Add the loopd serve command

Implemented-By: OpenCode session (model recorded in docs/implementer-log.md)

crates/loopd/src/main.rs

@@ -1,25 +1,49 @@
-//! `loopd`: the agent loop daemon. Its one command today is `selftest`, which runs the startup
-//! checks before `loopd` serves anyone.
+//! `loopd`: the agent loop daemon. It has two commands: `selftest`, which runs the startup checks
+//! before serving anyone, and `serve`, which runs those checks and then runs the channel server.
 
+use std::os::unix::fs::PermissionsExt;
+use std::os::unix::net::UnixListener;
 use std::path::Path;
 use std::process::ExitCode;
+use std::sync::Arc;
 
+use loopd::channel::{self, Context};
 use loopd::config::Config;
 use loopd::llama::Client;
-use loopd::selftest::run;
+use loopd::selftest::{SelfTestError, run};
+use loopd::tools::{FakeTools, Registry};
 
 fn main() -> ExitCode {
     let args: Vec<String> = std::env::args().skip(1).collect();
     let args: Vec<&str> = args.iter().map(String::as_str).collect();
     match args.as_slice() {
         ["selftest", "--config", path] => run_selftest(path),
+        ["serve", "--config", path] => run_serve(path),
         _ => {
             eprintln!("usage: loopd selftest --config <path>");
+            eprintln!("usage: loopd serve --config <path>");
             ExitCode::from(2)
         }
     }
 }
 
+/// The startup checks, with the lines `loopd` prints. Shared by `selftest` and `serve`.
+fn run_selftest_check(client: &Client) -> Result<(), SelfTestError> {
+    let mut on_step = |step: &str| {
+        eprintln!("selftest: {step}");
+    };
+    match run(client, &mut on_step) {
+        Ok(()) => {
+            eprintln!("selftest: ok");
+            Ok(())
+        }
+        Err(e) => {
+            eprintln!("selftest: FAILED: {e}");
+            Err(e)
+        }
+    }
+}
+
 fn run_selftest(path: &str) -> ExitCode {
     let cfg = match Config::load(Path::new(path)) {
         Ok(cfg) => cfg,
@@ -29,19 +53,66 @@ fn run_selftest(path: &str) -> ExitCode {
         }
     };
 
-    let mut on_step = |step: &str| {
-        eprintln!("selftest: {step}");
-    };
-    let result = run(&Client::new(cfg), &mut on_step);
+    let client = Client::new(cfg);
+    match run_selftest_check(&client) {
+        Ok(()) => ExitCode::SUCCESS,
+        Err(_) => ExitCode::from(1),
+    }
+}
 
-    match result {
-        Ok(()) => {
-            eprintln!("selftest: ok");
+fn run_serve(path: &str) -> ExitCode {
+    let cfg = match Config::load(Path::new(path)) {
+        Ok(cfg) => cfg,
+        Err(e) => {
+            eprintln!("loopd: {e}");
+            return ExitCode::from(1);
+        }
+    };
+
+    let socket = cfg.channel_socket();
+    if socket.exists()
+        && let Err(e) = std::fs::remove_file(&socket)
+    {
+        eprintln!(
+            "loopd: cannot remove the old socket at {}: {e}",
+            socket.display()
+        );
+        return ExitCode::from(1);
+    }
+
+    let client = Client::new(cfg.clone());
+    if run_selftest_check(&client).is_err() {
+        return ExitCode::from(1);
+    }
+
+    if let Some(parent) = socket.parent()
+        && let Err(e) = std::fs::create_dir_all(parent)
+    {
+        eprintln!("loopd: cannot create the socket directory: {e}");
+        return ExitCode::from(1);
+    }
+    let listener = match UnixListener::bind(&socket) {
+        Ok(listener) => listener,
+        Err(e) => {
+            eprintln!("loopd: cannot bind the socket at {}: {e}", socket.display());
+            return ExitCode::from(1);
+        }
+    };
+    if let Err(e) = std::fs::set_permissions(&socket, std::fs::Permissions::from_mode(0o600)) {
+        eprintln!("loopd: cannot set the mode of {}: {e}", socket.display());
+        return ExitCode::from(1);
+    }
+    eprintln!("loopd: serving on {}", socket.display());
+
+    let ctx = Arc::new(Context::new(
+        cfg,
+        client,
+        Box::new(FakeTools::new()),
+        Registry::m2b(),
+    ));
+    if let Err(e) = channel::serve(listener, ctx) {
+        eprintln!("loopd: the channel server stopped: {e}");
+        return ExitCode::from(1);
+    }
     ExitCode::SUCCESS
 }
-        Err(e) => {
-            eprintln!("selftest: FAILED: {e}");
-            ExitCode::from(1)
-        }
-    }
-}

