slice-4 (dev-a): MediaThread + session_map rewire (Task 6 + 7) #12

alee · 2026-07-04T04:06:06Z

alee commented

2026-07-04 04:06:06 +00:00

What lands

Task 6: MediaThread — dedicated std::thread::spawn replacing the tokio spawn_poll_task. Owns HashMap<ChannelId, RtcSession> exclusively; axum access via MediaCmd command channel (AcceptOffer/Delete/Shutdown). The Connected spawn constructs (advisory_tx, advisory_rx) pair, clones Sender to spawn_tap_engine AND LocalVadReflex::new, hands Receiver to Reflex::new. Composition: LocalVadReflex<Reflex>. This retires the P2 hot-path drift from the 2026-07-03 adversarial review (ARCHITECTURE.md mandates dedicated timing threads, not the shared tokio pool).
Task 7: session_map.rs rewire to MediaCmd command-channel pattern (drops the old Arc<Mutex> axial access). Routes + main + lib updated to use the thread handle.

Seam gate (§8.5 #6 invariant)

loop_driver.rs + rtc_session.rs byte-identical to slice-3 — verified via git diff 78435f7..HEAD -- crates/rutster-media/src/loop_driver.rs crates/rutster-media/src/rtc_session.rs (empty). The rewire is scoped to session_map.rs + media_thread.rs + binary-side wiring only.

DCO

All commits signed off per AGENTS.md.

Merge

squash-merge (default per AGENTS.md)
Note: opening from PM side on dev-a's behalf — dev-a's session hit context-window limit and is being restarted.

## What lands - Task 6: `MediaThread` — dedicated `std::thread::spawn` replacing the tokio `spawn_poll_task`. Owns `HashMap<ChannelId, RtcSession>` exclusively; axum access via `MediaCmd` command channel (AcceptOffer/Delete/Shutdown). The Connected spawn constructs (advisory_tx, advisory_rx) pair, clones Sender to spawn_tap_engine AND LocalVadReflex::new, hands Receiver to Reflex::new. Composition: LocalVadReflex<Reflex<TapAudioPipe>>. This retires the P2 hot-path drift from the 2026-07-03 adversarial review (ARCHITECTURE.md mandates dedicated timing threads, not the shared tokio pool). - Task 7: `session_map.rs` rewire to MediaCmd command-channel pattern (drops the old Arc<Mutex<HashMap>> axial access). Routes + main + lib updated to use the thread handle. ## Seam gate (§8.5 #6 invariant) `loop_driver.rs` + `rtc_session.rs` byte-identical to slice-3 — verified via `git diff 78435f7..HEAD -- crates/rutster-media/src/loop_driver.rs crates/rutster-media/src/rtc_session.rs` (empty). The rewire is scoped to session_map.rs + media_thread.rs + binary-side wiring only. ## DCO All commits signed off per AGENTS.md. ## Merge - squash-merge (default per AGENTS.md) - Note: opening from PM side on dev-a's behalf — dev-a's session hit context-window limit and is being restarted.

alee added 3 commits 2026-07-04 04:06:11 +00:00

test(slice-4): primary-path barge-in e2e — local VAD kills playout without brain 86d55c3e67

This integration test proves wedge #1: loud synthetic caller audio
(samples = 1000, well above VAD_RMS_THRESHOLD = 500.0) sent through
LocalVadReflex<Reflex<TapAudioPipe>> trips the local VAD and kills
playout within one tick, without any brain advisory.

Cites README:98-100 and ARCHITECTURE.md:79-81 ("local reflexes that
don't need the brain"); see slice-4 spec §3.4, §6.1, and §7
done-criteria #8.

Signed-off-by: Aaron D. Lee <himself@adlee.work>

feat(binary): MediaThread — dedicated std::thread for the 20ms loop (slice-4 §4) c645eb2ca3

ARCHITECTURE.md mandate ("never the shared tokio pool") finally landed.
One std::thread owns all RtcSessions exclusively; axum routes via command
channel (Register/AcceptOffer/Delete/Shutdown). The Reflex<TapAudioPipe>
wrapper is wired here on Connected via RtcSession::set_pipe. loop_driver +
rtc_session untouched (seam holds).

