config::parse("").unwrap());
+    assert_eq!(c, Config::default());
+}
+
+#[test]
+fn sockets_and_directories_default_to_places_under_home() {
+    let c = Config::load(&fixture("home_only.toml")).unwrap();
+    assert_eq!(c.paths.home, PathBuf::from("/srv/boxmaker"));
+    assert_eq!(
+        c.broker_socket(),
+        PathBuf::from("/srv/boxmaker/run/loop-broker/broker.sock")
+    );
+    assert_eq!(
+        c.admin_socket(),
+        PathBuf::from("/srv/boxmaker/run/owner-broker/admin.sock")
+    );
+    assert_eq!(c.audit_dir(), PathBuf::from("/srv/boxmaker/audit"));
+    assert_eq!(
+        c.state_dir(),
+        PathBuf::from("/srv/boxmaker/broker/sessions")
+    );
+    // The grants are not under home: the owner writes them, brokerd only reads them.
+    assert_eq!(c.paths.grants, PathBuf::from("/etc/boxmaker/grants"));
+}
+
+#[test]
+fn every_key_can_be_set() {
+    let c = Config::load(&fixture("full.toml")).unwrap();
+    assert_eq!(c.paths.home, PathBuf::from("/srv/boxmaker"));
+    assert_eq!(c.paths.grants, PathBuf::from("/srv/boxmaker-grants"));
+    assert_eq!(c.broker_socket(), PathBuf::from("/run/bx/broker.sock"));
+    assert_eq!(c.admin_socket(), PathBuf::from("/run/bx/admin.sock"));
+    assert_eq!(c.approvals.ttl_ms, 60_000);
+    // The two directories always follow home.
+    assert_eq!(c.audit_dir(), PathBuf::from("/srv/boxmaker/audit"));
+    assert_eq!(
+        c.state_dir(),
+        PathBuf::from("/srv/boxmaker/broker/sessions")
+    );
+}
+
+#[test]
+fn one_socket_set_leaves_the_other_at_its_default() {
+    let c =
+        Config::parse("[paths]\nhome = \"/h\"\n[sockets]\nadmin = \"/x/admin.sock\"\n").unwrap();
+    assert_eq!(c.admin_socket(), PathBuf::from("/x/admin.sock"));
+    assert_eq!(
+        c.broker_socket(),
+        PathBuf::from("/h/run/loop-broker/broker.sock")
+    );
+}
+
+#[test]
+fn unknown_keys_and_tables_are_errors() {
+    for name in ["unknown_key.toml", "unknown_table.toml", "wrong_type.toml"] {
+        match Config::load(&fixture(name)) {
+            Err(ConfigError::Parse(path, _)) => assert_eq!(path, fixture(name)),
+            other => panic!("{name}: expected a parse error, got {other:?}"),
+        }
+    }
+    // In every table, not only the one the fixture shows.
+    for text in [
+        "[paths]\nhome = \"/h\"\nhouse = \"/h\"\n",
+        "[sockets]\nbroker = \"/b.sock\"\nloop = \"/l.sock\"\n",
+        "[approvals]\nttl_ms = 1\nttl_s = 1\n",
+        "top = 1\n",
+        "[approvals]\nttl_ms = -5\n",
+    ] {
+        assert!(Config::parse(text).is_err(), "accepted: {text}");
+    }
+}
+
+#[test]
+fn a_missing_file_is_a_read_error_that_names_the_file() {
+    let path = fixture("does-not-exist.toml");
+    match Config::load(&path) {
+        Err(ConfigError::Read(p, _)) => assert_eq!(p, path),
+        other => panic!("expected a read error, got {other:?}"),
+    }
+    let text = Config::load(&path).unwrap_err().to_string();
+    assert!(text.contains("does-not-exist.toml"), "{text}");
+}
+
+#[test]
+fn a_parse_error_names_the_file_and_the_key() {
+    let text = Config::load(&fixture("unknown_key.toml"))
+        .unwrap_err()
+        .to_string();
+    assert!(text.contains("unknown_key.toml"), "{text}");
+    assert!(text.contains("ttl"), "{text}");
+}

crates/brokerd/tests/fixtures/config/empty.toml

@@ -0,0 +1 @@
+# Nothing set: every value is a default.

crates/brokerd/tests/fixtures/config/full.toml

@@ -0,0 +1,11 @@
+# Every key set.
+[paths]
+home = "/srv/boxmaker"
+grants = "/srv/boxmaker-grants"
+
+[sockets]
+broker = "/run/bx/broker.sock"
+admin = "/run/bx/admin.sock"
+
+[approvals]
+ttl_ms = 60000

crates/brokerd/tests/fixtures/config/home_only.toml

@@ -0,0 +1,2 @@
+[paths]
+home = "/srv/boxmaker"

crates/brokerd/tests/fixtures/config/unknown_key.toml

@@ -0,0 +1,3 @@
+[approvals]
+ttl_ms = 60000
+ttl = 5

crates/brokerd/tests/fixtures/config/unknown_table.toml

@@ -0,0 +1,2 @@
+[secrets]
+store = "/etc/boxmaker/secrets"

crates/brokerd/tests/fixtures/config/wrong_type.toml

@@ -0,0 +1,2 @@
+[approvals]
+ttl_ms = "15 min"

crates/brokerd/tests/fixtures/grants/empty/README.md

@@ -0,0 +1 @@
+An empty set of grants is valid: every call is denied with no_grant.

crates/brokerd/tests/fixtures/grants/many-bad/a-secret.toml

@@ -0,0 +1,8 @@
+tool = "http_fetch"
+mode = "auto"
+max_taint = "private"
+secret = "api-token"
+
+[constraints]
+hosts = ["api.example.com"]
+patterns = ["^GET "]

crates/brokerd/tests/fixtures/grants/many-bad/b-paths.toml

@@ -0,0 +1,7 @@
+tool = "read_file"
+mode = "auto"
+max_taint = "private"
+
+[constraints]
+paths = ["notes", "/home/kyle/../etc", "/"]
+hosts = ["example.com"]

crates/brokerd/tests/fixtures/grants/many-bad/c-syntax.toml

@@ -0,0 +1,3 @@
+tool = "shell"
+mode = "auto"
+max_taint =

crates/brokerd/tests/fixtures/grants/many-bad/notes-read.toml

@@ -0,0 +1,10 @@
+# The owner's notes: only the owner writes them, so their content is trusted.
+tool = "read_file"
+mode = "auto"
+max_taint = "secret"
+result_class = "private"
+untrusted = false
+expires = "2027-01-01T00:00:00.000Z"
+
+[constraints]
+paths = ["/home/kyle/notes"]

crates/brokerd/tests/fixtures/grants/one-bad/fetch-example.toml

@@ -0,0 +1,7 @@
+tool = "http_fetch"
+mode = "auto"
+max_taint = "private"
+result_class = "public"
+
+[constraints]
+hosts = ["example.com", "*.example.com"]

crates/brokerd/tests/fixtures/grants/one-bad/no-fetch-internal.toml

@@ -0,0 +1,7 @@
+# The owner meant `mode`. If this file were skipped, fetch-example would allow what it forbids.
+tool = "http_fetch"
+mdoe = "deny"
+max_taint = "secret"
+
+[constraints]
+hosts = ["internal.example.com"]

crates/brokerd/tests/fixtures/grants/one-bad/notes-read.toml

@@ -0,0 +1,10 @@
+# The owner's notes: only the owner writes them, so their content is trusted.
+tool = "read_file"
+mode = "auto"
+max_taint = "secret"
+result_class = "private"
+untrusted = false
+expires = "2027-01-01T00:00:00.000Z"
+
+[constraints]
+paths = ["/home/kyle/notes"]

crates/brokerd/tests/fixtures/grants/valid/README.md

@@ -0,0 +1 @@
+Grants for the tests. This file is not a grant and is ignored.

crates/brokerd/tests/fixtures/grants/valid/fetch-example.toml

@@ -0,0 +1,7 @@
+tool = "http_fetch"
+mode = "auto"
+max_taint = "private"
+result_class = "public"
+
+[constraints]
+hosts = ["example.com", "*.example.com"]

crates/brokerd/tests/fixtures/grants/valid/no-fetch-internal.toml

@@ -0,0 +1,6 @@
+tool = "http_fetch"
+mode = "deny"
+max_taint = "secret"
+
+[constraints]
+hosts = ["internal.example.com"]

crates/brokerd/tests/fixtures/grants/valid/notes-read.toml

@@ -0,0 +1,10 @@
+# The owner's notes: only the owner writes them, so their content is trusted.
+tool = "read_file"
+mode = "auto"
+max_taint = "secret"
+result_class = "private"
+untrusted = false
+expires = "2027-01-01T00:00:00.000Z"
+
+[constraints]
+paths = ["/home/kyle/notes"]

crates/brokerd/tests/fixtures/grants/valid/scratch-write.toml

@@ -0,0 +1,6 @@
+tool = "write_file"
+mode = "ask"
+max_taint = "private"
+
+[constraints]
+paths = ["/home/kyle/scratch", "/home/kyle/scratch/out"]

crates/brokerd/tests/fixtures/grants/valid/shell-bare.toml

@@ -0,0 +1,4 @@
+# A shell with nothing mounted.
+tool = "shell"
+mode = "ask"
+max_taint = "secret"

crates/brokerd/tests/grants.rs

@@ -0,0 +1,482 @@
+//! Tests for loading grant files. Do not edit these or the fixtures.
+//!
+//! One case per loading rule in the M3a spec, each with words its problem text must contain, and
+//! the rule that matters most: one invalid file makes the whole set invalid.
+
+#[path = "support/tmp.rs"]
+mod tmp;
+
+use brokerd::grants::{GrantSet, LoadedGrant, RUNBOOK, load, render, valid_id};
+use proto::{Constraints, DataClass, Grant, GrantProblem, Hash32, Mode};
+use std::path::{Path, PathBuf};
+use tmp::TempDir;
+
+fn fixture(case: &str) -> PathBuf {
+    Path::new(env!("CARGO_MANIFEST_DIR"))
+        .join("tests/fixtures/grants")
+        .join(case)
+}
+
+const GOOD: &str = "tool = \"read_file\"\nmode = \"auto\"\nmax_taint = \"secret\"\n\n\
+                    [constraints]\npaths = [\"/home/kyle/notes\"]\n";
+
+/// A directory holding one good grant and the given files; returns the problems of loading it.
+fn problems_of(files: &[(&str, &str)]) -> Vec<GrantProblem> {
+    let dir = TempDir::new("grants");
+    dir.write("good.toml", GOOD);
+    for (name, text) in files {
+        dir.write(name, text);
+    }
+    load(dir.path()).expect_err("the set should be invalid")
+}
+
+/// Exactly one problem, in `file`, whose text contains every one of `words`.
+fn one_problem(files: &[(&str, &str)], file: &str, words: &[&str]) -> GrantProblem {
+    let problems = problems_of(files);
+    assert_eq!(problems.len(), 1, "{problems:?}");
+    let p = problems.into_iter().next().unwrap();
+    assert_eq!(p.file, file);
+    for word in words {
+        assert!(p.problem.contains(word), "{:?} lacks {word:?}", p.problem);
+    }
+    p
+}
+
+fn body(tool: &str, mode: &str, rest: &str) -> String {
+    format!("tool = \"{tool}\"\nmode = \"{mode}\"\nmax_taint = \"secret\"\n{rest}")
+}
+
+#[test]
+fn the_valid_fixture_loads_in_id_order_with_file_hashes() {
+    let set = load(&fixture("valid")).unwrap();
+    let ids: Vec<&str> = set.grants().iter().map(|g| g.id.as_str()).collect();
+    assert_eq!(
+        ids,
+        [
+            "fetch-example",
+            "no-fetch-internal",
+            "notes-read",
+            "scratch-write",
+            "shell-bare"
+        ]
+    );
+    let notes = &set.grants()[2];
+    assert_eq!(notes.grant.tool, "read_file");
+    assert_eq!(notes.grant.mode, Mode::Auto);
+    assert!(!notes.grant.untrusted);
+    assert_eq!(notes.grant.constraints.paths, ["/home/kyle/notes"]);
+    let bytes = std::fs::read(fixture("valid").join("notes-read.toml")).unwrap();
+    assert_eq!(notes.sha256, proto::sha256(&bytes).unwrap());
+    // Defaults from `proto::Grant`.
+    let scratch = &set.grants()[3];
+    assert_eq!(scratch.grant.result_class, DataClass::Private);
+    assert!(scratch.grant.untrusted);
+    assert_eq!(scratch.grant.expires, None);
+}
+
+#[test]
+fn files_that_do_not_end_in_toml_are_ignored() {
+    let dir = TempDir::new("grants");
+    dir.write("good.toml", GOOD);
+    dir.write("good.toml~", "not toml at all {{{");
+    dir.write("good.toml.bak", "not toml at all {{{");
+    dir.write("README.md", "# notes");
+    dir.write("toml", "x");
+    std::fs::create_dir(dir.path().join("archive")).unwrap();
+    let set = load(dir.path()).unwrap();
+    assert_eq!(set.grants().len(), 1);
+    assert_eq!(set.grants()[0].id, "good");
+}
+
+#[test]
+fn an_empty_directory_is_a_valid_empty_set() {
+    let set = load(&fixture("empty")).unwrap();
+    assert!(set.grants().is_empty());
+    assert_eq!(set, GrantSet::default());
+}
+
+#[test]
+fn a_missing_directory_is_a_problem_not_an_empty_set() {
+    let missing = fixture("does-not-exist");
+    let problems = load(&missing).unwrap_err();
+    assert_eq!(problems.len(), 1);
+    assert!(problems[0].file.contains("does-not-exist"), "{problems:?}");
+    assert!(problems[0].problem.contains("cannot be read"));
+    // A file where the directory should be is the same.
+    let dir = TempDir::new("grants");
+    let file = dir.write("grants", "x");
+    assert!(load(&file).is_err());
+}
+
+/// The rule the whole design leans on. `fetch-example` alone would allow a fetch that the
+/// mistyped `no-fetch-internal` was written to forbid, so nothing loads at all.
+#[test]
+fn one_invalid_file_makes_the_whole_set_invalid() {
+    let problems = load(&fixture("one-bad")).unwrap_err();
+    assert_eq!(problems.len(), 1, "{problems:?}");
+    assert_eq!(problems[0].file, "no-fetch-internal.toml");
+    assert_eq!(problems[0].line, Some(3));
+    assert!(problems[0].problem.contains("mdoe"), "{problems:?}");
+    // The same directory without the bad file is fine.
+    let dir = TempDir::new("grants");
+    for name in ["notes-read.toml", "fetch-example.toml"] {
+        let text = std::fs::read_to_string(fixture("one-bad").join(name)).unwrap();
+        dir.write(name, &text);
+    }
+    assert_eq!(load(dir.path()).unwrap().grants().len(), 2);
+}
+
+#[test]
+fn every_problem_in_every_file_is_reported() {
+    let problems = load(&fixture("many-bad")).unwrap_err();
+    let got: Vec<(&str, Option<u64>)> =
+        problems.iter().map(|p| (p.file.as_str(), p.line)).collect();
+    assert_eq!(
+        got,
+        [
+            ("a-secret.toml", None),
+            ("a-secret.toml", None),
+            ("b-paths.toml", None),
+            ("b-paths.toml", None),
+            ("b-paths.toml", None),
+            ("b-paths.toml", None),
+            ("c-syntax.toml", Some(3)),
+        ],
+        "{problems:?}"
+    );
+    let all: String = problems
+        .iter()
+        .map(|p| format!("{}\n", p.problem))
+        .collect();
+    for words in [
+        "secrets are not supported until M4",
+        "patterns are not supported",
+        "read_file does not take hosts",
+        "\"notes\" is not a valid absolute path",
+        "\"/home/kyle/../etc\" is not a valid absolute path",
+        "a grant of the whole file system is not supported",
+    ] {
+        assert!(all.contains(words), "missing {words:?} in:\n{all}");
+    }
+}
+
+#[test]
+fn rule_1_unreadable_not_utf8_or_not_a_grant() {
+    one_problem(&[("bad.toml", "tool = ")], "bad.toml", &[]);
+    let p = one_problem(
+        &[("bad.toml", &body("shell", "auto", "colour = \"red\"\n"))],
+        "bad.toml",
+        &["colour"],
+    );
+    assert_eq!(p.line, Some(4));
+    one_problem(
+        &[("bad.toml", "tool = \"shell\"\nmode = \"auto\"\n")],
+        "bad.toml",
+        &["max_taint"],
+    );
+    one_problem(
+        &[("bad.toml", &body("shell", "sometimes", ""))],
+        "bad.toml",
+        &["sometimes"],
+    );
+    one_problem(
+        &[(
+            "bad.toml",
+            &body("shell", "auto", "[constraints]\ncwd = [\"/a\"]\n"),
+        )],
+        "bad.toml",
+        &["cwd"],
+    );
+
+    // Not UTF-8.
+    let dir = TempDir::new("grants");
+    dir.write("good.toml", GOOD);
+    std::fs::write(dir.path().join("latin1.toml"), b"tool = \"caf\xe9\"\n").unwrap();
+    let problems = load(dir.path()).unwrap_err();
+    assert_eq!(problems.len(), 1);
+    assert_eq!(problems[0].file, "latin1.toml");
+    assert!(problems[0].problem.contains("UTF-8"), "{problems:?}");
+
+    // Exists but cannot be read: a directory with a grant's name.
+    let dir = TempDir::new("grants");
+    dir.write("good.toml", GOOD);
+    std::fs::create_dir(dir.path().join("folder.toml")).unwrap();
+    let problems = load(dir.path()).unwrap_err();
+    assert_eq!(problems.len(), 1);
+    assert_eq!(problems[0].file, "folder.toml");
+    assert!(
+        problems[0].problem.contains("cannot be read"),
+        "{problems:?}"
+    );
+}
+
+#[test]
+fn rule_1_a_file_without_read_permission_is_a_problem() {
+    use std::os::unix::fs::PermissionsExt;
+    if tmp::running_as_root("rule_1_a_file_without_read_permission_is_a_problem") {
+        return;
+    }
+    let dir = TempDir::new("grants");
+    dir.write("good.toml", GOOD);
+    let locked = dir.write("locked.toml", GOOD);
+    std::fs::set_permissions(&locked, std::fs::Permissions::from_mode(0o000)).unwrap();
+    let problems = load(dir.path()).unwrap_err();
+    assert_eq!(problems.len(), 1);
+    assert_eq!(problems[0].file, "locked.toml");
+    assert!(
+        problems[0].problem.contains("cannot be read"),
+        "{problems:?}"
+    );
+}
+
+#[test]
+fn rule_2_the_file_stem_is_the_id() {
+    for id in ["a", "notes-read", "0", "a-1-b", &"x".repeat(64)] {
+        assert!(valid_id(id), "{id:?}");
+    }
+    for id in [
+        "",
+        "Notes",
+        "notes_read",
+        "notes.read",
+        "notes read",
+        ".hidden",
+        &"x".repeat(65),
+    ] {
+        assert!(!valid_id(id), "{id:?}");
+    }
+    one_problem(
+        &[("Bad_Name.toml", GOOD)],
+        "Bad_Name.toml",
+        &["not a valid grant id"],
+    );
+    one_problem(&[(".toml", GOOD)], ".toml", &["not a valid grant id"]);
+    one_problem(&[("a.b.toml", GOOD)], "a.b.toml", &["not a valid grant id"]);
+}
+
+#[test]
+fn rule_3_the_tool_is_one_of_the_four() {
+    for tool in ["echo", "clock", "Read_File", ""] {
+        one_problem(
+            &[("bad.toml", &body(tool, "auto", ""))],
+            "bad.toml",
+            &[
+                "unknown tool",
+                "read_file, write_file, shell and http_fetch",
+            ],
+        );
+    }
+}
+
+#[test]
+fn rules_4_and_5_secrets_and_patterns_are_not_supported() {
+    one_problem(
+        &[("bad.toml", &body("shell", "ask", "secret = \"token\"\n"))],
+        "bad.toml",
+        &["secrets are not supported until M4"],
+    );
+    one_problem(
+        &[(
+            "bad.toml",
+            &body("shell", "ask", "[constraints]\npatterns = [\"^ls\"]\n"),
+        )],
+        "bad.toml",
+        &["patterns are not supported"],
+    );
+    // An empty list is the same as no list.
+    let dir = TempDir::new("grants");
+    dir.write(
+        "ok.toml",
+        &body("shell", "ask", "[constraints]\npatterns = []\nhosts = []\n"),
+    );
+    assert!(load(dir.path()).is_ok());
+}
+
+/// The table of rule 6, cell by cell.
+#[test]
+fn rule_6_each_tool_takes_its_own_constraints() {
+    let paths = "[constraints]\npaths = [\"/a\"]\n";
+    let hosts = "[constraints]\nhosts = [\"example.com\"]\n";
+    let both = "[constraints]\npaths = [\"/a\"]\nhosts = [\"example.com\"]\n";
+    for tool in ["read_file", "write_file"] {
+        one_problem(
+            &[("bad.toml", &body(tool, "auto", ""))],
+            "bad.toml",
+            &[tool, "needs at least one path"],
+        );
+        one_problem(
+            &[("bad.toml", &body(tool, "auto", both))],
+            "bad.toml",
+            &[tool, "does not take hosts"],
+        );
+    }
+    one_problem(
+        &[("bad.toml", &body("shell", "auto", both))],
+        "bad.toml",
+        &["shell does not take hosts"],
+    );
+    one_problem(
+        &[("bad.toml", &body("http_fetch", "auto", ""))],
+        "bad.toml",
+        &["http_fetch needs at least one host"],
+    );
+    one_problem(
+        &[("bad.toml", &body("http_fetch", "auto", both))],
+        "bad.toml",
+        &["http_fetch does not take paths"],
+    );
+    // The allowed cells.
+    let dir = TempDir::new("grants");
+    dir.write("r.toml", &body("read_file", "auto", paths));
+    dir.write("w.toml", &body("write_file", "auto", paths));
+    dir.write("s1.toml", &body("shell", "auto", paths));
+    dir.write("s2.toml", &body("shell", "auto", ""));
+    dir.write("h.toml", &body("http_fetch", "auto", hosts));
+    assert_eq!(load(dir.path()).unwrap().grants().len(), 5);
+    // Two wrong cells in one file are two problems.
+    let wrong = body("http_fetch", "auto", paths);
+    assert_eq!(problems_of(&[("bad.toml", &wrong)]).len(), 2);
+}
+
+#[test]
+fn rule_7_paths_are_valid_absolute_paths_and_never_the_root() {
+    for bad in ["notes", "/a/../b", "/a//b", "/a/./b", "/a/", ""] {
+        let text = body(
+            "shell",
+            "auto",
+            &format!("[constraints]\npaths = [{bad:?}]\n"),
+        );
+        one_problem(
+            &[("bad.toml", &text)],
+            "bad.toml",
+            &["is not a valid absolute path"],
+        );
+    }
+    let root = body(
+        "shell",
+        "auto",
+        "[constraints]\npaths = [\"/home/kyle\", \"/\"]\n",
+    );
+    one_problem(
+        &[("bad.toml", &root)],
+        "bad.toml",
+        &["a grant of the whole file system is not supported"],
+    );
+}
+
+#[test]
+fn rule_8_hosts_are_valid_host_patterns() {
+    for bad in [
+        "Example.com",
+        "example.com:443",
+        "127.0.0.1",
+        "localhost",
+        "*.com",
+        "https://example.com",
+    ] {
+        let text = body(
+            "http_fetch",
+            "auto",
+            &format!("[constraints]\nhosts = [{bad:?}]\n"),
+        );
+        one_problem(
+            &[("bad.toml", &text)],
+            "bad.toml",
+            &[bad, "is not a valid host pattern"],
+        );
+    }
+}
+
+#[test]
+fn rule_9_a_deny_grant_applies_at_every_taint() {
+    for taint in ["public", "private"] {
+        let text = format!("tool = \"shell\"\nmode = \"deny\"\nmax_taint = \"{taint}\"\n");
+        one_problem(
+            &[("bad.toml", &text)],
+            "bad.toml",
+            &["a deny grant must apply at every taint"],
+        );
+    }
+    let dir = TempDir::new("grants");
+    dir.write("no-shell.toml", &body("shell", "deny", ""));
+    assert!(load(dir.path()).is_ok());
+    // The rule is about deny only.
+    dir.write(
+        "ask.toml",
+        "tool = \"shell\"\nmode = \"ask\"\nmax_taint = \"public\"\n",
+    );
+    assert!(load(dir.path()).is_ok());
+}
+
+fn loaded(id: &str, tool: &str, mode: Mode) -> LoadedGrant {
+    LoadedGrant {
+        id: id.to_string(),
+        grant: Grant {
+            tool: tool.to_string(),
+            mode,
+            max_taint: DataClass::Secret,
+            result_class: DataClass::Private,
+            untrusted: true,
+            expires: None,
+            secret: None,
+            constraints: Constraints::default(),
+        },
+        sha256: Hash32::ZERO,
+    }
+}
+
+/// `from_grants` is how tests and the property test build a set without files. It applies the
+/// same value rules, sorts by id, and refuses two grants with one id.
+#[test]
+fn from_grants_applies_the_value_rules() {
+    let set = GrantSet::from_grants(vec![
+        loaded("zz", "shell", Mode::Ask),
+        loaded("aa", "shell", Mode::Deny),
+    ])
+    .unwrap();
+    assert_eq!(set.grants()[0].id, "aa");
+    assert_eq!(set.grants()[1].id, "zz");
+
+    let problems = GrantSet::from_grants(vec![
+        loaded("ok", "shell", Mode::Auto),
+        loaded("no-paths", "read_file", Mode::Auto),
+        loaded("Bad", "shell", Mode::Auto),
+    ])
+    .unwrap_err();
+    let files: Vec<&str> = problems.iter().map(|p| p.file.as_str()).collect();
+    assert_eq!(files, ["Bad.toml", "no-paths.toml"]);
+
+    let twice = GrantSet::from_grants(vec![
+        loaded("same", "shell", Mode::Auto),
+        loaded("same", "shell", Mode::Ask),
+    ])
+    .unwrap_err();
+    assert!(
+        twice[0].problem.contains("two grants have this id"),
+        "{twice:?}"
+    );
+}
+
+#[test]
+fn render_prints_every_problem_and_then_the_runbook_pointer() {
+    let problems = [
+        GrantProblem {
+            file: "a.toml".to_string(),
+            line: Some(3),
+            problem: "unknown field `mdoe`".to_string(),
+        },
+        GrantProblem {
+            file: "Bad_Name.toml".to_string(),
+            line: None,
+            problem: "the file name is not a valid grant id".to_string(),
+        },
+    ];
+    assert_eq!(
+        render(&problems),
+        "a.toml:3: unknown field `mdoe`\n\
+         Bad_Name.toml: the file name is not a valid grant id\n\
+         see docs/runbook.md#grants-invalid\n"
+    );
+    assert_eq!(RUNBOOK, "see docs/runbook.md#grants-invalid");
+    assert!(render(&problems).trim_end().ends_with(RUNBOOK));
+}

crates/brokerd/tests/ledger.rs

@@ -0,0 +1,383 @@
+//! The ledger's first and third steps: decide and record; raise the state and record the result.
+//! And what happens after a failed append or a panic. Do not edit.
+
+#[path = "support/build.rs"]
+mod build;
+#[path = "support/rig.rs"]
+mod rig;
+#[path = "support/sink.rs"]
+mod sink;
+#[path = "support/tmp.rs"]
+mod tmp;
+
+use std::os::unix::fs::PermissionsExt;
+use std::panic::AssertUnwindSafe;
+
+use brokerd::ledger::{Call, Decided, Grants, NOT_RECORDED, POISONED, STOPPED};
+use brokerd::policy::{Label, SessionState};
+use build::{grant, now, read, set};
+use proto::{
+    AuditEvent, CallId, DataClass, DecisionRecord, DenyReason, GrantProblem, Mode, ResultStatus,
+    SessionId, ToolResponse,
+};
+use rig::Rig;
+
+fn one(grants: Vec<build::Build>) -> Grants {
+    Ok(set(grants))
+}
+
+fn notes(mode: Mode) -> Grants {
+    one(vec![grant("n", "read_file", mode).paths(&["/n"])])
+}
+
+fn call(label: Label) -> Call {
+    Call {
+        session: SessionId::new("s1").unwrap(),
+        call: CallId(1),
+        decision: 0,
+        label,
+    }
+}
+
+fn secret() -> Label {
+    Label {
+        class: DataClass::Secret,
+        untrusted: true,
+    }
+}
+
+fn result(content: &str, label: Label) -> ToolResponse {
+    ToolResponse::Result {
+        content: content.to_string(),
+        class: label.class,
+        untrusted: label.untrusted,
+        truncated: false,
+    }
+}
+
+#[test]
+fn an_allowed_call_is_recorded_in_full() {
+    let rig = Rig::new("ledger-allowed");
+    let ledger = rig.ledger();
+    let request = read("/n/a");
+    let arguments = request.arguments.clone();
+    match ledger.decide(request, &notes(Mode::Auto), now()) {
+        Decided::Allowed { decision, seq } => {
+            assert_eq!(seq, 0);
+            assert_eq!(decision.grant(), "n");
+        }
+        other => panic!("{other:?}"),
+    }
+    let records = rig.records();
+    assert_eq!(records.len(), 1);
+    assert_eq!(records[0].time, now());
+    assert_eq!(
+        records[0].event,
+        AuditEvent::Decision {
+            session: SessionId::new("s1").unwrap(),
+            call: CallId(1),
+            tool: "read_file".to_string(),
+            arguments,
+            outcome: DecisionRecord::Allowed {},
+            grant: Some("n".to_string()),
+            grant_sha256: Some(proto::sha256(b"n").unwrap()),
+            taint: DataClass::Private,
+            untrusted: false,
+        }
+    );
+}
+
+#[test]
+fn an_ask_is_recorded_as_ask_with_the_state_it_was_decided_at() {
+    let rig = Rig::new("ledger-ask");
+    let ledger = rig.ledger();
+    match ledger.decide(read("/n/a"), &notes(Mode::Ask), now()) {
+        Decided::Ask { ask, seq, state } => {
+            assert_eq!((seq, ask.grant()), (0, "n"));
+            assert_eq!(state, SessionState::default());
+        }
+        other => panic!("{other:?}"),
+    }
+    match &rig.events()[0] {
+        AuditEvent::Decision { outcome, grant, .. } => {
+            assert_eq!(*outcome, DecisionRecord::Ask {});
+            assert_eq!(grant.as_deref(), Some("n"));
+        }
+        other => panic!("{other:?}"),
+    }
+}
+
+#[test]
+fn a_denial_names_a_grant_only_when_a_grant_denied() {
+    let rig = Rig::new("ledger-denied");
+    let ledger = rig.ledger();
+    let none = ledger.decide(read("/n/a"), &one(Vec::new()), now());
+    assert!(
+        matches!(none, Decided::Denied(DenyReason::NoGrant)),
+        "{none:?}"
+    );
+    let deny = one(vec![grant("d", "read_file", Mode::Deny).paths(&["/n"])]);
+    let by = ledger.decide(read("/n/a"), &deny, now());
+    assert!(
+        matches!(by, Decided::Denied(DenyReason::DeniedByGrant)),
+        "{by:?}"
+    );
+    let events = rig.events();
+    let named: Vec<(DecisionRecord, Option<String>)> = events
+        .iter()
+        .map(|e| match e {
+            AuditEvent::Decision { outcome, grant, .. } => (outcome.clone(), grant.clone()),
+            other => panic!("{other:?}"),
+        })
+        .collect();
+    assert_eq!(
+        named,
+        [
+            (
+                DecisionRecord::Denied {
+                    reason: DenyReason::NoGrant
+                },
+                None
+            ),
+            (
+                DecisionRecord::Denied {
+                    reason: DenyReason::DeniedByGrant
+                },
+                Some("d".to_string())
+            ),
+        ]
+    );
+}
+
+#[test]
+fn invalid_grants_come_first_then_an_unreadable_state() {
+    let rig = Rig::new("ledger-order");
+    let ledger = rig.ledger();
+    std::fs::create_dir_all(rig.cfg.state_dir()).unwrap();
+    std::fs::write(rig.state_file("s1"), "not json").unwrap();
+    let invalid: Grants = Err(vec![GrantProblem {
+        file: "x.toml".to_string(),
+        line: None,
+        problem: "bad".to_string(),
+    }]);
+    let first = ledger.decide(read("/n/a"), &invalid, now());
+    assert!(
+        matches!(first, Decided::Denied(DenyReason::GrantsInvalid)),
+        "{first:?}"
+    );
+    let second = ledger.decide(read("/n/a"), &notes(Mode::Auto), now());
+    assert!(
+        matches!(second, Decided::Denied(DenyReason::StateUnreadable)),
+        "{second:?}"
+    );
+    // A state brokerd cannot read is recorded as the most sensitive one.
+    for event in rig.events() {
+        match event {
+            AuditEvent::Decision {
+                taint, untrusted, ..
+            } => assert_eq!((taint, untrusted), (DataClass::Secret, true)),
+            other => panic!("{other:?}"),
+        }
+    }
+    let damaged = rig.lines.with("see docs/runbook.md#broker-state-damaged");
+    assert!(!damaged.is_empty(), "{:?}", rig.lines.all());
+}
+
+#[test]
+fn a_failed_append_denies_this_call_and_every_later_one() {
+    let rig = Rig::new("ledger-stop");
+    let ledger = rig.ledger();
+    rig.switch.fail(true);
+    let first = ledger.decide(read("/n/a"), &notes(Mode::Auto), now());
+    assert!(
+        matches!(first, Decided::Denied(DenyReason::AuditUnavailable)),
+        "{first:?}"
+    );
+    assert_eq!(rig.switch.attempts(), 1);
+    // The sink would work again; the ledger does not try it.
+    rig.switch.fail(false);
+    let later = ledger.decide(read("/n/a"), &notes(Mode::Auto), now());
+    assert!(
+        matches!(later, Decided::Denied(DenyReason::AuditUnavailable)),
+        "{later:?}"
+    );
+    let finished = ledger.finish(&call(secret()), result("x", secret()), now());
+    assert_eq!(
+        finished,
+        ToolResponse::Failed {
+            message: NOT_RECORDED.to_string()
+        }
+    );
+    assert_eq!(rig.switch.attempts(), 1, "nothing more was written");
+    assert!(rig.records().is_empty());
+    assert!(!rig.state_file("s1").exists(), "the state was not raised");
+    assert!(!rig.lines.with(STOPPED).is_empty());
+    assert!(
+        rig.lines
+            .all()
+            .iter()
+            .all(|l| !l.contains("runbook") || l.ends_with("see docs/runbook.md#audit-unavailable")),
+        "{:?}",
+        rig.lines.all()
+    );
+}
+
+#[test]
+fn a_panic_while_holding_the_ledger_denies_every_later_call() {
+    let rig = Rig::new("ledger-poison");
+    let ledger = rig.ledger();
+    rig.switch.panic_next();
+    let panicked = std::panic::catch_unwind(AssertUnwindSafe(|| {
+        ledger.decide(read("/n/a"), &notes(Mode::Auto), now())
+    }));
+    assert!(panicked.is_err());
+    let later = ledger.decide(read("/n/a"), &notes(Mode::Auto), now());
+    assert!(
+        matches!(later, Decided::Denied(DenyReason::AuditUnavailable)),
+        "{later:?}"
+    );
+    assert_eq!(rig.switch.attempts(), 1);
+    assert!(
+        !rig.lines.with(POISONED).is_empty(),
+        "{:?}",
+        rig.lines.all()
+    );
+    assert!(POISONED.ends_with("see docs/runbook.md#audit-unavailable"));
+}
+
+#[test]
+fn a_result_raises_the_state_then_is_recorded() {
+    let rig = Rig::new("ledger-result");
+    let ledger = rig.ledger();
+    let answer = ledger.finish(&call(secret()), result("key", secret()), now());
+    assert_eq!(answer, result("key", secret()), "passed on unchanged");
+    let state = rig.state().read(&SessionId::new("s1").unwrap()).unwrap();
+    assert_eq!(
+        state,
+        SessionState {
+            taint: DataClass::Secret,
+            untrusted: true
+        }
+    );
+    assert_eq!(
+        rig.events(),
+        [AuditEvent::Result {
+            session: SessionId::new("s1").unwrap(),
+            call: CallId(1),
+            decision: 0,
+            status: ResultStatus::Result,
+            class: DataClass::Secret,
+            untrusted: true,
+            truncated: false,
+            bytes: 3,
+            sha256: proto::sha256(b"key").unwrap(),
+            taint_after: DataClass::Secret,
+        }]
+    );
+}
+
+#[test]
+fn taint_never_goes_down() {
+    let rig = Rig::new("ledger-down");
+    let ledger = rig.ledger();
+    let public = Label {
+        class: DataClass::Public,
+        untrusted: false,
+    };
+    ledger.finish(&call(secret()), result("a", secret()), now());
+    ledger.finish(&call(public), result("b", public), now());
+    let after: Vec<DataClass> = rig
+        .events()
+        .iter()
+        .map(|e| match e {
+            AuditEvent::Result { taint_after, .. } => *taint_after,
+            other => panic!("{other:?}"),
+        })
+        .collect();
+    assert_eq!(after, [DataClass::Secret, DataClass::Secret]);
+    let state = rig.state().read(&SessionId::new("s1").unwrap()).unwrap();
+    assert_eq!((state.taint, state.untrusted), (DataClass::Secret, true));
+}
+
+#[test]
+fn a_failure_changes_no_state_and_is_recorded_by_its_message() {
+    let rig = Rig::new("ledger-failed");
+    let ledger = rig.ledger();
+    let failed = ToolResponse::Failed {
+        message: "the tool timed out".to_string(),
+    };
+    assert_eq!(
+        ledger.finish(&call(secret()), failed.clone(), now()),
+        failed
+    );
+    assert!(!rig.state_file("s1").exists());
+    match &rig.events()[0] {
+        AuditEvent::Result {
+            status,
+            class,
+            bytes,
+            sha256,
+            taint_after,
+            ..
+        } => {
+            assert_eq!(*status, ResultStatus::Failed);
+            assert_eq!(
+                *class,
+                DataClass::Secret,
+                "the label the result would have had"
+            );
+            assert_eq!(*bytes, 18);
+            assert_eq!(*sha256, proto::sha256(b"the tool timed out").unwrap());
+            assert_eq!(*taint_after, DataClass::Private, "the taint before");
+        }
+        other => panic!("{other:?}"),
+    }
+}
+
+#[test]
+fn a_state_that_cannot_be_written_withholds_the_content() {
+    if tmp::running_as_root("a_state_that_cannot_be_written_withholds_the_content") {
+        return;
+    }
+    let rig = Rig::new("ledger-ro");
+    let ledger = rig.ledger();
+    let dir = rig.cfg.state_dir();
+    std::fs::create_dir_all(&dir).unwrap();
+    std::fs::set_permissions(&dir, std::fs::Permissions::from_mode(0o500)).unwrap();
+    let answer = ledger.finish(&call(secret()), result("key", secret()), now());
+    std::fs::set_permissions(&dir, std::fs::Permissions::from_mode(0o700)).unwrap();
+    assert_eq!(
+        answer,
+        ToolResponse::Failed {
+            message: NOT_RECORDED.to_string()
+        }
+    );
+    assert!(
+        rig.records().is_empty(),
+        "no Result for a state not on disk"
+    );
+    assert!(
+        !rig.lines
+            .with("see docs/runbook.md#broker-state-damaged")
+            .is_empty()
+    );
+}
+
+#[test]
+fn a_result_record_that_cannot_be_written_withholds_the_content() {
+    let rig = Rig::new("ledger-norecord");
+    let ledger = rig.ledger();
+    rig.switch.fail(true);
+    let answer = ledger.finish(&call(secret()), result("key", secret()), now());
+    assert_eq!(
+        answer,
+        ToolResponse::Failed {
+            message: NOT_RECORDED.to_string()
+        }
+    );
+    assert!(
+        !rig.lines
+            .with("see docs/runbook.md#audit-unavailable")
+            .is_empty()
+    );
+}