crates/loopd/tests/serve.rs

@@ -0,0 +1,122 @@
+//! Tests for the `loopd serve` command. Do not edit.
+
+mod support;
+
+use std::os::unix::fs::PermissionsExt;
+use std::process::{Command, Stdio};
+use std::time::Duration;
+use support::{FakeServer, Home, Reply};
+
+fn config_file(home: &Home, server: &FakeServer, expect_slots: u32) -> std::path::PathBuf {
+    let text = format!(
+        r#"
+[infer]
+socket = "{}"
+model = "test-model"
+[slots]
+main = 0
+background = 1
+[expect]
+template_sha256 = "f55f52930aa8bf44ab5cb85f99370fcc3c56e9a85640b812086d5330bce5d86b"
+n_ctx = 131072
+slots = {expect_slots}
+[limits]
+poll_ms = 40
+liveness_ms = 500
+retry_backoff_ms = [10]
+[paths]
+home = "{}"
+"#,
+        server.socket.display(),
+        home.dir.display()
+    );
+    let path = home.dir.join("config.toml");
+    std::fs::write(&path, text).unwrap();
+    path
+}
+
+fn healthy_routes(server: &FakeServer) {
+    server.route("/props", vec![Reply::fixture("props")]);
+    server.route(
+        "/v1/chat/completions",
+        vec![
+            Reply::fixture("tool_call"),
+            Reply::fixture("turn1"),
+            Reply::fixture("turn2"),
+            Reply::fixture("plain"),
+        ],
+    );
+}
+
+#[test]
+fn serve_runs_the_self_test_then_binds_the_socket_with_mode_0600() {
+    let home = Home::new();
+    let server = FakeServer::start();
+    healthy_routes(&server);
+    let config = config_file(&home, &server, 2);
+    let socket = home.dir.join("run").join("loop").join("loop.sock");
+    let mut child = Command::new(env!("CARGO_BIN_EXE_loopd"))
+        .args(["serve", "--config"])
+        .arg(&config)
+        .stderr(Stdio::piped())
+        .spawn()
+        .unwrap();
+    let mut up = false;
+    for _ in 0..200 {
+        if socket.exists() {
+            up = true;
+            break;
+        }
+        std::thread::sleep(Duration::from_millis(50));
+    }
+    let mode = std::fs::metadata(&socket).map(|m| m.permissions().mode() & 0o777);
+    let _ = child.kill();
+    let output = child.wait_with_output().unwrap();
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    assert!(up, "the socket never appeared; stderr: {stderr}");
+    assert_eq!(mode.unwrap(), 0o600, "{stderr}");
+    assert!(stderr.contains("selftest: ok"), "{stderr}");
+    assert!(stderr.contains("serving on"), "{stderr}");
+    assert_eq!(
+        server.requests_to("/v1/chat/completions").len(),
+        3,
+        "the three self-test completions ran"
+    );
+}
+
+#[test]
+fn serve_refuses_to_start_when_the_self_test_fails() {
+    let home = Home::new();
+    let server = FakeServer::start();
+    healthy_routes(&server);
+    let config = config_file(&home, &server, 3); // the fixture reports 2 slots
+    let output = Command::new(env!("CARGO_BIN_EXE_loopd"))
+        .args(["serve", "--config"])
+        .arg(&config)
+        .output()
+        .unwrap();
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    assert_eq!(output.status.code(), Some(1), "{stderr}");
+    assert!(stderr.contains("selftest: FAILED"), "{stderr}");
+    assert!(stderr.contains("slot count"), "{stderr}");
+    assert!(
+        !home.dir.join("run").join("loop").join("loop.sock").exists(),
+        "no socket was left behind"
+    );
+}
+
+#[test]
+fn usage_and_a_bad_config_are_reported() {
+    let output = Command::new(env!("CARGO_BIN_EXE_loopd"))
+        .arg("dance")
+        .output()
+        .unwrap();
+    assert_eq!(output.status.code(), Some(2));
+    assert!(String::from_utf8_lossy(&output.stderr).contains("usage"));
+    let output = Command::new(env!("CARGO_BIN_EXE_loopd"))
+        .args(["serve", "--config", "/nonexistent/config.toml"])
+        .output()
+        .unwrap();
+    assert_eq!(output.status.code(), Some(1));
+    assert!(String::from_utf8_lossy(&output.stderr).contains("config.toml"));
+}