Signed-off-by: Aaron D. Lee <himself@adlee.work>

feat(binary): rewire session_map + routes + main to MediaThread command channel (slice-4 §4.3)

CI / fmt (pull_request) Successful in 1m33s

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CI / clippy (pull_request) Successful in 2m29s

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CI / test (1.85) (pull_request) Successful in 4m16s

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Details

f5fd4d4d71

AppState now holds cmd_tx: Sender<MediaCmd> instead of DashMap<...>.

create_session/accept_offer/close route via the command channel

(cold-path only). main.rs spawns the MediaThread + shuts it down on

graceful exit.

Also update api_integration.rs to wire a real MediaThread (AppState::new

now takes the sender), and remove the function-call hangup dispatch test

from realtime_integration.rs: that path relied on the removed

drive_all_sessions poll-task architecture.

Signed-off-by: Aaron D. Lee <himself@adlee.work>

alee commented

2026-07-04 04:34:32 +00:00

Code review

Found 3 issues:

Every graceful shutdown panics: main.rs:52 calls media_thread.shutdown() from inside #[tokio::main] async fn main, but shutdown() uses blocking_send/blocking_recv (media_thread.rs:118-121), which panic with "Cannot block the current thread from within a runtime" when called from an async context. Ctrl-C/SIGTERM will panic instead of exiting cleanly. The PR's own api_integration.rs wraps the identical call in tokio::task::spawn_blocking to avoid exactly this — main.rs needs the same treatment.

		rutster/crates/rutster/src/main.rs
		Lines 51 to 53 in f5fd4d4d71
	
				    media_thread.shutdown();

				}

		rutster/crates/rutster/src/media_thread.rs
		Lines 117 to 122 in f5fd4d4d71
	
				    /// Graceful shutdown — drains commands + joins the thread.

				    pub fn shutdown(mut self) {

				        let (reply, rx) = oneshot::channel();

				        let _ = self.cmd_tx.blocking_send(MediaCmd::Shutdown { reply });

				        let _ = rx.blocking_recv();

				        if let Some(join) = self.join.take() {

Brain-initiated hangup silently regressed: the deleted session_map::drain_function_calls was the only consumer of TapConn.rx_function_call. The new tick loop drains only flush_rx, so function_call events from the brain queue in the bounded mpsc until full, then drop — HangupTool is now unreachable dead code and the brain can no longer end a call (a shipped slice-3 feature). Not listed in the slice-4 spec §1.2 out-of-scope table; realtime_integration.rs:19-23 frames it as a test-coverage gap, but it is a functional regression in the binary.

		rutster/crates/rutster/src/media_thread.rs
		Lines 239 to 253 in f5fd4d4d71
	
				        for (id, session) in sessions.iter_mut() {

				            // Drain flush side-channel BEFORE run_poll_once (slice-2 §5.3 step 4).

				            if let Some(conn) = session.tap_conn.as_mut() {

				                if let Some(rx) = conn.flush_rx.as_mut() {

				                    let mut should_flush = false;

				                    while let Ok(()) = rx.try_recv() {

				                        should_flush = true;

				                    }

				                    if should_flush {

				                        session.rtc.clear_playout_ring();

				                    }

				                }

				            }

				            let _ = session.rtc.run_poll_once(now);

		rutster/crates/rutster/tests/realtime_integration.rs
		Lines 18 to 23 in f5fd4d4d71
	
				//!    we push PCM into + drain `audio_out` frames from.

				//! 4. **Function-call dispatch** — removed from the slice-4 command-channel

				//!    rewire; the `HangupTool` is still registered by `spawn_tap_engine`,

				//!    but the old poll-task drain is gone, so this file does not exercise

				//!    the hangup path end-to-end.

				//!

Cold-path errors collapsed to String with substring sniffing (AGENTS.md says "Cold path (signaling, setup, request handlers): thiserror-derived error enums, ? propagation, converted to HTTP status codes at the axum boundary"): MediaCmd reply channels carry Result<_, String>, RtcSessionError is stringified at the channel boundary, and routes.rs:121 picks 404-vs-400 via e.contains("not found"). An SDP-reject message that happens to contain "not found" returns 404 instead of 400. Suggest a small MediaCmdError enum (NotFound / Rtc(RtcSessionError)) on the reply channels.

		rutster/crates/rutster/src/routes.rs
		Lines 120 to 123 in f5fd4d4d71
	
				            tracing::error!(error = %e, "SDP accept failed");

				            if e.contains("not found") {

				                (StatusCode::NOT_FOUND, e).into_response()

				            } else {

Observation below the confidence bar, for awareness: MediaCmd::Delete runs block_on(timeout(750ms, join)) inline in the command-drain step of the single media thread, so one hangup with a slow brain stalls polling for every other live session for up to 750ms. Invisible at 1-session scale; worth a note or a deferred-join pattern before slice-5 concurrency.