crates/brokerd/tests/ledger_answer.rs

@@ -0,0 +1,262 @@
+//! The ledger's second step: an approval decides again and is recorded; a refusal and an expiry
+//! are recorded as denials. Do not edit.
+
+#[path = "support/build.rs"]
+mod build;
+#[path = "support/rig.rs"]
+mod rig;
+#[path = "support/sink.rs"]
+mod sink;
+#[path = "support/tmp.rs"]
+mod tmp;
+
+use brokerd::approvals::Verdict;
+use brokerd::ledger::{Answer, Answered, Decided, Grants, Ledger};
+use brokerd::policy::{Ask, Label};
+use build::{grant, now, read, set};
+use proto::{
+    ApprovalAnswer, AuditEvent, CallId, DataClass, DecisionRecord, DenyReason, Mode, SessionId,
+};
+use rig::Rig;
+
+fn asking() -> Grants {
+    Ok(set(vec![grant("n", "read_file", Mode::Ask).paths(&["/n"])]))
+}
+
+fn pending(ledger: &Ledger) -> Ask {
+    match ledger.decide(read("/n/deep/a"), &asking(), now()) {
+        Decided::Ask { ask, seq: 0, .. } => ask,
+        other => panic!("{other:?}"),
+    }
+}
+
+fn bxctl() -> Answer {
+    Answer::Approved {
+        by: Some("bxctl".to_string()),
+    }
+}
+
+fn denied(reason: DenyReason) -> DecisionRecord {
+    DecisionRecord::Denied { reason }
+}
+
+fn verdict_reason(answered: &Answered) -> Option<DenyReason> {
+    match &answered.verdict {
+        Verdict::Run(_) => None,
+        Verdict::Denied(reason) => Some(*reason),
+    }
+}
+
+/// The one `Approval` record, as (answer, by, reason, outcome, grant).
+type Row = (
+    ApprovalAnswer,
+    Option<String>,
+    Option<String>,
+    DecisionRecord,
+    Option<String>,
+);
+
+fn approval(rig: &Rig) -> Row {
+    let events = rig.events();
+    assert_eq!(events.len(), 2, "a decision and one approval: {events:?}");
+    match &events[1] {
+        AuditEvent::Approval {
+            session,
+            call,
+            decision,
+            answer,
+            by,
+            post,
+            reason,
+            outcome,
+            grant,
+            ..
+        } => {
+            assert_eq!(session, &SessionId::new("s1").unwrap());
+            assert_eq!((*call, *decision, post), (CallId(1), 0, &None));
+            (
+                *answer,
+                by.clone(),
+                reason.clone(),
+                outcome.clone(),
+                grant.clone(),
+            )
+        }
+        other => panic!("{other:?}"),
+    }
+}
+
+#[test]
+fn an_approval_that_still_asks_lets_the_call_run() {
+    let rig = Rig::new("answer-ask");
+    let ledger = rig.ledger();
+    let ask = pending(&ledger);
+    let answered = ledger.answer(ask, 0, bxctl(), &asking(), now());
+    match &answered.verdict {
+        Verdict::Run(decision) => assert_eq!(decision.grant(), "n"),
+        other => panic!("{other:?}"),
+    }
+    assert_eq!(answered.outcome, DecisionRecord::Ask {});
+    let row = approval(&rig);
+    assert_eq!(
+        row,
+        (
+            ApprovalAnswer::Approved,
+            Some("bxctl".to_string()),
+            None,
+            DecisionRecord::Ask {},
+            Some("n".to_string())
+        )
+    );
+}
+
+#[test]
+fn an_approval_under_a_grant_that_is_now_auto_records_allowed() {
+    let rig = Rig::new("answer-auto");
+    let ledger = rig.ledger();
+    let ask = pending(&ledger);
+    let now_auto = Ok(set(vec![
+        grant("n", "read_file", Mode::Auto).paths(&["/n"]),
+    ]));
+    let answered = ledger.answer(ask, 0, bxctl(), &now_auto, now());
+    assert!(matches!(answered.verdict, Verdict::Run(_)));
+    assert_eq!(answered.outcome, DecisionRecord::Allowed {});
+}
+
+#[test]
+fn the_approval_names_the_grant_matched_now() {
+    let rig = Rig::new("answer-grant");
+    let ledger = rig.ledger();
+    let ask = pending(&ledger);
+    let wider = Ok(set(vec![
+        grant("n", "read_file", Mode::Ask).paths(&["/n"]),
+        grant("z-deep", "read_file", Mode::Ask).paths(&["/n/deep"]),
+    ]));
+    let answered = ledger.answer(ask, 0, bxctl(), &wider, now());
+    match &answered.verdict {
+        Verdict::Run(decision) => assert_eq!(decision.grant(), "z-deep"),
+        other => panic!("{other:?}"),
+    }
+    assert_eq!(approval(&rig).4.as_deref(), Some("z-deep"));
+}
+
+#[test]
+fn an_approval_after_the_grant_is_gone_is_denied() {
+    let rig = Rig::new("answer-gone");
+    let ledger = rig.ledger();
+    let ask = pending(&ledger);
+    let answered = ledger.answer(ask, 0, bxctl(), &Ok(set(Vec::new())), now());
+    assert_eq!(verdict_reason(&answered), Some(DenyReason::NoGrant));
+    assert_eq!(answered.outcome, denied(DenyReason::NoGrant));
+    let row = approval(&rig);
+    assert_eq!(
+        (row.0, row.3, row.4),
+        (ApprovalAnswer::Approved, denied(DenyReason::NoGrant), None)
+    );
+}
+
+#[test]
+fn an_approval_after_the_taint_rose_is_denied() {
+    let rig = Rig::new("answer-taint");
+    let ledger = rig.ledger();
+    let low = || {
+        Ok(set(vec![
+            grant("n", "read_file", Mode::Ask)
+                .paths(&["/n"])
+                .max_taint(DataClass::Private),
+        ]))
+    };
+    let ask = match ledger.decide(read("/n/a"), &low(), now()) {
+        Decided::Ask { ask, .. } => ask,
+        other => panic!("{other:?}"),
+    };
+    // Another call of the session read a secret while this one waited.
+    let s1 = SessionId::new("s1").unwrap();
+    let label = Label {
+        class: DataClass::Secret,
+        untrusted: false,
+    };
+    rig.state()
+        .raise(&s1, rig.state().read(&s1).unwrap(), label)
+        .unwrap();
+    let answered = ledger.answer(ask, 0, bxctl(), &low(), now());
+    assert_eq!(verdict_reason(&answered), Some(DenyReason::TaintTooHigh));
+    match &rig.events()[1] {
+        AuditEvent::Approval { taint, outcome, .. } => {
+            assert_eq!(*taint, DataClass::Secret, "the state at the re-decision");
+            assert_eq!(*outcome, denied(DenyReason::TaintTooHigh));
+        }
+        other => panic!("{other:?}"),
+    }
+}
+
+#[test]
+fn an_approval_with_invalid_grants_is_denied() {
+    let rig = Rig::new("answer-invalid");
+    let ledger = rig.ledger();
+    let ask = pending(&ledger);
+    let answered = ledger.answer(ask, 0, bxctl(), &Err(Vec::new()), now());
+    assert_eq!(verdict_reason(&answered), Some(DenyReason::GrantsInvalid));
+}
+
+#[test]
+fn a_refusal_is_recorded_with_the_owners_reason() {
+    let rig = Rig::new("answer-refuse");
+    let ledger = rig.ledger();
+    let ask = pending(&ledger);
+    let refused = Answer::Refused {
+        by: Some("bxctl".to_string()),
+        reason: Some("not now".to_string()),
+    };
+    let answered = ledger.answer(ask, 0, refused, &asking(), now());
+    assert_eq!(verdict_reason(&answered), Some(DenyReason::ApprovalRefused));
+    assert_eq!(
+        approval(&rig),
+        (
+            ApprovalAnswer::Refused,
+            Some("bxctl".to_string()),
+            Some("not now".to_string()),
+            denied(DenyReason::ApprovalRefused),
+            None
+        )
+    );
+}
+
+#[test]
+fn an_expiry_is_recorded_by_nobody() {
+    let rig = Rig::new("answer-expire");
+    let ledger = rig.ledger();
+    let ask = pending(&ledger);
+    let answered = ledger.answer(ask, 0, Answer::Expired, &asking(), now());
+    assert_eq!(verdict_reason(&answered), Some(DenyReason::ApprovalExpired));
+    assert_eq!(
+        approval(&rig),
+        (
+            ApprovalAnswer::Expired,
+            None,
+            None,
+            denied(DenyReason::ApprovalExpired),
+            None
+        )
+    );
+}
+
+#[test]
+fn an_approval_that_cannot_be_recorded_does_not_run() {
+    let rig = Rig::new("answer-norecord");
+    let ledger = rig.ledger();
+    let ask = pending(&ledger);
+    rig.switch.fail(true);
+    let answered = ledger.answer(ask, 0, bxctl(), &asking(), now());
+    assert_eq!(
+        verdict_reason(&answered),
+        Some(DenyReason::AuditUnavailable)
+    );
+    assert_eq!(answered.outcome, denied(DenyReason::AuditUnavailable));
+    assert_eq!(rig.events().len(), 1, "only the decision");
+    assert!(
+        !rig.lines
+            .with("see docs/runbook.md#audit-unavailable")
+            .is_empty()
+    );
+}

crates/brokerd/tests/policy.rs

@@ -0,0 +1,213 @@
+//! Table tests for `policy::decide`: which arguments each tool's grants cover. Do not edit.
+//! `policy_matching.rs` covers how a winner, a label and a reason are picked, `policy_redecide.rs`
+//! covers approvals, and `policy_property.rs` checks all of it against an oracle.
+
+#[path = "support/build.rs"]
+mod build;
+
+use brokerd::policy::decide;
+use build::{allowed, fetch, grant, now, private, read, reason, request, set, shell, write};
+use proto::{DenyReason, Mode};
+
+#[test]
+fn no_grants_means_no_grant() {
+    let none = set(vec![]);
+    for req in [
+        read("/etc/hosts"),
+        write("/tmp/x"),
+        shell(None),
+        fetch("https://example.com/"),
+    ] {
+        assert_eq!(
+            reason(decide(req, &none, private(), now())),
+            DenyReason::NoGrant
+        );
+    }
+}
+
+#[test]
+fn a_tool_that_is_not_one_of_the_four_is_no_grant_and_its_arguments_are_not_parsed() {
+    let grants = set(vec![grant("s", "shell", Mode::Auto)]);
+    for tool in ["echo", "clock", "call_tool", "", "Shell"] {
+        for arguments in ["{}", "not json", r#"{"command":"ls"}"#] {
+            let outcome = decide(request(tool, arguments), &grants, private(), now());
+            assert_eq!(
+                reason(outcome),
+                DenyReason::NoGrant,
+                "{tool:?} {arguments:?}"
+            );
+        }
+    }
+}
+
+/// Invalid arguments are refused before matching, so the answer is the same with a grant that
+/// would cover them, with a `deny` grant, and with no grant at all.
+#[test]
+fn invalid_arguments_are_refused_before_matching() {
+    let covering = set(vec![
+        grant("r", "read_file", Mode::Auto).paths(&["/home/kyle/notes"]),
+        grant("no", "read_file", Mode::Deny).paths(&["/home/kyle"]),
+    ]);
+    let none = set(vec![]);
+    for grants in [&covering, &none] {
+        for req in [
+            // The rows of the "Paths" table that are about form.
+            read("/home/kyle/notes/../.ssh/id"),
+            read("notes/a.md"),
+            read("/home/kyle//notes/./a.md"),
+            request("read_file", "{}"),
+            request(
+                "read_file",
+                r#"{"path":"/home/kyle/notes/a.md","mode":"r"}"#,
+            ),
+            request("read_file", "not json"),
+            write("/home/kyle/notes/"),
+            shell(Some("relative")),
+            fetch("http://example.com/"),
+            fetch("https://127.0.0.1/"),
+            fetch("https://user@example.com/"),
+        ] {
+            let text = req.arguments.clone();
+            assert_eq!(
+                reason(decide(req, grants, private(), now())),
+                DenyReason::InvalidArguments,
+                "{text}"
+            );
+        }
+    }
+}
+
+/// The "Paths" table, the rows about containment.
+#[test]
+fn read_file_is_covered_inside_a_granted_path() {
+    let grants = set(vec![
+        grant("notes", "read_file", Mode::Auto).paths(&["/home/kyle/notes"]),
+    ]);
+    for path in [
+        "/home/kyle/notes/a.md",
+        "/home/kyle/notes",
+        "/home/kyle/notes/x/y/z",
+    ] {
+        let d = allowed(decide(read(path), &grants, private(), now()));
+        assert_eq!(d.grant(), "notes");
+        assert_eq!(d.matched_path(), Some("/home/kyle/notes"));
+    }
+    for path in [
+        "/home/kyle/notes2/a.md",
+        "/home/kyle",
+        "/",
+        "/etc/passwd",
+        "/home/kyle/note",
+    ] {
+        assert_eq!(
+            reason(decide(read(path), &grants, private(), now())),
+            DenyReason::NoGrant,
+            "{path}"
+        );
+    }
+    // A grant is for one tool.
+    let outcome = decide(write("/home/kyle/notes/a.md"), &grants, private(), now());
+    assert_eq!(reason(outcome), DenyReason::NoGrant);
+}
+
+#[test]
+fn write_file_is_covered_inside_a_granted_path_but_not_at_the_path_itself() {
+    let grants = set(vec![
+        grant("scratch", "write_file", Mode::Auto)
+            .paths(&["/home/kyle/scratch", "/home/kyle/scratch/out"]),
+    ]);
+    let d = allowed(decide(
+        write("/home/kyle/scratch/a.txt"),
+        &grants,
+        private(),
+        now(),
+    ));
+    assert_eq!(d.matched_path(), Some("/home/kyle/scratch"));
+    // The longest path that holds the argument is the matched one.
+    let d = allowed(decide(
+        write("/home/kyle/scratch/out/b.txt"),
+        &grants,
+        private(),
+        now(),
+    ));
+    assert_eq!(d.matched_path(), Some("/home/kyle/scratch/out"));
+    // A granted path itself cannot be written, but it can lie inside another granted path.
+    let d = allowed(decide(
+        write("/home/kyle/scratch/out"),
+        &grants,
+        private(),
+        now(),
+    ));
+    assert_eq!(d.matched_path(), Some("/home/kyle/scratch"));
+    let outcome = decide(write("/home/kyle/scratch"), &grants, private(), now());
+    assert_eq!(reason(outcome), DenyReason::NoGrant);
+}
+
+#[test]
+fn shell_is_covered_by_no_paths_and_no_cwd_or_by_a_cwd_inside_a_path() {
+    let bare = set(vec![grant("bare", "shell", Mode::Auto)]);
+    let d = allowed(decide(shell(None), &bare, private(), now()));
+    assert_eq!((d.matched_path(), d.paths().len()), (None, 0));
+    assert_eq!(
+        reason(decide(shell(Some("/home/kyle")), &bare, private(), now())),
+        DenyReason::NoGrant
+    );
+
+    let scoped = set(vec![
+        grant("scoped", "shell", Mode::Auto).paths(&["/home/kyle/a", "/srv/b"]),
+    ]);
+    let d = allowed(decide(shell(Some("/srv/b/sub")), &scoped, private(), now()));
+    assert_eq!(d.matched_path(), Some("/srv/b"));
+    // The runner mounts every path of the grant, so the decision carries them all.
+    assert_eq!(d.paths(), ["/home/kyle/a", "/srv/b"]);
+    assert_eq!(
+        reason(decide(shell(None), &scoped, private(), now())),
+        DenyReason::NoGrant
+    );
+    assert_eq!(
+        reason(decide(shell(Some("/srv")), &scoped, private(), now())),
+        DenyReason::NoGrant
+    );
+}
+
+/// The "Hosts" table, row by row.
+#[test]
+fn http_fetch_is_covered_when_the_host_matches() {
+    let exact = set(vec![
+        grant("exact", "http_fetch", Mode::Auto).hosts(&["example.com"]),
+    ]);
+    let wild = set(vec![
+        grant("wild", "http_fetch", Mode::Auto).hosts(&["*.example.com"]),
+    ]);
+    let d = allowed(decide(
+        fetch("https://example.com/a?b=c"),
+        &exact,
+        private(),
+        now(),
+    ));
+    assert_eq!(d.hosts(), ["example.com"]);
+    assert_eq!(d.matched_path(), None);
+    assert_eq!(
+        reason(decide(
+            fetch("https://www.example.com/"),
+            &exact,
+            private(),
+            now()
+        )),
+        DenyReason::NoGrant
+    );
+    for url in ["https://www.example.com/", "https://a.b.example.com:443/x"] {
+        allowed(decide(fetch(url), &wild, private(), now()));
+    }
+    for url in [
+        "https://example.com/",
+        "https://badexample.com/",
+        "https://example.com.evil.org/",
+    ] {
+        assert_eq!(
+            reason(decide(fetch(url), &wild, private(), now())),
+            DenyReason::NoGrant,
+            "{url}"
+        );
+    }
+}

crates/brokerd/tests/policy_matching.rs

@@ -0,0 +1,363 @@
+//! Table tests for `policy::decide`: among the grants that cover a call, which one wins, what
+//! the result is labelled, and which reason is given when none is left. Do not edit.
+
+#[path = "support/build.rs"]
+mod build;
+
+use brokerd::policy::{Label, decide};
+use build::{
+    allowed, asked, denied, fetch, grant, now, private, read, reason, request, secret, set, shell,
+};
+use proto::{DataClass, DenyReason, Mode};
+
+#[test]
+fn the_most_restrictive_mode_wins_among_three_matching_grants() {
+    let paths = &["/home/kyle/notes"];
+    let auto = || grant("b-auto", "read_file", Mode::Auto).paths(paths);
+    let ask = || grant("c-ask", "read_file", Mode::Ask).paths(paths);
+    let deny = || grant("a-deny", "read_file", Mode::Deny).paths(paths);
+    let req = || read("/home/kyle/notes/a.md");
+
+    let denial = denied(decide(
+        req(),
+        &set(vec![auto(), ask(), deny()]),
+        private(),
+        now(),
+    ));
+    assert_eq!(denial.reason, DenyReason::DeniedByGrant);
+    assert_eq!(denial.grant.as_deref(), Some("a-deny"));
+    assert_eq!(denial.grant_sha256, Some(deny().done().sha256));
+
+    let ask_wins = asked(decide(req(), &set(vec![auto(), ask()]), private(), now()));
+    assert_eq!(ask_wins.grant(), "c-ask");
+    assert_eq!(
+        allowed(decide(req(), &set(vec![auto()]), private(), now())).grant(),
+        "b-auto"
+    );
+
+    // Deny beats a longer path and a lower id: the mode comes first.
+    let narrow_auto = grant("a-auto", "read_file", Mode::Auto).paths(&["/home/kyle/notes/deep"]);
+    let wide_deny = grant("z-deny", "read_file", Mode::Deny).paths(&["/home"]);
+    let outcome = decide(
+        read("/home/kyle/notes/deep/x"),
+        &set(vec![narrow_auto, wide_deny]),
+        private(),
+        now(),
+    );
+    assert_eq!(denied(outcome).grant.as_deref(), Some("z-deny"));
+}
+
+#[test]
+fn within_a_mode_the_longest_matched_path_wins_and_then_the_lowest_id() {
+    let grants = set(vec![
+        grant("a-wide", "read_file", Mode::Auto).paths(&["/home/kyle"]),
+        grant("z-narrow", "read_file", Mode::Auto).paths(&["/home/kyle/notes"]),
+    ]);
+    let d = allowed(decide(
+        read("/home/kyle/notes/a.md"),
+        &grants,
+        private(),
+        now(),
+    ));
+    assert_eq!(
+        (d.grant(), d.matched_path()),
+        ("z-narrow", Some("/home/kyle/notes"))
+    );
+    let d = allowed(decide(read("/home/kyle/other"), &grants, private(), now()));
+    assert_eq!(d.grant(), "a-wide");
+
+    // Equal paths: the lowest id in byte order, whatever order the grants were given in.
+    let tie = set(vec![
+        grant("g-10", "read_file", Mode::Auto).paths(&["/srv"]),
+        grant("g-2", "read_file", Mode::Auto).paths(&["/srv"]),
+        grant("g-1z", "read_file", Mode::Auto).paths(&["/srv"]),
+    ]);
+    assert_eq!(
+        allowed(decide(read("/srv/x"), &tie, private(), now())).grant(),
+        "g-10"
+    );
+
+    // Grants with no matched path all tie, so the id decides.
+    let hosts = set(vec![
+        grant("m", "http_fetch", Mode::Auto).hosts(&["*.example.com"]),
+        grant("b", "http_fetch", Mode::Auto).hosts(&["www.example.com"]),
+    ]);
+    let d = allowed(decide(
+        fetch("https://www.example.com/"),
+        &hosts,
+        private(),
+        now(),
+    ));
+    assert_eq!(d.grant(), "b");
+}
+
+/// The example in the spec. Whichever id sorts first, the read is labelled `secret`, and the
+/// narrower grant is the one recorded and mounted.
+#[test]
+fn the_label_is_combined_over_every_matching_grant() {
+    for (home, keys) in [("a-home", "b-keys"), ("z-home", "b-keys")] {
+        let grants = set(vec![
+            grant(home, "read_file", Mode::Auto)
+                .paths(&["/home/kyle"])
+                .trusted(),
+            grant(keys, "read_file", Mode::Auto)
+                .paths(&["/home/kyle/keys"])
+                .class(DataClass::Secret)
+                .trusted(),
+        ]);
+        let d = allowed(decide(
+            read("/home/kyle/keys/id"),
+            &grants,
+            private(),
+            now(),
+        ));
+        assert_eq!(d.grant(), keys);
+        assert_eq!(
+            d.label(),
+            Label {
+                class: DataClass::Secret,
+                untrusted: false
+            }
+        );
+        // Outside `keys` only the wide grant matches, so only its label counts.
+        let d = allowed(decide(read("/home/kyle/todo"), &grants, private(), now()));
+        assert_eq!(
+            d.label(),
+            Label {
+                class: DataClass::Private,
+                untrusted: false
+            }
+        );
+    }
+
+    // The winner says trusted and public; another matching grant says otherwise, and it counts.
+    let grants = set(vec![
+        grant("narrow", "read_file", Mode::Auto)
+            .paths(&["/srv/pub/docs"])
+            .class(DataClass::Public)
+            .trusted(),
+        grant("wide", "read_file", Mode::Auto)
+            .paths(&["/srv/pub"])
+            .class(DataClass::Private),
+    ]);
+    let d = allowed(decide(read("/srv/pub/docs/x"), &grants, private(), now()));
+    assert_eq!(d.grant(), "narrow");
+    assert_eq!(
+        d.label(),
+        Label {
+            class: DataClass::Private,
+            untrusted: true
+        }
+    );
+
+    // An `ask` winner carries the combined label too.
+    let grants = set(vec![
+        grant("asks", "read_file", Mode::Ask)
+            .paths(&["/srv"])
+            .class(DataClass::Public)
+            .trusted(),
+        grant("labels", "read_file", Mode::Auto)
+            .paths(&["/srv"])
+            .class(DataClass::Secret),
+    ]);
+    let ask = asked(decide(read("/srv/x"), &grants, private(), now()));
+    assert_eq!(
+        ask.label(),
+        Label {
+            class: DataClass::Secret,
+            untrusted: true
+        }
+    );
+}
+
+#[test]
+fn a_grant_ruled_out_by_taint_or_expiry_adds_nothing_to_the_label() {
+    let grants = set(vec![
+        grant("live", "read_file", Mode::Auto)
+            .paths(&["/srv"])
+            .class(DataClass::Public)
+            .trusted(),
+        grant("old", "read_file", Mode::Auto)
+            .paths(&["/srv"])
+            .class(DataClass::Secret)
+            .expires("2026-01-01T00:00:00.000Z"),
+    ]);
+    let d = allowed(decide(read("/srv/x"), &grants, private(), now()));
+    assert_eq!(
+        d.label(),
+        Label {
+            class: DataClass::Public,
+            untrusted: false
+        }
+    );
+}
+
+#[test]
+fn a_grant_expires_exactly_at_its_time() {
+    let at = |when: &str| set(vec![grant("g", "shell", Mode::Auto).expires(when)]);
+    let d = allowed(decide(
+        shell(None),
+        &at("2026-09-18T12:00:00.001Z"),
+        private(),
+        now(),
+    ));
+    assert_eq!(d.expires(), Some(build::ts("2026-09-18T12:00:00.001Z")));
+    for when in [
+        "2026-09-18T12:00:00.000Z",
+        "2026-09-18T11:59:59.999Z",
+        "2020-01-01T00:00:00.000Z",
+    ] {
+        assert_eq!(
+            reason(decide(shell(None), &at(when), private(), now())),
+            DenyReason::GrantExpired,
+            "{when}"
+        );
+    }
+    let never = set(vec![grant("g", "shell", Mode::Auto)]);
+    assert_eq!(
+        allowed(decide(shell(None), &never, private(), now())).expires(),
+        None
+    );
+}
+
+#[test]
+fn a_grant_applies_up_to_its_max_taint() {
+    let grants = set(vec![
+        grant("g", "shell", Mode::Auto).max_taint(DataClass::Private),
+    ]);
+    allowed(decide(shell(None), &grants, private(), now()));
+    allowed(decide(
+        shell(None),
+        &grants,
+        build::at(DataClass::Public),
+        now(),
+    ));
+    assert_eq!(
+        reason(decide(shell(None), &grants, secret(), now())),
+        DenyReason::TaintTooHigh
+    );
+    // The untrusted flag is not an input to matching.
+    let mut state = private();
+    state.untrusted = true;
+    allowed(decide(shell(None), &grants, state, now()));
+}
+
+#[test]
+fn the_reason_when_nothing_is_left() {
+    let expired = || grant("e", "shell", Mode::Auto).expires("2026-01-01T00:00:00.000Z");
+    let tainted = || grant("t", "shell", Mode::Auto).max_taint(DataClass::Private);
+    let both = || {
+        grant("b", "shell", Mode::Auto)
+            .expires("2026-01-01T00:00:00.000Z")
+            .max_taint(DataClass::Private)
+    };
+    let cases = [
+        // One candidate expired and another too tainted: expiry is reported first.
+        (set(vec![expired(), tainted()]), DenyReason::GrantExpired),
+        (set(vec![tainted(), both()]), DenyReason::TaintTooHigh),
+        // Ruled out by both is ruled out "only" by neither.
+        (set(vec![both()]), DenyReason::NoGrant),
+        (set(vec![expired()]), DenyReason::GrantExpired),
+    ];
+    for (grants, want) in cases {
+        assert_eq!(reason(decide(shell(None), &grants, secret(), now())), want);
+    }
+    // "Only by expiry" means it would have matched: an expired grant for other arguments, or
+    // for another tool, is no reason to say `grant_expired`.
+    let elsewhere = set(vec![
+        grant("p", "read_file", Mode::Auto)
+            .paths(&["/srv"])
+            .expires("2026-01-01T00:00:00.000Z"),
+        grant("w", "write_file", Mode::Auto)
+            .paths(&["/home"])
+            .expires("2026-01-01T00:00:00.000Z"),
+    ]);
+    assert_eq!(
+        reason(decide(read("/home/kyle/x"), &elsewhere, private(), now())),
+        DenyReason::NoGrant
+    );
+}
+
+#[test]
+fn a_deny_grant_denies_at_every_taint_until_it_expires() {
+    let grants = |deny_expires: Option<&str>| {
+        let deny = grant("no-internal", "http_fetch", Mode::Deny).hosts(&["internal.example.com"]);
+        let deny = match deny_expires {
+            Some(when) => deny.expires(when),
+            None => deny,
+        };
+        set(vec![
+            grant("any", "http_fetch", Mode::Auto).hosts(&["*.example.com"]),
+            deny,
+        ])
+    };
+    let url = "https://internal.example.com/";
+    for state in [build::at(DataClass::Public), private(), secret()] {
+        let denial = denied(decide(fetch(url), &grants(None), state, now()));
+        assert_eq!(denial.reason, DenyReason::DeniedByGrant);
+        assert_eq!(denial.grant.as_deref(), Some("no-internal"));
+    }
+    allowed(decide(
+        fetch("https://www.example.com/"),
+        &grants(None),
+        secret(),
+        now(),
+    ));
+    // An expired deny no longer denies: `expires` on a deny grant means "forbid this until then".
+    let lapsed = grants(Some("2026-09-18T12:00:00.000Z"));
+    assert_eq!(
+        allowed(decide(fetch(url), &lapsed, private(), now())).grant(),
+        "any"
+    );
+}
+
+/// Documented, not liked: an `ask` grant with a lower `max_taint` than an `auto` grant over the
+/// same arguments drops out when taint rises, and the call then runs without asking.
+#[test]
+fn an_ask_grant_with_a_lower_max_taint_stops_asking_when_taint_rises() {
+    let grants = set(vec![
+        grant("asks", "shell", Mode::Ask).max_taint(DataClass::Private),
+        grant("runs", "shell", Mode::Auto),
+    ]);
+    assert_eq!(
+        asked(decide(shell(None), &grants, private(), now())).grant(),
+        "asks"
+    );
+    assert_eq!(
+        allowed(decide(shell(None), &grants, secret(), now())).grant(),
+        "runs"
+    );
+}
+
+#[test]
+fn a_decision_and_an_ask_carry_what_the_broker_and_the_runner_need() {
+    let grants = set(vec![
+        grant("asks", "write_file", Mode::Ask)
+            .paths(&["/home/kyle/scratch"])
+            .expires("2027-01-01T00:00:00.000Z")
+            .class(DataClass::Public),
+    ]);
+    let req = request(
+        "write_file",
+        r#"{ "content": "hello", "path": "/home/kyle/scratch/a.txt" }"#,
+    );
+    let ask = asked(decide(req.clone(), &grants, private(), now()));
+    assert_eq!(ask.request(), &req);
+    assert_eq!(
+        ask.args().canonical_json(),
+        r#"{"path":"/home/kyle/scratch/a.txt","content":"hello"}"#
+    );
+    assert_eq!(ask.grant(), "asks");
+    assert_eq!(ask.grant_sha256(), proto::sha256(b"asks").unwrap());
+    assert_eq!(ask.matched_path(), Some("/home/kyle/scratch"));
+    assert_eq!(ask.paths(), ["/home/kyle/scratch"]);
+    assert!(ask.hosts().is_empty());
+    assert_eq!(ask.expires(), Some(build::ts("2027-01-01T00:00:00.000Z")));
+    assert_eq!(
+        ask.label(),
+        Label {
+            class: DataClass::Public,
+            untrusted: true
+        }
+    );
+}

crates/brokerd/tests/policy_property.rs

@@ -0,0 +1,234 @@
+//! Property test for `policy`: random grant sets, states and requests, each decided twice, once
+//! by `policy::decide` and once by an oracle. Every case must agree. Do not edit.
+//!
+//! The generator and the oracle are in `support/oracle.rs`. If this test fails, the oracle is
+//! the specification and `policy` is wrong.
+//!
+//! The generator is a seeded xorshift, so a failure can be replayed: the message names the seed
+//! and the case. `BOXMAKER_POLICY_SEED=<n>` runs one more seed, and `BOXMAKER_POLICY_CASES=<n>`
+//! changes how many cases each seed runs (default 3000).
+
+#[path = "support/oracle.rs"]
+mod oracle;
+
+use brokerd::grants::{GrantSet, LoadedGrant};
+use brokerd::policy::{Outcome, SessionState, decide, redecide};
+use oracle::{CLASSES, Expected, NOW_MS, Rng, oracle, some_grant, some_grants, some_request};
+use proto::{DataClass, DenyReason, Mode, Timestamp};
+
+const SEEDS: [u64; 5] = [1, 2, 3, 0xB0C5, 20_260_918];
+
+// ---------------------------------------------------------------------------------------------
+// The comparison.
+
+fn observed(outcome: &Outcome) -> Expected {
+    match outcome {
+        Outcome::Allowed(d) => Expected::Allowed {
+            grant: d.grant().to_string(),
+            path: d.matched_path().map(str::to_string),
+            class: d.label().class,
+            untrusted: d.label().untrusted,
+        },
+        Outcome::Ask(a) => Expected::Ask {
+            grant: a.grant().to_string(),
+            path: a.matched_path().map(str::to_string),
+            class: a.label().class,
+            untrusted: a.label().untrusted,
+        },
+        Outcome::Denied(denial) => Expected::Denied {
+            reason: denial.reason,
+            grant: denial.grant.clone(),
+        },
+    }
+}
+
+/// Allowed is 0, ask is 1, denied is 2.
+fn restrictiveness(expected: &Expected) -> u8 {
+    match expected {
+        Expected::Allowed { .. } => 0,
+        Expected::Ask { .. } => 1,
+        Expected::Denied { .. } => 2,
+    }
+}
+
+fn cases() -> usize {
+    match std::env::var("BOXMAKER_POLICY_CASES") {
+        Ok(text) => text
+            .parse()
+            .expect("BOXMAKER_POLICY_CASES must be a number"),
+        Err(_) => 3000,
+    }
+}
+
+fn seeds() -> Vec<u64> {
+    let mut seeds = SEEDS.to_vec();
+    if let Ok(text) = std::env::var("BOXMAKER_POLICY_SEED") {
+        seeds.push(text.parse().expect("BOXMAKER_POLICY_SEED must be a number"));
+    }
+    seeds
+}
+
+fn now() -> Timestamp {
+    Timestamp::from_unix_millis(NOW_MS).unwrap()
+}
+
+fn state(rng: &mut Rng) -> SessionState {
+    SessionState {
+        taint: rng.pick(&CLASSES),
+        untrusted: rng.chance(50),
+    }
+}
+
+fn valid(grants: &[LoadedGrant]) -> GrantSet {
+    GrantSet::from_grants(grants.to_vec()).expect("the generator only makes valid grants")
+}
+
+#[test]
+fn decide_agrees_with_the_oracle() {
+    let mut kinds = [0usize; 3];
+    for seed in seeds() {
+        let mut rng = Rng::new(seed);
+        for case in 0..cases() {
+            let grants = some_grants(&mut rng);
+            let request = some_request(&mut rng);
+            let state = state(&mut rng);
+            let want = oracle(&request, &grants, state);
+            let got = observed(&decide(request.clone(), &valid(&grants), state, now()));
+            assert_eq!(
+                got, want,
+                "seed {seed} case {case}\nrequest: {request:?}\nstate: {state:?}\ngrants: {grants:#?}"
+            );
+            kinds[restrictiveness(&want) as usize] += 1;
+        }
+    }
+    // The generator must reach every kind of outcome, or the test proves little.
+    for (kind, count) in ["allowed", "ask", "denied"].iter().zip(kinds) {
+        assert!(count > 200, "only {count} cases were {kind}");
+    }
+}
+
+#[test]
+fn redecide_agrees_with_the_oracle_under_new_grants_and_a_new_state() {
+    let mut approvals = 0;
+    for seed in seeds() {
+        let mut rng = Rng::new(seed ^ 0xA5A5);
+        for case in 0..cases() {
+            let grants = some_grants(&mut rng);
+            let request = some_request(&mut rng);
+            let first = state(&mut rng);
+            let Outcome::Ask(ask) = decide(request.clone(), &valid(&grants), first, now()) else {
+                continue;
+            };
+            approvals += 1;
+            // Half the time nothing has changed; otherwise the grants or the state have.
+            let (later_grants, later) = if rng.chance(50) {
+                (grants.clone(), first)
+            } else {
+                (some_grants(&mut rng), state(&mut rng))
+            };
+            let want = oracle(&request, &later_grants, later);
+            let got = redecide(ask, &valid(&later_grants), later, now());
+            let context = format!(
+                "seed {seed} case {case}\nrequest: {request:?}\nlater: {later:?}\ngrants: {later_grants:#?}"
+            );
+            match (want, got) {
+                (
+                    Expected::Allowed {
+                        grant,
+                        path,
+                        class,
+                        untrusted,
+                    },
+                    Ok(d),
+                )
+                | (
+                    Expected::Ask {
+                        grant,
+                        path,
+                        class,
+                        untrusted,
+                    },
+                    Ok(d),
+                ) => {
+                    assert_eq!(d.grant(), grant, "{context}");
+                    assert_eq!(d.matched_path().map(str::to_string), path, "{context}");
+                    assert_eq!(
+                        (d.label().class, d.label().untrusted),
+                        (class, untrusted),
+                        "{context}"
+                    );
+                    assert_eq!(d.request(), &request, "{context}");
+                }
+                (Expected::Denied { reason, grant }, Err(denial)) => {
+                    assert_eq!((denial.reason, denial.grant), (reason, grant), "{context}");
+                }
+                (want, got) => panic!("wanted {want:?}, got {got:?}\n{context}"),
+            }
+        }
+    }
+    assert!(approvals > 200, "only {approvals} cases asked");
+}
+
+/// Adding a `deny` grant to a set never makes any outcome less restrictive.
+#[test]
+fn adding_a_deny_grant_never_loosens_an_outcome() {
+    for seed in seeds() {
+        let mut rng = Rng::new(seed ^ 0x5A5A);
+        for case in 0..cases() {
+            let grants = some_grants(&mut rng);
+            let request = some_request(&mut rng);
+            let state = state(&mut rng);
+            let mut extra = some_grant(&mut rng, 90);
+            extra.grant.mode = Mode::Deny;
+            extra.grant.max_taint = DataClass::Secret;
+            let mut with_deny = grants.clone();
+            with_deny.push(extra);
+
+            let before = observed(&decide(request.clone(), &valid(&grants), state, now()));
+            let after = observed(&decide(request.clone(), &valid(&with_deny), state, now()));
+            assert!(
+                restrictiveness(&after) >= restrictiveness(&before),
+                "seed {seed} case {case}: {before:?} became {after:?}\nrequest: {request:?}\ngrants: {with_deny:#?}"
+            );
+        }
+    }
+}
+
+/// A call that is `denied_by_grant` at one taint is `denied_by_grant` at every higher taint:
+/// reading a secret can never switch off a prohibition.
+#[test]
+fn a_prohibition_holds_at_every_higher_taint() {
+    let mut prohibitions = 0;
+    for seed in seeds() {
+        let mut rng = Rng::new(seed ^ 0x0F0F);
+        for case in 0..cases() {
+            let grants = some_grants(&mut rng);
+            let request = some_request(&mut rng);
+            let mut denied_below = false;
+            for taint in CLASSES {
+                let state = SessionState {
+                    taint,
+                    untrusted: false,
+                };
+                let outcome = observed(&decide(request.clone(), &valid(&grants), state, now()));
+                let by_grant = matches!(
+                    outcome,
+                    Expected::Denied {
+                        reason: DenyReason::DeniedByGrant,
+                        ..
+                    }
+                );
+                assert!(
+                    by_grant || !denied_below,
+                    "seed {seed} case {case}: a deny stopped applying at {taint:?}\nrequest: {request:?}\ngrants: {grants:#?}"
+                );
+                denied_below = by_grant;
+            }
+            prohibitions += usize::from(denied_below);
+        }
+    }
+    assert!(
+        prohibitions > 200,
+        "only {prohibitions} cases were prohibited"
+    );
+}

crates/brokerd/tests/policy_redecide.rs

@@ -0,0 +1,117 @@
+//! Table tests for `policy::redecide`: an approval lets a call through only if the grants and
+//! the session's state, as they are when it is approved, still say `ask` or `auto`. Do not edit.
+
+#[path = "support/build.rs"]
+mod build;
+
+use brokerd::grants::GrantSet;
+use brokerd::policy::{Ask, Label, Outcome, decide, redecide};
+use build::{grant, now, private, read, secret, set};
+use proto::{DataClass, DenyReason, Mode};
+
+const PATH: &str = "/home/kyle/notes/a.md";
+
+fn asking() -> build::Build {
+    grant("asks", "read_file", Mode::Ask).paths(&["/home/kyle/notes"])
+}
+
+/// An `Ask` for `PATH`, decided under `asking()` alone at `private`.
+fn pending() -> Ask {
+    match decide(read(PATH), &set(vec![asking()]), private(), now()) {
+        Outcome::Ask(ask) => ask,
+        other => panic!("expected ask, got {other:?}"),
+    }
+}
+
+#[test]
+fn still_ask_lets_the_call_run_under_the_same_grant() {
+    let decision = redecide(pending(), &set(vec![asking()]), private(), now()).unwrap();
+    assert_eq!(decision.grant(), "asks");
+    assert_eq!(decision.request(), &read(PATH));
+    assert_eq!(decision.matched_path(), Some("/home/kyle/notes"));
+    assert_eq!(
+        decision.label(),
+        Label {
+            class: DataClass::Private,
+            untrusted: true
+        }
+    );
+}
+
+#[test]
+fn auto_now_lets_the_call_run_under_the_grant_that_matches_now() {
+    // The owner has since replaced the ask grant with an auto grant of another name and label.
+    let grants = set(vec![
+        grant("now-auto", "read_file", Mode::Auto)
+            .paths(&["/home/kyle"])
+            .class(DataClass::Secret)
+            .trusted(),
+    ]);
+    let decision = redecide(pending(), &grants, private(), now()).unwrap();
+    assert_eq!(decision.grant(), "now-auto");
+    assert_eq!(decision.grant_sha256(), proto::sha256(b"now-auto").unwrap());
+    assert_eq!(decision.matched_path(), Some("/home/kyle"));
+    assert_eq!(decision.paths(), ["/home/kyle"]);
+    assert_eq!(
+        decision.label(),
+        Label {
+            class: DataClass::Secret,
+            untrusted: false
+        }
+    );
+}
+
+#[test]
+fn the_grant_file_was_removed() {
+    let denial = redecide(pending(), &GrantSet::default(), private(), now()).unwrap_err();
+    assert_eq!(denial.reason, DenyReason::NoGrant);
+    assert_eq!(denial.grant, None);
+}
+
+#[test]
+fn the_taint_rose_past_max_taint_while_the_approval_waited() {
+    let narrow = || asking().max_taint(DataClass::Private);
+    let ask = match decide(read(PATH), &set(vec![narrow()]), private(), now()) {
+        Outcome::Ask(ask) => ask,
+        other => panic!("expected ask, got {other:?}"),
+    };
+    let denial = redecide(ask, &set(vec![narrow()]), secret(), now()).unwrap_err();
+    assert_eq!(denial.reason, DenyReason::TaintTooHigh);
+}
+
+#[test]
+fn the_grant_expired_while_the_approval_waited() {
+    let grants = set(vec![asking().expires("2026-09-18T12:10:00.000Z")]);
+    let ask = match decide(read(PATH), &grants, private(), now()) {
+        Outcome::Ask(ask) => ask,
+        other => panic!("expected ask, got {other:?}"),
+    };
+    assert_eq!(ask.expires(), Some(build::ts("2026-09-18T12:10:00.000Z")));
+    let later = build::ts("2026-09-18T12:10:00.000Z");
+    let denial = redecide(ask, &grants, private(), later).unwrap_err();
+    assert_eq!(denial.reason, DenyReason::GrantExpired);
+}
+
+#[test]
+fn a_deny_grant_was_added_while_the_approval_waited() {
+    let grants = set(vec![
+        asking(),
+        grant("no-notes", "read_file", Mode::Deny).paths(&["/home/kyle"]),
+    ]);
+    let denial = redecide(pending(), &grants, private(), now()).unwrap_err();
+    assert_eq!(denial.reason, DenyReason::DeniedByGrant);
+    assert_eq!(denial.grant.as_deref(), Some("no-notes"));
+    assert_eq!(
+        denial.grant_sha256,
+        Some(proto::sha256(b"no-notes").unwrap())
+    );
+}
+
+#[test]
+fn the_grants_now_cover_other_arguments_only() {
+    let grants = set(vec![
+        grant("asks", "read_file", Mode::Ask).paths(&["/home/kyle/other"]),
+    ]);
+    let denial = redecide(pending(), &grants, private(), now()).unwrap_err();
+    assert_eq!(denial.reason, DenyReason::NoGrant);
+}

