brokerd: config, [gateway] socket for Mattermost approvals

crates/brokerd/src/config.rs

@@ -45,6 +45,14 @@ impl Default for Approvals {
     }
 }
 
+/// `[gateway]`: where `gatewayd` takes approvals to post in Mattermost. Without the section,
+/// Mattermost approvals are off and only `bxctl` answers. An empty path means the default.
+#[derive(Debug, Clone, PartialEq, Eq, Deserialize, Default)]
+#[serde(deny_unknown_fields, default)]
+pub struct Gateway {
+    pub socket: PathBuf,
+}
+
 fn default_podman() -> PathBuf {
     PathBuf::from("podman")
 }
@@ -129,6 +137,8 @@ pub struct Config {
     pub approvals: Approvals,
     #[serde(default)]
     pub runner: Option<Runner>,
+    #[serde(default)]
+    pub gateway: Option<Gateway>,
 }
 
 /// The longest an approval may wait: a day, the longest `loopd` waits after a pending frame.
@@ -262,6 +272,15 @@ impl Config {
             self.sockets.admin.clone()
         }
     }
+    /// `gateway.sock`, when `[gateway]` is set.
+    pub fn gateway_socket(&self) -> Option<PathBuf> {
+        let gateway = self.gateway.as_ref()?;
+        if gateway.socket.as_os_str().is_empty() {
+            Some(self.paths.home.join("run/gateway/gateway.sock"))
+        } else {
+            Some(gateway.socket.clone())
+        }
+    }
     pub fn audit_dir(&self) -> PathBuf {
         self.paths.home.join("audit")
     }

crates/brokerd/tests/config_gateway.rs

@@ -0,0 +1,43 @@
+//! `[gateway]` in `brokerd.toml`: absent means Mattermost approvals are off; an empty socket is
+//! the default under `home` (M4b spec, section 3). Do not edit.
+
+use std::path::PathBuf;
+
+use brokerd::config::Config;
+
+fn parse(text: &str) -> Config {
+    Config::parse(&format!("[paths]\nhome = \"/srv/bx\"\n{text}")).unwrap()
+}
+
+#[test]
+fn without_the_section_approvals_stay_in_bxctl() {
+    let config = parse("");
+    assert_eq!(config.gateway, None);
+    assert_eq!(config.gateway_socket(), None);
+}
+
+#[test]
+fn an_empty_section_or_socket_is_the_default() {
+    let default = Some(PathBuf::from("/srv/bx/run/gateway/gateway.sock"));
+    assert_eq!(parse("[gateway]\n").gateway_socket(), default);
+    assert_eq!(
+        parse("[gateway]\nsocket = \"\"\n").gateway_socket(),
+        default
+    );
+}
+
+#[test]
+fn a_socket_path_is_used_as_given() {
+    let config = parse("[gateway]\nsocket = \"/run/bx/gw.sock\"\n");
+    assert_eq!(
+        config.gateway_socket(),
+        Some(PathBuf::from("/run/bx/gw.sock"))
+    );
+}
+
+#[test]
+fn unknown_keys_are_errors() {
+    assert!(Config::parse("[gateway]\nsockets = \"/x\"\n").is_err());
+    assert!(Config::parse("[gateway]\nsocket = \"/x\"\nenabled = true\n").is_err());
+    assert!(Config::parse("[gatewy]\nsocket = \"/x\"\n").is_err());
+}

crates/brokerd/tests/support/rig.rs

@@ -41,6 +41,7 @@ impl Rig {
             sockets: Sockets::default(),
             approvals: Approvals { ttl_ms },
             runner: None,
+            gateway: None,
         };
         Rig {
             dir,

docs/implementer-log.md

@@ -6,6 +6,7 @@ reviewer adds findings under "Reviews" once per milestone.
 
 | Task | Date | Status | Gate runs | First gate | Deviations | Notes | Model |
 |---|---|---|---|---|---|---|---|
+| M4b/05-brokerd-config-gateway | 2026-09-24 | done | 1 | pass | none | Copied `docs/plans/M4b/files/crates/brokerd/tests/config_gateway.rs` and the new `support/rig.rs` (whose `Config` gained `gateway: None`) into `crates/brokerd/tests/`. In `config.rs`: added the `Gateway { socket: PathBuf }` struct (`#[serde(deny_unknown_fields, default)]`) before `default_podman`, the `gateway: Option<Gateway>` field (with `#[serde(default)]`) after `runner` in `Config`, and the `gateway_socket()` method before `audit_dir` — `None` when the section is absent, the default `<home>/run/gateway/gateway.sock` when the socket is empty, else the path as given. `cargo fmt --all` then `cargo test -p brokerd` green with `config_gateway` 4 passed; `make gate` prints `gate: ok` on the first run. | ? |
 | M4b/04-brokerd-answer-post | 2026-09-24 | done | 1 | pass | none | Moved `enum Answer` and `struct Answered` from `ledger.rs` into `approvals.rs` before `pub struct Entry` (with doc comments), added `pub use crate::approvals::{Answer, Answered};` next to the `Verdict` use and `DecisionRecord` to the `use proto` line in `approvals.rs`. Added the `post` field to `Answer::Approved`/`Answer::Refused`, threaded it through `ledger::answer` (step 3 binds `post`, step 6 writes it into `AuditEvent::Approval` instead of `None`), and gave the two `bxctl` answers in `admin.rs` `post: None`. Added `Table::contains` before `take`. Copied `ledger_post.rs`, `broker_pending.rs`, `broker_sequence.rs` and `ledger_answer.rs` into `crates/brokerd/tests/`; every suite passes, `ledger_post` 3 passed, `ledger.rs` is 487 lines, and `make gate` prints `gate: ok` on the first run. | ? |
 | M4b/03-bxctl-deny | 2026-09-24 | done | 1 | pass | none | Copied `docs/plans/M4b/files/crates/bxctl/tests/cli_deny.rs` into `crates/bxctl/tests/`. In `parse`, `"refuse" => parse_refuse(rest, home)` became `"refuse" | "deny" => parse_refuse(rest, home)`, so `deny` produces the same `Command::Refuse` as `refuse` for every argument list including the error cases. Added a blank line and the two-line `bxctl deny <id> [--reason TEXT] [--admin-socket PATH]` / `Another name for refuse.` block to `USAGE` after the `refuse` block, keeping the two-space and six-space indents. The copied test's `deny_parses_as_refuse` and `usage_names_deny` both failed before the changes and pass after; `cargo test -p bxctl` is green and `make gate` prints `gate: ok` on the first run. | ? |
 | M4b/02-proto-gateway-wire | 2026-09-24 | done | 2 | fail | none | Copied `gateway.rs`, `gateway_wire.rs` and the eight `gateway_*.json` fixtures into place; added `pub mod gateway;` after `pub mod frame;` and the re-export to `lib.rs`, the four `Message` variants plus the `use` to `wire.rs`, and the four `kind` arms (changing "fourteen" to "eighteen") in `broker.rs`. Filled `is_mattermost_id` (`id.len() == 26 && every byte a-z0-9`) and `ApprovalReply::check` in the given order: `by`, `post`, then a reason over `MAX_REASON` chars by `chars().count()`. All 3 `gateway_wire` tests pass; the first `make gate` failed on clippy `collapsible_if`, fixed by collapsing the nested `if let` into a let-chain guard, and the second prints `gate: ok`. | ? |