docs/implementer-log.md

@@ -37,6 +37,7 @@ reviewer adds findings under "Reviews" once per milestone.
 | M2b/05-loopd-session | 2026-09-18 | done | 2 | fail | none | Copied the given test byte-identical and wrote crates/loopd/src/session.rs: `Session` (id, dir, baseline, records, appended log file, next_call) and `SessionError` (Exists/NotFound/Io/Torn/Baseline/Encode) with derived Debug, Display and std::error::Error::source. `create` refuses an existing dir, writes `0.baseline.json`, opens `0.jsonl` with `create_new`+`append`, and appends a `SessionStart` (`Timestamp::now()`, epoch 0, the slot, `baseline.hash()`). `open` reads the baseline from the file (not `system.md`), requires every log line to end in `\n` and parse as a `LogRecord` else `Torn` with the 1-based line and reason, and sets `next_call` to one past the highest `ToolResult` call. `append` encodes, writes, `sync_data()`, then pushes to memory. All 7 session tests pass. First gate failed on clippy: split the `source()` arm that bound three different error types into three arms, removed the redundant `.write(true)` (implied by `append`), and used `path.display()` for the `Torn` path. | ? |
 | M2b/06-loopd-turn | 2026-09-18 | done | 1 | pass | none | Wrote crates/loopd/src/turn.rs (299 lines) and registered `pub mod turn;` in lib.rs; copied the two given tests and three fixtures byte-identical. `TurnError` (SessionFull/TurnLimit/Infer/Session, Display + std::error::Error + From<SessionError>), `TurnOutcome`, `Runtime`, `is_context_full` (the one 400 whose JSON `error.type` is `exceed_context_size_error`), and `run_turn`: append User, build the ChatRequest (slot, messages, tools, thinking), capture `last_usage`, `chat_with_retry` mapping ChatEvent->TurnEvent (dropping ToolCallDelta), append Assistant then Usage, report cache loss between the two conversations, and on no tool calls return `TurnOutcome { content: completion.content.unwrap_or_default(), usage }`; otherwise iterate tool calls under the iteration cap with a repeated-call detector (first repeat returns "already called", a second repeat is TurnLimit), `cap_result`, and `dispatch` (find_tool/call_tool local, every other tool — including read_file — to the port). `run_call` maps Dispatch::Local and every ToolResponse variant to (text, Public, untrusted). Two compile fixes before the gate: `u64::try_from(*ahead).unwrap_or(u64::MAX)` (usize has no From<u64>) and `let Ok(value) = from_str(body) else { return false }` (a temporary borrow); `session.baseline()` returns a reference so it is bound inside the loop. All 6 turn and 9 limits tests pass; `make gate` prints `gate: ok`. | ? |
 | M2b/07-loopd-channel | 2026-09-18 | done | 3 | fail | none | Wrote crates/loopd/src/channel.rs and registered `pub mod channel;` in lib.rs. `Context` holds a private `Mutex<HashSet<SessionId>>`; `serve` accepts forever with one thread per connection and returns on an accept error; `handle` does the seven steps (read_frame with Closed-before-anything, turn-only, mark busy, open-or-create plus run_turn streaming events, release before the final frame, error-code mapping, quiet write failure). The busy guard is a `Held` struct that borrows the context immutably and holds a clone of the id but never the lock, and it is dropped before sending turn_done or error so a client can send the next turn the moment it reads the last one — that is what keeps `a_busy_session_is_refused_at_once` and the concurrent-session test correct. Channel test reported `6 passed` ten runs in a row, all clean. Two fixes before a clean gate: `cargo fmt` import order and a clippy `question_mark` on the accept loop, re-run after each. | ? |
+| M2b/08-loopd-serve | 2026-09-18 | done | 2 | fail | none | Rewrote crates/loopd/src/main.rs into two commands, `selftest` and `serve`, both sharing `run_selftest_check` so the self-test lines are identical. `serve` loads config (exit 1 on failure), removes an existing socket via `channel_socket()` before the self-test, runs the self-test and exits 1 without binding on failure, then creates the socket's parent dir, binds, sets mode 0600 with `std::fs::set_permissions`, prints `serving on`, and calls `channel::serve` with a `Context` from the config, client, `Box::new(FakeTools::new())` and `Registry::m2b()`. Anything else prints both usages and exits 2. The `serve_refuses...` test's "no socket left behind" holds because the socket is removed before the self-test and binding happens only after it passes. First gate run failed on two clippy `collapsible_if` lints; collapsed the two nested `if let` into edition-2024 let-chains and re-ran, which passed. `cargo test -p loopd --test serve` reports 3 passed. | ? |
 
 
 ## Reviews