crates/brokerd/tests/runner.rs

@@ -0,0 +1,175 @@
+//! The runner seam: what `run` puts in the `RunSpec` for each tool, and what it answers. Do not
+//! edit.
+
+#[path = "support/build.rs"]
+mod build;
+#[path = "support/runtime.rs"]
+mod runtime;
+
+use brokerd::args::{ToolArgs, ToolName};
+use brokerd::policy::{Decision, Outcome, SessionState, decide};
+use brokerd::runner::{Mount, REFUSING, Refusing, RunError, RunOutput, run};
+use build::{grant, now, read, request, set};
+use proto::{DataClass, Mode, ToolRequest, ToolResponse};
+use runtime::Recording;
+
+fn allowed(grants: Vec<build::Build>, request: ToolRequest) -> Decision {
+    match decide(request, &set(grants), SessionState::default(), now()) {
+        Outcome::Allowed(decision) => decision,
+        other => panic!("the test's call is not allowed: {other:?}"),
+    }
+}
+
+fn mount(path: &str, writable: bool) -> Mount {
+    Mount {
+        path: path.to_string(),
+        writable,
+    }
+}
+
+#[test]
+fn read_file_mounts_the_matched_path_read_only_and_has_no_network() {
+    let d = allowed(
+        vec![grant("notes", "read_file", Mode::Auto).paths(&["/h/notes", "/h/notes/deep"])],
+        read("/h/notes/deep/a.md"),
+    );
+    let rt = Recording::answering("text");
+    run(d, rt.as_ref());
+    let seen = rt.seen();
+    assert_eq!(seen.len(), 1);
+    assert_eq!(seen[0].tool, ToolName::ReadFile);
+    assert_eq!(
+        seen[0].arguments,
+        ToolArgs::ReadFile {
+            path: "/h/notes/deep/a.md".to_string()
+        }
+    );
+    // The longest path that holds the argument, and only that one.
+    assert_eq!(seen[0].mounts, [mount("/h/notes/deep", false)]);
+    assert_eq!(seen[0].egress, None);
+}
+
+#[test]
+fn write_file_mounts_the_matched_path_writable() {
+    // A grant path equal to the argument does not count, so `/s/out` is written through `/s`.
+    let d = allowed(
+        vec![grant("s", "write_file", Mode::Auto).paths(&["/s", "/s/out"])],
+        request("write_file", r#"{"path":"/s/out","content":"x"}"#),
+    );
+    let rt = Recording::answering("");
+    run(d, rt.as_ref());
+    let seen = rt.seen();
+    assert_eq!(seen[0].tool, ToolName::WriteFile);
+    assert_eq!(seen[0].mounts, [mount("/s", true)]);
+    assert_eq!(seen[0].egress, None);
+}
+
+#[test]
+fn shell_mounts_every_path_of_the_grant_writable() {
+    let d = allowed(
+        vec![grant("sh", "shell", Mode::Auto).paths(&["/a", "/b/c"])],
+        request("shell", r#"{"command":"ls","cwd":"/b/c/d"}"#),
+    );
+    let rt = Recording::answering("");
+    run(d, rt.as_ref());
+    let seen = rt.seen();
+    assert_eq!(seen[0].tool, ToolName::Shell);
+    assert_eq!(seen[0].mounts, [mount("/a", true), mount("/b/c", true)]);
+    assert_eq!(seen[0].egress, None);
+}
+
+#[test]
+fn shell_without_paths_mounts_nothing() {
+    let d = allowed(
+        vec![grant("sh", "shell", Mode::Auto)],
+        request("shell", r#"{"command":"date"}"#),
+    );
+    let rt = Recording::answering("");
+    run(d, rt.as_ref());
+    let seen = rt.seen();
+    assert_eq!(seen[0].mounts, []);
+    assert_eq!(seen[0].egress, None);
+}
+
+#[test]
+fn http_fetch_mounts_nothing_and_may_reach_the_grants_hosts_only() {
+    let d = allowed(
+        vec![grant("web", "http_fetch", Mode::Auto).hosts(&["example.com", "*.example.org"])],
+        request("http_fetch", r#"{"url":"https://www.example.org/x"}"#),
+    );
+    let rt = Recording::answering("");
+    run(d, rt.as_ref());
+    let seen = rt.seen();
+    assert_eq!(seen[0].tool, ToolName::HttpFetch);
+    assert_eq!(seen[0].mounts, []);
+    assert_eq!(
+        seen[0].egress,
+        Some(vec!["example.com".to_string(), "*.example.org".to_string()])
+    );
+}
+
+#[test]
+fn a_result_carries_the_label_combined_over_every_matching_grant() {
+    // `b-keys` has the longer path and wins the mount; the label is the highest class of both
+    // grants, and untrusted because `a-home` says so.
+    let d = allowed(
+        vec![
+            grant("a-home", "read_file", Mode::Auto)
+                .paths(&["/home/kyle"])
+                .class(DataClass::Private),
+            grant("b-keys", "read_file", Mode::Auto)
+                .paths(&["/home/kyle/keys"])
+                .class(DataClass::Secret)
+                .trusted(),
+        ],
+        read("/home/kyle/keys/id"),
+    );
+    let rt = Recording::with(Ok(RunOutput {
+        content: "key".to_string(),
+        truncated: true,
+    }));
+    let answer = run(d, rt.as_ref());
+    assert_eq!(
+        answer,
+        ToolResponse::Result {
+            content: "key".to_string(),
+            class: DataClass::Secret,
+            untrusted: true,
+            truncated: true,
+        }
+    );
+    assert_eq!(rt.seen()[0].mounts, [mount("/home/kyle/keys", false)]);
+}
+
+#[test]
+fn a_run_error_is_a_failure_with_the_runtimes_sentence() {
+    for error in [
+        RunError::Failed("the tool timed out".to_string()),
+        RunError::Unavailable("the container could not start".to_string()),
+    ] {
+        let d = allowed(
+            vec![grant("n", "read_file", Mode::Auto).paths(&["/n"])],
+            read("/n/a"),
+        );
+        let text = match &error {
+            RunError::Failed(t) | RunError::Unavailable(t) => t.clone(),
+        };
+        let rt = Recording::with(Err(error));
+        assert_eq!(run(d, rt.as_ref()), ToolResponse::Failed { message: text });
+    }
+}
+
+#[test]
+fn the_production_runtime_refuses_every_call() {
+    assert_eq!(REFUSING, "the runner arrives in M3b");
+    let d = allowed(
+        vec![grant("n", "read_file", Mode::Auto).paths(&["/n"])],
+        read("/n/a"),
+    );
+    assert_eq!(
+        run(d, &Refusing),
+        ToolResponse::Failed {
+            message: REFUSING.to_string()
+        }
+    );
+}

crates/brokerd/tests/serve.rs

@@ -0,0 +1,405 @@
+//! `brokerd serve` as a process: its startup, both sockets, and the expiry thread. Do not edit.
+
+#[path = "support/tmp.rs"]
+mod tmp;
+
+use std::os::unix::fs::PermissionsExt;
+use std::os::unix::net::{UnixListener, UnixStream};
+use std::path::{Path, PathBuf};
+use std::process::{Child, Command, Output, Stdio};
+use std::time::{Duration, Instant};
+
+use brokerd::audit::RECOVERED_NOTICE;
+use brokerd::runner::REFUSING;
+use proto::{
+    AuditEvent, CallId, DenyReason, Empty, Envelope, ErrorCode, Message, PROTOCOL_VERSION,
+    ResultStatus, SessionId, ToolRequest, ToolResponse,
+};
+use tmp::TempDir;
+
+struct Home {
+    dir: TempDir,
+    config: PathBuf,
+}
+
+impl Home {
+    fn new(tag: &str, ttl_ms: u64) -> Home {
+        let dir = TempDir::new(tag);
+        std::fs::create_dir_all(dir.path().join("grants")).unwrap();
+        let text = format!(
+            "[paths]\nhome = \"{home}\"\ngrants = \"{home}/grants\"\n[approvals]\nttl_ms = {ttl_ms}\n",
+            home = dir.path().display()
+        );
+        let config = dir.write("brokerd.toml", &text);
+        Home { dir, config }
+    }
+
+    fn path(&self, relative: &str) -> PathBuf {
+        self.dir.path().join(relative)
+    }
+
+    fn tools(&self) -> PathBuf {
+        self.path("run/loop-broker/broker.sock")
+    }
+
+    fn admin(&self) -> PathBuf {
+        self.path("run/owner-broker/admin.sock")
+    }
+
+    fn grant(&self, id: &str, mode: &str) {
+        let text = format!(
+            "tool = \"read_file\"\nmode = \"{mode}\"\nmax_taint = \"secret\"\n\
+             result_class = \"private\"\nuntrusted = false\n[constraints]\npaths = [\"/n\"]\n"
+        );
+        std::fs::write(self.path(&format!("grants/{id}.toml")), text).unwrap();
+    }
+
+    fn command(&self, extra: &[&str]) -> Command {
+        let mut command = Command::new(env!("CARGO_BIN_EXE_brokerd"));
+        command
+            .args(["serve", "--config"])
+            .arg(&self.config)
+            .args(extra);
+        command
+    }
+
+    /// Starts `brokerd serve` and waits until both sockets answer.
+    fn serve(&self) -> Running {
+        let child = self
+            .command(&[])
+            .stdout(Stdio::null())
+            .stderr(Stdio::piped())
+            .spawn()
+            .unwrap();
+        let running = Running(Some(child));
+        let until = Instant::now() + Duration::from_secs(10);
+        while UnixStream::connect(self.tools()).is_err()
+            || UnixStream::connect(self.admin()).is_err()
+        {
+            assert!(Instant::now() < until, "brokerd never listened");
+            std::thread::sleep(Duration::from_millis(20));
+        }
+        running
+    }
+
+    /// Runs `brokerd serve` expecting it to exit by itself.
+    fn run(&self, extra: &[&str]) -> Output {
+        self.command(extra).output().unwrap()
+    }
+
+    fn events(&self) -> Vec<AuditEvent> {
+        let dir = self.path("audit");
+        let mut names: Vec<String> = std::fs::read_dir(&dir)
+            .unwrap()
+            .map(|e| e.unwrap().file_name().into_string().unwrap())
+            .filter(|n| n.ends_with(".jsonl"))
+            .collect();
+        names.sort();
+        names
+            .iter()
+            .flat_map(|n| {
+                let text = std::fs::read_to_string(dir.join(n)).unwrap();
+                text.lines()
+                    .map(|l| serde_json::from_str::<proto::AuditRecord>(l).unwrap().event)
+                    .collect::<Vec<_>>()
+            })
+            .collect()
+    }
+}
+
+/// Kills the daemon when dropped; `stop` returns what it printed.
+struct Running(Option<Child>);
+
+impl Running {
+    fn stop(mut self) -> String {
+        let mut child = self.0.take().unwrap();
+        child.kill().unwrap();
+        let output = child.wait_with_output().unwrap();
+        String::from_utf8_lossy(&output.stderr).to_string()
+    }
+}
+
+impl Drop for Running {
+    fn drop(&mut self) {
+        if let Some(child) = &mut self.0 {
+            let _ = child.kill();
+            let _ = child.wait();
+        }
+    }
+}
+
+fn mode(path: &Path) -> u32 {
+    std::fs::metadata(path).unwrap().permissions().mode() & 0o777
+}
+
+fn exchange(socket: &Path, id: u64, msg: Message) -> Vec<Envelope> {
+    let mut stream = UnixStream::connect(socket).unwrap();
+    stream
+        .set_read_timeout(Some(Duration::from_secs(10)))
+        .unwrap();
+    let env = Envelope {
+        v: PROTOCOL_VERSION,
+        id,
+        r#final: true,
+        msg,
+    };
+    proto::write_frame(&mut stream, &env).unwrap();
+    let mut frames = Vec::new();
+    loop {
+        let env = proto::read_frame(&mut stream).unwrap();
+        let last = env.r#final;
+        frames.push(env);
+        if last {
+            return frames;
+        }
+    }
+}
+
+fn read_notes(call: u64) -> Message {
+    Message::ToolRequest(ToolRequest {
+        session: SessionId::new("s1").unwrap(),
+        call: CallId(call),
+        tool: "read_file".to_string(),
+        arguments: r#"{"path":"/n/a"}"#.to_string(),
+    })
+}
+
+fn last_response(frames: &[Envelope]) -> &ToolResponse {
+    match &frames.last().unwrap().msg {
+        Message::ToolResponse(r) => r,
+        other => panic!("{other:?}"),
+    }
+}
+
+fn stderr(output: &Output) -> String {
+    String::from_utf8_lossy(&output.stderr).to_string()
+}
+
+#[test]
+fn it_makes_its_directories_0700_and_its_sockets_0600() {
+    let home = Home::new("serve-modes", 900_000);
+    // One directory found too open, one made.
+    std::fs::create_dir_all(home.path("run/owner-broker")).unwrap();
+    std::fs::set_permissions(
+        home.path("run/owner-broker"),
+        std::fs::Permissions::from_mode(0o755),
+    )
+    .unwrap();
+    let running = home.serve();
+    assert_eq!(mode(&home.path("run/loop-broker")), 0o700);
+    assert_eq!(mode(&home.path("run/owner-broker")), 0o700);
+    assert_eq!(mode(&home.tools()), 0o600);
+    assert_eq!(mode(&home.admin()), 0o600);
+    assert_eq!(mode(&home.path("audit")), 0o700);
+    let printed = running.stop();
+    assert!(printed.contains("serving"), "{printed}");
+}
+
+#[test]
+fn a_stale_socket_is_replaced() {
+    let home = Home::new("serve-stale", 900_000);
+    std::fs::create_dir_all(home.path("run/loop-broker")).unwrap();
+    drop(UnixListener::bind(home.tools()).unwrap());
+    assert!(home.tools().exists(), "the stale socket file is there");
+    let _running = home.serve();
+    let frames = exchange(&home.tools(), 3, read_notes(3));
+    assert_eq!(
+        last_response(&frames),
+        &ToolResponse::Denied {
+            reason: DenyReason::NoGrant
+        }
+    );
+}
+
+#[test]
+fn a_second_brokerd_on_the_same_home_refuses_to_start() {
+    let home = Home::new("serve-twice", 900_000);
+    let _running = home.serve();
+    let second = home.run(&[]);
+    assert_eq!(second.status.code(), Some(1));
+    let text = stderr(&second);
+    assert!(text.contains("brokerd is already running"), "{text}");
+    assert!(
+        text.trim_end()
+            .ends_with("see docs/runbook.md#brokerd-already-running"),
+        "{text}"
+    );
+    // The first still has its sockets.
+    let frames = exchange(&home.admin(), 1, Message::Approvals(Empty {}));
+    assert!(matches!(frames[0].msg, Message::ApprovalList(_)));
+}
+
+#[test]
+fn it_answers_each_socket_and_refuses_the_other_kinds() {
+    let home = Home::new("serve-kinds", 900_000);
+    home.grant("notes", "auto");
+    let running = home.serve();
+    let frames = exchange(&home.tools(), 7, read_notes(7));
+    assert_eq!(frames[0].id, 7);
+    // The production runtime runs nothing.
+    assert_eq!(
+        last_response(&frames),
+        &ToolResponse::Failed {
+            message: REFUSING.to_string()
+        }
+    );
+    let wrong = exchange(&home.tools(), 8, Message::Approvals(Empty {}));
+    assert!(matches!(&wrong[0].msg, Message::Error(e) if e.code == ErrorCode::Forbidden));
+    let wrong = exchange(&home.admin(), 9, read_notes(9));
+    assert!(matches!(&wrong[0].msg, Message::Error(e) if e.code == ErrorCode::Forbidden));
+    let printed = running.stop();
+    assert!(
+        printed.contains("approvals on broker.sock\nsee docs/runbook.md#socket-forbidden"),
+        "{printed}"
+    );
+    assert!(
+        printed.contains("tool_request on admin.sock\nsee docs/runbook.md#socket-forbidden"),
+        "{printed}"
+    );
+    assert!(matches!(
+        home.events().as_slice(),
+        [
+            AuditEvent::Decision { .. },
+            AuditEvent::Result {
+                status: ResultStatus::Failed,
+                ..
+            }
+        ]
+    ));
+}
+
+#[test]
+fn an_approval_nobody_answers_expires() {
+    let home = Home::new("serve-expire", 100);
+    home.grant("notes", "ask");
+    let _running = home.serve();
+    let started = Instant::now();
+    let frames = exchange(&home.tools(), 2, read_notes(2));
+    assert_eq!(frames.len(), 2, "{frames:?}");
+    assert!(matches!(
+        &frames[0].msg,
+        Message::ToolResponse(ToolResponse::PendingApproval { approval: 0, .. })
+    ));
+    assert_eq!(
+        last_response(&frames),
+        &ToolResponse::Denied {
+            reason: DenyReason::ApprovalExpired
+        }
+    );
+    // The expiry thread looks every second.
+    assert!(
+        started.elapsed() < Duration::from_secs(5),
+        "{:?}",
+        started.elapsed()
+    );
+}
+
+fn copy_case(home: &Home, case: &str, only: &[&str]) {
+    let from = format!(
+        "{}/../proto/tests/fixtures/audit/{case}",
+        env!("CARGO_MANIFEST_DIR")
+    );
+    std::fs::create_dir_all(home.path("audit")).unwrap();
+    for name in only {
+        std::fs::copy(
+            format!("{from}/{name}"),
+            home.path(&format!("audit/{name}")),
+        )
+        .unwrap();
+    }
+}
+
+fn snapshot(dir: &Path) -> Vec<(String, Vec<u8>)> {
+    let mut all: Vec<(String, Vec<u8>)> = std::fs::read_dir(dir)
+        .unwrap()
+        .map(|e| e.unwrap())
+        .filter(|e| e.file_name().to_string_lossy().ends_with(".jsonl"))
+        .map(|e| {
+            (
+                e.file_name().into_string().unwrap(),
+                std::fs::read(e.path()).unwrap(),
+            )
+        })
+        .collect();
+    all.sort();
+    all
+}
+
+#[test]
+fn a_broken_chain_stops_it_before_any_socket_and_nothing_is_written() {
+    let home = Home::new("serve-broken", 900_000);
+    copy_case(&home, "changed-byte", &["2026-09-17.jsonl"]);
+    let before = snapshot(&home.path("audit"));
+    let output = home.run(&[]);
+    assert_eq!(output.status.code(), Some(1));
+    let text = stderr(&output);
+    assert!(text.contains("2026-09-17.jsonl:4: "), "{text}");
+    assert!(
+        text.trim_end()
+            .ends_with("see docs/runbook.md#audit-chain-broken"),
+        "{text}"
+    );
+    assert_eq!(snapshot(&home.path("audit")), before);
+    assert!(!home.tools().exists() && !home.admin().exists());
+}
+
+#[test]
+fn a_torn_tail_is_recovered_and_it_serves() {
+    let home = Home::new("serve-torn", 900_000);
+    copy_case(
+        &home,
+        "torn-tail",
+        &["2026-09-17.jsonl", "2026-09-18.jsonl"],
+    );
+    let running = home.serve();
+    let printed = running.stop();
+    assert!(printed.contains(RECOVERED_NOTICE), "{printed}");
+    assert!(RECOVERED_NOTICE.ends_with("see docs/runbook.md#audit-recovered"));
+}
+
+#[test]
+fn accept_break_with_nothing_to_accept_exits_2() {
+    let home = Home::new("serve-nothing", 900_000);
+    let output = home.run(&["--accept-break"]);
+    assert_eq!(output.status.code(), Some(2));
+    assert!(
+        stderr(&output).contains("nothing to accept"),
+        "{}",
+        stderr(&output)
+    );
+}
+
+#[test]
+fn bad_arguments_and_bad_configs_do_not_start() {
+    let brokerd = env!("CARGO_BIN_EXE_brokerd");
+    for args in [
+        &[][..],
+        &["serve"][..],
+        &["serve", "--config"][..],
+        &["serve", "--config", "a", "--config", "b"][..],
+        &["serve", "--config", "a", "--loud"][..],
+        &["run", "--config", "a"][..],
+    ] {
+        let output = Command::new(brokerd).args(args).output().unwrap();
+        assert_eq!(output.status.code(), Some(2), "{args:?}");
+        assert!(
+            stderr(&output).starts_with("usage: brokerd serve"),
+            "{args:?}"
+        );
+    }
+    let home = Home::new("serve-config", 900_000);
+    std::fs::write(&home.config, "[paths]\nhoem = \"/x\"\n").unwrap();
+    let output = home.run(&[]);
+    assert_eq!(output.status.code(), Some(1));
+    assert!(
+        stderr(&output).contains("brokerd.toml"),
+        "{}",
+        stderr(&output)
+    );
+    std::fs::remove_file(&home.config).unwrap();
+    assert_eq!(home.run(&[]).status.code(), Some(1));
+    assert!(
+        !home.path("audit").exists(),
+        "nothing made before the config is read"
+    );
+}

crates/brokerd/tests/serve_accept_break.rs

@@ -0,0 +1,111 @@
+//! `brokerd serve --accept-break` on a real break, through the binary: it records the break and
+//! serves, and the next plain start serves too (spec section 12, "Audit edges"; missing from the
+//! given tests, found in the M3a review).
+
+#[path = "support/tmp.rs"]
+mod tmp;
+
+use std::io::Read;
+use std::os::unix::net::UnixStream;
+use std::path::Path;
+use std::process::{Command, Stdio};
+use std::time::{Duration, Instant};
+
+use brokerd::audit::verify_dir;
+use tmp::TempDir;
+
+/// Start `brokerd serve` with `extra`, wait until it listens, stop it, and return its stderr.
+fn serve_once(config: &Path, tools: &Path, extra: &[&str]) -> String {
+    let mut child = Command::new(env!("CARGO_BIN_EXE_brokerd"))
+        .args(["serve", "--config"])
+        .arg(config)
+        .args(extra)
+        .stdout(Stdio::null())
+        .stderr(Stdio::piped())
+        .spawn()
+        .unwrap();
+    let until = Instant::now() + Duration::from_secs(10);
+    while UnixStream::connect(tools).is_err() {
+        if let Some(status) = child.try_wait().unwrap() {
+            let mut err = String::new();
+            child
+                .stderr
+                .take()
+                .unwrap()
+                .read_to_string(&mut err)
+                .unwrap();
+            panic!("brokerd exited with {status}: {err}");
+        }
+        assert!(Instant::now() < until, "brokerd never listened");
+        std::thread::sleep(Duration::from_millis(20));
+    }
+    child.kill().unwrap();
+    child.wait().unwrap();
+    let mut err = String::new();
+    child
+        .stderr
+        .take()
+        .unwrap()
+        .read_to_string(&mut err)
+        .unwrap();
+    err
+}
+
+#[test]
+fn a_break_is_accepted_and_the_next_plain_start_serves() {
+    let dir = TempDir::new("accept-break");
+    let audit = dir.path().join("audit");
+    std::fs::create_dir_all(&audit).unwrap();
+    std::fs::create_dir_all(dir.path().join("grants")).unwrap();
+    let fixture =
+        Path::new(env!("CARGO_MANIFEST_DIR")).join("../proto/tests/fixtures/audit/changed-byte");
+    // The damage is in the first file; an ordinary start checks only the latest, so copy that one
+    // alone, as `audit_startup.rs` does.
+    std::fs::copy(
+        fixture.join("2026-09-17.jsonl"),
+        audit.join("2026-09-17.jsonl"),
+    )
+    .unwrap();
+    let config = dir.write(
+        "brokerd.toml",
+        &format!(
+            "[paths]\nhome = \"{0}\"\ngrants = \"{0}/grants\"\n",
+            dir.path().display()
+        ),
+    );
+    let tools = dir.path().join("run/loop-broker/broker.sock");
+
+    // A plain start must refuse: wait for it to exit, and fail (not hang) if it serves instead.
+    let mut plain = Command::new(env!("CARGO_BIN_EXE_brokerd"))
+        .args(["serve", "--config"])
+        .arg(&config)
+        .stdout(Stdio::null())
+        .stderr(Stdio::null())
+        .spawn()
+        .unwrap();
+    let until = Instant::now() + Duration::from_secs(10);
+    let status = loop {
+        if let Some(status) = plain.try_wait().unwrap() {
+            break status;
+        }
+        if Instant::now() > until {
+            plain.kill().unwrap();
+            panic!("a plain start served on a broken chain");
+        }
+        std::thread::sleep(Duration::from_millis(20));
+    };
+    assert_eq!(status.code(), Some(1), "a plain start refuses first");
+
+    let printed = serve_once(&config, &tools, &["--accept-break"]);
+    assert!(
+        printed.contains("audit: accepted the break at"),
+        "{printed}"
+    );
+
+    let printed = serve_once(&config, &tools, &[]);
+    assert!(!printed.contains("accepted the break"), "{printed}");
+
+    let report = verify_dir(&audit).unwrap();
+    assert_eq!(report.failure, None, "{:?}", report.failure);
+    assert_eq!(report.accepted_breaks.len(), 1);
+}

crates/brokerd/tests/serve_pointers.rs

@@ -0,0 +1,203 @@
+//! `brokerd serve` fails closed at startup with a runbook pointer for every reason it cannot start,
+//! and never panics on its own command line. Found in the M3a review (findings 3 and 7).
+
+#[path = "support/tmp.rs"]
+mod tmp;
+
+use std::ffi::OsStr;
+use std::os::unix::ffi::OsStrExt;
+use std::path::Path;
+use std::process::{Command, Output};
+
+use tmp::TempDir;
+
+const START_FAILED: &str = "see docs/runbook.md#brokerd-start-failed";
+
+fn brokerd<I: IntoIterator<Item = S>, S: AsRef<OsStr>>(args: I) -> Output {
+    Command::new(env!("CARGO_BIN_EXE_brokerd"))
+        .args(args)
+        .output()
+        .unwrap()
+}
+
+fn stderr(out: &Output) -> String {
+    String::from_utf8_lossy(&out.stderr).into_owned()
+}
+
+/// A config whose home is `dir`, with `sockets` as the `[sockets]` table's body.
+fn config(dir: &TempDir, sockets: &str) -> std::path::PathBuf {
+    let home = dir.path().join("home");
+    let grants = dir.path().join("grants");
+    std::fs::create_dir_all(&grants).unwrap();
+    std::fs::create_dir_all(&home).unwrap();
+    dir.write(
+        "brokerd.toml",
+        &format!(
+            "[paths]\nhome = \"{}\"\ngrants = \"{}\"\n[sockets]\n{sockets}\n",
+            home.display(),
+            grants.display()
+        ),
+    )
+}
+
+fn fails_with_pointer(out: &Output) {
+    assert_eq!(out.status.code(), Some(1), "{}", stderr(out));
+    assert!(
+        stderr(out).trim_end().ends_with(START_FAILED),
+        "{:?} must end with {START_FAILED:?}",
+        stderr(out)
+    );
+}
+
+#[test]
+fn a_missing_config_names_the_entry() {
+    let dir = TempDir::new("ptr-missing");
+    let out = brokerd([
+        OsStr::new("serve"),
+        OsStr::new("--config"),
+        dir.path().join("nope.toml").as_os_str(),
+    ]);
+    fails_with_pointer(&out);
+}
+
+#[test]
+fn an_invalid_config_names_the_entry() {
+    let dir = TempDir::new("ptr-invalid");
+    let path = dir.write("brokerd.toml", "[paths]\nhome = 3\n");
+    let out = brokerd([
+        OsStr::new("serve"),
+        OsStr::new("--config"),
+        path.as_os_str(),
+    ]);
+    fails_with_pointer(&out);
+}
+
+#[test]
+fn a_socket_that_cannot_be_bound_names_the_entry() {
+    let dir = TempDir::new("ptr-bind");
+    let long = dir.path().join("s".repeat(120)).join("broker.sock");
+    let path = config(&dir, &format!("broker = \"{}\"", long.display()));
+    fails_with_pointer(&brokerd([
+        OsStr::new("serve"),
+        OsStr::new("--config"),
+        path.as_os_str(),
+    ]));
+}
+
+#[test]
+fn a_socket_directory_that_cannot_be_made_names_the_entry() {
+    let dir = TempDir::new("ptr-dir");
+    let file = dir.write("a-file", "");
+    let path = config(
+        &dir,
+        &format!("broker = \"{}\"", file.join("run/broker.sock").display()),
+    );
+    fails_with_pointer(&brokerd([
+        OsStr::new("serve"),
+        OsStr::new("--config"),
+        path.as_os_str(),
+    ]));
+}
+
+/// The socket's directory is made private (0700). Through a symbolic link that would change the
+/// directory it points to, so a link is refused, and the target keeps its mode.
+#[test]
+fn a_socket_directory_that_is_a_symbolic_link_is_refused() {
+    use std::os::unix::fs::PermissionsExt;
+    let dir = TempDir::new("ptr-link");
+    let shared = dir.path().join("shared");
+    std::fs::create_dir(&shared).unwrap();
+    std::fs::set_permissions(&shared, std::fs::Permissions::from_mode(0o755)).unwrap();
+    let link = dir.path().join("link");
+    std::os::unix::fs::symlink(&shared, &link).unwrap();
+    let path = config(
+        &dir,
+        &format!("broker = \"{}\"", link.join("broker.sock").display()),
+    );
+
+    let out = brokerd([
+        OsStr::new("serve"),
+        OsStr::new("--config"),
+        path.as_os_str(),
+    ]);
+    fails_with_pointer(&out);
+    assert!(stderr(&out).contains("symbolic link"), "{}", stderr(&out));
+    let mode = std::fs::metadata(&shared).unwrap().permissions().mode() & 0o777;
+    assert_eq!(mode, 0o755, "the link's target keeps its mode");
+}
+
+/// A socket directly in `/` would make `/` private: refused before anything is changed.
+#[test]
+fn a_socket_in_the_root_directory_is_refused() {
+    let dir = TempDir::new("ptr-root");
+    let path = config(&dir, "broker = \"/broker.sock\"");
+    let out = brokerd([
+        OsStr::new("serve"),
+        OsStr::new("--config"),
+        path.as_os_str(),
+    ]);
+    fails_with_pointer(&out);
+    assert!(
+        stderr(&out).contains("directory of its own"),
+        "{}",
+        stderr(&out)
+    );
+}
+
+/// A config path that is not UTF-8 is still a path: it is read (here: not found), not a panic.
+#[test]
+fn a_config_path_that_is_not_utf8_is_read_as_a_path() {
+    let dir = TempDir::new("ptr-os");
+    let name = dir.path().join(OsStr::from_bytes(b"conf-\xff.toml"));
+    let out = brokerd([
+        OsStr::new("serve"),
+        OsStr::new("--config"),
+        name.as_os_str(),
+    ]);
+    fails_with_pointer(&out);
+}
+
+/// A flag that is not UTF-8 is not a flag brokerd knows: usage, exit 2, no panic.
+#[test]
+fn a_flag_that_is_not_utf8_is_a_usage_error() {
+    let out = brokerd([OsStr::new("serve"), OsStr::from_bytes(b"--\xff")]);
+    assert_eq!(out.status.code(), Some(2), "{}", stderr(&out));
+    assert!(stderr(&out).starts_with("usage: brokerd serve"));
+    let out = brokerd([OsStr::from_bytes(b"\xff")]);
+    assert_eq!(out.status.code(), Some(2), "{}", stderr(&out));
+}
+
+#[test]
+fn the_entries_exist() {
+    let runbook = std::fs::read_to_string(
+        Path::new(env!("CARGO_MANIFEST_DIR")).join("../../docs/runbook.md"),
+    )
+    .unwrap();
+    for entry in ["## brokerd-start-failed", "## brokerd-listener-lost"] {
+        assert!(runbook.lines().any(|l| l == entry), "{entry}");
+    }
+}
+
+/// `[approvals] ttl_ms` is between 1 ms and a day: `loopd` waits at most a day after a pending
+/// frame, so a longer approval would be abandoned while `bxctl` still listed it.
+#[test]
+fn an_approval_ttl_outside_a_day_is_a_config_error() {
+    for ttl in ["0", "86400001", "18446744073709551615"] {
+        let dir = TempDir::new("ptr-ttl");
+        std::fs::create_dir_all(dir.path().join("grants")).unwrap();
+        let path = dir.write(
+            "brokerd.toml",
+            &format!(
+                "[paths]\nhome = \"{0}\"\ngrants = \"{0}/grants\"\n[approvals]\nttl_ms = {ttl}\n",
+                dir.path().display()
+            ),
+        );
+        let out = brokerd([
+            OsStr::new("serve"),
+            OsStr::new("--config"),
+            path.as_os_str(),
+        ]);
+        fails_with_pointer(&out);
+        assert!(stderr(&out).contains("ttl_ms"), "{ttl}: {}", stderr(&out));
+    }
+}

crates/brokerd/tests/state.rs

@@ -0,0 +1,281 @@
+//! Tests for the session state files. Do not edit.
+
+#[path = "support/tmp.rs"]
+mod tmp;
+
+use brokerd::policy::{Label, SessionState};
+use brokerd::state::{RUNBOOK, StateError, StateStore};
+use proto::{DataClass, SessionId};
+use std::os::unix::fs::PermissionsExt;
+use tmp::TempDir;
+
+fn id(text: &str) -> SessionId {
+    SessionId::new(text).unwrap()
+}
+
+fn label(class: DataClass, untrusted: bool) -> Label {
+    Label { class, untrusted }
+}
+
+fn state(taint: DataClass, untrusted: bool) -> SessionState {
+    SessionState { taint, untrusted }
+}
+
+/// The store's directory is two levels below the temporary one and does not exist yet, as on a
+/// fresh install.
+fn store(home: &TempDir) -> StateStore {
+    StateStore::new(&home.path().join("broker/sessions"))
+}
+
+#[test]
+fn a_session_with_no_file_is_private_and_trusted() {
+    let home = TempDir::new("state");
+    let store = store(&home);
+    let fresh = store.read(&id("chat-1")).unwrap();
+    assert_eq!(fresh, state(DataClass::Private, false));
+    assert_eq!(fresh, SessionState::default());
+    // Reading creates nothing.
+    assert!(!home.path().join("broker").exists());
+}
+
+#[test]
+fn the_first_result_creates_the_file_and_its_directory() {
+    let home = TempDir::new("state");
+    let store = store(&home);
+    let session = id("chat-1");
+    let next = store
+        .raise(
+            &session,
+            SessionState::default(),
+            label(DataClass::Private, false),
+        )
+        .unwrap();
+    assert_eq!(next, state(DataClass::Private, false));
+
+    let path = home.path().join("broker/sessions/chat-1.json");
+    assert_eq!(store.path(&session), path);
+    assert_eq!(
+        std::fs::read_to_string(&path).unwrap(),
+        "{\"taint\":\"private\",\"untrusted\":false}\n"
+    );
+    let mode = |p: &std::path::Path| std::fs::metadata(p).unwrap().permissions().mode() & 0o777;
+    assert_eq!(mode(&path), 0o600);
+    assert_eq!(mode(&home.path().join("broker/sessions")), 0o700);
+    assert_eq!(mode(&home.path().join("broker")), 0o700);
+    // No temporary file is left behind.
+    assert!(!home.path().join("broker/sessions/chat-1.json.tmp").exists());
+    assert_eq!(store.read(&session).unwrap(), next);
+}
+
+#[test]
+fn taint_and_the_untrusted_flag_only_go_up() {
+    let home = TempDir::new("state");
+    let store = store(&home);
+    let session = id("s");
+    let steps = [
+        (
+            label(DataClass::Public, false),
+            state(DataClass::Private, false),
+        ),
+        (
+            label(DataClass::Private, true),
+            state(DataClass::Private, true),
+        ),
+        (
+            label(DataClass::Secret, false),
+            state(DataClass::Secret, true),
+        ),
+        (
+            label(DataClass::Public, false),
+            state(DataClass::Secret, true),
+        ),
+        (
+            label(DataClass::Private, false),
+            state(DataClass::Secret, true),
+        ),
+    ];
+    let mut current = store.read(&session).unwrap();
+    for (result, want) in steps {
+        current = store.raise(&session, current, result).unwrap();
+        assert_eq!(current, want);
+        assert_eq!(store.read(&session).unwrap(), want, "what is on disk");
+    }
+    assert_eq!(
+        std::fs::read_to_string(store.path(&session)).unwrap(),
+        "{\"taint\":\"secret\",\"untrusted\":true}\n"
+    );
+}
+
+#[test]
+fn sessions_do_not_share_state() {
+    let home = TempDir::new("state");
+    let store = store(&home);
+    store
+        .raise(
+            &id("a"),
+            SessionState::default(),
+            label(DataClass::Secret, true),
+        )
+        .unwrap();
+    assert_eq!(store.read(&id("b")).unwrap(), SessionState::default());
+    assert_eq!(
+        store.read(&id("a")).unwrap(),
+        state(DataClass::Secret, true)
+    );
+}
+
+/// A file that exists but does not hold a valid state is an error, never "no file".
+#[test]
+fn a_damaged_file_is_an_error_that_names_the_file_and_the_runbook() {
+    let home = TempDir::new("state");
+    let store = store(&home);
+    std::fs::create_dir_all(home.path().join("broker/sessions")).unwrap();
+    let session = id("hurt");
+    for text in [
+        "",
+        "{",
+        "null",
+        "[]",
+        "{\"taint\":\"secret\"}",
+        "{\"untrusted\":false}",
+        "{\"taint\":\"internal\",\"untrusted\":false}",
+        "{\"taint\":\"secret\",\"untrusted\":\"no\"}",
+        "{\"taint\":\"secret\",\"untrusted\":false,\"note\":1}",
+        "{\"taint\":\"secret\",\"untrusted\":false} trailing",
+        // A session is never below private, so this file was not written by brokerd.
+        "{\"taint\":\"public\",\"untrusted\":false}",
+    ] {
+        std::fs::write(store.path(&session), text).unwrap();
+        let err = store.read(&session).expect_err(text);
+        assert!(
+            matches!(err, StateError::Unreadable(..)),
+            "{text:?}: {err:?}"
+        );
+        let shown = err.to_string();
+        assert!(shown.contains("hurt.json"), "{shown}");
+        assert!(shown.ends_with(RUNBOOK), "{shown}");
+    }
+    assert_eq!(RUNBOOK, "see docs/runbook.md#broker-state-damaged");
+    // A good file with or without its final newline reads fine.
+    for text in [
+        "{\"taint\":\"secret\",\"untrusted\":true}\n",
+        "{\"taint\":\"secret\",\"untrusted\":true}",
+    ] {
+        std::fs::write(store.path(&session), text).unwrap();
+        assert_eq!(
+            store.read(&session).unwrap(),
+            state(DataClass::Secret, true)
+        );
+    }
+    // Not valid UTF-8, and a directory where the file should be.
+    std::fs::write(store.path(&session), b"\xff\xfe").unwrap();
+    assert!(matches!(
+        store.read(&session),
+        Err(StateError::Unreadable(..))
+    ));
+    std::fs::remove_file(store.path(&session)).unwrap();
+    std::fs::create_dir(store.path(&session)).unwrap();
+    assert!(matches!(
+        store.read(&session),
+        Err(StateError::Unreadable(..))
+    ));
+}
+
+#[test]
+fn a_file_without_read_permission_is_an_error_not_a_fresh_session() {
+    if tmp::running_as_root("a_file_without_read_permission_is_an_error_not_a_fresh_session") {
+        return;
+    }
+    let home = TempDir::new("state");
+    let store = store(&home);
+    let session = id("locked");
+    store
+        .raise(
+            &session,
+            SessionState::default(),
+            label(DataClass::Secret, false),
+        )
+        .unwrap();
+    let path = store.path(&session);
+    std::fs::set_permissions(&path, std::fs::Permissions::from_mode(0o000)).unwrap();
+    assert!(matches!(
+        store.read(&session),
+        Err(StateError::Unreadable(..))
+    ));
+    std::fs::set_permissions(&path, std::fs::Permissions::from_mode(0o600)).unwrap();
+}
+
+#[test]
+fn a_failed_write_is_an_error_and_leaves_the_old_state() {
+    if tmp::running_as_root("a_failed_write_is_an_error_and_leaves_the_old_state") {
+        return;
+    }
+    let home = TempDir::new("state");
+    let store = store(&home);
+    let session = id("s");
+    let before = store
+        .raise(
+            &session,
+            SessionState::default(),
+            label(DataClass::Private, true),
+        )
+        .unwrap();
+
+    let dir = home.path().join("broker/sessions");
+    std::fs::set_permissions(&dir, std::fs::Permissions::from_mode(0o500)).unwrap();
+    let err = store
+        .raise(&session, before, label(DataClass::Secret, false))
+        .expect_err("the directory is read-only");
+    std::fs::set_permissions(&dir, std::fs::Permissions::from_mode(0o700)).unwrap();
+
+    assert!(matches!(err, StateError::Write(..)), "{err:?}");
+    let shown = err.to_string();
+    assert!(shown.contains("s.json"), "{shown}");
+    assert!(shown.ends_with(RUNBOOK), "{shown}");
+    assert_eq!(store.read(&session).unwrap(), before);
+}
+
+/// A `.tmp` file beside the state is a write that did not finish. It is not the state, it does
+/// not stop the next write, and the next write replaces it.
+#[test]
+fn a_leftover_tmp_file_is_neither_read_nor_in_the_way() {
+    let home = TempDir::new("state");
+    let store = store(&home);
+    let session = id("s");
+    let dir = home.path().join("broker/sessions");
+    std::fs::create_dir_all(&dir).unwrap();
+    std::fs::write(dir.join("s.json.tmp"), "{\"taint\":\"secret\",\"untr").unwrap();
+
+    assert_eq!(store.read(&session).unwrap(), SessionState::default());
+    let next = store
+        .raise(
+            &session,
+            SessionState::default(),
+            label(DataClass::Secret, false),
+        )
+        .unwrap();
+    assert_eq!(store.read(&session).unwrap(), next);
+    assert!(!dir.join("s.json.tmp").exists());
+}
+
+#[test]
+fn raise_trusts_the_state_it_is_given_not_the_file() {
+    // The caller read the state under the ledger lock a moment ago; `raise` does not read again.
+    let home = TempDir::new("state");
+    let store = store(&home);
+    let session = id("s");
+    let given = state(DataClass::Secret, true);
+    let next = store
+        .raise(&session, given, label(DataClass::Public, false))
+        .unwrap();
+    assert_eq!(next, given);
+    // Even a state below private is lifted to private on the way to disk.
+    let low = store
+        .raise(
+            &id("low"),
+            state(DataClass::Public, false),
+            label(DataClass::Public, false),
+        )
+        .unwrap();
+    assert_eq!(low, state(DataClass::Private, false));
+}