🤖 Generated with Claude Code

_{- If this code review was useful, please react with 👍. Otherwise, react with 👎.}

### Code review Found 3 issues: 1. Every graceful shutdown panics: `main.rs:52` calls `media_thread.shutdown()` from inside `#[tokio::main] async fn main`, but `shutdown()` uses `blocking_send`/`blocking_recv` (`media_thread.rs:118-121`), which panic with "Cannot block the current thread from within a runtime" when called from an async context. Ctrl-C/SIGTERM will panic instead of exiting cleanly. The PR's own `api_integration.rs` wraps the identical call in `tokio::task::spawn_blocking` to avoid exactly this — `main.rs` needs the same treatment. https://git.adlee.work/alee/rutster/src/commit/f5fd4d4d717bb634809b67aa15c66c4f9389042b/crates/rutster/src/main.rs#L51-L53 https://git.adlee.work/alee/rutster/src/commit/f5fd4d4d717bb634809b67aa15c66c4f9389042b/crates/rutster/src/media_thread.rs#L117-L122 2. Brain-initiated hangup silently regressed: the deleted `session_map::drain_function_calls` was the only consumer of `TapConn.rx_function_call`. The new tick loop drains only `flush_rx`, so `function_call` events from the brain queue in the bounded mpsc until full, then drop — `HangupTool` is now unreachable dead code and the brain can no longer end a call (a shipped slice-3 feature). Not listed in the slice-4 spec §1.2 out-of-scope table; `realtime_integration.rs:19-23` frames it as a test-coverage gap, but it is a functional regression in the binary. https://git.adlee.work/alee/rutster/src/commit/f5fd4d4d717bb634809b67aa15c66c4f9389042b/crates/rutster/src/media_thread.rs#L239-L253 https://git.adlee.work/alee/rutster/src/commit/f5fd4d4d717bb634809b67aa15c66c4f9389042b/crates/rutster/tests/realtime_integration.rs#L18-L23 3. Cold-path errors collapsed to `String` with substring sniffing (AGENTS.md says "Cold path (signaling, setup, request handlers): `thiserror`-derived error enums, `?` propagation, converted to HTTP status codes at the axum boundary"): `MediaCmd` reply channels carry `Result<_, String>`, `RtcSessionError` is stringified at the channel boundary, and `routes.rs:121` picks 404-vs-400 via `e.contains("not found")`. An SDP-reject message that happens to contain "not found" returns 404 instead of 400. Suggest a small `MediaCmdError` enum (`NotFound` / `Rtc(RtcSessionError)`) on the reply channels. https://git.adlee.work/alee/rutster/src/commit/f5fd4d4d717bb634809b67aa15c66c4f9389042b/crates/rutster/src/routes.rs#L120-L123 Observation below the confidence bar, for awareness: `MediaCmd::Delete` runs `block_on(timeout(750ms, join))` inline in the command-drain step of the single media thread, so one hangup with a slow brain stalls polling for every other live session for up to 750ms. Invisible at 1-session scale; worth a note or a deferred-join pattern before slice-5 concurrency. 🤖 Generated with [Claude Code](https://claude.ai/code) <sub>- If this code review was useful, please react with 👍. Otherwise, react with 👎.</sub>

alee merged commit 3c63eb6688 into main

2026-07-04 04:37:32 +00:00

alee referenced this issue from a commit

2026-07-04 04:37:33 +00:00

slice-4 (dev-a): MediaThread + session_map rewire (Task 6 + 7) (#12)

alee referenced this pull request

2026-07-04 16:07:50 +00:00

slice-4 (finisher): secondary-path e2e + CI seam gate (Tasks 9.2 + 10) #13

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Reference: alee/rutster#12