crates/brokerd/tests/support/audit_dir.rs

@@ -0,0 +1,98 @@
+//! Temporary audit directories for the audit tests. Do not edit.
+
+#![allow(dead_code)] // each test file uses its own part of this
+
+use std::collections::BTreeMap;
+use std::path::{Path, PathBuf};
+use std::sync::atomic::{AtomicU32, Ordering};
+
+use proto::{AuditEvent, CallId, DataClass, DecisionRecord, SessionId, Timestamp};
+
+pub const D1: &str = "2026-09-17.jsonl";
+pub const D2: &str = "2026-09-18.jsonl";
+
+static NEXT: AtomicU32 = AtomicU32::new(0);
+
+/// A directory under the system's temporary directory, removed when dropped.
+pub struct TempDir {
+    pub path: PathBuf,
+}
+
+impl TempDir {
+    /// A path that does not exist yet.
+    pub fn unmade(tag: &str) -> TempDir {
+        let n = NEXT.fetch_add(1, Ordering::SeqCst);
+        let name = format!("brokerd-{tag}-{}-{n}", std::process::id());
+        let path = std::env::temp_dir().join(name);
+        let _ = std::fs::remove_dir_all(&path);
+        TempDir { path }
+    }
+
+    /// A copy of the fixture log `case` from `crates/proto/tests/fixtures/audit/`. With `only`,
+    /// just those files: damage in an older file is not seen by an ordinary start, so tests of
+    /// the startup check copy the damaged file alone.
+    pub fn case(case: &str, only: Option<&[&str]>) -> TempDir {
+        let dir = TempDir::unmade(case);
+        std::fs::create_dir_all(&dir.path).unwrap();
+        let from = format!(
+            "{}/../proto/tests/fixtures/audit/{case}",
+            env!("CARGO_MANIFEST_DIR")
+        );
+        let mut copied = 0;
+        for entry in std::fs::read_dir(&from).unwrap_or_else(|e| panic!("{from}: {e}")) {
+            let entry = entry.unwrap();
+            let name = entry.file_name().into_string().unwrap();
+            if only.is_none_or(|names| names.contains(&name.as_str())) {
+                std::fs::copy(entry.path(), dir.path.join(&name)).unwrap();
+                copied += 1;
+            }
+        }
+        assert!(copied > 0, "{from}: nothing copied");
+        dir
+    }
+}
+
+impl Drop for TempDir {
+    fn drop(&mut self) {
+        let _ = std::fs::remove_dir_all(&self.path);
+    }
+}
+
+/// Every log file in `dir` with its bytes.
+pub fn snapshot(dir: &Path) -> BTreeMap<String, Vec<u8>> {
+    std::fs::read_dir(dir)
+        .unwrap()
+        .map(|entry| entry.unwrap())
+        .filter(|entry| entry.file_name().to_string_lossy().ends_with(".jsonl"))
+        .map(|entry| {
+            let name = entry.file_name().into_string().unwrap();
+            (name, std::fs::read(entry.path()).unwrap())
+        })
+        .collect()
+}
+
+pub fn lines(dir: &Path, file: &str) -> Vec<String> {
+    let text = std::fs::read_to_string(dir.join(file)).unwrap();
+    text.lines().map(str::to_string).collect()
+}
+
+pub fn ts(s: &str) -> Timestamp {
+    Timestamp::parse(s).unwrap()
+}
+
+/// A denied decision for call `call`: an event that leaves nothing open in the report.
+pub fn denied(call: u64) -> AuditEvent {
+    AuditEvent::Decision {
+        session: SessionId::new("chat-1").unwrap(),
+        call: CallId(call),
+        tool: "read_file".to_string(),
+        arguments: r#"{"path":"/etc/hosts"}"#.to_string(),
+        outcome: DecisionRecord::Denied {
+            reason: proto::DenyReason::NoGrant,
+        },
+        grant: None,
+        grant_sha256: None,
+        taint: DataClass::Private,
+        untrusted: false,
+    }
+}

crates/brokerd/tests/support/build.rs

@@ -0,0 +1,156 @@
+//! Builders for grants and requests, for the policy tests. Do not edit.
+//!
+//! Included with `#[path = "support/build.rs"] mod build;`.
+
+#![allow(dead_code)] // each test file uses a different part of this module
+
+use brokerd::grants::{GrantSet, LoadedGrant};
+use brokerd::policy::{Ask, Decision, Denial, Outcome, SessionState};
+use proto::{
+    CallId, Constraints, DataClass, DenyReason, Grant, Mode, SessionId, Timestamp, ToolRequest,
+};
+
+/// The moment every policy test decides at.
+pub const NOW: &str = "2026-09-18T12:00:00.000Z";
+
+pub fn ts(text: &str) -> Timestamp {
+    Timestamp::parse(text).unwrap()
+}
+
+pub fn now() -> Timestamp {
+    ts(NOW)
+}
+
+pub struct Build(LoadedGrant);
+
+/// A grant with the widest settings: it applies at every taint, never expires, and labels its
+/// results `private` and untrusted. Each test narrows what it is about.
+pub fn grant(id: &str, tool: &str, mode: Mode) -> Build {
+    Build(LoadedGrant {
+        id: id.to_string(),
+        grant: Grant {
+            tool: tool.to_string(),
+            mode,
+            max_taint: DataClass::Secret,
+            result_class: DataClass::Private,
+            untrusted: true,
+            expires: None,
+            secret: None,
+            constraints: Constraints::default(),
+        },
+        // Stands in for the file's hash, and differs from grant to grant.
+        sha256: proto::sha256(id.as_bytes()).unwrap(),
+    })
+}
+
+impl Build {
+    pub fn paths(mut self, paths: &[&str]) -> Build {
+        self.0.grant.constraints.paths = paths.iter().map(|p| p.to_string()).collect();
+        self
+    }
+    pub fn hosts(mut self, hosts: &[&str]) -> Build {
+        self.0.grant.constraints.hosts = hosts.iter().map(|h| h.to_string()).collect();
+        self
+    }
+    pub fn max_taint(mut self, class: DataClass) -> Build {
+        self.0.grant.max_taint = class;
+        self
+    }
+    pub fn class(mut self, class: DataClass) -> Build {
+        self.0.grant.result_class = class;
+        self
+    }
+    pub fn trusted(mut self) -> Build {
+        self.0.grant.untrusted = false;
+        self
+    }
+    pub fn expires(mut self, at: &str) -> Build {
+        self.0.grant.expires = Some(ts(at));
+        self
+    }
+    pub fn done(self) -> LoadedGrant {
+        self.0
+    }
+}
+
+pub fn set(grants: Vec<Build>) -> GrantSet {
+    GrantSet::from_grants(grants.into_iter().map(Build::done).collect())
+        .unwrap_or_else(|problems| panic!("the test's grants are not valid: {problems:?}"))
+}
+
+pub fn request(tool: &str, arguments: &str) -> ToolRequest {
+    ToolRequest {
+        session: SessionId::new("s1").unwrap(),
+        call: CallId(1),
+        tool: tool.to_string(),
+        arguments: arguments.to_string(),
+    }
+}
+
+pub fn read(path: &str) -> ToolRequest {
+    request("read_file", &format!(r#"{{"path":"{path}"}}"#))
+}
+
+pub fn write(path: &str) -> ToolRequest {
+    request(
+        "write_file",
+        &format!(r#"{{"path":"{path}","content":"x"}}"#),
+    )
+}
+
+pub fn shell(cwd: Option<&str>) -> ToolRequest {
+    match cwd {
+        Some(cwd) => request("shell", &format!(r#"{{"command":"ls","cwd":"{cwd}"}}"#)),
+        None => request("shell", r#"{"command":"ls"}"#),
+    }
+}
+
+pub fn fetch(url: &str) -> ToolRequest {
+    request("http_fetch", &format!(r#"{{"url":"{url}"}}"#))
+}
+
+pub fn at(taint: DataClass) -> SessionState {
+    SessionState {
+        taint,
+        untrusted: false,
+    }
+}
+
+pub fn private() -> SessionState {
+    at(DataClass::Private)
+}
+
+pub fn secret() -> SessionState {
+    at(DataClass::Secret)
+}
+
+pub fn allowed(outcome: Outcome) -> Decision {
+    match outcome {
+        Outcome::Allowed(decision) => decision,
+        other => panic!("expected allowed, got {other:?}"),
+    }
+}
+
+pub fn asked(outcome: Outcome) -> Ask {
+    match outcome {
+        Outcome::Ask(ask) => ask,
+        other => panic!("expected ask, got {other:?}"),
+    }
+}
+
+pub fn denied(outcome: Outcome) -> Denial {
+    match outcome {
+        Outcome::Denied(denial) => denial,
+        other => panic!("expected denied, got {other:?}"),
+    }
+}
+
+/// The reason of a denial. Only `denied_by_grant` may name a grant.
+pub fn reason(outcome: Outcome) -> DenyReason {
+    let denial = denied(outcome);
+    if denial.reason != DenyReason::DeniedByGrant {
+        assert_eq!(denial.grant, None, "only denied_by_grant names a grant");
+        assert_eq!(denial.grant_sha256, None);
+    }
+    denial.reason
+}

crates/brokerd/tests/support/client.rs

@@ -0,0 +1,79 @@
+//! A client for `broker::handle` and `admin::handle` over a socket pair, and a `Broker` built on
+//! a `Rig`. Do not edit.
+//!
+//! Included with `#[path = "support/client.rs"] mod client;`, beside `rig`, `runtime`, `sink`
+//! and `tmp`.
+
+#![allow(dead_code)] // each test file uses a different part of this module
+
+use std::os::unix::net::UnixStream;
+use std::sync::Arc;
+use std::time::Duration;
+
+use brokerd::broker::{self, Broker};
+use proto::{Envelope, Message, PROTOCOL_VERSION, ToolRequest};
+
+use crate::rig::Rig;
+use crate::runtime::{Recording, Shared};
+
+pub trait Serve {
+    /// A `Broker` on this rig's home, with `runtime` and the rig's flaky sink and log.
+    fn broker(&self, runtime: &Arc<Recording>) -> Arc<Broker>;
+}
+
+impl Serve for Rig {
+    fn broker(&self, runtime: &Arc<Recording>) -> Arc<Broker> {
+        let runtime = Box::new(Shared(Arc::clone(runtime)));
+        Arc::new(Broker::new(
+            self.cfg.clone(),
+            self.ledger(),
+            runtime,
+            self.lines.sink(),
+        ))
+    }
+}
+
+/// A connection to `handler` running on its own thread, with `msg` already sent under `id`.
+pub fn open(
+    broker: &Arc<Broker>,
+    handler: fn(UnixStream, &Broker),
+    id: u64,
+    msg: Message,
+) -> UnixStream {
+    let (mut client, server) = UnixStream::pair().unwrap();
+    let broker = Arc::clone(broker);
+    std::thread::spawn(move || handler(server, &broker));
+    let env = Envelope {
+        v: PROTOCOL_VERSION,
+        id,
+        r#final: true,
+        msg,
+    };
+    proto::write_frame(&mut client, &env).unwrap();
+    client
+}
+
+/// The next frame, waiting at most ten seconds. Once the handler has closed its end, macOS
+/// refuses the timeout with EINVAL (22); the frame is buffered by then and the read cannot block.
+pub fn next(stream: &mut UnixStream) -> Envelope {
+    if let Err(e) = stream.set_read_timeout(Some(Duration::from_secs(10))) {
+        let peer_closed = cfg!(target_vendor = "apple") && e.raw_os_error() == Some(22);
+        assert!(peer_closed, "set_read_timeout: {e}");
+    }
+    proto::read_frame(stream).unwrap()
+}
+
+/// Sends a tool request to `broker::handle` and reads every frame up to the final one.
+pub fn call(broker: &Arc<Broker>, req: ToolRequest) -> Vec<Envelope> {
+    let id = req.call.0;
+    let mut stream = open(broker, broker::handle, id, Message::ToolRequest(req));
+    let mut frames = Vec::new();
+    loop {
+        let env = next(&mut stream);
+        let last = env.r#final;
+        frames.push(env);
+        if last {
+            return frames;
+        }
+    }
+}

crates/brokerd/tests/support/oracle.rs

@@ -0,0 +1,388 @@
+//! The generator and the oracle of the policy property test. Do not edit.
+//!
+//! Included with `#[path = "support/oracle.rs"] mod oracle;`.
+//!
+//! The oracle is written to be obviously right, not fast or short. It shares no code with
+//! `brokerd`: it splits paths and host names into their parts itself and compares the parts.
+//! If the property test fails, the oracle is the specification and `policy` is wrong.
+
+#![allow(dead_code)] // the property test does not use every helper in every build
+
+use brokerd::grants::LoadedGrant;
+use brokerd::policy::SessionState;
+use proto::{
+    CallId, Constraints, DataClass, DenyReason, Grant, Mode, SessionId, Timestamp, ToolRequest,
+};
+
+/// The moment every case is decided at: 2026-09-18T12:00:00.000Z.
+pub const NOW_MS: u64 = 1_789_732_800_000;
+
+// ---------------------------------------------------------------------------------------------
+// The generator.
+
+pub struct Rng(u64);
+
+impl Rng {
+    pub fn new(seed: u64) -> Rng {
+        // xorshift must not start at zero.
+        Rng(seed.wrapping_mul(0x9E37_79B9_7F4A_7C15) | 1)
+    }
+    pub fn next(&mut self) -> u64 {
+        let mut x = self.0;
+        x ^= x << 13;
+        x ^= x >> 7;
+        x ^= x << 17;
+        self.0 = x;
+        x
+    }
+    pub fn below(&mut self, n: usize) -> usize {
+        (self.next() % n as u64) as usize
+    }
+    pub fn pick<T: Copy>(&mut self, items: &[T]) -> T {
+        items[self.below(items.len())]
+    }
+    pub fn chance(&mut self, percent: u64) -> bool {
+        self.next() % 100 < percent
+    }
+}
+
+pub const TOOLS: [&str; 4] = ["read_file", "write_file", "shell", "http_fetch"];
+pub const CLASSES: [DataClass; 3] = [DataClass::Public, DataClass::Private, DataClass::Secret];
+pub const MODES: [Mode; 3] = [Mode::Auto, Mode::Ask, Mode::Deny];
+pub const HOSTS: [&str; 6] = [
+    "example.com",
+    "www.example.com",
+    "a.b.example.com",
+    "other.org",
+    "www.other.org",
+    "badexample.com",
+];
+pub const PATTERNS: [&str; 6] = [
+    "example.com",
+    "*.example.com",
+    "www.example.com",
+    "*.b.example.com",
+    "other.org",
+    "*.other.org",
+];
+
+/// A path of one to four components over a tiny alphabet, so that grants and requests overlap
+/// often: `/a`, `/a/b`, `/ab/a/c` and so on. `ab` is there to catch prefix matching by bytes.
+pub fn path(rng: &mut Rng) -> String {
+    let depth = 1 + rng.below(4);
+    let mut text = String::new();
+    for _ in 0..depth {
+        text.push('/');
+        text.push_str(rng.pick(&["a", "b", "c", "ab"]));
+    }
+    text
+}
+
+pub fn some_grant(rng: &mut Rng, id: usize) -> LoadedGrant {
+    let tool = rng.pick(&TOOLS);
+    let mode = rng.pick(&MODES);
+    let mut constraints = Constraints::default();
+    match tool {
+        "http_fetch" => {
+            for _ in 0..1 + rng.below(2) {
+                constraints.hosts.push(rng.pick(&PATTERNS).to_string());
+            }
+        }
+        "shell" if rng.chance(40) => {}
+        _ => {
+            for _ in 0..1 + rng.below(3) {
+                constraints.paths.push(path(rng));
+            }
+        }
+    }
+    // Expiry around the moment of decision: before it, exactly at it, after it, or never.
+    let expires = match rng.below(5) {
+        0 => Some(NOW_MS - 1),
+        1 => Some(NOW_MS),
+        2 => Some(NOW_MS + 1),
+        _ => None,
+    };
+    LoadedGrant {
+        id: format!("g{id:02}"),
+        grant: Grant {
+            tool: tool.to_string(),
+            mode,
+            // A deny grant must apply at every taint, or the set is invalid.
+            max_taint: if mode == Mode::Deny {
+                DataClass::Secret
+            } else {
+                rng.pick(&CLASSES)
+            },
+            result_class: rng.pick(&CLASSES),
+            untrusted: rng.chance(50),
+            expires: expires.map(|ms| Timestamp::from_unix_millis(ms).unwrap()),
+            secret: None,
+            constraints,
+        },
+        sha256: proto::sha256(format!("file {id}").as_bytes()).unwrap(),
+    }
+}
+
+/// Zero to seven grants, with ids handed out in a scrambled order so that the order of the list
+/// says nothing about the order of the ids.
+pub fn some_grants(rng: &mut Rng) -> Vec<LoadedGrant> {
+    let count = rng.below(8);
+    let mut ids: Vec<usize> = (0..count).collect();
+    for i in (1..ids.len()).rev() {
+        ids.swap(i, rng.below(i + 1));
+    }
+    ids.into_iter().map(|id| some_grant(rng, id)).collect()
+}
+
+pub fn some_request(rng: &mut Rng) -> ToolRequest {
+    let (tool, arguments) = match rng.below(20) {
+        0 => ("echo".to_string(), "{}".to_string()),
+        1 => ("read_file".to_string(), r#"{"path":"a/b"}"#.to_string()),
+        2 => (
+            "shell".to_string(),
+            r#"{"command":"ls","cwd":"/a/../b"}"#.to_string(),
+        ),
+        3 => (
+            "http_fetch".to_string(),
+            r#"{"url":"http://example.com/"}"#.to_string(),
+        ),
+        4 => ("write_file".to_string(), r#"{"path":"/a/b"}"#.to_string()),
+        _ => match rng.pick(&TOOLS) {
+            "read_file" => (
+                "read_file".to_string(),
+                format!(r#"{{"path":"{}"}}"#, path(rng)),
+            ),
+            "write_file" => (
+                "write_file".to_string(),
+                format!(r#"{{"path":"{}","content":"x"}}"#, path(rng)),
+            ),
+            "shell" if rng.chance(40) => ("shell".to_string(), r#"{"command":"ls"}"#.to_string()),
+            "shell" => (
+                "shell".to_string(),
+                format!(r#"{{"command":"ls","cwd":"{}"}}"#, path(rng)),
+            ),
+            _ => (
+                "http_fetch".to_string(),
+                format!(r#"{{"url":"https://{}/x"}}"#, rng.pick(&HOSTS)),
+            ),
+        },
+    };
+    ToolRequest {
+        session: SessionId::new("prop").unwrap(),
+        call: CallId(1),
+        tool,
+        arguments,
+    }
+}
+
+// ---------------------------------------------------------------------------------------------
+// The oracle.
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Expected {
+    Allowed {
+        grant: String,
+        path: Option<String>,
+        class: DataClass,
+        untrusted: bool,
+    },
+    Ask {
+        grant: String,
+        path: Option<String>,
+        class: DataClass,
+        untrusted: bool,
+    },
+    Denied {
+        reason: DenyReason,
+        grant: Option<String>,
+    },
+}
+
+pub fn parts(path: &str) -> Vec<&str> {
+    path.split('/').filter(|part| !part.is_empty()).collect()
+}
+
+/// `inner` is `outer` or lies under it: `outer`'s components are the first of `inner`'s.
+pub fn under(outer: &str, inner: &str) -> bool {
+    let (outer, inner) = (parts(outer), parts(inner));
+    outer.len() <= inner.len() && outer.iter().zip(&inner).all(|(a, b)| a == b)
+}
+
+pub fn host_fits(pattern: &str, host: &str) -> bool {
+    let host: Vec<&str> = host.split('.').collect();
+    match pattern.strip_prefix("*.") {
+        None => pattern.split('.').collect::<Vec<_>>() == host,
+        Some(base) => {
+            let base: Vec<&str> = base.split('.').collect();
+            host.len() > base.len() && host[host.len() - base.len()..] == base[..]
+        }
+    }
+}
+
+/// What the oracle needs from a request: `None` if the broker must refuse it before matching.
+pub enum Call {
+    UnknownTool,
+    Invalid,
+    Read(String),
+    Write(String),
+    Shell(Option<String>),
+    Fetch(String),
+}
+
+pub fn understand(request: &ToolRequest) -> Call {
+    if !TOOLS.contains(&request.tool.as_str()) {
+        return Call::UnknownTool;
+    }
+    // The generator only ever writes the five invalid forms below.
+    let text = request.arguments.as_str();
+    let invalid = text.contains("\"a/b\"")
+        || text.contains("..")
+        || text.contains("http://")
+        || (request.tool == "write_file" && !text.contains("content"));
+    if invalid {
+        return Call::Invalid;
+    }
+    let value: serde_json::Value = serde_json::from_str(text).unwrap();
+    let field = |name: &str| value.get(name).and_then(|v| v.as_str()).map(str::to_string);
+    match request.tool.as_str() {
+        "read_file" => Call::Read(field("path").unwrap()),
+        "write_file" => Call::Write(field("path").unwrap()),
+        "shell" => Call::Shell(field("cwd")),
+        _ => {
+            let url = field("url").unwrap();
+            let host = url
+                .trim_start_matches("https://")
+                .split('/')
+                .next()
+                .unwrap();
+            Call::Fetch(host.to_string())
+        }
+    }
+}
+
+/// Whether the grant covers the call, and with which of its paths (the longest that holds it).
+pub fn coverage(grant: &Grant, call: &Call) -> Option<Option<String>> {
+    let holding = |path: &str, itself_counts: bool| -> Option<Option<String>> {
+        let mut best: Option<&String> = None;
+        for candidate in &grant.constraints.paths {
+            if !under(candidate, path) || (!itself_counts && parts(candidate) == parts(path)) {
+                continue;
+            }
+            if best.is_none_or(|b| candidate.len() > b.len()) {
+                best = Some(candidate);
+            }
+        }
+        best.map(|b| Some(b.clone()))
+    };
+    match call {
+        Call::Read(path) => holding(path, true),
+        Call::Write(path) => holding(path, false),
+        Call::Shell(None) if grant.constraints.paths.is_empty() => Some(None),
+        Call::Shell(None) => None,
+        Call::Shell(Some(cwd)) => holding(cwd, true),
+        Call::Fetch(host) => grant
+            .constraints
+            .hosts
+            .iter()
+            .any(|pattern| host_fits(pattern, host))
+            .then_some(None),
+        Call::UnknownTool | Call::Invalid => None,
+    }
+}
+
+pub fn oracle(request: &ToolRequest, grants: &[LoadedGrant], state: SessionState) -> Expected {
+    let denied = |reason| Expected::Denied {
+        reason,
+        grant: None,
+    };
+    let call = understand(request);
+    match call {
+        Call::UnknownTool => return denied(DenyReason::NoGrant),
+        Call::Invalid => return denied(DenyReason::InvalidArguments),
+        _ => {}
+    }
+
+    struct Left<'a> {
+        id: &'a str,
+        mode: Mode,
+        path: Option<String>,
+        class: DataClass,
+        untrusted: bool,
+    }
+    let mut left: Vec<Left> = Vec::new();
+    let (mut would_match_but_expired, mut would_match_but_tainted) = (false, false);
+    for loaded in grants {
+        let g = &loaded.grant;
+        if g.tool != request.tool {
+            continue;
+        }
+        let Some(path) = coverage(g, &call) else {
+            continue;
+        };
+        let expired = g.expires.is_some_and(|at| at.unix_millis() <= NOW_MS);
+        let tainted = state.taint > g.max_taint;
+        if expired && !tainted {
+            would_match_but_expired = true;
+        }
+        if tainted && !expired {
+            would_match_but_tainted = true;
+        }
+        if !expired && !tainted {
+            left.push(Left {
+                id: &loaded.id,
+                mode: g.mode,
+                path,
+                class: g.result_class,
+                untrusted: g.untrusted,
+            });
+        }
+    }
+    if left.is_empty() {
+        return if would_match_but_expired {
+            denied(DenyReason::GrantExpired)
+        } else if would_match_but_tainted {
+            denied(DenyReason::TaintTooHigh)
+        } else {
+            denied(DenyReason::NoGrant)
+        };
+    }
+
+    let class = left.iter().map(|l| l.class).max().unwrap();
+    let untrusted = left.iter().any(|l| l.untrusted);
+    // The winner: try each mode from the most restrictive; within it the longest path, then
+    // the lowest id.
+    for mode in [Mode::Deny, Mode::Ask, Mode::Auto] {
+        let mut of_mode: Vec<&Left> = left.iter().filter(|l| l.mode == mode).collect();
+        if of_mode.is_empty() {
+            continue;
+        }
+        of_mode.sort_by(|a, b| {
+            let (la, lb) = (
+                a.path.as_ref().map_or(0, String::len),
+                b.path.as_ref().map_or(0, String::len),
+            );
+            lb.cmp(&la).then(a.id.cmp(b.id))
+        });
+        let winner = of_mode[0];
+        let (grant, path) = (winner.id.to_string(), winner.path.clone());
+        return match mode {
+            Mode::Deny => Expected::Denied {
+                reason: DenyReason::DeniedByGrant,
+                grant: Some(grant),
+            },
+            Mode::Ask => Expected::Ask {
+                grant,
+                path,
+                class,
+                untrusted,
+            },
+            Mode::Auto => Expected::Allowed {
+                grant,
+                path,
+                class,
+                untrusted,
+            },
+        };
+    }
+    unreachable!("left is not empty, so one of the three modes has a grant")
+}

crates/brokerd/tests/support/rig.rs

@@ -0,0 +1,118 @@
+//! A home for ledger and broker tests: grants, audit log, session state, a flaky audit sink and
+//! a log to read. Do not edit.
+//!
+//! Included with `#[path = "support/rig.rs"] mod rig;`, beside `tmp` and `sink`. The broker
+//! tests add `client`.
+
+#![allow(dead_code)] // each test file uses a different part of this module
+
+use std::path::PathBuf;
+
+use brokerd::audit::Writer;
+use brokerd::config::{Approvals, Config, Paths, Sockets};
+use brokerd::ledger::Ledger;
+use brokerd::state::StateStore;
+use proto::{AuditEvent, AuditRecord, CallId, SessionId, ToolRequest};
+
+use crate::sink::{Flaky, Lines, Switch};
+use crate::tmp::TempDir;
+
+pub struct Rig {
+    pub dir: TempDir,
+    pub cfg: Config,
+    pub switch: Switch,
+    pub lines: Lines,
+}
+
+impl Rig {
+    pub fn new(tag: &str) -> Rig {
+        Rig::with_ttl(tag, 900_000)
+    }
+
+    pub fn with_ttl(tag: &str, ttl_ms: u64) -> Rig {
+        let dir = TempDir::new(tag);
+        let grants = dir.path().join("grants");
+        std::fs::create_dir_all(&grants).unwrap();
+        let cfg = Config {
+            paths: Paths {
+                home: dir.path().to_path_buf(),
+                grants,
+            },
+            sockets: Sockets::default(),
+            approvals: Approvals { ttl_ms },
+        };
+        Rig {
+            dir,
+            cfg,
+            switch: Switch::default(),
+            lines: Lines::default(),
+        }
+    }
+
+    pub fn state(&self) -> StateStore {
+        StateStore::new(&self.cfg.state_dir())
+    }
+
+    /// Opens the audit log (once: the writer holds its lock) behind the flaky sink.
+    pub fn ledger(&self) -> Ledger {
+        let opened = Writer::open(&self.cfg.audit_dir(), false).unwrap();
+        let sink = Flaky {
+            writer: opened.writer,
+            switch: self.switch.clone(),
+        };
+        Ledger::new(Box::new(sink), self.state(), self.lines.sink())
+    }
+
+    /// Writes `grants/<id>.toml`.
+    pub fn grant(&self, id: &str, text: &str) {
+        std::fs::write(self.cfg.paths.grants.join(format!("{id}.toml")), text).unwrap();
+    }
+
+    pub fn remove_grant(&self, id: &str) {
+        std::fs::remove_file(self.cfg.paths.grants.join(format!("{id}.toml"))).unwrap();
+    }
+
+    pub fn state_file(&self, session: &str) -> PathBuf {
+        self.cfg.state_dir().join(format!("{session}.json"))
+    }
+
+    /// Every record in the audit log, in order.
+    pub fn records(&self) -> Vec<AuditRecord> {
+        let dir = self.cfg.audit_dir();
+        let mut names: Vec<String> = std::fs::read_dir(&dir)
+            .unwrap()
+            .map(|e| e.unwrap().file_name().into_string().unwrap())
+            .filter(|n| n.ends_with(".jsonl"))
+            .collect();
+        names.sort();
+        let mut out = Vec::new();
+        for name in names {
+            let text = std::fs::read_to_string(dir.join(name)).unwrap();
+            for line in text.lines() {
+                out.push(serde_json::from_str(line).unwrap());
+            }
+        }
+        out
+    }
+
+    pub fn events(&self) -> Vec<AuditEvent> {
+        self.records().into_iter().map(|r| r.event).collect()
+    }
+}
+
+/// A grant file's text. `extra` goes before `[constraints]`, `constraints` after it.
+pub fn grant_text(tool: &str, mode: &str, extra: &str, constraints: &str) -> String {
+    format!(
+        "tool = \"{tool}\"\nmode = \"{mode}\"\nmax_taint = \"secret\"\nresult_class = \"private\"\n\
+         untrusted = false\n{extra}\n[constraints]\n{constraints}\n"
+    )
+}
+
+pub fn request(session: &str, call: u64, tool: &str, arguments: &str) -> ToolRequest {
+    ToolRequest {
+        session: SessionId::new(session).unwrap(),
+        call: CallId(call),
+        tool: tool.to_string(),
+        arguments: arguments.to_string(),
+    }
+}

crates/brokerd/tests/support/runtime.rs

@@ -0,0 +1,70 @@
+//! A runtime that records what it is asked to run, for the runner and broker tests. Do not edit.
+//!
+//! Included with `#[path = "support/runtime.rs"] mod runtime;`.
+
+#![allow(dead_code)] // each test file uses a different part of this module
+
+use std::sync::{Arc, Mutex};
+
+use brokerd::args::{ToolArgs, ToolName};
+use brokerd::runner::{Mount, RunError, RunOutput, RunSpec, Runtime};
+
+/// What one `run` was given, copied out of the `RunSpec`.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Seen {
+    pub tool: ToolName,
+    pub arguments: ToolArgs,
+    pub mounts: Vec<Mount>,
+    pub egress: Option<Vec<String>>,
+}
+
+pub struct Recording {
+    seen: Mutex<Vec<Seen>>,
+    answer: Result<RunOutput, RunError>,
+}
+
+impl Recording {
+    /// Answers every call with `content`, not truncated.
+    pub fn answering(content: &str) -> Arc<Recording> {
+        Recording::with(Ok(RunOutput {
+            content: content.to_string(),
+            truncated: false,
+        }))
+    }
+
+    pub fn with(answer: Result<RunOutput, RunError>) -> Arc<Recording> {
+        Arc::new(Recording {
+            seen: Mutex::new(Vec::new()),
+            answer,
+        })
+    }
+
+    pub fn seen(&self) -> Vec<Seen> {
+        self.seen.lock().unwrap().clone()
+    }
+
+    pub fn count(&self) -> usize {
+        self.seen.lock().unwrap().len()
+    }
+}
+
+impl Runtime for Recording {
+    fn run(&self, spec: &RunSpec) -> Result<RunOutput, RunError> {
+        self.seen.lock().unwrap().push(Seen {
+            tool: spec.tool(),
+            arguments: spec.arguments().clone(),
+            mounts: spec.mounts().to_vec(),
+            egress: spec.egress().map(<[String]>::to_vec),
+        });
+        self.answer.clone()
+    }
+}
+
+/// Lets a test keep its `Arc<Recording>` while the broker owns a `Box<dyn Runtime>`.
+pub struct Shared(pub Arc<Recording>);
+
+impl Runtime for Shared {
+    fn run(&self, spec: &RunSpec) -> Result<RunOutput, RunError> {
+        self.0.run(spec)
+    }
+}

crates/brokerd/tests/support/sink.rs

@@ -0,0 +1,78 @@
+//! An audit sink that fails on demand, and a log that tests can read. Do not edit.
+//!
+//! Included with `#[path = "support/sink.rs"] mod sink;`.
+
+#![allow(dead_code)] // each test file uses a different part of this module
+
+use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
+use std::sync::{Arc, Mutex};
+
+use brokerd::audit::{AuditError, Writer};
+use brokerd::ledger::AuditSink;
+use proto::{AuditEvent, Timestamp};
+
+/// Switches shared between a test and its `Flaky` sink.
+#[derive(Clone, Default)]
+pub struct Switch {
+    fail: Arc<AtomicBool>,
+    panic: Arc<AtomicBool>,
+    attempts: Arc<AtomicUsize>,
+}
+
+impl Switch {
+    /// Every append from now on fails, without writing anything.
+    pub fn fail(&self, on: bool) {
+        self.fail.store(on, Ordering::SeqCst);
+    }
+    /// The next append panics, as a bug part-way through a write would.
+    pub fn panic_next(&self) {
+        self.panic.store(true, Ordering::SeqCst);
+    }
+    /// How many appends the ledger has asked for.
+    pub fn attempts(&self) -> usize {
+        self.attempts.load(Ordering::SeqCst)
+    }
+}
+
+/// A real `Writer` behind a switch.
+pub struct Flaky {
+    pub writer: Writer,
+    pub switch: Switch,
+}
+
+impl AuditSink for Flaky {
+    fn append(&mut self, time: Timestamp, event: AuditEvent) -> Result<u64, AuditError> {
+        self.switch.attempts.fetch_add(1, Ordering::SeqCst);
+        if self.switch.panic.swap(false, Ordering::SeqCst) {
+            panic!("a bug part-way through a write");
+        }
+        if self.switch.fail.load(Ordering::SeqCst) {
+            return Err(AuditError::Io {
+                what: "cannot write to the test log".to_string(),
+                source: std::io::Error::other("the disk is full"),
+            });
+        }
+        self.writer.append(time, event)
+    }
+}
+
+/// Collects every line a ledger or broker prints.
+#[derive(Clone, Default)]
+pub struct Lines(Arc<Mutex<Vec<String>>>);
+
+impl Lines {
+    pub fn sink(&self) -> Box<dyn Fn(&str) + Send + Sync> {
+        let lines = Arc::clone(&self.0);
+        Box::new(move |line| lines.lock().unwrap().push(line.to_string()))
+    }
+    pub fn all(&self) -> Vec<String> {
+        self.0.lock().unwrap().clone()
+    }
+    /// The lines that hold `text`.
+    pub fn with(&self, text: &str) -> Vec<String> {
+        self.all()
+            .into_iter()
+            .filter(|l| l.contains(text))
+            .collect()
+    }
+}

crates/brokerd/tests/support/tmp.rs

@@ -0,0 +1,57 @@
+//! Temporary directories for tests. Do not edit.
+//!
+//! Included with `#[path = "support/tmp.rs"] mod tmp;`. No crate is used: the name is made from
+//! the process id and a counter, and the directory is removed when the value is dropped.
+
+#![allow(dead_code)] // each test file uses a different part of this module
+
+use std::path::{Path, PathBuf};
+use std::sync::atomic::{AtomicU32, Ordering};
+
+static NEXT: AtomicU32 = AtomicU32::new(0);
+
+pub struct TempDir(PathBuf);
+
+impl TempDir {
+    pub fn new(tag: &str) -> TempDir {
+        let n = NEXT.fetch_add(1, Ordering::SeqCst);
+        let path = std::env::temp_dir().join(format!("bx-{tag}-{}-{n}", std::process::id()));
+        let _ = std::fs::remove_dir_all(&path);
+        std::fs::create_dir_all(&path).unwrap();
+        TempDir(path)
+    }
+
+    pub fn path(&self) -> &Path {
+        &self.0
+    }
+
+    /// Writes `text` to `name` inside the directory and returns the full path.
+    pub fn write(&self, name: &str, text: &str) -> PathBuf {
+        let path = self.0.join(name);
+        std::fs::write(&path, text).unwrap();
+        path
+    }
+}
+
+impl Drop for TempDir {
+    fn drop(&mut self) {
+        // Put back the permissions a test may have taken away, or the removal fails.
+        use std::os::unix::fs::PermissionsExt;
+        let _ = std::fs::set_permissions(&self.0, std::fs::Permissions::from_mode(0o700));
+        let _ = std::fs::remove_dir_all(&self.0);
+    }
+}
+
+/// True when the tests run as root, for whom file permissions do not apply. Tests that depend on
+/// a permission error print why they are skipped and return.
+pub fn running_as_root(test: &str) -> bool {
+    let probe = TempDir::new("rootprobe");
+    let file = probe.write("probe", "x");
+    use std::os::unix::fs::PermissionsExt;
+    std::fs::set_permissions(&file, std::fs::Permissions::from_mode(0o000)).unwrap();
+    let root = std::fs::read(&file).is_ok();
+    if root {
+        eprintln!("{test}: skipped, because this user can read a mode 000 file (root?)");
+    }
+    root
+}

crates/bxctl/src/admin.rs

@@ -0,0 +1,297 @@
+//! The owner's admin commands over admin.sock: approvals, approve, refuse, grants check.
+
+use std::io::{self, Write};
+use std::os::unix::net::UnixStream;
+use std::path::{Path, PathBuf};
+
+use proto::{
+    Approve, DecisionRecord, DenyReason, Empty, Envelope, ErrorCode, FrameError, Message,
+    PROTOCOL_VERSION, PendingApproval, Refuse, Timestamp, WireError, read_frame, write_frame,
+};
+
+use crate::chat::code_name;
+use crate::escape::escape_json_text;
+
+/// How long `bxctl` waits for `brokerd` to take or answer an admin request.
+pub const ADMIN_TIMEOUT: std::time::Duration = std::time::Duration::from_secs(30);
+
+// Ask brokerd for one message and read one answer, waiting at most `ADMIN_TIMEOUT`.
+pub fn request(socket: &Path, msg: Message) -> Result<Message, AdminError> {
+    request_with_timeout(socket, msg, ADMIN_TIMEOUT)
+}
+
+/// `request` with another limit on each read and write, so a `brokerd` that accepts and never
+/// answers cannot hang `bxctl`, or a `chat` turn waiting on an approval.
+pub fn request_with_timeout(
+    socket: &Path,
+    msg: Message,
+    timeout: std::time::Duration,
+) -> Result<Message, AdminError> {
+    let mut stream =
+        UnixStream::connect(socket).map_err(|e| AdminError::Connect(socket.to_path_buf(), e))?;
+    stream
+        .set_read_timeout(Some(timeout))
+        .and_then(|()| stream.set_write_timeout(Some(timeout)))
+        .map_err(|e| AdminError::Connect(socket.to_path_buf(), e))?;
+    let env = Envelope {
+        v: PROTOCOL_VERSION,
+        id: 1,
+        r#final: true,
+        msg,
+    };
+    write_frame(&mut stream, &env).map_err(AdminError::Frame)?;
+    let answer = read_frame(&mut stream).map_err(|e| match e {
+        FrameError::Io(io)
+            if matches!(
+                io.kind(),
+                io::ErrorKind::WouldBlock | io::ErrorKind::TimedOut
+            ) =>
+        {
+            AdminError::NoAnswer(timeout)
+        }
+        other => AdminError::Frame(other),
+    })?;
+    if answer.id != 1 || !answer.r#final {
+        return Err(AdminError::Protocol(
+            "expected an answer for request 1".to_string(),
+        ));
+    }
+    match answer.msg {
+        Message::Error(w) => Err(AdminError::Refused(w)),
+        other => Ok(other),
+    }
+}
+
+// Ask brokerd for the list of approvals waiting, or report an answer of the wrong kind.
+pub fn list(socket: &Path) -> Result<Vec<PendingApproval>, AdminError> {
+    match request(socket, Message::Approvals(Empty {}))? {
+        Message::ApprovalList(list) => Ok(list.items),
+        _ => Err(AdminError::Protocol(
+            "expected an approval list".to_string(),
+        )),
+    }
+}
+
+#[derive(Debug)]
+pub enum AdminError {
+    Connect(PathBuf, std::io::Error),
+    Frame(FrameError),
+    Refused(WireError),
+    Protocol(String),
+    /// Writing the output failed; the caller stops rather than write again.
+    Io(std::io::Error),
+    /// The request was sent and no answer came in time, so what brokerd did is not known.
+    NoAnswer(std::time::Duration),
+}
+
+impl std::fmt::Display for AdminError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            AdminError::Connect(p, e) => write!(f, "cannot reach brokerd at {}: {e}", p.display()),
+            // serde quotes the offending text of a bad frame, decoded: escape it.
+            AdminError::Frame(e) => write!(f, "{}", escape_json_text(&e.to_string())),
+            // The detail may carry text from the inference server or a tool: escape it.
+            AdminError::Refused(w) => {
+                write!(f, "{}: {}", code_name(w.code), escape_json_text(&w.detail))
+            }
+            AdminError::Protocol(s) => write!(f, "{s}"),
+            AdminError::Io(e) => write!(f, "{e}"),
+            AdminError::NoAnswer(t) => write!(
+                f,
+                "brokerd did not answer within {} s; whether it acted is unknown: check `bxctl approvals` and `bxctl audit verify`",
+                t.as_secs_f64()
+            ),
+        }
+    }
+}
+
+// An error writing the output is its own kind, so the caller can stop instead of writing again.
+impl From<std::io::Error> for AdminError {
+    fn from(e: std::io::Error) -> Self {
+        AdminError::Io(e)
+    }
+}
+
+impl std::error::Error for AdminError {}
+
+pub fn cmd_approvals(
+    socket: &Path,
+    now: Timestamp,
+    out: &mut dyn Write,
+) -> Result<bool, AdminError> {
+    let items = list(socket)?;
+    if items.is_empty() {
+        writeln!(out, "no pending approvals")?;
+    } else {
+        for item in &items {
+            write_block(out, item, now)?;
+        }
+    }
+    Ok(true)
+}
+
+pub fn cmd_approve(socket: &Path, approval: u64, out: &mut dyn Write) -> Result<bool, AdminError> {
+    let msg = match request(socket, Message::Approve(Approve { approval })) {
+        Ok(m) => m,
+        Err(AdminError::Refused(w)) if w.code == ErrorCode::NoSuchApproval => {
+            writeln!(
+                out,
+                "{approval}: no such approval (already answered or expired)"
+            )?;
+            return Ok(false);
+        }
+        Err(e) => return Err(e),
+    };
+    match msg {
+        Message::ApproveResult(result) => match result.outcome {
+            DecisionRecord::Allowed {} | DecisionRecord::Ask {} => {
+                writeln!(out, "approved {approval}: runs")?;
+                Ok(true)
+            }
+            DecisionRecord::Denied { reason } => {
+                writeln!(out, "approved {approval}: denied ({})", reason_name(reason))?;
+                Ok(false)
+            }
+        },
+        _ => Err(AdminError::Protocol("unexpected answer".to_string())),
+    }
+}
+
+pub fn cmd_refuse(
+    socket: &Path,
+    approval: u64,
+    reason: Option<&str>,
+    out: &mut dyn Write,
+) -> Result<bool, AdminError> {
+    let msg = match request(
+        socket,
+        Message::Refuse(Refuse {
+            approval,
+            reason: reason.map(str::to_string),
+        }),
+    ) {
+        Ok(m) => m,
+        Err(AdminError::Refused(w)) if w.code == ErrorCode::NoSuchApproval => {
+            writeln!(
+                out,
+                "{approval}: no such approval (already answered or expired)"
+            )?;
+            return Ok(false);
+        }
+        Err(e) => return Err(e),
+    };
+    match msg {
+        Message::Ok(_) => {
+            writeln!(out, "refused {approval}")?;
+            Ok(true)
+        }
+        _ => Err(AdminError::Protocol("unexpected answer".to_string())),
+    }
+}
+
+pub fn cmd_grants_check(socket: &Path, out: &mut dyn Write) -> Result<bool, AdminError> {
+    let msg = request(socket, Message::CheckGrants(Empty {}))?;
+    match msg {
+        Message::GrantsReport(report) => {
+            if report.problems.is_empty() {
+                writeln!(out, "grants: ok")?;
+                Ok(true)
+            } else {
+                for problem in &report.problems {
+                    writeln!(
+                        out,
+                        "{}{}: {}",
+                        escape_json_text(&problem.file),
+                        match problem.line {
+                            Some(line) => format!(":{line}"),
+                            None => String::new(),
+                        },
+                        escape_json_text(&problem.problem)
+                    )?;
+                }
+                Ok(false)
+            }
+        }
+        _ => Err(AdminError::Protocol("unexpected answer".to_string())),
+    }
+}
+
+pub fn reason_name(reason: DenyReason) -> &'static str {
+    match reason {
+        DenyReason::NoGrant => "no_grant",
+        DenyReason::GrantExpired => "grant_expired",
+        DenyReason::TaintTooHigh => "taint_too_high",
+        DenyReason::DeniedByGrant => "denied_by_grant",
+        DenyReason::ApprovalRefused => "approval_refused",
+        DenyReason::ApprovalExpired => "approval_expired",
+        DenyReason::GrantsInvalid => "grants_invalid",
+        DenyReason::AuditUnavailable => "audit_unavailable",
+        DenyReason::InvalidArguments => "invalid_arguments",
+        DenyReason::StateUnreadable => "state_unreadable",
+    }
+}
+
+// The approvals table is one block per item: a summary line, then the tool and arguments.
+pub fn write_block(out: &mut dyn Write, item: &PendingApproval, now: Timestamp) -> io::Result<()> {
+    let age = now.unix_millis().saturating_sub(item.created.unix_millis());
+    let until = item.expires.unix_millis().saturating_sub(now.unix_millis());
+    writeln!(
+        out,
+        "{}  {} ago  {}  session {}  grant {}  taint {}",
+        item.approval,
+        span(age),
+        expiry(until, now >= item.expires),
+        session_shown(item.session.as_str()),
+        escape_json_text(&item.grant),
+        taint_name(item.taint),
+    )?;
+    writeln!(
+        out,
+        "    {} {}",
+        escape_json_text(&item.tool),
+        escape_json_text(&item.arguments)
+    )?;
+    Ok(())
+}
+
+// A span of whole seconds, minutes, or hours, rounded down.
+fn span(ms: u64) -> String {
+    let secs = ms / 1000;
+    let mins = secs / 60;
+    let hours = mins / 60;
+    if mins == 0 {
+        format!("{secs} s")
+    } else if hours == 0 {
+        format!("{mins} min")
+    } else {
+        format!("{hours} h")
+    }
+}
+
+// Whether the approval has expired, or how long until it does.
+fn expiry(until: u64, expired: bool) -> String {
+    if expired {
+        "expired".to_string()
+    } else {
+        format!("expires in {}", span(until))
+    }
+}
+
+// A session id longer than ten characters is cut to nine and an ellipsis.
+fn session_shown(session: &str) -> String {
+    if session.chars().count() > 10 {
+        let head: String = session.chars().take(9).collect();
+        format!("{head}…")
+    } else {
+        session.to_string()
+    }
+}
+
+// The taint of a decision is its wire name.
+fn taint_name(taint: proto::DataClass) -> &'static str {
+    match taint {
+        proto::DataClass::Public => "public",
+        proto::DataClass::Private => "private",
+        proto::DataClass::Secret => "secret",
+    }
+}

crates/bxctl/src/chat.rs

@@ -1,14 +1,17 @@
 //! `bxctl chat`: a turn client over `loop.sock` and a printer for the events it receives.
 
-use std::io::Write;
+use std::io::{BufRead, Write};
-
-use proto::{
-    Envelope, ErrorCode, Message, PROTOCOL_VERSION, SessionId, Turn, TurnDone, TurnEvent,
-    WireError, read_frame, write_frame,
-};
 use std::os::unix::net::UnixStream;
 use std::path::Path;
 
+use proto::{
+    DenyReason, Envelope, ErrorCode, Message, PROTOCOL_VERSION, SessionId, Timestamp, Turn,
+    TurnDone, TurnEvent, WireError, read_frame, write_frame,
+};
+
+use crate::admin;
+use crate::escape::{escape_json_text, escape_model_text};
+
 #[derive(Debug)]
 pub enum ChatError {
     Connect(std::io::Error),
@@ -21,8 +24,12 @@ impl std::fmt::Display for ChatError {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
             ChatError::Connect(e) => write!(f, "{e}"),
-            ChatError::Frame(e) => write!(f, "{e}"),
+            // serde quotes the offending text of a bad frame, decoded: escape it.
-            ChatError::Refused(w) => write!(f, "{}: {}", code_name(w.code), w.detail),
+            ChatError::Frame(e) => write!(f, "{}", escape_json_text(&e.to_string())),
+            // The detail may carry the inference server's body: escape it like model text.
+            ChatError::Refused(w) => {
+                write!(f, "{}: {}", code_name(w.code), escape_json_text(&w.detail))
+            }
             ChatError::Protocol(s) => write!(f, "{s}"),
         }
     }
@@ -39,7 +46,7 @@ impl std::error::Error for ChatError {
 }
 
 // The ErrorCode name in snake_case, spelled out in words for the owner reading a failure.
-fn code_name(code: ErrorCode) -> &'static str {
+pub fn code_name(code: ErrorCode) -> &'static str {
     match code {
         ErrorCode::BadFrame => "bad frame",
         ErrorCode::BadVersion => "bad version",
@@ -51,6 +58,8 @@ fn code_name(code: ErrorCode) -> &'static str {
         ErrorCode::NoSuchSession => "no such session",
         ErrorCode::SessionExists => "session exists",
         ErrorCode::Inference => "inference",
+        ErrorCode::Forbidden => "forbidden",
+        ErrorCode::NoSuchApproval => "no such approval",
     }
 }
 
@@ -140,7 +149,7 @@ impl Printer {
                         out.write_all(b"\x1b[2m")?;
                         self.dimmed_open = true;
                     }
-                    out.write_all(text.as_bytes())?;
+                    out.write_all(escape_model_text(text).as_bytes())?;
                 }
             }
             TurnEvent::Content { text } => {
@@ -149,11 +158,12 @@ impl Printer {
                     self.dimmed_open = false;
                 }
                 if self.stream_content {
-                    out.write_all(text.as_bytes())?;
+                    out.write_all(escape_model_text(text).as_bytes())?;
                 }
             }
             TurnEvent::ToolCallStarted { name } => {
                 self.close_dimmed(out)?;
+                let name = escape_model_text(name);
                 writeln!(out, "[tool {name}]")?;
             }
             TurnEvent::ToolResult {
@@ -162,6 +172,7 @@ impl Printer {
                 truncated,
             } => {
                 self.close_dimmed(out)?;
+                let name = escape_model_text(name);
                 if *truncated {
                     writeln!(out, "[{name}: {class:?}, truncated]")?;
                 } else {
@@ -181,7 +192,8 @@ impl Printer {
                 self.close_dimmed(out)?;
                 writeln!(
                     out,
-                    "[retrying: attempt {attempt} in {after_ms} ms: {error}]"
+                    "[retrying: attempt {attempt} in {after_ms} ms: {}]",
+                    escape_json_text(error)
                 )?;
             }
             TurnEvent::ThinkingCapped { tokens } => {
@@ -193,6 +205,32 @@ impl Printer {
                 writeln!(out, "[cache loss: {got} of {expected}]")?;
             }
             TurnEvent::Queued { .. } | TurnEvent::Progress { .. } => {}
+            TurnEvent::ApprovalPending { .. } => {
+                self.close_dimmed(out)?;
+            }
+            TurnEvent::ToolDenied { name, reason } => {
+                self.close_dimmed(out)?;
+                let shown = escape_model_text(name);
+                writeln!(out, "[denied {shown}: {}]", admin::reason_name(*reason))?;
+                match reason {
+                    DenyReason::GrantsInvalid => {
+                        writeln!(out, "see docs/runbook.md#grants-invalid")?;
+                    }
+                    DenyReason::AuditUnavailable => {
+                        writeln!(out, "see docs/runbook.md#audit-unavailable")?;
+                    }
+                    DenyReason::StateUnreadable => {
+                        writeln!(out, "see docs/runbook.md#broker-state-damaged")?;
+                    }
+                    DenyReason::NoGrant
+                    | DenyReason::GrantExpired
+                    | DenyReason::TaintTooHigh
+                    | DenyReason::DeniedByGrant
+                    | DenyReason::ApprovalRefused
+                    | DenyReason::ApprovalExpired
+                    | DenyReason::InvalidArguments => {}
+                }
+            }
         }
         out.flush()
     }
@@ -209,3 +247,112 @@ impl Printer {
         Ok(())
     }
 }
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum OnPending {
+    EventOnly,
+    Show,
+    Ask,
+}
+
+pub struct Approvals<'a> {
+    pub admin_socket: &'a Path,
+    pub on_pending: OnPending,
+}
+
+pub struct TurnIo<'a> {
+    pub printer: &'a mut Printer,
+    pub input: &'a mut dyn BufRead,
+    pub out: &'a mut dyn Write,
+}
+
+pub fn handle_pending(
+    admin_socket: &Path,
+    approval: u64,
+    ask: bool,
+    now: Timestamp,
+    input: &mut dyn BufRead,
+    out: &mut dyn Write,
+) -> std::io::Result<()> {
+    let items = match admin::list(admin_socket) {
+        Ok(items) => items,
+        Err(e) => {
+            writeln!(out, "approval {approval}: cannot ask brokerd: {e}")?;
+            return Ok(());
+        }
+    };
+    let Some(item) = items.iter().find(|item| item.approval == approval) else {
+        writeln!(out, "approval {approval} is no longer pending")?;
+        return Ok(());
+    };
+    out.write_all(b"\x1b[0m")?;
+    admin::write_block(out, item, now)?;
+    if !ask {
+        return Ok(());
+    }
+    write!(out, "type {approval} to approve, anything else refuses: ")?;
+    out.flush()?;
+    let mut line = String::new();
+    input.read_line(&mut line)?;
+    if line.ends_with('\n') {
+        line.pop();
+    }
+    if line.ends_with('\r') {
+        line.pop();
+    }
+    let result = if line == approval.to_string() {
+        admin::cmd_approve(admin_socket, approval, out)
+    } else {
+        admin::cmd_refuse(admin_socket, approval, None, out)
+    };
+    match result {
+        Ok(_) => Ok(()),
+        // The output itself failed: writing another line to it would fail the same way.
+        Err(admin::AdminError::Io(e)) => Err(e),
+        Err(e) => {
+            writeln!(out, "approval {approval}: {e}")?;
+            Ok(())
+        }
+    }
+}
+
+/// The outer error is a failed write to `io.out`; the inner one is the turn's.
+pub fn stream_turn(
+    socket: &Path,
+    session: &SessionId,
+    text: &str,
+    resume: bool,
+    approvals: &Approvals<'_>,
+    io: &mut TurnIo<'_>,
+) -> std::io::Result<Result<TurnDone, ChatError>> {
+    let mut err = None;
+    let outcome = run_turn(socket, session, text, resume, &mut |event| {
+        if err.is_some() {
+            return;
+        }
+        if let Err(e) = io.printer.event(io.out, event) {
+            err = Some(e);
+            return;
+        }
+        if let TurnEvent::ApprovalPending { approval, .. } = event
+            && approvals.on_pending != OnPending::EventOnly
+        {
+            let ask = approvals.on_pending == OnPending::Ask;
+            if let Err(e) = handle_pending(
+                approvals.admin_socket,
+                *approval,
+                ask,
+                Timestamp::now(),
+                io.input,
+                io.out,
+            ) {
+                err = Some(e);
+            }
+        }
+    });
+    if let Some(e) = err {
+        return Err(e);
+    }
+    io.printer.end_reasoning(io.out)?;
+    Ok(outcome)
+}

crates/bxctl/src/cli.rs

@@ -0,0 +1,290 @@
+//! `bxctl` command-line parsing: the subcommands, the shared `USAGE` and `ChatOptions`.
+
+use std::path::{Path, PathBuf};
+
+use proto::SessionId;
+
+// Shown on stderr for any usage error. It names every subcommand and the flags they share, so a
+// single line tells the owner what they can type.
+pub const USAGE: &str = "\
+usage: bxctl <command> [options]
+
+  bxctl chat [--socket PATH] [--admin-socket PATH] [--session ID] [--say TEXT] [--no-thinking] [--json]
+      Talk to loopd.
+
+  bxctl approvals [--admin-socket PATH]
+      List the approvals waiting for a decision.
+
+  bxctl approve <id> [--admin-socket PATH]
+      Approve approval <id>.
+
+  bxctl refuse <id> [--reason TEXT] [--admin-socket PATH]
+      Refuse approval <id>, recording a reason.
+
+  bxctl grants check [--admin-socket PATH]
+      Check that the grants load.
+
+  bxctl audit verify [--home DIR]
+      Check the audit log's hash chain, reading the files directly.";
+
+// The options every `chat` call carries. `socket` is the loop socket; `admin_socket` is the admin
+// socket the other subcommands use. Both default to the paths under `$BOXMAKER_HOME`.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct ChatOptions {
+    pub socket: PathBuf,
+    pub admin_socket: PathBuf,
+    pub session: Option<SessionId>,
+    pub show_thinking: bool,
+    pub say: Option<String>,
+    pub json: bool,
+}
+
+impl ChatOptions {
+    pub fn default(home: &Path) -> Self {
+        ChatOptions {
+            socket: home.join("run").join("loop").join("loop.sock"),
+            admin_socket: default_admin_socket(home),
+            session: None,
+            show_thinking: true,
+            say: None,
+            json: false,
+        }
+    }
+}
+
+// Why `parse` rejected the arguments. There is only one kind: the arguments were wrong.
+#[derive(Debug, PartialEq, Eq)]
+pub struct UsageError;
+
+impl std::fmt::Display for UsageError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "invalid arguments")
+    }
+}
+
+impl std::error::Error for UsageError {}
+
+// What the owner asked for. `Chat` carries its options; every admin subcommand carries the admin
+// socket to use (defaulted from `$BOXMAKER_HOME`) plus whatever only it needs.
+#[derive(Debug, PartialEq, Eq)]
+pub enum Command {
+    Chat(ChatOptions),
+    Approvals {
+        admin_socket: PathBuf,
+    },
+    Approve {
+        admin_socket: PathBuf,
+        approval: u64,
+    },
+    Refuse {
+        admin_socket: PathBuf,
+        approval: u64,
+        reason: Option<String>,
+    },
+    GrantsCheck {
+        admin_socket: PathBuf,
+    },
+    AuditVerify {
+        home: PathBuf,
+    },
+}
+
+pub fn parse(args: &[String], home: &Path) -> Result<Command, UsageError> {
+    let (command, rest) = match args.split_first() {
+        Some((c, r)) => (c.as_str(), r),
+        None => return Err(UsageError),
+    };
+    match command {
+        "chat" => parse_chat(rest, home),
+        "approvals" => parse_approvals(rest, home),
+        "approve" => parse_approve(rest, home),
+        "refuse" => parse_refuse(rest, home),
+        "grants" => parse_grants(rest, home),
+        "audit" => parse_audit(rest, home),
+        // A flag before the command, or any unknown command, is not valid.
+        _ => Err(UsageError),
+    }
+}
+
+fn default_admin_socket(home: &Path) -> PathBuf {
+    home.join("run").join("owner-broker").join("admin.sock")
+}
+
+fn parse_chat(args: &[String], home: &Path) -> Result<Command, UsageError> {
+    let mut opts = ChatOptions::default(home);
+    let mut i = 0;
+    while i < args.len() {
+        match args[i].as_str() {
+            "--socket" => opts.socket = PathBuf::from(value_at(args, i)?),
+            "--admin-socket" => opts.admin_socket = PathBuf::from(value_at(args, i)?),
+            "--session" => opts.session = Some(parse_session(&value_at(args, i)?)?),
+            "--say" => opts.say = Some(value_at(args, i)?),
+            "--no-thinking" => {
+                opts.show_thinking = false;
+                i += 1;
+                continue;
+            }
+            "--json" => {
+                opts.json = true;
+                i += 1;
+                continue;
+            }
+            _ => return Err(UsageError),
+        }
+        i += 2;
+    }
+    Ok(Command::Chat(opts))
+}
+
+fn parse_approvals(args: &[String], home: &Path) -> Result<Command, UsageError> {
+    let mut admin_socket = default_admin_socket(home);
+    let mut i = 0;
+    while i < args.len() {
+        match args[i].as_str() {
+            "--admin-socket" => admin_socket = PathBuf::from(value_at(args, i)?),
+            // Anything else is a stray argument or an unknown flag.
+            _ => return Err(UsageError),
+        }
+        i += 2;
+    }
+    Ok(Command::Approvals { admin_socket })
+}
+
+fn parse_approve(args: &[String], home: &Path) -> Result<Command, UsageError> {
+    let mut admin_socket = default_admin_socket(home);
+    let mut approval = None;
+    let mut i = 0;
+    while i < args.len() {
+        match args[i].as_str() {
+            "--admin-socket" => {
+                admin_socket = PathBuf::from(value_at(args, i)?);
+                i += 2;
+                continue;
+            }
+            other => {
+                if approval.is_some() {
+                    return Err(UsageError);
+                }
+                approval = Some(parse_id(other)?);
+                i += 1;
+            }
+        }
+    }
+    match approval {
+        Some(approval) => Ok(Command::Approve {
+            admin_socket,
+            approval,
+        }),
+        None => Err(UsageError),
+    }
+}
+
+fn parse_refuse(args: &[String], home: &Path) -> Result<Command, UsageError> {
+    let mut admin_socket = default_admin_socket(home);
+    let mut approval = None;
+    let mut reason = None;
+    let mut i = 0;
+    while i < args.len() {
+        match args[i].as_str() {
+            "--admin-socket" => {
+                admin_socket = PathBuf::from(value_at(args, i)?);
+                i += 2;
+                continue;
+            }
+            "--reason" => {
+                if reason.is_some() {
+                    return Err(UsageError);
+                }
+                reason = Some(verify_reason(&value_at(args, i)?)?);
+                i += 2;
+                continue;
+            }
+            other => {
+                if approval.is_some() {
+                    return Err(UsageError);
+                }
+                approval = Some(parse_id(other)?);
+                i += 1;
+            }
+        }
+    }
+    match approval {
+        Some(approval) => Ok(Command::Refuse {
+            admin_socket,
+            approval,
+            reason,
+        }),
+        None => Err(UsageError),
+    }
+}
+
+fn parse_grants(args: &[String], home: &Path) -> Result<Command, UsageError> {
+    let rest = match args.first().map(String::as_str) {
+        Some("check") => &args[1..],
+        _ => return Err(UsageError),
+    };
+    let mut admin_socket = default_admin_socket(home);
+    let mut i = 0;
+    while i < rest.len() {
+        match rest[i].as_str() {
+            "--admin-socket" => admin_socket = PathBuf::from(value_at(rest, i)?),
+            _ => return Err(UsageError),
+        }
+        i += 2;
+    }
+    Ok(Command::GrantsCheck { admin_socket })
+}
+
+fn parse_audit(args: &[String], home: &Path) -> Result<Command, UsageError> {
+    let rest = match args.first().map(String::as_str) {
+        Some("verify") => &args[1..],
+        _ => return Err(UsageError),
+    };
+    let mut home = home.to_path_buf();
+    let mut i = 0;
+    while i < rest.len() {
+        match rest[i].as_str() {
+            "--home" => home = PathBuf::from(value_at(rest, i)?),
+            _ => return Err(UsageError),
+        }
+        i += 2;
+    }
+    Ok(Command::AuditVerify { home })
+}
+
+// The argument after the flag at `i`, taken as the value even when it looks like a flag, so a value
+// is a value.
+fn value_at(args: &[String], i: usize) -> Result<String, UsageError> {
+    args.get(i + 1).cloned().ok_or(UsageError)
+}
+
+// An approval id is ASCII digits that fit in u64 and nothing else; `str::parse::<u64>` alone would
+// accept `+41`, so the digit check comes first.
+fn parse_id(value: &str) -> Result<u64, UsageError> {
+    if value.is_empty() || !value.bytes().all(|b| b.is_ascii_digit()) {
+        return Err(UsageError);
+    }
+    value.parse::<u64>().map_err(|_| UsageError)
+}
+
+// A session id is a valid id, and one that is purely numeric must fit in u64 so it is never
+// mistaken for an approval id.
+fn parse_session(value: &str) -> Result<SessionId, UsageError> {
+    match SessionId::new(value) {
+        Ok(id) => {
+            if value.bytes().all(|b| b.is_ascii_digit()) && value.parse::<u64>().is_err() {
+                return Err(UsageError);
+            }
+            Ok(id)
+        }
+        Err(_) => Err(UsageError),
+    }
+}
+
+// A refuse reason must be present; its content is unvalidated on the client.
+fn verify_reason(reason: &str) -> Result<String, UsageError> {
+    if reason.is_empty() {
+        return Err(UsageError);
+    }
+    Ok(reason.to_string())
+}

crates/bxctl/src/escape.rs

@@ -0,0 +1,43 @@
+//! The two text-escape helpers the owner's client needs.
+
+// The control bytes, the zero-width and Unicode line/paragraph separators, and the BOM. A code
+// point in any of these ranges must never reach the terminal raw.
+const ESCAPE_RANGES: &[(u32, u32)] = &[
+    (0x0000, 0x001f),
+    (0x007f, 0x009f),
+    (0x200b, 0x200f),
+    (0x2028, 0x202e),
+    (0x2060, 0x2069),
+    (0xfeff, 0xfeff),
+];
+
+pub fn escape_json_text(s: &str) -> String {
+    escape(s, false)
+}
+
+pub fn escape_model_text(s: &str) -> String {
+    escape(s, true)
+}
+
+fn escape(s: &str, model_text: bool) -> String {
+    let mut out = String::with_capacity(s.len());
+    for c in s.chars() {
+        let cp = u32::from(c);
+        if should_escape(c, model_text) {
+            out.push_str(&format!("\\u{:04x}", cp));
+        } else {
+            out.push(c);
+        }
+    }
+    out
+}
+
+// A control point is escaped, except that model text keeps \n and \t.
+fn should_escape(c: char, model_text: bool) -> bool {
+    let cp = u32::from(c);
+    if ESCAPE_RANGES.iter().any(|(lo, hi)| cp >= *lo && cp <= *hi) {
+        !(model_text && (cp == 0x09 || cp == 0x0a))
+    } else {
+        false
+    }
+}

crates/bxctl/src/lib.rs

@@ -1,3 +1,7 @@
 //! The owner's command-line tool.
 
+pub mod admin;
 pub mod chat;
+pub mod cli;
+pub mod escape;
+pub mod verify;

crates/bxctl/src/main.rs

@@ -4,139 +4,133 @@ use std::io::{BufRead, BufReader, Write};
 use std::path::{Path, PathBuf};
 use std::process::ExitCode;
 
-use bxctl::chat::{ChatError, Printer, new_session_id, run_turn};
+use bxctl::admin::{self, AdminError};
-use proto::{ErrorCode, SessionId, TurnDone, TurnEvent};
+use bxctl::chat::{Approvals, ChatError, OnPending, Printer, TurnIo, new_session_id, stream_turn};
-
+use bxctl::cli::{self, ChatOptions, Command, USAGE};
-const USAGE: &str =
+use bxctl::escape::escape_model_text;
-    "usage: bxctl chat [--socket <path>] [--session <id>] [--no-thinking] [--say <text>] [--json]";
+use proto::{ErrorCode, SessionId, Timestamp, TurnDone};
-
-struct Options {
-    socket: PathBuf,
-    session: Option<SessionId>,
-    show_thinking: bool,
-    say: Option<String>,
-    json: bool,
-}
 
 fn main() -> ExitCode {
-    let args: Vec<String> = std::env::args().skip(1).collect();
+    // `args_os`, because `args` panics on an argument that is not UTF-8. bxctl's arguments are
-    if args.first().map(String::as_str) != Some("chat") {
+    // text (ids, messages, paths it prints back), so such an argument is a usage error.
-        eprintln!("{USAGE}");
+    let args: Vec<String> = match std::env::args_os()
-        return ExitCode::from(2);
+        .skip(1)
-    }
+        .map(|a| a.into_string())
-    match parse_chat(&args[1..]) {
+        .collect()
-        Ok(opts) => run(&opts),
+    {
-        Err(()) => {
+        Ok(args) => args,
-            eprintln!("{USAGE}");
+        Err(_) => {
-            ExitCode::from(2)
+            eprintln!("bxctl: an argument is not valid UTF-8\n{USAGE}");
+            return ExitCode::from(2);
         }
-    }
-}
-
-fn parse_chat(args: &[String]) -> Result<Options, ()> {
-    let mut opts = Options {
-        socket: default_socket(),
-        session: None,
-        show_thinking: true,
-        say: None,
-        json: false,
     };
-    let mut i = 0;
+    // $BOXMAKER_HOME defaults to /var/lib/boxmaker; defaults for the sockets are read from it.
-    while i < args.len() {
+    let home = std::env::var_os("BOXMAKER_HOME")
-        match args[i].as_str() {
-            "--socket" => {
-                i += 1;
-                match args.get(i) {
-                    Some(p) => opts.socket = PathBuf::from(p),
-                    None => return Err(()),
-                }
-            }
-            "--session" => {
-                i += 1;
-                match args.get(i) {
-                    Some(s) => match SessionId::new(s) {
-                        Ok(id) => opts.session = Some(id),
-                        Err(_) => return Err(()),
-                    },
-                    None => return Err(()),
-                }
-            }
-            "--say" => {
-                i += 1;
-                match args.get(i) {
-                    Some(t) => opts.say = Some(t.to_string()),
-                    None => return Err(()),
-                }
-            }
-            "--no-thinking" => opts.show_thinking = false,
-            "--json" => opts.json = true,
-            _ => return Err(()),
-        }
-        i += 1;
-    }
-    Ok(opts)
-}
-
-// The base directory: $BOXMAKER_HOME if set, otherwise the system location the brief fixes.
-fn default_socket() -> PathBuf {
-    let base = std::env::var_os("BOXMAKER_HOME")
         .map(PathBuf::from)
         .unwrap_or_else(|| PathBuf::from("/var/lib/boxmaker"));
-    base.join("run").join("loop").join("loop.sock")
+    // Parse before connecting, so a usage error exits 2 even without a broker.
-}
+    let command = match cli::parse(&args, &home) {
-
+        Ok(command) => command,
-// A writer that records the first io error it hits, so the on_event closure (which cannot return a
+        Err(_) => {
-// Result) does not lose a write failure. The error is checked after run_turn returns.
+            eprintln!("{USAGE}");
-struct Sink<'a> {
+            return ExitCode::from(2);
-    out: &'a mut (dyn Write + 'static),
+        }
-    err: Option<std::io::Error>,
+    };
-}
+    match command {
-
+        Command::Chat(opts) => run(&opts),
-impl Sink<'_> {
+        Command::Approvals { admin_socket } => exit(|| cmd_approvals(&admin_socket)),
-    fn event(&mut self, printer: &mut Printer, event: &TurnEvent) {
+        Command::Approve {
-        if self.err.is_none() {
+            admin_socket,
-            self.err = printer.event(self.out, event).err();
+            approval,
+        } => exit(|| cmd_approve(&admin_socket, approval)),
+        Command::Refuse {
+            admin_socket,
+            approval,
+            reason,
+        } => exit(|| cmd_refuse(&admin_socket, approval, reason.as_deref())),
+        Command::GrantsCheck { admin_socket } => exit(|| cmd_grants_check(&admin_socket)),
+        Command::AuditVerify { home } => {
+            let mut out = std::io::stdout().lock();
+            match bxctl::verify::run(&home, &mut out) {
+                Ok(true) => ExitCode::SUCCESS,
+                Ok(false) => ExitCode::from(1),
+                Err(e) => {
+                    eprintln!(
+                        "bxctl: cannot read the audit log under {}: {e}",
+                        home.display()
+                    );
+                    ExitCode::from(1)
+                }
+            }
         }
     }
 }
 
-// Runs one turn, streaming events through `printer` to `out`. Returns the turn outcome, or the
+// Run a command, mapping its result to an exit code: success for true, 1 for false or an error.
-// first io error that occurred while writing.
+fn exit<F: FnOnce() -> Result<bool, AdminError>>(f: F) -> ExitCode {
-fn stream_turn(
+    match f() {
-    socket: &Path,
+        Ok(true) => ExitCode::SUCCESS,
-    session: &SessionId,
+        Ok(false) => ExitCode::from(1),
-    text: &str,
+        Err(e) => {
-    resume: bool,
+            eprintln!("bxctl: {e}");
-    sink: &mut Sink,
+            ExitCode::from(1)
-    printer: &mut Printer,
+        }
-) -> Result<Result<TurnDone, ChatError>, std::io::Error> {
-    let outcome = run_turn(socket, session, text, resume, &mut |event| {
-        sink.event(printer, event)
-    });
-    // Flush any dimmed block left open before reporting the turn's result.
-    if sink.err.is_none() {
-        printer.end_reasoning(sink.out)?;
-    }
-    match sink.err.take() {
-        Some(e) => Err(e),
-        None => Ok(outcome),
     }
 }
 
-fn run(opts: &Options) -> ExitCode {
+fn cmd_approvals(admin: &Path) -> Result<bool, AdminError> {
+    let mut out = std::io::stdout().lock();
+    admin::cmd_approvals(admin, Timestamp::now(), &mut out)
+}
+
+fn cmd_approve(admin: &Path, id: u64) -> Result<bool, AdminError> {
+    let mut out = std::io::stdout().lock();
+    admin::cmd_approve(admin, id, &mut out)
+}
+
+fn cmd_refuse(admin: &Path, id: u64, reason: Option<&str>) -> Result<bool, AdminError> {
+    let mut out = std::io::stdout().lock();
+    admin::cmd_refuse(admin, id, reason, &mut out)
+}
+
+fn cmd_grants_check(admin: &Path) -> Result<bool, AdminError> {
+    let mut out = std::io::stdout().lock();
+    admin::cmd_grants_check(admin, &mut out)
+}
+
+fn on_pending(opts: &ChatOptions) -> OnPending {
+    if opts.json {
+        OnPending::EventOnly
+    } else if opts.say.is_some() {
+        OnPending::Show
+    } else {
+        OnPending::Ask
+    }
+}
+
+fn run(opts: &ChatOptions) -> ExitCode {
+    let stdin = std::io::stdin();
+    let mut input = BufReader::new(stdin.lock());
     match &opts.say {
-        Some(text) => run_say(opts, text),
+        Some(text) => run_say(opts, text, &mut input),
-        None => run_interactive(opts),
+        None => run_interactive(opts, &mut input),
     }
 }
 
-fn run_say(opts: &Options, text: &str) -> ExitCode {
+fn run_say(opts: &ChatOptions, text: &str, input: &mut dyn BufRead) -> ExitCode {
     let session = match &opts.session {
         Some(s) => s.clone(),
         None => new_session_id(),
     };
     let mut printer = Printer::new(opts.show_thinking, opts.json);
-    let code = run_turn_twice(opts, &session, text, opts.session.is_some(), &mut printer);
+    let code = run_turn_twice(
+        opts,
+        &session,
+        text,
+        opts.session.is_some(),
+        &mut printer,
+        input,
+    );
     match code {
         Ok(()) => ExitCode::SUCCESS,
         Err(RunError::Io(e)) => {
@@ -152,19 +146,25 @@ fn run_say(opts: &Options, text: &str) -> ExitCode {
 
 // Runs a --say turn, retrying once when the named session does not exist.
 fn run_turn_twice(
-    opts: &Options,
+    opts: &ChatOptions,
     session: &SessionId,
     text: &str,
     resume: bool,
     printer: &mut Printer,
+    input: &mut dyn BufRead,
 ) -> Result<(), RunError> {
     let stderr = std::io::stderr();
     let mut handle = stderr.lock();
-    let mut sink = Sink {
+    let approvals = Approvals {
-        out: &mut handle,
+        admin_socket: &opts.admin_socket,
-        err: None,
+        on_pending: on_pending(opts),
     };
-    match stream_turn(&opts.socket, session, text, resume, &mut sink, printer) {
+    let mut io = TurnIo {
+        printer,
+        input,
+        out: &mut handle,
+    };
+    match stream_turn(&opts.socket, session, text, resume, &approvals, &mut io) {
         Err(e) => Err(RunError::Io(e)),
         Ok(Ok(done)) => {
             write_answer(opts, &done).map_err(RunError::Io)?;
@@ -172,11 +172,12 @@ fn run_turn_twice(
         }
         Ok(Err(ChatError::Refused(w))) if w.code == ErrorCode::NoSuchSession => {
             // The named session does not exist: retry once, creating it (resume=false).
-            let mut sink = Sink {
+            let mut io = TurnIo {
+                printer,
+                input,
                 out: &mut handle,
-                err: None,
             };
-            match stream_turn(&opts.socket, session, text, false, &mut sink, printer) {
+            match stream_turn(&opts.socket, session, text, false, &approvals, &mut io) {
                 Err(e) => Err(RunError::Io(e)),
                 Ok(Ok(done)) => {
                     write_answer(opts, &done).map_err(RunError::Io)?;
@@ -189,11 +190,9 @@ fn run_turn_twice(
     }
 }
 
-fn run_interactive(opts: &Options) -> ExitCode {
+fn run_interactive(opts: &ChatOptions, reader: &mut dyn BufRead) -> ExitCode {
     let mut printer = Printer::new(opts.show_thinking, opts.json);
     let mut session = None;
-    let stdin = std::io::stdin();
-    let mut reader = BufReader::new(stdin.lock());
     loop {
         eprint!("> ");
         let _ = std::io::stderr().flush();
@@ -222,17 +221,22 @@ fn run_interactive(opts: &Options) -> ExitCode {
         }
         let stderr = std::io::stderr();
         let mut handle = stderr.lock();
-        let mut sink = Sink {
+        let approvals = Approvals {
+            admin_socket: &opts.admin_socket,
+            on_pending: on_pending(opts),
+        };
+        let mut io = TurnIo {
+            printer: &mut printer,
+            input: reader,
             out: &mut handle,
-            err: None,
         };
         match stream_turn(
             &opts.socket,
             this_session,
             text,
             resume,
-            &mut sink,
+            &approvals,
-            &mut printer,
+            &mut io,
         ) {
             Err(e) => {
                 eprintln!("bxctl: {e}");
@@ -255,7 +259,7 @@ fn run_interactive(opts: &Options) -> ExitCode {
 }
 
 // The plain answer goes to stdout; in --json mode the TurnDone goes to stderr after the events.
-fn write_answer(opts: &Options, done: &TurnDone) -> std::io::Result<()> {
+fn write_answer(opts: &ChatOptions, done: &TurnDone) -> std::io::Result<()> {
     if opts.json {
         let line = serde_json::to_string(done).map_err(std::io::Error::other)?;
         let mut err = std::io::stderr().lock();
@@ -264,7 +268,7 @@ fn write_answer(opts: &Options, done: &TurnDone) -> std::io::Result<()> {
     }
     let stdout = std::io::stdout();
     let mut out = stdout.lock();
-    out.write_all(done.content.as_bytes())?;
+    out.write_all(escape_model_text(&done.content).as_bytes())?;
     out.write_all(b"\n")?;
     out.flush()
 }

crates/bxctl/src/verify.rs

@@ -0,0 +1,90 @@
+//! Verifies the whole audit log under a home directory with `proto::ChainVerifier`, reading the
+//! files itself so it works when `brokerd` will not start.
+
+use std::io::Write;
+use std::path::Path;
+
+use proto::ChainVerifier;
+
+/// Verifies the whole audit log under `home` and prints the report to `out`.
+/// `Ok(true)`: the chain verifies. `Ok(false)`: it does not. `Err`: the log cannot be read.
+pub fn run(home: &Path, out: &mut dyn Write) -> std::io::Result<bool> {
+    let audit_dir = home.join("audit");
+    let mut names: Vec<String> = Vec::new();
+    let mut skipped: Vec<String> = Vec::new();
+    for entry in std::fs::read_dir(&audit_dir)? {
+        let entry = entry?;
+        let name = match entry.file_name().into_string() {
+            Ok(name) => name,
+            Err(raw) => {
+                skipped.push(raw.to_string_lossy().into_owned());
+                continue;
+            }
+        };
+        if proto::is_audit_log_name(&name) {
+            names.push(name);
+        } else if name.ends_with(".jsonl") {
+            // Looks like a log file but is not named as one: brokerd ignores it too. Say so, so
+            // that nobody takes "ok" to cover it.
+            skipped.push(name);
+        }
+    }
+    names.sort();
+
+    let mut verifier = ChainVerifier::new();
+    for name in &names {
+        let bytes = std::fs::read(audit_dir.join(name))?;
+        verifier.feed(name, &bytes);
+    }
+    let report = verifier.finish();
+
+    if let Some(failure) = &report.failure {
+        writeln!(out, "{}:{}: {}", failure.file, failure.line, failure.what)?;
+        writeln!(out, "see docs/runbook.md#audit-chain-broken")?;
+        write_skipped(out, &skipped)?;
+        return Ok(false);
+    }
+
+    let head = match report.head {
+        Some(hash) => format!("head {}", hash.to_hex()),
+        None => "head none".to_string(),
+    };
+    writeln!(out, "audit: ok, {} records, {}", report.records, head)?;
+    for loc in &report.recoveries {
+        writeln!(out, "recovered line: {}:{}", loc.file, loc.line)?;
+    }
+    for loc in &report.accepted_breaks {
+        writeln!(out, "accepted break: {}:{}", loc.file, loc.line)?;
+    }
+    for seq in &report.abandoned {
+        writeln!(out, "pending or abandoned: approval {}", seq)?;
+    }
+    for seq in &report.unfinished {
+        writeln!(out, "running or unfinished: decision {}", seq)?;
+    }
+    for loc in &report.clock_warnings {
+        writeln!(out, "clock went backwards: {}:{}", loc.file, loc.line)?;
+    }
+    if let Some(torn) = &report.torn_tail {
+        writeln!(
+            out,
+            "torn final line: {}:{} (brokerd recovers it at its next start)",
+            torn.at.file, torn.at.line
+        )?;
+    }
+    write_skipped(out, &skipped)?;
+    Ok(true)
+}
+
+/// One line per file in `audit/` that looks like a log but is not named as one; neither `brokerd`
+/// nor this check reads it. Names are escaped: a file name can hold anything.
+fn write_skipped(out: &mut dyn Write, skipped: &[String]) -> std::io::Result<()> {
+    for name in skipped {
+        writeln!(
+            out,
+            "not an audit log file, not checked: {}",
+            crate::escape::escape_json_text(name)
+        )?;
+    }
+    Ok(())
+}

crates/bxctl/tests/admin.rs

@@ -0,0 +1,497 @@
+//! Tests for `bxctl`'s admin client and the commands built on it, against a fake `brokerd`.
+//! Do not edit.
+
+mod support;
+
+use bxctl::admin::{
+    AdminError, cmd_approvals, cmd_approve, cmd_grants_check, cmd_refuse, list, reason_name,
+    request, write_block,
+};
+use proto::{
+    Approve, DecisionRecord, DenyReason, Empty, Envelope, ErrorCode, GrantProblem, GrantsReport,
+    Message, PROTOCOL_VERSION, Refuse,
+};
+use std::process::Command;
+use support::{brokerd_with, fake_brokerd, fake_brokerd_frames, pending, ts, wire_error};
+
+const BACKSLASH: char = '\\';
+
+/// The escape for one code point, built and never spelled out (see `tests/escape.rs`).
+fn esc(code: u32) -> String {
+    format!("{BACKSLASH}u{code:04x}")
+}
+
+fn text(out: Vec<u8>) -> String {
+    String::from_utf8(out).unwrap()
+}
+
+const ALLOWED: DecisionRecord = DecisionRecord::Allowed {};
+
+// ---- the client ----
+
+#[test]
+fn request_sends_one_final_frame_with_id_1_and_returns_the_answer() {
+    let fake = fake_brokerd_frames(|request| {
+        assert_eq!(request.v, PROTOCOL_VERSION);
+        assert_eq!(request.id, 1);
+        assert!(request.r#final);
+        vec![Envelope {
+            v: PROTOCOL_VERSION,
+            id: 1,
+            r#final: true,
+            msg: Message::Ok(Empty {}),
+        }]
+    });
+    let answer = request(&fake.socket, Message::CheckGrants(Empty {})).unwrap();
+    assert_eq!(answer, Message::Ok(Empty {}));
+    assert_eq!(fake.requests(), vec![Message::CheckGrants(Empty {})]);
+}
+
+#[test]
+fn an_error_frame_is_refused_with_its_code_and_detail() {
+    let fake = fake_brokerd(|_| wire_error(ErrorCode::Forbidden, "not on this socket"));
+    match request(&fake.socket, Message::Approvals(Empty {})) {
+        Err(AdminError::Refused(w)) => {
+            assert_eq!(w.code, ErrorCode::Forbidden);
+            assert_eq!(w.detail, "not on this socket");
+        }
+        other => panic!("{other:?}"),
+    }
+    let e = request(&fake.socket, Message::Approvals(Empty {})).unwrap_err();
+    assert_eq!(e.to_string(), "forbidden: not on this socket");
+}
+
+#[test]
+fn an_answer_that_is_not_final_or_has_another_id_is_a_protocol_error() {
+    let not_final = fake_brokerd_frames(|request| {
+        vec![Envelope {
+            v: PROTOCOL_VERSION,
+            id: request.id,
+            r#final: false,
+            msg: Message::Ok(Empty {}),
+        }]
+    });
+    assert!(matches!(
+        request(&not_final.socket, Message::Approvals(Empty {})),
+        Err(AdminError::Protocol(_))
+    ));
+    let other_id = fake_brokerd_frames(|request| {
+        vec![Envelope {
+            v: PROTOCOL_VERSION,
+            id: request.id + 1,
+            r#final: true,
+            msg: Message::Ok(Empty {}),
+        }]
+    });
+    assert!(matches!(
+        request(&other_id.socket, Message::Approvals(Empty {})),
+        Err(AdminError::Protocol(_))
+    ));
+}
+
+#[test]
+fn a_connection_closed_without_an_answer_is_a_frame_error() {
+    let fake = fake_brokerd_frames(|_| Vec::new());
+    assert!(matches!(
+        request(&fake.socket, Message::Approvals(Empty {})),
+        Err(AdminError::Frame(_))
+    ));
+}
+
+#[test]
+fn no_brokerd_is_a_connect_error_that_names_the_socket() {
+    let missing = support::temp_socket("nobody-listens.sock");
+    let e = request(&missing, Message::Approvals(Empty {})).unwrap_err();
+    assert!(matches!(e, AdminError::Connect(_, _)), "{e:?}");
+    let message = e.to_string();
+    assert!(message.starts_with("cannot reach brokerd at "), "{message}");
+    assert!(message.contains(missing.to_str().unwrap()), "{message}");
+}
+
+#[test]
+fn list_returns_the_items_and_rejects_any_other_kind() {
+    let items = vec![pending(41, "shell", "{}"), pending(44, "read_file", "{}")];
+    let fake = brokerd_with(items.clone(), ALLOWED);
+    assert_eq!(list(&fake.socket).unwrap(), items);
+    assert_eq!(fake.requests(), vec![Message::Approvals(Empty {})]);
+
+    let wrong = fake_brokerd(|_| Message::Ok(Empty {}));
+    assert!(matches!(list(&wrong.socket), Err(AdminError::Protocol(_))));
+}
+
+#[test]
+fn reason_names_are_the_wire_names() {
+    for reason in [
+        DenyReason::NoGrant,
+        DenyReason::GrantExpired,
+        DenyReason::TaintTooHigh,
+        DenyReason::DeniedByGrant,
+        DenyReason::ApprovalRefused,
+        DenyReason::ApprovalExpired,
+        DenyReason::GrantsInvalid,
+        DenyReason::AuditUnavailable,
+        DenyReason::InvalidArguments,
+        DenyReason::StateUnreadable,
+    ] {
+        let wire = serde_json::to_string(&reason).unwrap();
+        assert_eq!(format!("\"{}\"", reason_name(reason)), wire);
+    }
+}
+
+// ---- the block ----
+
+fn block(item: &proto::PendingApproval, now: &str) -> String {
+    let mut out = Vec::new();
+    write_block(&mut out, item, ts(now)).unwrap();
+    text(out)
+}
+
+#[test]
+fn the_block_is_two_lines_in_this_exact_form() {
+    let item = pending(
+        41,
+        "shell",
+        r#"{"command":"rm -rf /home/kyle/scratch/build","cwd":"/home/kyle/scratch"}"#,
+    );
+    assert_eq!(
+        block(&item, "2026-09-18T12:02:00.000Z"),
+        concat!(
+            "41  2 min ago  expires in 13 min  session chat-1758…  grant shell-scratch  taint private\n",
+            "    shell {\"command\":\"rm -rf /home/kyle/scratch/build\",\"cwd\":\"/home/kyle/scratch\"}\n",
+        )
+    );
+}
+
+#[test]
+fn times_are_whole_seconds_minutes_or_hours_rounded_down() {
+    let item = pending(41, "shell", "{}");
+    let first = |now: &str| block(&item, now).lines().next().unwrap().to_string();
+    // created 12:00:00, expires 12:15:00
+    assert!(first("2026-09-18T12:00:00.000Z").starts_with("41  0 s ago  expires in 15 min  "));
+    assert!(first("2026-09-18T12:00:59.999Z").starts_with("41  59 s ago  expires in 14 min  "));
+    assert!(first("2026-09-18T12:01:00.000Z").starts_with("41  1 min ago  expires in 14 min  "));
+    assert!(first("2026-09-18T12:14:30.000Z").starts_with("41  14 min ago  expires in 30 s  "));
+    // At or after `expires` there is nothing left to wait for.
+    assert!(first("2026-09-18T12:15:00.000Z").starts_with("41  15 min ago  expired  "));
+    assert!(first("2026-09-18T14:05:00.000Z").starts_with("41  2 h ago  expired  "));
+    // A clock that is behind the broker's must not underflow.
+    assert!(first("2026-09-18T11:59:00.000Z").starts_with("41  0 s ago  expires in 16 min  "));
+
+    let mut long = pending(41, "shell", "{}");
+    long.expires = ts("2026-09-18T15:30:00.000Z");
+    assert!(block(&long, "2026-09-18T12:00:00.000Z").starts_with("41  0 s ago  expires in 3 h  "));
+}
+
+#[test]
+fn a_session_id_longer_than_ten_characters_is_cut_to_nine_and_an_ellipsis() {
+    let mut item = pending(41, "shell", "{}");
+    for (id, shown) in [
+        ("s1", "session s1  "),
+        ("abcdefghij", "session abcdefghij  "),
+        ("abcdefghijk", "session abcdefghi…  "),
+    ] {
+        item.session = proto::SessionId::new(id).unwrap();
+        let got = block(&item, "2026-09-18T12:00:00.000Z");
+        assert!(got.contains(shown), "{id}: {got}");
+    }
+}
+
+#[test]
+fn taint_is_the_wire_name() {
+    let mut item = pending(41, "shell", "{}");
+    item.taint = proto::DataClass::Secret;
+    assert!(block(&item, "2026-09-18T12:00:00.000Z").contains("  taint secret\n"));
+}
+
+/// Whatever `brokerd` sends is printed as data: tool, grant and arguments all go through
+/// `escape_json_text`.
+#[test]
+fn nothing_in_the_block_reaches_the_terminal_raw() {
+    let rlo = char::from_u32(0x202e).unwrap();
+    let zwsp = char::from_u32(0x200b).unwrap();
+    let isolate = char::from_u32(0x2066).unwrap();
+    let arguments =
+        format!("{{\"path\":\"/home/kyle/notes/{rlo}dm.terces{zwsp}{isolate}\x1b[8m\x1b[2J\"}}");
+    let mut item = pending(41, "read\x1b[1mfile", &arguments);
+    item.grant = "notes\nread".to_string();
+    let got = block(&item, "2026-09-18T12:00:00.000Z");
+    for c in ['\x1b', rlo, zwsp, isolate] {
+        assert!(!got.contains(c), "U+{:04X} in {got:?}", u32::from(c));
+    }
+    assert_eq!(got.matches('\n').count(), 2, "still two lines: {got:?}");
+    assert!(
+        got.contains(&format!(
+            "/home/kyle/notes/{}dm.terces{}{}{}[8m{}[2J",
+            esc(0x202e),
+            esc(0x200b),
+            esc(0x2066),
+            esc(0x1b),
+            esc(0x1b)
+        )),
+        "{got:?}"
+    );
+    assert!(
+        got.contains(&format!("    read{}[1mfile ", esc(0x1b))),
+        "{got:?}"
+    );
+    assert!(
+        got.contains(&format!("grant notes{}read  ", esc(0x0a))),
+        "{got:?}"
+    );
+}
+
+// ---- the commands ----
+
+#[test]
+fn approvals_prints_one_block_per_item_in_the_order_given() {
+    let fake = brokerd_with(
+        vec![
+            pending(41, "shell", r#"{"command":"ls"}"#),
+            pending(44, "read_file", r#"{"path":"/home/kyle/notes/a.md"}"#),
+        ],
+        ALLOWED,
+    );
+    let mut out = Vec::new();
+    let ok = cmd_approvals(&fake.socket, ts("2026-09-18T12:02:00.000Z"), &mut out).unwrap();
+    assert!(ok);
+    let got = text(out);
+    let lines: Vec<&str> = got.lines().collect();
+    assert_eq!(lines.len(), 4, "{got}");
+    assert!(lines[0].starts_with("41  2 min ago  "), "{got}");
+    assert_eq!(lines[1], r#"    shell {"command":"ls"}"#);
+    assert!(lines[2].starts_with("44  2 min ago  "), "{got}");
+    assert_eq!(
+        lines[3],
+        r#"    read_file {"path":"/home/kyle/notes/a.md"}"#
+    );
+}
+
+#[test]
+fn approvals_with_nothing_pending_says_so() {
+    let fake = brokerd_with(Vec::new(), ALLOWED);
+    let mut out = Vec::new();
+    assert!(cmd_approvals(&fake.socket, ts("2026-09-18T12:00:00.000Z"), &mut out).unwrap());
+    assert_eq!(text(out), "no pending approvals\n");
+}
+
+#[test]
+fn approve_reports_the_re_decision() {
+    // `ask` and `allowed` both let the call run; only a denial stops it.
+    for (outcome, line, ok) in [
+        (DecisionRecord::Allowed {}, "approved 41: runs\n", true),
+        (DecisionRecord::Ask {}, "approved 41: runs\n", true),
+        (
+            DecisionRecord::Denied {
+                reason: DenyReason::NoGrant,
+            },
+            "approved 41: denied (no_grant)\n",
+            false,
+        ),
+        (
+            DecisionRecord::Denied {
+                reason: DenyReason::TaintTooHigh,
+            },
+            "approved 41: denied (taint_too_high)\n",
+            false,
+        ),
+        (
+            DecisionRecord::Denied {
+                reason: DenyReason::AuditUnavailable,
+            },
+            "approved 41: denied (audit_unavailable)\n",
+            false,
+        ),
+    ] {
+        let fake = brokerd_with(vec![pending(41, "shell", "{}")], outcome);
+        let mut out = Vec::new();
+        assert_eq!(cmd_approve(&fake.socket, 41, &mut out).unwrap(), ok);
+        assert_eq!(text(out), line);
+        assert_eq!(
+            fake.requests(),
+            vec![Message::Approve(Approve { approval: 41 })]
+        );
+    }
+}
+
+#[test]
+fn refuse_sends_the_reason_when_there_is_one() {
+    for reason in [None, Some("not on a Friday")] {
+        let fake = brokerd_with(vec![pending(41, "shell", "{}")], ALLOWED);
+        let mut out = Vec::new();
+        assert!(cmd_refuse(&fake.socket, 41, reason, &mut out).unwrap());
+        assert_eq!(text(out), "refused 41\n");
+        assert_eq!(
+            fake.requests(),
+            vec![Message::Refuse(Refuse {
+                approval: 41,
+                reason: reason.map(str::to_string)
+            })]
+        );
+    }
+}
+
+#[test]
+fn an_unknown_or_answered_id_is_reported_the_same_way_by_both() {
+    let fake = brokerd_with(vec![pending(41, "shell", "{}")], ALLOWED);
+    let want = "99: no such approval (already answered or expired)\n";
+    let mut out = Vec::new();
+    assert!(!cmd_approve(&fake.socket, 99, &mut out).unwrap());
+    assert_eq!(text(out), want);
+    let mut out = Vec::new();
+    assert!(!cmd_refuse(&fake.socket, 99, None, &mut out).unwrap());
+    assert_eq!(text(out), want);
+}
+
+/// Every exit of every command: any other error frame is an error, and so is an answer of the
+/// wrong kind. Nothing is printed for them.
+#[test]
+fn other_errors_and_wrong_kinds_are_errors_for_every_command() {
+    let refused = fake_brokerd(|_| wire_error(ErrorCode::Internal, "boom"));
+    let wrong = fake_brokerd(|_| {
+        Message::GrantsReport(GrantsReport {
+            problems: Vec::new(),
+        })
+    });
+    let wrong_for_grants = fake_brokerd(|_| Message::Ok(Empty {}));
+    let now = ts("2026-09-18T12:00:00.000Z");
+
+    let mut out = Vec::new();
+    assert!(matches!(
+        cmd_approvals(&refused.socket, now, &mut out),
+        Err(AdminError::Refused(_))
+    ));
+    assert!(matches!(
+        cmd_approve(&refused.socket, 41, &mut out),
+        Err(AdminError::Refused(_))
+    ));
+    assert!(matches!(
+        cmd_refuse(&refused.socket, 41, None, &mut out),
+        Err(AdminError::Refused(_))
+    ));
+    assert!(matches!(
+        cmd_grants_check(&refused.socket, &mut out),
+        Err(AdminError::Refused(_))
+    ));
+    assert!(matches!(
+        cmd_approvals(&wrong.socket, now, &mut out),
+        Err(AdminError::Protocol(_))
+    ));
+    assert!(matches!(
+        cmd_approve(&wrong.socket, 41, &mut out),
+        Err(AdminError::Protocol(_))
+    ));
+    assert!(matches!(
+        cmd_refuse(&wrong.socket, 41, None, &mut out),
+        Err(AdminError::Protocol(_))
+    ));
+    assert!(matches!(
+        cmd_grants_check(&wrong_for_grants.socket, &mut out),
+        Err(AdminError::Protocol(_))
+    ));
+    assert_eq!(text(out), "", "an error prints nothing on the output");
+}
+
+#[test]
+fn grants_check_prints_ok_or_every_problem() {
+    let fine = fake_brokerd(|_| {
+        Message::GrantsReport(GrantsReport {
+            problems: Vec::new(),
+        })
+    });
+    let mut out = Vec::new();
+    assert!(cmd_grants_check(&fine.socket, &mut out).unwrap());
+    assert_eq!(text(out), "grants: ok\n");
+    assert_eq!(fine.requests(), vec![Message::CheckGrants(Empty {})]);
+
+    let broken = fake_brokerd(|_| {
+        Message::GrantsReport(GrantsReport {
+            problems: vec![
+                GrantProblem {
+                    file: "notes-read.toml".to_string(),
+                    line: Some(3),
+                    problem: "unknown field `mod`".to_string(),
+                },
+                GrantProblem {
+                    file: "Bad Name.toml".to_string(),
+                    line: None,
+                    problem: "the file name is not a valid grant id".to_string(),
+                },
+                GrantProblem {
+                    file: "x.toml".to_string(),
+                    line: Some(1),
+                    problem: "two\nlines".to_string(),
+                },
+            ],
+        })
+    });
+    let mut out = Vec::new();
+    assert!(!cmd_grants_check(&broken.socket, &mut out).unwrap());
+    assert_eq!(
+        text(out),
+        format!(
+            "notes-read.toml:3: unknown field `mod`\n\
+             Bad Name.toml: the file name is not a valid grant id\n\
+             x.toml:1: two{}lines\n",
+            esc(0x0a)
+        ),
+        "every problem, one line each; file and problem go through escape_json_text"
+    );
+}
+
+// ---- the binary ----
+
+fn bxctl(args: &[&str], socket: &std::path::Path) -> std::process::Output {
+    Command::new(env!("CARGO_BIN_EXE_bxctl"))
+        .args(args)
+        .arg("--admin-socket")
+        .arg(socket)
+        .output()
+        .unwrap()
+}
+
+#[test]
+fn the_binary_prints_on_stdout_and_sets_the_exit_status() {
+    let fake = brokerd_with(
+        vec![pending(41, "shell", r#"{"command":"ls"}"#)],
+        DecisionRecord::Denied {
+            reason: DenyReason::DeniedByGrant,
+        },
+    );
+    let output = bxctl(&["approvals"], &fake.socket);
+    assert_eq!(output.status.code(), Some(0));
+    let stdout = String::from_utf8_lossy(&output.stdout);
+    assert!(
+        stdout.ends_with("    shell {\"command\":\"ls\"}\n"),
+        "{stdout}"
+    );
+
+    let output = bxctl(&["approve", "41"], &fake.socket);
+    assert_eq!(output.status.code(), Some(1));
+    assert_eq!(
+        String::from_utf8_lossy(&output.stdout),
+        "approved 41: denied (denied_by_grant)\n"
+    );
+
+    let output = bxctl(&["refuse", "41", "--reason", "no"], &fake.socket);
+    assert_eq!(output.status.code(), Some(0));
+    assert_eq!(String::from_utf8_lossy(&output.stdout), "refused 41\n");
+
+    let output = bxctl(&["refuse", "7"], &fake.socket);
+    assert_eq!(output.status.code(), Some(1));
+    assert_eq!(
+        String::from_utf8_lossy(&output.stdout),
+        "7: no such approval (already answered or expired)\n"
+    );
+}
+
+#[test]
+fn the_binary_reports_an_error_on_stderr_with_status_1() {
+    let fake = fake_brokerd(|_| wire_error(ErrorCode::Internal, "boom"));
+    let output = bxctl(&["grants", "check"], &fake.socket);
+    assert_eq!(output.status.code(), Some(1));
+    assert_eq!(String::from_utf8_lossy(&output.stdout), "");
+    assert_eq!(
+        String::from_utf8_lossy(&output.stderr),
+        "bxctl: internal: boom\n"
+    );
+}

crates/bxctl/tests/admin_timeout.rs

@@ -0,0 +1,42 @@
+//! A `brokerd` that accepts and never answers does not hang `bxctl` (M3a review finding 9).
+
+use std::os::unix::net::UnixListener;
+use std::time::{Duration, Instant};
+
+use bxctl::admin::{ADMIN_TIMEOUT, request_with_timeout};
+use proto::{Empty, Message};
+
+#[test]
+fn the_default_is_thirty_seconds() {
+    assert_eq!(ADMIN_TIMEOUT, Duration::from_secs(30));
+}
+
+#[test]
+fn a_silent_brokerd_is_an_error_after_the_timeout() {
+    let dir = std::env::temp_dir().join(format!("bx-admin-timeout-{}", std::process::id()));
+    let _ = std::fs::remove_dir_all(&dir);
+    std::fs::create_dir_all(&dir).unwrap();
+    let socket = dir.join("admin.sock");
+    let listener = UnixListener::bind(&socket).unwrap();
+    let held = std::thread::spawn(move || {
+        let (stream, _) = listener.accept().unwrap();
+        std::thread::sleep(Duration::from_millis(2_000));
+        drop(stream);
+    });
+
+    let started = Instant::now();
+    let got = request_with_timeout(
+        &socket,
+        Message::Approvals(Empty {}),
+        Duration::from_millis(200),
+    );
+    let took = started.elapsed();
+    let text = got.expect_err("a silent brokerd is an error").to_string();
+    assert!(
+        text.contains("whether it acted is unknown"),
+        "brokerd may have approved and run the call before going quiet: {text}"
+    );
+    assert!(took < Duration::from_millis(1_500), "waited {took:?}");
+    held.join().unwrap();
+    let _ = std::fs::remove_dir_all(&dir);
+}

crates/bxctl/tests/args_os.rs

@@ -0,0 +1,19 @@
+//! An argument that is not UTF-8 is a usage error, not a panic (M3a review finding 7).
+
+use std::ffi::OsStr;
+use std::os::unix::ffi::OsStrExt;
+use std::process::Command;
+
+#[test]
+fn an_argument_that_is_not_utf8_is_a_usage_error() {
+    let out = Command::new(env!("CARGO_BIN_EXE_bxctl"))
+        .args([OsStr::new("approve"), OsStr::from_bytes(b"4\xff")])
+        .output()
+        .unwrap();
+    assert_eq!(out.status.code(), Some(2));
+    let err = String::from_utf8_lossy(&out.stderr);
+    assert!(
+        err.starts_with("bxctl: an argument is not valid UTF-8"),
+        "{err}"
+    );
+}

crates/bxctl/tests/chat_approvals.rs

@@ -0,0 +1,487 @@
+//! Tests for approvals in `bxctl chat`, against a fake `loopd` and a fake `brokerd`. Do not edit.
+//!
+//! What the owner is shown comes from `brokerd`, never from `loopd`'s event, and only the
+//! approval's id, typed in full, approves.
+
+mod support;
+
+use bxctl::chat::{Approvals, OnPending, Printer, TurnIo, handle_pending, stream_turn};
+use proto::{
+    Approve, DecisionRecord, Empty, ErrorCode, Message, Refuse, SessionId, Timestamp, TurnEvent,
+};
+use std::io::{BufRead, Cursor, Write};
+use std::path::Path;
+use std::process::{Command, Stdio};
+use support::{FakeBrokerd, brokerd_with, fake_brokerd, fake_loopd, pending, ts, wire_error};
+
+const BACKSLASH: char = '\\';
+const NOW: &str = "2026-09-18T12:02:00.000Z";
+const PROMPT: &str = "type 41 to approve, anything else refuses: ";
+
+/// The escape for one code point, built and never spelled out (see `tests/escape.rs`).
+fn esc(code: u32) -> String {
+    format!("{BACKSLASH}u{code:04x}")
+}
+
+fn approvals_request() -> Message {
+    Message::Approvals(Empty {})
+}
+
+fn approve_request() -> Message {
+    Message::Approve(Approve { approval: 41 })
+}
+
+fn refuse_request() -> Message {
+    Message::Refuse(Refuse {
+        approval: 41,
+        reason: None,
+    })
+}
+
+/// A `brokerd` with approval 41 pending, for `shell`.
+fn broker() -> FakeBrokerd {
+    brokerd_with(
+        vec![pending(41, "shell", r#"{"command":"ls"}"#)],
+        DecisionRecord::Allowed {},
+    )
+}
+
+/// Runs `handle_pending` for approval 41 with `typed` waiting on stdin. Returns what was
+/// printed and what was left unread.
+fn handle(socket: &Path, ask: bool, typed: &str) -> (String, String) {
+    let mut input = Cursor::new(typed.as_bytes().to_vec());
+    let mut out = Vec::new();
+    handle_pending(socket, 41, ask, ts(NOW), &mut input, &mut out).unwrap();
+    let mut left = String::new();
+    std::io::Read::read_to_string(&mut input, &mut left).unwrap();
+    (String::from_utf8(out).unwrap(), left)
+}
+
+// ---- handle_pending ----
+
+#[test]
+fn the_block_then_the_question_and_the_id_approves() {
+    let fake = broker();
+    let (out, left) = handle(&fake.socket, true, "41\n");
+    assert_eq!(
+        out,
+        format!(
+            "\x1b[0m41  2 min ago  expires in 13 min  session chat-1758…  grant shell-scratch  \
+             taint private\n    shell {{\"command\":\"ls\"}}\n{PROMPT}approved 41: runs\n"
+        ),
+        "attributes reset, the block, the question, the outcome"
+    );
+    assert_eq!(left, "");
+    assert_eq!(
+        fake.requests(),
+        vec![approvals_request(), approve_request()]
+    );
+}
+
+#[test]
+fn the_id_with_a_carriage_return_also_approves() {
+    let fake = broker();
+    handle(&fake.socket, true, "41\r\n");
+    assert_eq!(
+        fake.requests(),
+        vec![approvals_request(), approve_request()]
+    );
+}
+
+/// Everything that is not exactly the id refuses: `y`, a near miss, an empty line, the end of
+/// the input.
+#[test]
+fn anything_else_refuses() {
+    for typed in [
+        "y\n",
+        "Y\n",
+        "yes\n",
+        "\n",
+        "",
+        " 41\n",
+        "41 \n",
+        "041\n",
+        "+41\n",
+        "4 1\n",
+        "42\n",
+        "approve 41\n",
+        "41",
+    ] {
+        let fake = broker();
+        let (out, _) = handle(&fake.socket, true, typed);
+        if typed == "41" {
+            // The last line of the input need not end in a newline; it is still the id.
+            assert_eq!(
+                fake.requests(),
+                vec![approvals_request(), approve_request()]
+            );
+            continue;
+        }
+        assert_eq!(
+            fake.requests(),
+            vec![approvals_request(), refuse_request()],
+            "{typed:?}"
+        );
+        assert!(
+            out.ends_with(&format!("{PROMPT}refused 41\n")),
+            "{typed:?}: {out:?}"
+        );
+    }
+}
+
+/// A line typed while the turn ran is already waiting when the question is asked. It is the
+/// answer, it is not the id, so it refuses; and only that one line is read.
+#[test]
+fn a_line_already_waiting_refuses_and_only_one_line_is_read() {
+    let fake = broker();
+    let (_, left) = handle(&fake.socket, true, "are you still there?\n41\n");
+    assert_eq!(fake.requests(), vec![approvals_request(), refuse_request()]);
+    assert_eq!(left, "41\n", "the next line is left for the chat");
+}
+
+#[test]
+fn an_id_that_is_not_listed_is_no_longer_pending_and_nothing_is_asked() {
+    let fake = brokerd_with(
+        vec![pending(40, "shell", "{}"), pending(42, "shell", "{}")],
+        DecisionRecord::Allowed {},
+    );
+    let (out, left) = handle(&fake.socket, true, "41\n");
+    assert_eq!(out, "approval 41 is no longer pending\n");
+    assert_eq!(left, "41\n", "nothing was read");
+    assert_eq!(fake.requests(), vec![approvals_request()]);
+}
+
+#[test]
+fn without_ask_the_block_is_shown_and_nothing_is_asked_or_read() {
+    let fake = broker();
+    let (out, left) = handle(&fake.socket, false, "41\n");
+    assert!(out.starts_with("\x1b[0m41  2 min ago  "), "{out:?}");
+    assert!(out.ends_with("    shell {\"command\":\"ls\"}\n"), "{out:?}");
+    assert!(!out.contains("to approve"), "{out:?}");
+    assert_eq!(left, "41\n");
+    assert_eq!(fake.requests(), vec![approvals_request()]);
+}
+
+#[test]
+fn a_brokerd_that_cannot_be_reached_is_reported_and_nothing_is_asked() {
+    let missing = support::temp_socket("nobody-listens.sock");
+    let (out, left) = handle(&missing, true, "41\n");
+    assert!(
+        out.starts_with("approval 41: cannot ask brokerd: cannot reach brokerd at "),
+        "{out:?}"
+    );
+    assert!(out.ends_with('\n') && out.lines().count() == 1, "{out:?}");
+    assert_eq!(left, "41\n");
+}
+
+/// The approval can expire between the list and the answer.
+#[test]
+fn an_answer_that_comes_too_late_is_reported() {
+    let fake = fake_brokerd(|msg| match msg {
+        Message::Approvals(_) => Message::ApprovalList(proto::ApprovalList {
+            items: vec![pending(41, "shell", "{}")],
+        }),
+        _ => wire_error(ErrorCode::NoSuchApproval, "no such approval"),
+    });
+    let (out, _) = handle(&fake.socket, true, "41\n");
+    assert!(
+        out.ends_with(&format!(
+            "{PROMPT}41: no such approval (already answered or expired)\n"
+        )),
+        "{out:?}"
+    );
+    let (out, _) = handle(&fake.socket, true, "no\n");
+    assert!(
+        out.ends_with(&format!(
+            "{PROMPT}41: no such approval (already answered or expired)\n"
+        )),
+        "{out:?}"
+    );
+}
+
+/// Any other failure of the answer is reported on one line, and the turn goes on: the call is
+/// still pending at `brokerd`, and `bxctl approve` from another terminal can answer it.
+#[test]
+fn an_answer_that_fails_is_reported_and_is_not_an_error() {
+    let fake = fake_brokerd(|msg| match msg {
+        Message::Approvals(_) => Message::ApprovalList(proto::ApprovalList {
+            items: vec![pending(41, "shell", "{}")],
+        }),
+        _ => wire_error(ErrorCode::Internal, "boom"),
+    });
+    let (out, _) = handle(&fake.socket, true, "41\n");
+    assert!(
+        out.ends_with(&format!("{PROMPT}approval 41: internal: boom\n")),
+        "{out:?}"
+    );
+}
+
+/// What `brokerd` sends is printed as data here too.
+#[test]
+fn the_block_in_chat_is_escaped() {
+    let rlo = char::from_u32(0x202e).unwrap();
+    let arguments = format!("{{\"path\":\"/home/kyle/{rlo}dm\x1b[8m\"}}");
+    let fake = brokerd_with(
+        vec![pending(41, "read_file", &arguments)],
+        DecisionRecord::Allowed {},
+    );
+    let (out, _) = handle(&fake.socket, false, "");
+    assert_eq!(out.matches('\x1b').count(), 1, "only the reset: {out:?}");
+    assert!(!out.contains(rlo), "{out:?}");
+    assert!(
+        out.contains(&format!("/home/kyle/{}dm{}[8m", esc(0x202e), esc(0x1b))),
+        "{out:?}"
+    );
+}
+
+struct Broken;
+
+impl Write for Broken {
+    fn write(&mut self, _: &[u8]) -> std::io::Result<usize> {
+        Err(std::io::Error::other("the terminal went away"))
+    }
+    fn flush(&mut self) -> std::io::Result<()> {
+        Err(std::io::Error::other("the terminal went away"))
+    }
+}
+
+/// Every write can fail, and none is ignored: not the "no longer pending" line, not the block,
+/// not the question. Nothing is approved for an owner who was shown nothing.
+#[test]
+fn a_failed_write_is_an_error_and_nothing_is_answered() {
+    let fake = broker();
+    let mut input = Cursor::new(b"41\n".to_vec());
+    assert!(handle_pending(&fake.socket, 41, true, ts(NOW), &mut input, &mut Broken).is_err());
+    assert_eq!(fake.requests(), vec![approvals_request()]);
+
+    let none = brokerd_with(Vec::new(), DecisionRecord::Allowed {});
+    let mut input = Cursor::new(Vec::new());
+    assert!(handle_pending(&none.socket, 41, true, ts(NOW), &mut input, &mut Broken).is_err());
+}
+
+// ---- stream_turn ----
+
+fn pending_event(tool: &str) -> TurnEvent {
+    TurnEvent::ApprovalPending {
+        approval: 41,
+        tool: tool.to_string(),
+        expires: Timestamp::parse("2026-09-18T12:15:00.000Z").unwrap(),
+    }
+}
+
+/// Runs one turn against a fake `loopd` that sends `events`. Returns what was printed.
+fn turn(
+    events: Vec<TurnEvent>,
+    admin_socket: &Path,
+    on_pending: OnPending,
+    json: bool,
+    typed: &str,
+) -> String {
+    let loopd = fake_loopd(events, "done");
+    let mut printer = Printer::new(true, json);
+    let mut input: Box<dyn BufRead> = Box::new(Cursor::new(typed.as_bytes().to_vec()));
+    let mut out = Vec::new();
+    let approvals = Approvals {
+        admin_socket,
+        on_pending,
+    };
+    let mut io = TurnIo {
+        printer: &mut printer,
+        input: &mut *input,
+        out: &mut out,
+    };
+    let done = stream_turn(
+        &loopd.socket,
+        &SessionId::new("s1").unwrap(),
+        "go",
+        false,
+        &approvals,
+        &mut io,
+    )
+    .unwrap()
+    .unwrap();
+    assert_eq!(done.content, "done");
+    String::from_utf8(out).unwrap()
+}
+
+/// A compromised `loopd` must not choose what the owner sees: the event says `read_file`, the
+/// broker's entry says `shell`, and the block says `shell`.
+#[test]
+fn the_block_comes_from_brokerd_not_from_the_event() {
+    let fake = broker();
+    let out = turn(
+        vec![pending_event("read_file")],
+        &fake.socket,
+        OnPending::Ask,
+        false,
+        "41\n",
+    );
+    assert!(out.contains("    shell {\"command\":\"ls\"}\n"), "{out:?}");
+    assert!(!out.contains("read_file"), "{out:?}");
+    assert_eq!(
+        fake.requests(),
+        vec![approvals_request(), approve_request()]
+    );
+}
+
+#[test]
+fn the_turn_goes_on_after_the_answer() {
+    let fake = broker();
+    let out = turn(
+        vec![
+            TurnEvent::Reasoning {
+                text: "hm".to_string(),
+            },
+            pending_event("shell"),
+            TurnEvent::Content {
+                text: "It ran.".to_string(),
+            },
+        ],
+        &fake.socket,
+        OnPending::Ask,
+        false,
+        "41\n",
+    );
+    assert!(
+        out.starts_with("\x1b[2mhm\x1b[0m\n\x1b[0m41  "),
+        "reasoning is ended before the block: {out:?}"
+    );
+    assert!(out.ends_with("approved 41: runs\nIt ran."), "{out:?}");
+}
+
+#[test]
+fn show_prints_the_block_and_answers_nothing() {
+    let fake = broker();
+    let out = turn(
+        vec![pending_event("shell")],
+        &fake.socket,
+        OnPending::Show,
+        false,
+        "41\n",
+    );
+    assert!(out.contains("    shell {\"command\":\"ls\"}\n"), "{out:?}");
+    assert!(!out.contains("to approve"), "{out:?}");
+    assert_eq!(fake.requests(), vec![approvals_request()]);
+}
+
+#[test]
+fn event_only_prints_the_json_line_and_never_asks_brokerd() {
+    let fake = broker();
+    let out = turn(
+        vec![pending_event("shell")],
+        &fake.socket,
+        OnPending::EventOnly,
+        true,
+        "41\n",
+    );
+    let lines: Vec<&str> = out.lines().collect();
+    assert_eq!(lines.len(), 1, "{out:?}");
+    let event: serde_json::Value = serde_json::from_str(lines[0]).unwrap();
+    assert_eq!(event["event"], "approval_pending");
+    assert_eq!(event["approval"], 41);
+    assert_eq!(fake.requests(), Vec::<Message>::new());
+}
+
+// ---- the binary ----
+
+fn chat(loopd: &Path, brokerd: &Path, extra: &[&str], typed: &str) -> std::process::Output {
+    let mut child = Command::new(env!("CARGO_BIN_EXE_bxctl"))
+        .args(["chat", "--socket"])
+        .arg(loopd)
+        .arg("--admin-socket")
+        .arg(brokerd)
+        .args(extra)
+        .stdin(Stdio::piped())
+        .stdout(Stdio::piped())
+        .stderr(Stdio::piped())
+        .spawn()
+        .unwrap();
+    {
+        let mut stdin = child.stdin.take().unwrap();
+        stdin.write_all(typed.as_bytes()).unwrap();
+    }
+    child.wait_with_output().unwrap()
+}
+
+/// With a pipe, everything typed is in the reader's buffer before the first turn is sent. The
+/// approval's answer must come from that same reader: a second reader on stdin would see the
+/// end of the input, and refuse.
+#[test]
+fn interactive_mode_reads_the_answer_from_the_same_input_as_the_chat() {
+    let loopd = fake_loopd(vec![pending_event("shell")], "ok");
+    let fake = broker();
+    let output = chat(&loopd.socket, &fake.socket, &[], "go\n41\n/quit\n");
+    assert!(output.status.success());
+    assert_eq!(
+        fake.requests(),
+        vec![approvals_request(), approve_request()]
+    );
+    assert_eq!(
+        *loopd.turns.lock().unwrap(),
+        vec!["go".to_string()],
+        "the answer was not sent to the model as a message"
+    );
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    assert!(stderr.contains(PROMPT), "{stderr}");
+    assert!(stderr.contains("approved 41: runs"), "{stderr}");
+}
+
+#[test]
+fn interactive_mode_refuses_on_a_stray_line() {
+    let loopd = fake_loopd(vec![pending_event("shell")], "ok");
+    let fake = broker();
+    let output = chat(&loopd.socket, &fake.socket, &[], "go\ny\n/quit\n");
+    assert!(output.status.success());
+    assert_eq!(fake.requests(), vec![approvals_request(), refuse_request()]);
+    assert_eq!(*loopd.turns.lock().unwrap(), vec!["go".to_string()]);
+}
+
+#[test]
+fn say_shows_the_block_and_answers_nothing() {
+    let loopd = fake_loopd(vec![pending_event("read_file")], "ok");
+    let fake = broker();
+    let output = chat(&loopd.socket, &fake.socket, &["--say", "go"], "41\n");
+    assert!(output.status.success());
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    assert!(
+        stderr.contains("    shell {\"command\":\"ls\"}\n"),
+        "{stderr}"
+    );
+    assert!(!stderr.contains("to approve"), "{stderr}");
+    assert_eq!(fake.requests(), vec![approvals_request()]);
+}
+
+#[test]
+fn json_prints_only_json_and_never_asks_brokerd() {
+    let loopd = fake_loopd(vec![pending_event("shell")], "ok");
+    let fake = broker();
+    let output = chat(
+        &loopd.socket,
+        &fake.socket,
+        &["--json", "--say", "go"],
+        "41\n",
+    );
+    assert!(output.status.success());
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    for line in stderr.lines() {
+        assert!(
+            serde_json::from_str::<serde_json::Value>(line).is_ok(),
+            "not JSON: {line}"
+        );
+    }
+    assert_eq!(stderr.lines().count(), 2, "the event and the done frame");
+    assert_eq!(fake.requests(), Vec::<Message>::new());
+}
+
+/// The answer on stdout is the model's text too.
+#[test]
+fn the_answer_on_stdout_is_printed_as_data() {
+    let loopd = fake_loopd(Vec::new(), "a\x1b[8mb\n\tc");
+    let fake = broker();
+    let output = chat(&loopd.socket, &fake.socket, &["--say", "go"], "");
+    assert!(output.status.success());
+    assert_eq!(
+        String::from_utf8_lossy(&output.stdout),
+        format!("a{}[8mb\n\tc\n", esc(0x1b))
+    );
+}

crates/bxctl/tests/chat_print.rs

@@ -0,0 +1,224 @@
+//! Tests for how `bxctl chat` prints what the model wrote and what `brokerd` denied. Do not edit.
+
+use bxctl::chat::Printer;
+use proto::{DataClass, DenyReason, Timestamp, TurnEvent};
+
+const BACKSLASH: char = '\\';
+
+/// The escape for one code point, built and never spelled out (see `tests/escape.rs`).
+fn esc(code: u32) -> String {
+    format!("{BACKSLASH}u{code:04x}")
+}
+
+fn print(printer: &mut Printer, events: &[TurnEvent]) -> String {
+    let mut out = Vec::new();
+    for e in events {
+        printer.event(&mut out, e).unwrap();
+    }
+    printer.end_reasoning(&mut out).unwrap();
+    String::from_utf8(out).unwrap()
+}
+
+fn denied(name: &str, reason: DenyReason) -> TurnEvent {
+    TurnEvent::ToolDenied {
+        name: name.to_string(),
+        reason,
+    }
+}
+
+#[test]
+fn a_denial_shows_its_reason_by_its_wire_name() {
+    let mut p = Printer::new(true, false);
+    assert_eq!(
+        print(&mut p, &[denied("read_file", DenyReason::NoGrant)]),
+        "[denied read_file: no_grant]\n"
+    );
+}
+
+/// Walks all ten reasons: the three that mean the harness is refusing to work carry their
+/// runbook entry on the next line, and the other seven carry nothing.
+#[test]
+fn the_three_fail_closed_denials_point_to_the_runbook_and_no_other_does() {
+    let cases = [
+        (DenyReason::NoGrant, "no_grant", None),
+        (DenyReason::GrantExpired, "grant_expired", None),
+        (DenyReason::TaintTooHigh, "taint_too_high", None),
+        (DenyReason::DeniedByGrant, "denied_by_grant", None),
+        (DenyReason::ApprovalRefused, "approval_refused", None),
+        (DenyReason::ApprovalExpired, "approval_expired", None),
+        (DenyReason::InvalidArguments, "invalid_arguments", None),
+        (
+            DenyReason::GrantsInvalid,
+            "grants_invalid",
+            Some("see docs/runbook.md#grants-invalid"),
+        ),
+        (
+            DenyReason::AuditUnavailable,
+            "audit_unavailable",
+            Some("see docs/runbook.md#audit-unavailable"),
+        ),
+        (
+            DenyReason::StateUnreadable,
+            "state_unreadable",
+            Some("see docs/runbook.md#broker-state-damaged"),
+        ),
+    ];
+    for (reason, name, pointer) in cases {
+        let mut p = Printer::new(true, false);
+        let got = print(&mut p, &[denied("shell", reason)]);
+        let want = match pointer {
+            Some(pointer) => format!("[denied shell: {name}]\n{pointer}\n"),
+            None => format!("[denied shell: {name}]\n"),
+        };
+        assert_eq!(got, want);
+    }
+}
+
+#[test]
+fn a_denial_ends_an_open_reasoning_block_first() {
+    let mut p = Printer::new(true, false);
+    let got = print(
+        &mut p,
+        &[
+            TurnEvent::Reasoning {
+                text: "hm".to_string(),
+            },
+            denied("shell", DenyReason::NoGrant),
+        ],
+    );
+    assert_eq!(got, "\x1b[2mhm\x1b[0m\n[denied shell: no_grant]\n");
+}
+
+#[test]
+fn reasoning_and_content_are_printed_as_data() {
+    let hostile = "a\x1b[8mb\x07c\rd";
+    let mut p = Printer::new(true, false);
+    let got = print(
+        &mut p,
+        &[
+            TurnEvent::Reasoning {
+                text: hostile.to_string(),
+            },
+            TurnEvent::Content {
+                text: hostile.to_string(),
+            },
+        ],
+    );
+    let shown = format!("a{}[8mb{}c{}d", esc(0x1b), esc(0x07), esc(0x0d));
+    // The only escape sequences left are the printer's own: dim on, dim off.
+    assert_eq!(got, format!("\x1b[2m{shown}\x1b[0m\n{shown}"));
+}
+
+#[test]
+fn invisible_and_direction_changing_characters_are_shown() {
+    let rlo = char::from_u32(0x202e).unwrap();
+    let mut p = Printer::new(true, false);
+    let got = print(
+        &mut p,
+        &[TurnEvent::Content {
+            text: format!("see {rlo}txt.exe"),
+        }],
+    );
+    assert_eq!(got, format!("see {}txt.exe", esc(0x202e)));
+}
+
+#[test]
+fn newlines_and_tabs_in_model_text_pass_through() {
+    let mut p = Printer::new(true, false);
+    let got = print(
+        &mut p,
+        &[TurnEvent::Content {
+            text: "one\n\ttwo\n".to_string(),
+        }],
+    );
+    assert_eq!(got, "one\n\ttwo\n");
+}
+
+/// The model chooses tool names too: every place a name is printed escapes it.
+#[test]
+fn tool_names_are_printed_as_data_everywhere() {
+    let name = "sh\x1b[2Jell";
+    let shown = format!("sh{}[2Jell", esc(0x1b));
+    let mut p = Printer::new(true, false);
+    let got = print(
+        &mut p,
+        &[
+            TurnEvent::ToolCallStarted {
+                name: name.to_string(),
+            },
+            TurnEvent::ToolResult {
+                name: name.to_string(),
+                class: DataClass::Public,
+                truncated: false,
+            },
+            TurnEvent::ToolResult {
+                name: name.to_string(),
+                class: DataClass::Private,
+                truncated: true,
+            },
+            denied(name, DenyReason::NoGrant),
+        ],
+    );
+    assert_eq!(
+        got,
+        format!(
+            "[tool {shown}]\n[{shown}: Public]\n[{shown}: Private, truncated]\n\
+             [denied {shown}: no_grant]\n"
+        )
+    );
+    assert!(!got.contains('\x1b'));
+}
+
+/// The printer shows nothing for a pending approval: the block comes from `brokerd`, through
+/// `handle_pending`. It still ends an open reasoning block, so the block is not dimmed.
+#[test]
+fn a_pending_approval_prints_nothing_itself_but_ends_the_reasoning_block() {
+    let pending = TurnEvent::ApprovalPending {
+        approval: 41,
+        tool: "read_file".to_string(),
+        expires: Timestamp::parse("2026-09-18T12:15:00.000Z").unwrap(),
+    };
+    let mut p = Printer::new(true, false);
+    assert_eq!(print(&mut p, std::slice::from_ref(&pending)), "");
+    let mut p = Printer::new(true, false);
+    let got = print(
+        &mut p,
+        &[
+            TurnEvent::Reasoning {
+                text: "hm".to_string(),
+            },
+            pending,
+        ],
+    );
+    assert_eq!(got, "\x1b[2mhm\x1b[0m\n");
+}
+
+#[test]
+fn json_mode_prints_the_new_events_as_json_lines() {
+    let mut p = Printer::new(true, true);
+    let got = print(
+        &mut p,
+        &[
+            TurnEvent::ApprovalPending {
+                approval: 41,
+                tool: "read_file".to_string(),
+                expires: Timestamp::parse("2026-09-18T12:15:00.000Z").unwrap(),
+            },
+            denied("shell", DenyReason::GrantsInvalid),
+        ],
+    );
+    let lines: Vec<serde_json::Value> = got
+        .lines()
+        .map(|l| serde_json::from_str(l).unwrap())
+        .collect();
+    assert_eq!(
+        lines,
+        vec![
+            serde_json::json!({"event": "approval_pending", "approval": 41,
+                "tool": "read_file", "expires": "2026-09-18T12:15:00.000Z"}),
+            serde_json::json!({"event": "tool_denied", "name": "shell",
+                "reason": "grants_invalid"}),
+        ]
+    );
+    assert!(!got.contains("runbook"), "json mode adds no prose");
+}

crates/bxctl/tests/cli.rs

@@ -0,0 +1,283 @@
+//! Tests for `bxctl`'s command line. Do not edit.
+
+use bxctl::cli::{ChatOptions, Command, USAGE, UsageError, parse};
+use proto::SessionId;
+use std::path::{Path, PathBuf};
+use std::process::Command as Process;
+
+const HOME: &str = "/srv/bx";
+
+fn args(words: &[&str]) -> Vec<String> {
+    words.iter().map(|w| w.to_string()).collect()
+}
+
+fn ok(words: &[&str]) -> Command {
+    parse(&args(words), Path::new(HOME)).unwrap_or_else(|_| panic!("{words:?} must parse"))
+}
+
+fn bad(words: &[&str]) {
+    assert_eq!(
+        parse(&args(words), Path::new(HOME)),
+        Err(UsageError),
+        "{words:?} must be a usage error"
+    );
+}
+
+fn default_admin() -> PathBuf {
+    PathBuf::from("/srv/bx/run/owner-broker/admin.sock")
+}
+
+#[test]
+fn chat_defaults_come_from_home() {
+    assert_eq!(
+        ok(&["chat"]),
+        Command::Chat(ChatOptions {
+            socket: PathBuf::from("/srv/bx/run/loop/loop.sock"),
+            admin_socket: default_admin(),
+            session: None,
+            show_thinking: true,
+            say: None,
+            json: false,
+        })
+    );
+}
+
+#[test]
+fn chat_takes_every_flag_in_any_order() {
+    assert_eq!(
+        ok(&[
+            "chat",
+            "--json",
+            "--admin-socket",
+            "/tmp/a.sock",
+            "--say",
+            "hello there",
+            "--no-thinking",
+            "--session",
+            "s-1",
+            "--socket",
+            "/tmp/l.sock",
+        ]),
+        Command::Chat(ChatOptions {
+            socket: PathBuf::from("/tmp/l.sock"),
+            admin_socket: PathBuf::from("/tmp/a.sock"),
+            session: Some(SessionId::new("s-1").unwrap()),
+            show_thinking: false,
+            say: Some("hello there".to_string()),
+            json: true,
+        })
+    );
+}
+
+#[test]
+fn chat_usage_errors() {
+    bad(&["chat", "--session", "Not Valid!"]);
+    bad(&["chat", "--session"]);
+    bad(&["chat", "--socket"]);
+    bad(&["chat", "--admin-socket"]);
+    bad(&["chat", "--say"]);
+    bad(&["chat", "--dance"]);
+    bad(&["chat", "stray"]);
+}
+
+#[test]
+fn approvals() {
+    assert_eq!(
+        ok(&["approvals"]),
+        Command::Approvals {
+            admin_socket: default_admin()
+        }
+    );
+    assert_eq!(
+        ok(&["approvals", "--admin-socket", "/tmp/a.sock"]),
+        Command::Approvals {
+            admin_socket: PathBuf::from("/tmp/a.sock")
+        }
+    );
+    bad(&["approvals", "41"]);
+    bad(&["approvals", "--admin-socket"]);
+    bad(&["approvals", "--reason", "x"]);
+}
+
+#[test]
+fn approve() {
+    assert_eq!(
+        ok(&["approve", "41"]),
+        Command::Approve {
+            admin_socket: default_admin(),
+            approval: 41
+        }
+    );
+    // The flag may come before or after the id.
+    for words in [
+        ["approve", "--admin-socket", "/tmp/a.sock", "41"],
+        ["approve", "41", "--admin-socket", "/tmp/a.sock"],
+    ] {
+        assert_eq!(
+            ok(&words),
+            Command::Approve {
+                admin_socket: PathBuf::from("/tmp/a.sock"),
+                approval: 41
+            }
+        );
+    }
+    assert_eq!(
+        ok(&["approve", "18446744073709551615"]),
+        Command::Approve {
+            admin_socket: default_admin(),
+            approval: u64::MAX
+        }
+    );
+}
+
+/// An id is decimal digits and nothing else. `str::parse::<u64>` alone would accept `+41`.
+#[test]
+fn an_approval_id_is_only_digits() {
+    bad(&["approve"]);
+    bad(&["approve", "41", "42"]);
+    bad(&["approve", "+41"]);
+    bad(&["approve", "-1"]);
+    bad(&["approve", "4 1"]);
+    bad(&["approve", " 41"]);
+    bad(&["approve", "0x29"]);
+    bad(&["approve", "forty-one"]);
+    bad(&["approve", ""]);
+    bad(&["approve", "18446744073709551616"]);
+    bad(&["approve", "41", "--reason", "x"]);
+    bad(&["refuse"]);
+    bad(&["refuse", "+41"]);
+    bad(&["refuse", "41", "42"]);
+}
+
+#[test]
+fn refuse() {
+    assert_eq!(
+        ok(&["refuse", "41"]),
+        Command::Refuse {
+            admin_socket: default_admin(),
+            approval: 41,
+            reason: None
+        }
+    );
+    assert_eq!(
+        ok(&[
+            "refuse",
+            "41",
+            "--reason",
+            "not on a Friday",
+            "--admin-socket",
+            "/tmp/a.sock"
+        ]),
+        Command::Refuse {
+            admin_socket: PathBuf::from("/tmp/a.sock"),
+            approval: 41,
+            reason: Some("not on a Friday".to_string())
+        }
+    );
+    // A value is a value, even when it looks like a flag.
+    assert_eq!(
+        ok(&["refuse", "--reason", "--admin-socket", "41"]),
+        Command::Refuse {
+            admin_socket: default_admin(),
+            approval: 41,
+            reason: Some("--admin-socket".to_string())
+        }
+    );
+    bad(&["refuse", "41", "--reason"]);
+    bad(&["refuse", "41", "--reason", "a", "--reason", "b"]);
+}
+
+#[test]
+fn grants_check_and_audit_verify() {
+    assert_eq!(
+        ok(&["grants", "check"]),
+        Command::GrantsCheck {
+            admin_socket: default_admin()
+        }
+    );
+    assert_eq!(
+        ok(&["grants", "check", "--admin-socket", "/tmp/a.sock"]),
+        Command::GrantsCheck {
+            admin_socket: PathBuf::from("/tmp/a.sock")
+        }
+    );
+    assert_eq!(
+        ok(&["audit", "verify"]),
+        Command::AuditVerify {
+            home: PathBuf::from(HOME)
+        }
+    );
+    assert_eq!(
+        ok(&["audit", "verify", "--home", "/tmp/h"]),
+        Command::AuditVerify {
+            home: PathBuf::from("/tmp/h")
+        }
+    );
+    bad(&["grants"]);
+    bad(&["grants", "list"]);
+    bad(&["grants", "check", "extra"]);
+    bad(&["audit"]);
+    bad(&["audit", "verify", "--home"]);
+    bad(&["audit", "verify", "--admin-socket", "/tmp/a.sock"]);
+}
+
+#[test]
+fn anything_else_is_a_usage_error() {
+    bad(&[]);
+    bad(&["dance"]);
+    bad(&["--admin-socket", "/tmp/a.sock", "approvals"]);
+}
+
+#[test]
+fn usage_names_every_command() {
+    for word in [
+        "bxctl chat",
+        "bxctl approvals",
+        "bxctl approve <id>",
+        "bxctl refuse <id>",
+        "bxctl grants check",
+        "bxctl audit verify",
+        "--admin-socket",
+        "--reason",
+        "--home",
+    ] {
+        assert!(USAGE.contains(word), "usage lacks {word:?}");
+    }
+}
+
+#[test]
+fn the_binary_prints_usage_and_exits_2() {
+    for words in [
+        vec![],
+        vec!["dance"],
+        vec!["approve", "+41"],
+        vec!["refuse"],
+    ] {
+        let output = Process::new(env!("CARGO_BIN_EXE_bxctl"))
+            .args(&words)
+            .output()
+            .unwrap();
+        assert_eq!(output.status.code(), Some(2), "{words:?}");
+        assert_eq!(String::from_utf8_lossy(&output.stdout), "", "{words:?}");
+        assert!(
+            String::from_utf8_lossy(&output.stderr).contains("bxctl approve <id>"),
+            "{words:?}"
+        );
+    }
+}
+
+/// The default sockets are under `$BOXMAKER_HOME`. Nothing listens there, so the command fails
+/// to connect, and says where it tried.
+#[test]
+fn the_binary_finds_the_admin_socket_under_boxmaker_home() {
+    let home = std::env::temp_dir().join(format!("bxctl-cli-home-{}", std::process::id()));
+    let output = Process::new(env!("CARGO_BIN_EXE_bxctl"))
+        .arg("approvals")
+        .env("BOXMAKER_HOME", &home)
+        .output()
+        .unwrap();
+    assert_eq!(output.status.code(), Some(1));
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    let want = home.join("run/owner-broker/admin.sock");
+    assert!(stderr.contains(want.to_str().unwrap()), "{stderr}");
+}

crates/bxctl/tests/escape.rs

@@ -0,0 +1,150 @@
+//! Tests for `bxctl::escape`: text the model wrote is printed as data. Do not edit.
+//!
+//! The expected escapes are built by `esc`, never spelled out, so that nothing that handles this
+//! file can turn one into the character it stands for.
+
+use bxctl::escape::{escape_json_text, escape_model_text};
+
+const BACKSLASH: char = '\\';
+
+/// The escape for one code point: a backslash, `u`, and four lowercase hex digits.
+fn esc(code: u32) -> String {
+    format!("{BACKSLASH}u{code:04x}")
+}
+
+fn ch(code: u32) -> char {
+    char::from_u32(code).unwrap()
+}
+
+/// Every code point that must be escaped, as inclusive ranges.
+const HIDDEN: [(u32, u32); 6] = [
+    (0x0000, 0x001f),
+    (0x007f, 0x009f),
+    (0x200b, 0x200f),
+    (0x2028, 0x202e),
+    (0x2060, 0x2069),
+    (0xfeff, 0xfeff),
+];
+
+fn hidden(code: u32) -> bool {
+    HIDDEN.iter().any(|(lo, hi)| (*lo..=*hi).contains(&code))
+}
+
+/// Walks every code point below U+11000, not a sample: each is either escaped exactly or left
+/// exactly as it is.
+#[test]
+fn every_listed_code_point_is_escaped_and_no_other() {
+    let mut escaped = 0;
+    for code in 0..0x11000u32 {
+        let Some(c) = char::from_u32(code) else {
+            continue; // the surrogates are not characters
+        };
+        let text = format!("a{c}b");
+        let got = escape_json_text(&text);
+        if hidden(code) {
+            escaped += 1;
+            assert_eq!(got, format!("a{}b", esc(code)), "U+{code:04X}");
+        } else {
+            assert_eq!(got, text, "U+{code:04X} must pass through");
+        }
+    }
+    assert_eq!(escaped, 32 + 33 + 5 + 7 + 10 + 1, "the six ranges, in full");
+}
+
+#[test]
+fn the_edges_of_each_range() {
+    for (lo, hi) in HIDDEN {
+        assert_eq!(escape_json_text(&ch(lo).to_string()), esc(lo));
+        assert_eq!(escape_json_text(&ch(hi).to_string()), esc(hi));
+        if lo > 0 {
+            let before = ch(lo - 1).to_string();
+            assert_eq!(escape_json_text(&before), before, "U+{:04X}", lo - 1);
+        }
+        let after = ch(hi + 1).to_string();
+        assert_eq!(escape_json_text(&after), after, "U+{:04X}", hi + 1);
+    }
+}
+
+#[test]
+fn hex_digits_are_lowercase_and_there_are_always_four() {
+    assert_eq!(escape_json_text("\x1b"), esc(0x1b));
+    assert!(escape_json_text("\x1b").ends_with("001b"));
+    assert!(escape_json_text("\0").ends_with("0000"));
+    assert!(escape_json_text(&ch(0xfeff).to_string()).ends_with("feff"));
+    assert!(escape_json_text(&ch(0x202e).to_string()).ends_with("202e"));
+}
+
+#[test]
+fn an_escape_sequence_cannot_reach_the_terminal() {
+    let text = "before\x1b[8mhidden\x1b[0m\x07after";
+    let got = escape_json_text(text);
+    assert!(!got.contains('\x1b') && !got.contains('\x07'), "{got:?}");
+    assert_eq!(
+        got,
+        format!(
+            "before{}[8mhidden{}[0m{}after",
+            esc(0x1b),
+            esc(0x1b),
+            esc(0x07)
+        )
+    );
+}
+
+#[test]
+fn a_path_cannot_be_shown_backwards() {
+    // U+202E makes a terminal draw what follows from right to left.
+    let text = format!("/home/kyle/notes/{}dm.terces", ch(0x202e));
+    assert_eq!(
+        escape_json_text(&text),
+        format!("/home/kyle/notes/{}dm.terces", esc(0x202e))
+    );
+    let text = format!("a{}b{}c", ch(0x200b), ch(0x2066));
+    assert_eq!(
+        escape_json_text(&text),
+        format!("a{}b{}c", esc(0x200b), esc(0x2066))
+    );
+}
+
+#[test]
+fn ordinary_text_is_unchanged() {
+    for text in [
+        "",
+        "plain",
+        r#"{"command":"ls -l","cwd":"/home/kyle"}"#,
+        "naïve café 日本語 🙂",
+        "a backslash \\ and a quote \" stay as they are",
+    ] {
+        assert_eq!(escape_json_text(text), text);
+        assert_eq!(escape_model_text(text), text);
+    }
+}
+
+#[test]
+fn json_text_escapes_newline_and_tab_but_model_text_keeps_them() {
+    let text = "one\n\ttwo\r\n";
+    assert_eq!(
+        escape_json_text(text),
+        format!("one{}{}two{}{}", esc(0x0a), esc(0x09), esc(0x0d), esc(0x0a))
+    );
+    assert_eq!(
+        escape_model_text(text),
+        format!("one\n\ttwo{}\n", esc(0x0d)),
+        "only newline and tab pass; a carriage return could overwrite the line"
+    );
+}
+
+#[test]
+fn model_text_escapes_everything_else_the_same_way() {
+    for (lo, hi) in HIDDEN {
+        for code in lo..=hi {
+            if code == 0x0a || code == 0x09 {
+                continue;
+            }
+            assert_eq!(
+                escape_model_text(&ch(code).to_string()),
+                esc(code),
+                "U+{code:04X}"
+            );
+        }
+    }
+}

crates/bxctl/tests/escape_details.rs

@@ -0,0 +1,75 @@
+//! Text from `brokerd` or the inference server is escaped like model text before it reaches the
+//! terminal: a `retrying` error and every error detail (M3a review finding 10).
+
+use bxctl::admin::AdminError;
+use bxctl::chat::{ChatError, Printer};
+use proto::{ErrorCode, TurnEvent, WireError};
+
+const ESC: char = '\u{1b}';
+
+fn hostile() -> String {
+    format!("the server responded with 503: {ESC}[2J{ESC}]0;owned\u{7}\u{202e}")
+}
+
+fn clean(text: &str) {
+    for c in text.chars() {
+        let cp = u32::from(c);
+        assert!(
+            cp >= 0x20 && !(0x7f..=0x9f).contains(&cp) && !(0x2028..=0x202e).contains(&cp)
+                || c == '\n',
+            "raw {cp:#x} in {text:?}"
+        );
+    }
+}
+
+#[test]
+fn a_retrying_error_is_escaped() {
+    let mut out = Vec::new();
+    let mut printer = Printer::new(true, false);
+    printer
+        .event(
+            &mut out,
+            &TurnEvent::Retrying {
+                attempt: 1,
+                after_ms: 2000,
+                error: hostile(),
+            },
+        )
+        .unwrap();
+    let text = String::from_utf8(out).unwrap();
+    clean(&text);
+    assert!(text.contains("\\u001b[2J"), "{text}");
+}
+
+#[test]
+fn an_error_detail_is_escaped_in_chat_and_admin_errors() {
+    let wire = WireError {
+        code: ErrorCode::Inference,
+        detail: hostile(),
+    };
+    for text in [
+        ChatError::Refused(wire.clone()).to_string(),
+        AdminError::Refused(wire).to_string(),
+    ] {
+        clean(&text);
+        assert!(text.contains("\\u202e"), "{text}");
+    }
+}
+
+/// A frame that does not decode is reported with serde's message, which quotes the offending
+/// text after JSON decoding: from a compromised peer that can be raw escape sequences.
+#[test]
+fn a_frame_error_is_escaped() {
+    let bad = r#"{"v":1,"id":1,"final":true,"msg":{"kind":"\u001b[2J\u202e"}}"#;
+    let error = serde_json::from_str::<proto::Envelope>(bad).unwrap_err();
+    for text in [
+        ChatError::Frame(proto::FrameError::Json(
+            serde_json::from_str::<proto::Envelope>(bad).unwrap_err(),
+        ))
+        .to_string(),
+        AdminError::Frame(proto::FrameError::Json(error)).to_string(),
+    ] {
+        clean(&text);
+        assert!(text.contains("\\u001b"), "{text}");
+    }
+}

crates/bxctl/tests/support/mod.rs

@@ -0,0 +1,186 @@
+//! Scripted stand-ins for `brokerd`'s admin socket and for `loopd`, for tests. Do not edit.
+
+#![allow(dead_code)] // each test file uses a different part of this module
+
+use proto::{
+    ApprovalList, CallId, DataClass, Envelope, ErrorCode, Message, PROTOCOL_VERSION,
+    PendingApproval, SessionId, Timestamp, TurnDone, TurnEvent, Usage, WireError, read_frame,
+    write_frame,
+};
+use std::os::unix::net::UnixListener;
+use std::path::PathBuf;
+use std::sync::atomic::{AtomicU32, Ordering};
+use std::sync::{Arc, Mutex};
+use std::thread;
+
+static NEXT: AtomicU32 = AtomicU32::new(0);
+
+/// A socket path in a fresh temporary directory.
+pub fn temp_socket(name: &str) -> PathBuf {
+    let n = NEXT.fetch_add(1, Ordering::SeqCst);
+    let dir = std::env::temp_dir().join(format!("bxctl-m3a-{}-{n}", std::process::id()));
+    std::fs::create_dir_all(&dir).unwrap();
+    dir.join(name)
+}
+
+pub fn ts(text: &str) -> Timestamp {
+    Timestamp::parse(text).unwrap()
+}
+
+pub struct FakeBrokerd {
+    pub socket: PathBuf,
+    /// Every request message received, in order.
+    pub requests: Arc<Mutex<Vec<Message>>>,
+}
+
+impl FakeBrokerd {
+    pub fn requests(&self) -> Vec<Message> {
+        self.requests.lock().unwrap().clone()
+    }
+}
+
+/// Serves `admin.sock`: one request per connection, answered with the frames `answer` returns,
+/// written exactly as given (so a test can send a wrong id or a frame that is not final). An
+/// empty list closes the connection without an answer.
+pub fn fake_brokerd_frames(
+    answer: impl Fn(&Envelope) -> Vec<Envelope> + Send + 'static,
+) -> FakeBrokerd {
+    let socket = temp_socket("admin.sock");
+    let listener = UnixListener::bind(&socket).unwrap();
+    let requests = Arc::new(Mutex::new(Vec::new()));
+    let seen = Arc::clone(&requests);
+    thread::spawn(move || {
+        for stream in listener.incoming() {
+            let Ok(mut stream) = stream else { continue };
+            let Ok(request) = read_frame(&mut stream) else {
+                continue;
+            };
+            seen.lock().unwrap().push(request.msg.clone());
+            for frame in answer(&request) {
+                if write_frame(&mut stream, &frame).is_err() {
+                    break; // the client went away; the next connection is still served
+                }
+            }
+        }
+    });
+    FakeBrokerd { socket, requests }
+}
+
+/// The usual case: one final frame with the request's id.
+pub fn fake_brokerd(answer: impl Fn(&Message) -> Message + Send + 'static) -> FakeBrokerd {
+    fake_brokerd_frames(move |request| {
+        vec![Envelope {
+            v: PROTOCOL_VERSION,
+            id: request.id,
+            r#final: true,
+            msg: answer(&request.msg),
+        }]
+    })
+}
+
+pub fn wire_error(code: ErrorCode, detail: &str) -> Message {
+    Message::Error(WireError {
+        code,
+        detail: detail.to_string(),
+    })
+}
+
+/// A pending approval created at 12:00:00 that expires at 12:15:00 on 2026-09-18.
+pub fn pending(approval: u64, tool: &str, arguments: &str) -> PendingApproval {
+    PendingApproval {
+        approval,
+        session: SessionId::new("chat-1758196800-123456789").unwrap(),
+        call: CallId(7),
+        tool: tool.to_string(),
+        arguments: arguments.to_string(),
+        grant: "shell-scratch".to_string(),
+        taint: DataClass::Private,
+        created: ts("2026-09-18T12:00:00.000Z"),
+        expires: ts("2026-09-18T12:15:00.000Z"),
+    }
+}
+
+/// A `brokerd` with these approvals pending. `approve` is answered with `outcome`, `refuse` with
+/// `ok`; both answer `no_such_approval` for an id that is not in the list.
+pub fn brokerd_with(items: Vec<PendingApproval>, outcome: proto::DecisionRecord) -> FakeBrokerd {
+    fake_brokerd(move |msg| {
+        let known = |id: u64| items.iter().any(|item| item.approval == id);
+        match msg {
+            Message::Approvals(_) => Message::ApprovalList(ApprovalList {
+                items: items.clone(),
+            }),
+            Message::Approve(a) if known(a.approval) => {
+                Message::ApproveResult(proto::ApproveResult {
+                    outcome: outcome.clone(),
+                })
+            }
+            Message::Refuse(r) if known(r.approval) => Message::Ok(proto::Empty {}),
+            Message::Approve(_) | Message::Refuse(_) => {
+                wire_error(ErrorCode::NoSuchApproval, "no such approval")
+            }
+            _ => wire_error(ErrorCode::BadMessage, "not an admin request"),
+        }
+    })
+}
+
+pub struct FakeLoopd {
+    pub socket: PathBuf,
+    /// The content of every turn received, in order.
+    pub turns: Arc<Mutex<Vec<String>>>,
+}
+
+pub fn usage() -> Usage {
+    Usage {
+        cache_n: 10,
+        prompt_n: 5,
+        predicted_n: 7,
+        reasoning_tokens: 3,
+        thinking_capped: false,
+    }
+}
+
+/// Serves `loop.sock`: every turn gets the same events, then `turn_done` with `answer`. It does
+/// not wait for an approval to be answered: `bxctl` deals with each event before it reads the
+/// next frame, so the order of what it does is fixed all the same.
+pub fn fake_loopd(events: Vec<TurnEvent>, answer: &str) -> FakeLoopd {
+    let socket = temp_socket("loop.sock");
+    let listener = UnixListener::bind(&socket).unwrap();
+    let turns = Arc::new(Mutex::new(Vec::new()));
+    let seen = Arc::clone(&turns);
+    let answer = answer.to_string();
+    thread::spawn(move || {
+        for stream in listener.incoming() {
+            let Ok(mut stream) = stream else { continue };
+            let Ok(request) = read_frame(&mut stream) else {
+                continue;
+            };
+            let Message::Turn(turn) = request.msg else {
+                continue;
+            };
+            seen.lock().unwrap().push(turn.content);
+            let mut frames: Vec<(bool, Message)> = events
+                .iter()
+                .map(|e| (false, Message::TurnEvent(e.clone())))
+                .collect();
+            frames.push((
+                true,
+                Message::TurnDone(TurnDone {
+                    content: answer.clone(),
+                    usage: usage(),
+                }),
+            ));
+            for (last, msg) in frames {
+                let frame = Envelope {
+                    v: PROTOCOL_VERSION,
+                    id: request.id,
+                    r#final: last,
+                    msg,
+                };
+                if write_frame(&mut stream, &frame).is_err() {
+                    break;
+                }
+            }
+        }
+    });
+    FakeLoopd { socket, turns }
+}

crates/bxctl/tests/verify.rs

@@ -0,0 +1,179 @@
+//! `bxctl audit verify` against the fixture logs in `crates/proto/tests/fixtures/audit/`.
+//! Do not edit. The output is compared byte for byte: the owner reads it, and so do scripts.
+
+use std::path::PathBuf;
+use std::sync::atomic::{AtomicU32, Ordering};
+
+static NEXT: AtomicU32 = AtomicU32::new(0);
+
+/// A home directory whose `audit/` is a copy of the fixture log `case`. Removed when dropped.
+struct Home {
+    path: PathBuf,
+}
+
+impl Home {
+    fn with_case(case: &str) -> Home {
+        let n = NEXT.fetch_add(1, Ordering::SeqCst);
+        let name = format!("bxctl-verify-{}-{n}", std::process::id());
+        let path = std::env::temp_dir().join(name);
+        let _ = std::fs::remove_dir_all(&path);
+        let audit = path.join("audit");
+        std::fs::create_dir_all(&audit).unwrap();
+        let from = format!(
+            "{}/../proto/tests/fixtures/audit/{case}",
+            env!("CARGO_MANIFEST_DIR")
+        );
+        for entry in std::fs::read_dir(&from).unwrap_or_else(|e| panic!("{from}: {e}")) {
+            let entry = entry.unwrap();
+            std::fs::copy(entry.path(), audit.join(entry.file_name())).unwrap();
+        }
+        Home { path }
+    }
+}
+
+impl Drop for Home {
+    fn drop(&mut self) {
+        let _ = std::fs::remove_dir_all(&self.path);
+    }
+}
+
+fn run(case: &str) -> (bool, String) {
+    let home = Home::with_case(case);
+    // What brokerd leaves beside the log must not be read as part of it.
+    std::fs::write(home.path.join("audit/.lock"), "").unwrap();
+    let mut out = Vec::new();
+    let ok = bxctl::verify::run(&home.path, &mut out).unwrap();
+    (ok, String::from_utf8(out).unwrap())
+}
+
+/// The hex of the hash of the last line of `file` in `case`.
+fn head_of(case: &str, file: &str) -> String {
+    let path = format!(
+        "{}/../proto/tests/fixtures/audit/{case}/{file}",
+        env!("CARGO_MANIFEST_DIR")
+    );
+    let text = std::fs::read_to_string(path).unwrap();
+    proto::sha256(text.lines().last().unwrap().as_bytes())
+        .unwrap()
+        .to_hex()
+}
+
+#[test]
+fn a_good_log() {
+    let (ok, out) = run("good");
+    assert!(ok);
+    let head = head_of("good", "2026-09-18.jsonl");
+    assert_eq!(
+        out,
+        format!(
+            "audit: ok, 10 records, head {head}\n\
+             pending or abandoned: approval 6\n\
+             running or unfinished: decision 7\n"
+        )
+    );
+}
+
+#[test]
+fn everything_worth_knowing_is_listed_one_per_line() {
+    let (ok, out) = run("recovered-next-day");
+    assert!(ok);
+    let lines: Vec<&str> = out.lines().collect();
+    assert!(
+        lines[0].starts_with("audit: ok, 11 records, head "),
+        "{out}"
+    );
+    assert_eq!(
+        lines[1..],
+        [
+            "recovered line: 2026-09-17.jsonl:6",
+            "pending or abandoned: approval 7",
+            "running or unfinished: decision 8",
+        ]
+    );
+
+    let (ok, out) = run("accepted-break-older-file");
+    assert!(ok);
+    assert!(
+        out.contains("\naccepted break: 2026-09-18.jsonl:6\n"),
+        "{out}"
+    );
+
+    let (ok, out) = run("clock-back");
+    assert!(ok);
+    assert!(
+        out.ends_with("\nclock went backwards: 2026-09-18.jsonl:6\n"),
+        "{out}"
+    );
+}
+
+/// A torn final line is what a crash, or a `brokerd` in the middle of a write, leaves. It is
+/// reported and is not a failure.
+#[test]
+fn a_torn_tail_is_reported_and_is_ok() {
+    let (ok, out) = run("torn-tail");
+    assert!(ok);
+    assert!(out.starts_with("audit: ok, 10 records, head "), "{out}");
+    assert!(
+        out.ends_with(
+            "\ntorn final line: 2026-09-18.jsonl:6 (brokerd recovers it at its next start)\n"
+        ),
+        "{out}"
+    );
+}
+
+#[test]
+fn a_broken_chain_is_two_lines_and_false() {
+    let cases = [
+        (
+            "changed-byte",
+            "2026-09-17.jsonl:4: prev is not the hash of the line before",
+        ),
+        ("deleted-line", "2026-09-17.jsonl:3: seq is 3, expected 2"),
+        (
+            "cut-short",
+            "2026-09-17.jsonl:3: does not parse as an audit record",
+        ),
+        (
+            "file-not-chained",
+            "2026-09-18.jsonl:1: does not chain from the last line of the file before",
+        ),
+        (
+            "break-wrong-line",
+            "2026-09-17.jsonl:4: prev is not the hash of the line before",
+        ),
+    ];
+    for (case, first) in cases {
+        let (ok, out) = run(case);
+        assert!(!ok, "{case}");
+        assert_eq!(
+            out,
+            format!("{first}\nsee docs/runbook.md#audit-chain-broken\n"),
+            "{case}"
+        );
+    }
+}
+
+#[test]
+fn an_empty_audit_directory_is_an_empty_log() {
+    let home = Home::with_case("good");
+    for entry in std::fs::read_dir(home.path.join("audit")).unwrap() {
+        std::fs::remove_file(entry.unwrap().path()).unwrap();
+    }
+    let mut out = Vec::new();
+    assert!(bxctl::verify::run(&home.path, &mut out).unwrap());
+    assert_eq!(
+        String::from_utf8(out).unwrap(),
+        "audit: ok, 0 records, head none\n"
+    );
+}
+
+/// A home with no audit directory is a mistake in `--home`, not a clean log.
+#[test]
+fn a_missing_audit_directory_is_an_error() {
+    let home = Home::with_case("good");
+    std::fs::remove_dir_all(home.path.join("audit")).unwrap();
+    let mut out = Vec::new();
+    let error = bxctl::verify::run(&home.path, &mut out).unwrap_err();
+    assert_eq!(error.kind(), std::io::ErrorKind::NotFound);
+    assert!(out.is_empty());
+}

crates/bxctl/tests/verify_skipped.rs

@@ -0,0 +1,38 @@
+//! `bxctl audit verify` says which files in `audit/` it did not read: a file that looks like a
+//! log but is not named as one is ignored by `brokerd` too, and "ok" must not seem to cover it.
+
+use std::path::PathBuf;
+
+fn home(tag: &str) -> PathBuf {
+    let dir = std::env::temp_dir().join(format!("bx-verify-skip-{tag}-{}", std::process::id()));
+    let _ = std::fs::remove_dir_all(&dir);
+    std::fs::create_dir_all(dir.join("audit")).unwrap();
+    let fixture =
+        PathBuf::from(env!("CARGO_MANIFEST_DIR")).join("../proto/tests/fixtures/audit/good");
+    for entry in std::fs::read_dir(fixture).unwrap() {
+        let entry = entry.unwrap();
+        std::fs::copy(entry.path(), dir.join("audit").join(entry.file_name())).unwrap();
+    }
+    dir
+}
+
+#[test]
+fn a_stray_jsonl_file_is_named_and_the_log_still_verifies() {
+    let dir = home("stray");
+    std::fs::write(dir.join("audit/2026-0x-19.jsonl"), "x\n").unwrap();
+    std::fs::write(dir.join("audit/notes.txt"), "not a log\n").unwrap();
+    let mut out = Vec::new();
+    let ok = bxctl::verify::run(&dir, &mut out).unwrap();
+    let text = String::from_utf8(out).unwrap();
+    assert!(ok, "{text}");
+    assert!(text.starts_with("audit: ok, 10 records"), "{text}");
+    assert!(
+        text.contains("not an audit log file, not checked: 2026-0x-19.jsonl"),
+        "{text}"
+    );
+    assert!(
+        !text.contains("notes.txt"),
+        "only files that look like logs: {text}"
+    );
+    let _ = std::fs::remove_dir_all(&dir);
+}

crates/inferproxy/src/main.rs

@@ -7,7 +7,11 @@ use std::process;
 use inferproxy::{Limits, serve};
 
 fn main() {
-    let args: Vec<String> = env::args().collect();
+    // `args_os`, because `args` panics on an argument that is not UTF-8.
+    let args: Vec<String> = match env::args_os().map(|a| a.into_string()).collect() {
+        Ok(args) => args,
+        Err(_) => usage(),
+    };
     let mut listen: Option<String> = None;
     let mut upstream: Option<String> = None;
     let mut i = 1;

crates/inferproxy/tests/args_os.rs

@@ -0,0 +1,14 @@
+//! An argument that is not UTF-8 is a usage error, not a panic (M3a review finding 7).
+
+use std::ffi::OsStr;
+use std::os::unix::ffi::OsStrExt;
+use std::process::Command;
+
+#[test]
+fn an_argument_that_is_not_utf8_is_a_usage_error() {
+    let out = Command::new(env!("CARGO_BIN_EXE_inferproxy"))
+        .args([OsStr::new("--listen"), OsStr::from_bytes(b"/tmp/\xff.sock")])
+        .output()
+        .unwrap();
+    assert_eq!(out.status.code(), Some(2));
+}

crates/loopd/src/baseline.rs

@@ -25,6 +25,7 @@ pub enum BaselineError {
     Read(PathBuf, std::io::Error),
     Parse(PathBuf, serde_json::Error),
     Hash,
+    Core(PathBuf, std::io::Error),
 }
 
 impl std::fmt::Display for BaselineError {
@@ -33,6 +34,11 @@ impl std::fmt::Display for BaselineError {
             BaselineError::Read(path, err) => write!(f, "{}: {err}", path.display()),
             BaselineError::Parse(path, err) => write!(f, "{}: {err}", path.display()),
             BaselineError::Hash => write!(f, "hashing the baseline failed"),
+            BaselineError::Core(path, err) => write!(
+                f,
+                "{}: {err}; see docs/runbook.md#core-memory-unreadable",
+                path.display()
+            ),
         }
     }
 }
@@ -58,7 +64,7 @@ impl Baseline {
             // A missing file is fine; an unreadable one is reported so the owner is not given a
             // session without the memory they curated and no sign of it.
             Err(e) if e.kind() != std::io::ErrorKind::NotFound => {
-                return Err(BaselineError::Read(core.clone(), e));
+                return Err(BaselineError::Core(core.clone(), e));
             }
             Err(_) => {}
         }

crates/loopd/src/broker_port.rs

@@ -0,0 +1,235 @@
+//! The tool port to `brokerd`: one connection per call, a deadline per frame, and plain failures.
+//!
+//! Whatever goes wrong reaching `brokerd` or reading its frames, the model gets a plain failure and
+//! the turn goes on. Every failure prints one line ending at `#broker-unavailable`.
+
+use std::os::unix::net::UnixStream;
+use std::path::PathBuf;
+use std::time::{Duration, Instant};
+
+use crate::tools::{Pending, ToolPort};
+use proto::{
+    Envelope, FrameError, Message, PROTOCOL_VERSION, Timestamp, ToolRequest, ToolResponse,
+    read_frame, write_frame,
+};
+
+/// The failure every outage reaches the model as.
+pub const UNAVAILABLE: &str = "the tool broker is unavailable";
+/// What the model is told when no broker is configured.
+pub const NOT_CONFIGURED: &str = "no tool broker is configured";
+/// The failure a request too big for one frame reaches.
+pub const TOO_LARGE: &str = "the request is too large for the tool broker";
+/// The longest `BrokerPort` waits for an answer after a pending frame, whatever its `expires`
+/// says, so a turn cannot be parked for ever by a far expiry.
+pub const MAX_PENDING_WAIT: Duration = Duration::from_secs(24 * 60 * 60);
+/// The runbook entry every outage line ends with.
+pub const POINTER: &str = "see docs/runbook.md#broker-unavailable";
+
+/// "loopd: {UNAVAILABLE}: {why}; {POINTER}"
+pub fn unavailable_line(why: &str) -> String {
+    format!("loopd: {UNAVAILABLE}: {why}; {POINTER}")
+}
+
+/// "loopd: {NOT_CONFIGURED}: every tool call except the core ones will fail; {POINTER}"
+pub fn not_configured_line() -> String {
+    format!("loopd: {NOT_CONFIGURED}: every tool call except the core ones will fail; {POINTER}")
+}
+
+/// Reads through `stream`, but only what is left before `until`: a read past the deadline fails
+/// with a timeout, so a peer that sends one byte at a time cannot hold the turn.
+struct Deadline<'a> {
+    stream: &'a UnixStream,
+    until: Instant,
+}
+
+impl std::io::Read for Deadline<'_> {
+    fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
+        let left = self.until.saturating_duration_since(Instant::now());
+        if left.is_zero() {
+            return Err(std::io::Error::from(std::io::ErrorKind::TimedOut));
+        }
+        crate::socket::set_read_timeout(self.stream, left)?;
+        let mut stream = self.stream; // `Read` is implemented for `&UnixStream`
+        stream.read(buf)
+    }
+}
+
+/// The tool port to `brokerd`. One connection per call, with a deadline per frame.
+pub struct BrokerPort {
+    socket: PathBuf,
+    timeout: Duration,
+    pending_cap: Duration,
+    log: Box<dyn Fn(&str) + Send + Sync>,
+}
+
+impl BrokerPort {
+    pub fn new(socket: PathBuf, timeout: Duration) -> BrokerPort {
+        BrokerPort {
+            socket,
+            timeout,
+            pending_cap: MAX_PENDING_WAIT,
+            log: Box::new(|l| eprintln!("{l}")),
+        }
+    }
+
+    /// The same port with another cap on the wait after a pending frame (`MAX_PENDING_WAIT`).
+    pub fn with_pending_cap(self, pending_cap: Duration) -> BrokerPort {
+        BrokerPort {
+            pending_cap,
+            ..self
+        }
+    }
+
+    pub fn with_log(
+        socket: PathBuf,
+        timeout: Duration,
+        log: Box<dyn Fn(&str) + Send + Sync>,
+    ) -> BrokerPort {
+        BrokerPort {
+            socket,
+            timeout,
+            pending_cap: MAX_PENDING_WAIT,
+            log,
+        }
+    }
+}
+
+impl ToolPort for BrokerPort {
+    fn call(&self, request: &ToolRequest, on_pending: &mut dyn FnMut(&Pending)) -> ToolResponse {
+        let want = request.call.0;
+
+        // The first deadline, taken before connecting.
+        let mut until = match Instant::now().checked_add(self.timeout) {
+            Some(until) => until,
+            None => return self.unavailable("the timeout is too large"),
+        };
+
+        // Exit 2.
+        let mut stream = match UnixStream::connect(&self.socket) {
+            Ok(stream) => stream,
+            Err(e) => {
+                return self
+                    .unavailable(&format!("cannot connect to {}: {e}", self.socket.display()));
+            }
+        };
+
+        // Exit 3. `set_write_timeout` fails for a zero timeout.
+        if let Err(e) = stream.set_write_timeout(Some(self.timeout)) {
+            return self.unavailable(&format!("cannot set a timeout: {e}"));
+        }
+
+        // Exit 4. One request frame; the broker is fine if it is too large to send.
+        let request_frame = Envelope {
+            v: PROTOCOL_VERSION,
+            id: want,
+            r#final: true,
+            msg: Message::ToolRequest(request.clone()),
+        };
+        if let Err(e) = write_frame(&mut stream, &request_frame) {
+            return match e {
+                FrameError::TooLarge(_) => ToolResponse::Failed {
+                    message: TOO_LARGE.to_string(),
+                },
+                _ => self.unavailable(&format!("cannot send the request: {e}")),
+            };
+        }
+
+        // Exit 5-11, once per frame. A pending frame is reported, then we read again.
+        let mut seen_pending = false;
+        loop {
+            let mut deadline = Deadline {
+                stream: &stream,
+                until,
+            };
+            let env = match read_frame(&mut deadline) {
+                Ok(env) => env,
+                // Exit 5.
+                Err(FrameError::Closed) => {
+                    return self.unavailable("the connection closed before the final answer");
+                }
+                Err(FrameError::Io(e))
+                    if e.kind() == std::io::ErrorKind::WouldBlock
+                        || e.kind() == std::io::ErrorKind::TimedOut =>
+                {
+                    return self.unavailable("no answer in time");
+                }
+                Err(e) => return self.unavailable(&format!("bad frame: {e}")),
+            };
+
+            // Exit 6.
+            if env.id != want {
+                return self
+                    .unavailable(&format!("an answer for request {}, not {}", env.id, want));
+            }
+
+            let r#final = env.r#final;
+            // Exit 7.
+            let resp = match env.msg {
+                Message::ToolResponse(resp) => resp,
+                Message::Error(e) => {
+                    return self
+                        .unavailable(&format!("the broker reported an error: {}", e.detail));
+                }
+                _ => return self.unavailable("an unexpected message"),
+            };
+
+            match resp {
+                // Exit 8.
+                ToolResponse::PendingApproval { approval, expires } => {
+                    if r#final {
+                        return self.unavailable("a pending frame marked final");
+                    }
+                    // Exit 10.
+                    if seen_pending {
+                        return self.unavailable("a second pending frame");
+                    }
+                    let wait = expires
+                        .unix_millis()
+                        .saturating_sub(Timestamp::now().unix_millis());
+                    let wait = Duration::from_millis(wait).min(self.pending_cap);
+                    until = match Instant::now().checked_add(wait) {
+                        Some(until) => until,
+                        None => return self.unavailable("an expiry too far away"),
+                    };
+                    until = match until.checked_add(self.timeout) {
+                        Some(until) => until,
+                        None => return self.unavailable("an expiry too far away"),
+                    };
+                    seen_pending = true;
+                    on_pending(&Pending { approval, expires });
+                }
+                // Exit 9 and 11.
+                ToolResponse::Result { .. }
+                | ToolResponse::Failed { .. }
+                | ToolResponse::Denied { .. } => {
+                    if r#final {
+                        return resp;
+                    }
+                    return self.unavailable("an answer not marked final");
+                }
+            }
+        }
+    }
+}
+
+/// The one failure no outage reaches the model as, and the one line printed with it.
+impl BrokerPort {
+    fn unavailable(&self, why: &str) -> ToolResponse {
+        (self.log)(&unavailable_line(why));
+        ToolResponse::Failed {
+            message: UNAVAILABLE.to_string(),
+        }
+    }
+}
+
+/// The port used when no broker is configured: every call fails with `NOT_CONFIGURED` and prints
+/// nothing.
+pub struct NoBroker;
+
+impl ToolPort for NoBroker {
+    fn call(&self, _request: &ToolRequest, _on_pending: &mut dyn FnMut(&Pending)) -> ToolResponse {
+        ToolResponse::Failed {
+            message: NOT_CONFIGURED.to_string(),
+        }
+    }
+}

crates/loopd/src/config.rs

@@ -136,6 +136,23 @@ impl Default for Baseline {
     }
 }
 
+/// The tool broker (`brokerd`). No socket means no broker: every non-core tool call fails.
+#[derive(Debug, Clone, PartialEq, Eq, Deserialize)]
+#[serde(deny_unknown_fields, default)]
+pub struct Broker {
+    pub socket: Option<std::path::PathBuf>,
+    pub timeout_ms: u64,
+}
+
+impl Default for Broker {
+    fn default() -> Self {
+        Self {
+            socket: None,
+            timeout_ms: 120_000,
+        }
+    }
+}
+
 #[derive(Debug, Clone, PartialEq, Deserialize)]
 #[serde(deny_unknown_fields)]
 pub struct Config {
@@ -154,6 +171,8 @@ pub struct Config {
     pub r#loop: Loop,
     #[serde(default)]
     pub baseline: Baseline,
+    #[serde(default)]
+    pub broker: Broker,
 }
 
 #[derive(Debug)]

crates/loopd/src/http.rs

@@ -151,9 +151,7 @@ impl Connection {
     }
 
     pub fn set_read_timeout(&self, timeout: Duration) -> Result<(), HttpError> {
-        self.stream
+        crate::socket::set_read_timeout(&self.stream, timeout).map_err(HttpError::Io)
-            .set_read_timeout(Some(timeout))
-            .map_err(HttpError::Io)
     }
 
     pub fn received_any(&self) -> bool {

crates/loopd/src/lib.rs

@@ -1,12 +1,14 @@
 //! The agent loop: sessions, prompt assembly and memory. It holds no authority.
 
 pub mod baseline;
+pub mod broker_port;
 pub mod channel;
 pub mod config;
 pub mod http;
 pub mod llama;
 pub mod selftest;
 pub mod session;
+pub mod socket;
 pub mod sse;
 pub mod tools;
 pub mod turn;

crates/loopd/src/main.rs

@@ -6,19 +6,22 @@ use std::os::unix::net::UnixListener;
 use std::path::Path;
 use std::process::ExitCode;
 use std::sync::Arc;
+use std::time::Duration;
 
+use loopd::broker_port::{BrokerPort, NoBroker, not_configured_line};
 use loopd::channel::{self, Context};
 use loopd::config::Config;
 use loopd::llama::Client;
 use loopd::selftest::{SelfTestError, run};
-use loopd::tools::{FakeTools, Registry};
+use loopd::tools::{Registry, ToolPort};
 
 fn main() -> ExitCode {
-    let args: Vec<String> = std::env::args().skip(1).collect();
+    // `args_os`: the config path need not be UTF-8, and `args` would panic on one that is not.
-    let args: Vec<&str> = args.iter().map(String::as_str).collect();
+    let args: Vec<std::ffi::OsString> = std::env::args_os().skip(1).collect();
-    match args.as_slice() {
+    let words: Vec<Option<&str>> = args.iter().map(|a| a.to_str()).collect();
-        ["selftest", "--config", path] => run_selftest(path),
+    match (words.as_slice(), args.get(2)) {
-        ["serve", "--config", path] => run_serve(path),
+        ([Some("selftest"), Some("--config"), _], Some(path)) => run_selftest(Path::new(path)),
+        ([Some("serve"), Some("--config"), _], Some(path)) => run_serve(Path::new(path)),
         _ => {
             eprintln!("usage: loopd selftest --config <path>");
             eprintln!("usage: loopd serve --config <path>");
@@ -38,14 +41,14 @@ fn run_selftest_check(client: &Client) -> Result<(), SelfTestError> {
             Ok(())
         }
         Err(e) => {
-            eprintln!("selftest: FAILED: {e}");
+            eprintln!("selftest: FAILED: {e}; see docs/runbook.md#loopd-selftest-failed");
             Err(e)
         }
     }
 }
 
-fn run_selftest(path: &str) -> ExitCode {
+fn run_selftest(path: &Path) -> ExitCode {
-    let cfg = match Config::load(Path::new(path)) {
+    let cfg = match Config::load(path) {
         Ok(cfg) => cfg,
         Err(e) => {
             eprintln!("loopd: {e}");
@@ -60,8 +63,8 @@ fn run_selftest(path: &str) -> ExitCode {
     }
 }
 
-fn run_serve(path: &str) -> ExitCode {
+fn run_serve(path: &Path) -> ExitCode {
-    let cfg = match Config::load(Path::new(path)) {
+    let cfg = match Config::load(path) {
         Ok(cfg) => cfg,
         Err(e) => {
             eprintln!("loopd: {e}");
@@ -104,12 +107,17 @@ fn run_serve(path: &str) -> ExitCode {
     }
     eprintln!("loopd: serving on {}", socket.display());
 
-    let ctx = Arc::new(Context::new(
+    let port: Box<dyn ToolPort> = match &cfg.broker.socket {
-        cfg,
+        Some(socket) => Box::new(BrokerPort::new(
-        client,
+            socket.clone(),
-        Box::new(FakeTools::new()),
+            Duration::from_millis(cfg.broker.timeout_ms),
-        Registry::m2b(),
+        )),
-    ));
+        None => {
+            eprintln!("{}", not_configured_line());
+            Box::new(NoBroker)
+        }
+    };
+    let ctx = Arc::new(Context::new(cfg, client, port, Registry::m3a()));
     if let Err(e) = channel::serve(listener, ctx) {
         eprintln!("loopd: the channel server stopped: {e}");
         return ExitCode::from(1);

crates/loopd/src/session.rs

@@ -29,7 +29,11 @@ impl std::fmt::Display for SessionError {
             SessionError::Exists(id) => write!(f, "session already exists: {}", id.as_str()),
             SessionError::NotFound(id) => write!(f, "session not found: {}", id.as_str()),
             SessionError::Io(path, err) => write!(f, "{}: {err}", path.display()),
-            SessionError::Torn { path, line, why } => write!(f, "{}:{line}: {why}", path.display()),
+            SessionError::Torn { path, line, why } => write!(
+                f,
+                "{}:{line}: {why}; see docs/runbook.md#session-log-damaged",
+                path.display()
+            ),
             SessionError::Baseline(err) => write!(f, "{err}"),
             SessionError::Encode(err) => write!(f, "{err}"),
         }

crates/loopd/src/socket.rs

@@ -0,0 +1,21 @@
+//! Unix socket options that behave the same on Linux and macOS.
+
+use std::io;
+use std::os::unix::net::UnixStream;
+use std::time::Duration;
+
+/// `EINVAL` on Darwin (`sys/errno.h`); std does not name it and a crate for one number is too much.
+#[cfg(target_vendor = "apple")]
+const EINVAL: i32 = 22;
+
+/// Set the read timeout for the next read. macOS refuses every socket option with `EINVAL` once
+/// the peer has closed (XNU `sosetoptlock`: both `SS_CANTRCVMORE` and `SS_CANTSENDMORE` set), even
+/// with unread data still buffered. A read on such a socket returns that data or the end at once
+/// and cannot block, so there is no timeout left to set and the refusal is not an error.
+pub fn set_read_timeout(stream: &UnixStream, timeout: Duration) -> io::Result<()> {
+    match stream.set_read_timeout(Some(timeout)) {
+        #[cfg(target_vendor = "apple")]
+        Err(e) if e.raw_os_error() == Some(EINVAL) => Ok(()),
+        other => other,
+    }
+}

crates/loopd/src/tools.rs

@@ -7,7 +7,20 @@ use crate::llama::ToolSchema;
 /// The seam every tool call goes through. `loopd` answers `find_tool` and `call_tool` itself;
 /// anything else, including grants, is passed to the port (`brokerd`).
 pub trait ToolPort: Send + Sync {
-    fn call(&self, request: &proto::ToolRequest) -> proto::ToolResponse;
+    /// Returns the final answer, never `PendingApproval`. If the broker says the call is waiting
+    /// for the owner, the port calls `on_pending` once and goes on waiting.
+    fn call(
+        &self,
+        request: &proto::ToolRequest,
+        on_pending: &mut dyn FnMut(&Pending),
+    ) -> proto::ToolResponse;
+}
+
+/// One waiting call, as the broker reports it.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct Pending {
+    pub approval: u64,
+    pub expires: proto::Timestamp,
 }
 
 #[derive(Debug, Clone, PartialEq)]
@@ -26,7 +39,9 @@ impl Registry {
         Registry { entries }
     }
 
-    /// The tool set for the M2b epoch: `clock` (core) and `echo` (not core).
+    /// The tool set for the M2b epoch: `clock` (core) and `echo` (not core). This is the test
+    /// registry: `echo` exists only in `FakeTools` and the recorded conversations, and `loopd
+    /// serve` never uses it.
     pub fn m2b() -> Registry {
         Registry::new(vec![
             Entry {
@@ -40,6 +55,33 @@ impl Registry {
         ])
     }
 
+    /// The tool set for the M3a epoch: `clock` (core), then the four tools `brokerd` decides on.
+    /// The core entries match `m2b()`, so the tools array is unchanged.
+    pub fn m3a() -> Registry {
+        Registry::new(vec![
+            Entry {
+                schema: clock_schema(),
+                core: true,
+            },
+            Entry {
+                schema: read_file_schema(),
+                core: false,
+            },
+            Entry {
+                schema: write_file_schema(),
+                core: false,
+            },
+            Entry {
+                schema: shell_schema(),
+                core: false,
+            },
+            Entry {
+                schema: http_fetch_schema(),
+                core: false,
+            },
+        ])
+    }
+
     /// The fixed tools array: core entries, then `find_tool`, then `call_tool`.
     pub fn core_schemas(&self) -> Vec<ToolSchema> {
         let mut schemas: Vec<ToolSchema> = self
@@ -76,6 +118,7 @@ impl Registry {
 
 pub const FIND_TOOL: &str = "find_tool";
 pub const CALL_TOOL: &str = "call_tool";
+pub const CLOCK: &str = "clock";
 
 pub fn clock_schema() -> ToolSchema {
     ToolSchema {
@@ -102,6 +145,65 @@ pub fn echo_schema() -> ToolSchema {
     }
 }
 
+pub fn read_file_schema() -> ToolSchema {
+    ToolSchema {
+        name: "read_file".to_string(),
+        description: "Read a text file. Needs a grant from the owner for the path.".to_string(),
+        parameters: serde_json::json!({
+            "type": "object",
+            "properties": {
+                "path": { "type": "string", "description": "The absolute path of the file." }
+            },
+            "required": ["path"]
+        }),
+    }
+}
+
+pub fn write_file_schema() -> ToolSchema {
+    ToolSchema {
+        name: "write_file".to_string(),
+        description: "Write a text file, replacing it. Needs a grant from the owner for the path."
+            .to_string(),
+        parameters: serde_json::json!({
+            "type": "object",
+            "properties": {
+                "path": { "type": "string", "description": "The absolute path of the file." },
+                "content": { "type": "string", "description": "The whole new content of the file." }
+            },
+            "required": ["path", "content"]
+        }),
+    }
+}
+
+pub fn shell_schema() -> ToolSchema {
+    ToolSchema {
+        name: "shell".to_string(),
+        description: "Run a shell command in a sandbox. Needs a grant from the owner.".to_string(),
+        parameters: serde_json::json!({
+            "type": "object",
+            "properties": {
+                "command": { "type": "string", "description": "The command line to run." },
+                "cwd": { "type": "string", "description": "The absolute path of the directory to run it in." }
+            },
+            "required": ["command"]
+        }),
+    }
+}
+
+pub fn http_fetch_schema() -> ToolSchema {
+    ToolSchema {
+        name: "http_fetch".to_string(),
+        description: "Fetch an https URL. Needs a grant from the owner for the host.".to_string(),
+        parameters: serde_json::json!({
+            "type": "object",
+            "properties": {
+                "url": { "type": "string", "description": "The URL. It must start with https://" }
+            },
+            "required": ["url"]
+        }),
+    }
+}
+
 fn find_tool_schema() -> ToolSchema {
     ToolSchema {
         name: "find_tool".to_string(),
@@ -157,6 +259,9 @@ pub fn dispatch(registry: &Registry, name: &str, arguments: &str) -> Dispatch {
     if name == CALL_TOOL {
         return dispatch_call_tool(registry, arguments);
     }
+    if name == CLOCK {
+        return Dispatch::Local(proto::Timestamp::now().to_rfc3339());
+    }
     Dispatch::Port {
         tool: name.to_string(),
         arguments: arguments.to_string(),
@@ -224,6 +329,32 @@ pub fn cap_result(text: &str, cap: usize) -> (String, bool) {
     (result, true)
 }
 
+/// The one fixed sentence a denial reaches the model as, named by its reason.
+pub fn denial_text(reason: proto::DenyReason) -> &'static str {
+    match reason {
+        proto::DenyReason::NoGrant => "Denied: no grant allows this call.",
+        proto::DenyReason::GrantExpired => "Denied: the grant for this call has expired.",
+        proto::DenyReason::TaintTooHigh => {
+            "Denied: this session has seen data too sensitive for this call."
+        }
+        proto::DenyReason::DeniedByGrant => "Denied: a grant forbids this call.",
+        proto::DenyReason::ApprovalRefused => "Denied: the owner refused this call.",
+        proto::DenyReason::ApprovalExpired => {
+            "Denied: the approval request expired without an answer."
+        }
+        proto::DenyReason::InvalidArguments => "Denied: the arguments are not valid for this tool.",
+        proto::DenyReason::GrantsInvalid => {
+            "Denied: the grant files have an error; the owner has been told."
+        }
+        proto::DenyReason::AuditUnavailable => {
+            "Denied: the audit log cannot be written; the owner has been told."
+        }
+        proto::DenyReason::StateUnreadable => {
+            "Denied: this session's broker state is damaged; the owner has been told."
+        }
+    }
+}
+
 pub struct FakeTools {
     calls: Mutex<Vec<proto::ToolRequest>>,
 }
@@ -247,19 +378,17 @@ impl FakeTools {
 }
 
 impl ToolPort for FakeTools {
-    fn call(&self, request: &proto::ToolRequest) -> proto::ToolResponse {
+    fn call(
+        &self,
+        request: &proto::ToolRequest,
+        _on_pending: &mut dyn FnMut(&Pending),
+    ) -> proto::ToolResponse {
         self.calls
             .lock()
             .unwrap_or_else(|p| p.into_inner())
             .push(request.clone());
 
         match request.tool.as_str() {
-            "clock" => proto::ToolResponse::Result {
-                content: proto::Timestamp::now().to_rfc3339(),
-                class: proto::DataClass::Public,
-                untrusted: false,
-                truncated: false,
-            },
             "echo" => match serde_json::from_str::<serde_json::Value>(&request.arguments) {
                 Ok(serde_json::Value::Object(obj)) => {
                     match obj.get("text").and_then(|v| v.as_str()) {

crates/loopd/src/turn.rs

@@ -7,7 +7,7 @@ use crate::config::Config;
 use crate::llama::info::{CacheOutcome, cache_outcome};
 use crate::llama::{ChatEvent, ChatRequest, Client, InferError};
 use crate::session::{Session, SessionError};
-use crate::tools::{Registry, ToolPort, cap_result, dispatch};
+use crate::tools::{Registry, ToolPort, cap_result, denial_text, dispatch};
 use proto::{CallId, DataClass, LogRecord, Timestamp, ToolRequest, ToolResponse, TurnEvent, Usage};
 
 /// What one turn can fail with, beyond the inference server.
@@ -230,7 +230,7 @@ pub fn run_turn(
                     false,
                 )
             } else {
-                run_call(rt, session, call, call_id)
+                run_call(rt, session, call, call_id, on_event)
             };
 
             let (text, truncated) = cap_result(&text, rt.cfg.r#loop.tool_result_cap);
@@ -260,6 +260,7 @@ fn run_call(
     session: &Session,
     call: &proto::ToolCall,
     call_id: CallId,
+    on_event: &mut dyn FnMut(&TurnEvent),
 ) -> (String, DataClass, bool) {
     match dispatch(rt.registry, &call.name, &call.arguments) {
         crate::tools::Dispatch::Local(text) => (text, DataClass::Public, false),
@@ -270,7 +271,14 @@ fn run_call(
                 tool,
                 arguments,
             };
-            match rt.port.call(&request) {
+            let response = rt.port.call(&request, &mut |pending| {
+                on_event(&TurnEvent::ApprovalPending {
+                    approval: pending.approval,
+                    tool: request.tool.clone(),
+                    expires: pending.expires,
+                });
+            });
+            match response {
                 ToolResponse::Result {
                     content,
                     class,
@@ -282,14 +290,15 @@ fn run_call(
                     DataClass::Public,
                     false,
                 ),
-                ToolResponse::Denied { reason } => (
+                ToolResponse::Denied { reason } => {
-                    format!("The call was denied: {reason:?}"),
+                    on_event(&TurnEvent::ToolDenied {
-                    DataClass::Public,
+                        name: request.tool.clone(),
-                    false,
+                        reason,
-                ),
+                    });
+                    (denial_text(reason).to_string(), DataClass::Public, false)
+                }
                 ToolResponse::PendingApproval { .. } => (
-                    "This version of loopd cannot wait for approval; the call was rejected."
+                    "The tool failed: the tool broker gave no final answer".to_string(),
-                        .to_string(),
                     DataClass::Public,
                     false,
                 ),

crates/loopd/tests/args_os.rs

@@ -0,0 +1,36 @@
+//! A config path that is not UTF-8 is read as a path, not a panic (M3a review finding 7).
+
+use std::ffi::OsStr;
+use std::os::unix::ffi::OsStrExt;
+use std::process::Command;
+
+#[test]
+fn a_config_path_that_is_not_utf8_is_read_as_a_path() {
+    let path = std::env::temp_dir().join(OsStr::from_bytes(b"loopd-missing-\xff.toml"));
+    let out = Command::new(env!("CARGO_BIN_EXE_loopd"))
+        .args([
+            OsStr::new("selftest"),
+            OsStr::new("--config"),
+            path.as_os_str(),
+        ])
+        .output()
+        .unwrap();
+    assert_eq!(
+        out.status.code(),
+        Some(1),
+        "a config error, not a panic (101)"
+    );
+}
+
+#[test]
+fn a_flag_that_is_not_utf8_is_a_usage_error() {
+    let out = Command::new(env!("CARGO_BIN_EXE_loopd"))
+        .args([
+            OsStr::from_bytes(b"serve\xff"),
+            OsStr::new("--config"),
+            OsStr::new("x"),
+        ])
+        .output()
+        .unwrap();
+    assert_eq!(out.status.code(), Some(2));
+}

crates/loopd/tests/broker_port.rs

@@ -0,0 +1,314 @@
+//! Tests for `BrokerPort` against a fake `brokerd` on a temporary socket: answers, approvals and
+//! timeouts. Frames that break the protocol are in `broker_port_bad.rs`. Do not edit.
+
+#[path = "support/broker.rs"]
+mod fake;
+
+use std::io::Write;
+use std::os::unix::net::UnixListener;
+use std::thread;
+use std::time::Duration;
+
+use fake::{assert_unavailable, broker, call, frame, in_ms, request, result, send, socket_path};
+use loopd::broker_port::{BrokerPort, NoBroker, POINTER, TOO_LARGE};
+use loopd::tools::{Pending, ToolPort};
+use proto::{
+    DenyReason, Message, PROTOCOL_VERSION, Timestamp, ToolResponse, read_frame, write_frame,
+};
+
+#[test]
+fn a_result_comes_back_as_it_was_sent() {
+    let (socket, broker) = broker(|stream, request| {
+        send(stream, request.id, true, result("hello\n"));
+    });
+    let got = call(socket, 2_000, &request());
+    assert_eq!(got.response, result("hello\n"));
+    assert!(got.pending.is_empty());
+    assert!(got.lines.is_empty(), "nothing to report: {:?}", got.lines);
+
+    // What the broker received: one final frame holding exactly the request.
+    let sent = broker.join().unwrap();
+    assert_eq!(sent.v, PROTOCOL_VERSION);
+    assert!(sent.r#final, "a request is a single final frame");
+    assert_eq!(sent.msg, Message::ToolRequest(request()));
+}
+
+#[test]
+fn every_denial_and_a_failure_come_back_as_they_were_sent() {
+    let mut answers: Vec<ToolResponse> = [
+        DenyReason::NoGrant,
+        DenyReason::GrantExpired,
+        DenyReason::TaintTooHigh,
+        DenyReason::DeniedByGrant,
+        DenyReason::ApprovalRefused,
+        DenyReason::ApprovalExpired,
+        DenyReason::GrantsInvalid,
+        DenyReason::AuditUnavailable,
+        DenyReason::InvalidArguments,
+        DenyReason::StateUnreadable,
+    ]
+    .into_iter()
+    .map(|reason| ToolResponse::Denied { reason })
+    .collect();
+    answers.push(ToolResponse::Failed {
+        message: "the runner arrives in M3b".to_string(),
+    });
+    for answer in answers {
+        let reply = answer.clone();
+        let (socket, broker) = broker(move |stream, request| {
+            send(stream, request.id, true, reply);
+        });
+        let got = call(socket, 2_000, &request());
+        assert_eq!(got.response, answer);
+        assert!(
+            got.lines.is_empty(),
+            "a denial is not an outage: {:?}",
+            got.lines
+        );
+        broker.join().unwrap();
+    }
+}
+
+#[test]
+fn a_pending_frame_reaches_the_callback_and_the_final_frame_is_the_answer() {
+    let expires = in_ms(60_000);
+    let (socket, broker) = broker(move |stream, request| {
+        let pending = ToolResponse::PendingApproval {
+            approval: 41,
+            expires,
+        };
+        send(stream, request.id, false, pending);
+        thread::sleep(Duration::from_millis(150));
+        send(stream, request.id, true, result("approved"));
+    });
+    let got = call(socket, 2_000, &request());
+    assert_eq!(got.response, result("approved"));
+    assert_eq!(
+        got.pending,
+        [Pending {
+            approval: 41,
+            expires
+        }],
+        "called once, with the frame's values"
+    );
+    assert!(got.lines.is_empty(), "{:?}", got.lines);
+    broker.join().unwrap();
+}
+
+#[test]
+fn an_answer_after_expires_but_within_the_timeout_of_it_is_delivered() {
+    // expires in 100 ms, timeout 1,500 ms: the port waits until 1,600 ms. The answer comes at
+    // about 400 ms, well after `expires`: an approval given at the last moment still gets the
+    // whole timeout to run.
+    let (socket, broker) = broker(|stream, request| {
+        let pending = ToolResponse::PendingApproval {
+            approval: 1,
+            expires: in_ms(100),
+        };
+        send(stream, request.id, false, pending);
+        thread::sleep(Duration::from_millis(400));
+        send(stream, request.id, true, result("late but good"));
+    });
+    let got = call(socket, 1_500, &request());
+    assert_eq!(got.response, result("late but good"));
+    assert!(got.lines.is_empty(), "{:?}", got.lines);
+    broker.join().unwrap();
+}
+
+#[test]
+fn an_expiry_that_has_already_passed_still_leaves_the_timeout() {
+    let (socket, broker) = broker(|stream, request| {
+        let pending = ToolResponse::PendingApproval {
+            approval: 1,
+            expires: Timestamp::parse("2020-01-01T00:00:00.000Z").unwrap(),
+        };
+        send(stream, request.id, false, pending);
+        thread::sleep(Duration::from_millis(200));
+        send(stream, request.id, true, result("fine"));
+    });
+    let got = call(socket, 1_500, &request());
+    assert_eq!(got.response, result("fine"));
+    broker.join().unwrap();
+}
+
+#[test]
+fn no_socket_is_unavailable() {
+    let socket = socket_path();
+    let _ = std::fs::remove_file(&socket);
+    let got = call(socket.clone(), 2_000, &request());
+    assert_unavailable(&got, "no socket file");
+    assert!(
+        got.lines[0].contains(&socket.display().to_string()),
+        "the line names the socket: {}",
+        got.lines[0]
+    );
+    assert!(got.took < Duration::from_millis(1_500), "{:?}", got.took);
+}
+
+#[test]
+fn a_broker_that_closes_without_answering_is_unavailable() {
+    let (socket, broker) = broker(|_, _| {});
+    let got = call(socket, 2_000, &request());
+    assert_unavailable(&got, "closed before any frame");
+    assert!(
+        got.took < Duration::from_millis(1_500),
+        "a close is seen at once: {:?}",
+        got.took
+    );
+    broker.join().unwrap();
+}
+
+#[test]
+fn a_broker_that_closes_while_pending_is_unavailable() {
+    let (socket, broker) = broker(|stream, request| {
+        let pending = ToolResponse::PendingApproval {
+            approval: 3,
+            expires: in_ms(60_000),
+        };
+        send(stream, request.id, false, pending);
+        // brokerd was restarted: the connection just ends.
+    });
+    let got = call(socket, 2_000, &request());
+    assert_unavailable(&got, "closed while pending");
+    assert_eq!(got.pending.len(), 1, "the pending frame was reported first");
+    assert!(got.took < Duration::from_millis(1_500), "{:?}", got.took);
+    broker.join().unwrap();
+}
+
+#[test]
+fn a_broker_that_never_answers_is_unavailable_after_the_timeout() {
+    let (socket, broker) = broker(|_, _| thread::sleep(Duration::from_millis(1_200)));
+    let got = call(socket, 300, &request());
+    assert_unavailable(&got, "silence");
+    assert!(
+        got.took >= Duration::from_millis(250),
+        "gave up early: {:?}",
+        got.took
+    );
+    assert!(
+        got.took < Duration::from_millis(1_100),
+        "gave up late: {:?}",
+        got.took
+    );
+    broker.join().unwrap();
+}
+
+#[test]
+fn a_pending_call_nobody_answers_ends_at_expires_plus_the_timeout() {
+    let (socket, broker) = broker(|stream, request| {
+        let pending = ToolResponse::PendingApproval {
+            approval: 3,
+            expires: in_ms(300),
+        };
+        send(stream, request.id, false, pending);
+        thread::sleep(Duration::from_millis(1_800));
+    });
+    let got = call(socket, 300, &request());
+    assert_unavailable(&got, "silence while pending");
+    assert!(
+        got.took >= Duration::from_millis(550),
+        "it must wait for expires (300) plus the timeout (300): {:?}",
+        got.took
+    );
+    assert!(
+        got.took < Duration::from_millis(1_700),
+        "gave up late: {:?}",
+        got.took
+    );
+    broker.join().unwrap();
+}
+
+#[test]
+fn the_timeout_is_a_deadline_for_the_frame_not_for_each_read() {
+    // The four header bytes arrive 250 ms apart, the last at 1,000 ms. A port that only sets a
+    // 600 ms read timeout sees every single read succeed and returns the result; a port with a
+    // deadline gives up at 600 ms. The answer tells them apart, so no timing is asserted.
+    let (socket, broker) = broker(|stream, request| {
+        let mut bytes = Vec::new();
+        write_frame(
+            &mut bytes,
+            &frame(request.id, true, Message::ToolResponse(result("slow"))),
+        )
+        .unwrap();
+        for byte in bytes.iter().take(4) {
+            thread::sleep(Duration::from_millis(250));
+            if stream.write_all(&[*byte]).is_err() {
+                return;
+            }
+        }
+        let _ = stream.write_all(&bytes[4..]);
+    });
+    let got = call(socket, 600, &request());
+    assert_unavailable(&got, "a trickled frame");
+    broker.join().unwrap();
+}
+
+#[test]
+fn a_zero_timeout_fails_closed_and_does_not_panic() {
+    let (socket, _broker) = broker(|stream, request| {
+        send(stream, request.id, true, result("too late"));
+    });
+    let got = call(socket, 0, &request());
+    assert_unavailable(&got, "timeout_ms = 0");
+}
+
+#[test]
+fn a_request_too_large_for_a_frame_is_its_own_failure() {
+    // Nothing is sent, so the fake broker sees a connection that closes or none at all.
+    let path = socket_path();
+    let _ = std::fs::remove_file(&path);
+    let _listener = UnixListener::bind(&path).unwrap();
+    let mut big = request();
+    big.arguments = format!(r#"{{"path":"/{}"}}"#, "a".repeat(proto::MAX_FRAME));
+    let got = call(path, 1_000, &big);
+    assert_eq!(
+        got.response,
+        ToolResponse::Failed {
+            message: TOO_LARGE.to_string()
+        }
+    );
+    assert!(
+        got.lines.is_empty(),
+        "the broker is fine; this is not an outage: {:?}",
+        got.lines
+    );
+}
+
+#[test]
+fn every_call_is_its_own_connection() {
+    let path = socket_path();
+    let _ = std::fs::remove_file(&path);
+    let listener = UnixListener::bind(&path).unwrap();
+    let server = thread::spawn(move || {
+        for n in 0..3u64 {
+            let (mut stream, _) = listener.accept().unwrap();
+            let request = read_frame(&mut stream).unwrap();
+            send(
+                &mut stream,
+                request.id,
+                true,
+                result(&format!("answer {n}")),
+            );
+        }
+    });
+    let port = BrokerPort::new(path, Duration::from_millis(2_000));
+    for n in 0..3 {
+        let got = port.call(&request(), &mut |_| {});
+        assert_eq!(got, result(&format!("answer {n}")));
+    }
+    server.join().unwrap();
+}
+
+#[test]
+fn without_a_broker_every_call_fails_in_words_the_model_can_repeat() {
+    let mut seen = 0;
+    let got = NoBroker.call(&request(), &mut |_| seen += 1);
+    assert_eq!(
+        got,
+        ToolResponse::Failed {
+            message: "no tool broker is configured".to_string()
+        }
+    );
+    assert_eq!(seen, 0);
+    assert_eq!(POINTER, "see docs/runbook.md#broker-unavailable");
+}