stream-json: background-task notification doesn't wake idle session (race in runAsyncAgentLifecycle)

Symptom: When a background agent completes while the main session is idle (between turns, waiting for stdin/FIFO), the <task-notification> sits in the queue indefinitely until the next user message triggers a turn. Observed gap: 1m51s idle with notification enqueued but undelivered.

Root cause (traced in v2.1.86-dev.20260326):

In runAsyncAgentLifecycle:

completeAgentTask(agentResult, rootSetAppState);        // task.status → "completed" → hasRunningBg = FALSE
let handoffWarning = await classifyHandoffIfNeeded(...); // async (runs when mode === "auto")
let worktreeResult = await getWorktreeResult();          // async
enqueueAgentNotification({...});                         // NOW hasQueued = TRUE

The do-while in runHeadlessStreaming polls every 100ms:

do {
  await drainCommandQueue();
  let hasRunningBg = getRunningTasks(state).some(...);
  let hasQueued = hasCommandsInQueue();
  if (hasRunningBg || hasQueued) { ...; await sleep(100); }
} while (waitingForAgents);

During the two await gaps in runAsyncAgentLifecycle, a poll tick fires, sees hasRunningBg=false && hasQueued=false, exits the do-while, emits result, and run() returns idle. The later enqueuePendingNotification (priority later) fires queueChanged.emit(), but stream-json's subscribeToCommandQueue handler only aborts for priority="now" — it doesn't re-trigger run().

REPL doesn't hit this: useSyncExternalStore(subscribeToCommandQueue) + useEffect → processQueueIfReady means any queueChanged emission triggers a drain.

Suggested fix: Reorder runAsyncAgentLifecycle to call enqueueAgentNotification before completeAgentTask sets status="completed" — the 100ms poll never sees both false. Alternatively: add a run() trigger to runHeadlessStreaming's subscribeToCommandQueue callback for any enqueue (not just priority=now), guarded by if (!running).

Repro trace: session 0e97d6af-ff32-4b68-8375-792a79ecbcdc, transcript lines 27852–27927. Enqueue at 20:43:08, dequeue at 20:45:52 (after next user prompt's turn).

Additional data from scheduled task session (v2.1.87, 2026-04-09)

Confirming this race condition in a production scheduled task pipeline (headless, no user present).

Setup

Orchestrator spawns 4–6 background agents simultaneously via Agent tool (run_in_background: true)
Scheduled task mode (no REPL — exactly the runHeadlessStreaming path described above)

Results: 3/13 notifications silently dropped (23%)

Writer batch (4 agents):

Agent	Completed	Notification
writer-batch-1	04:32:12	✅
writer-batch-2	04:32:20	✅
writer-batch-3	04:32:31	✅
writer-batch-4	04:32:40	❌ dropped

Fact-checker batch (6 agents):

Agent	Completed	Notification
fc-batch-1	07:49:46	✅
fc-batch-2	07:49:54	✅
fc-batch-3	07:50:01	✅
fc-batch-4	07:50:09	❌ dropped
fc-batch-5	07:50:15	✅
fc-batch-6	07:50:22	✅

Image-gen batch (3 agents):

Agent	Completed	Notification
img-batch-1	08:16:55	✅
img-batch-2	08:17:01	❌ dropped
img-batch-3	08:17:06	✅

All 13 agents completed successfully (stop_reason: "end_turn", output files written). The race between completeAgentTask and enqueuePendingNotification matches exactly — the dropped notifications were never delivered despite agents finishing.

Impact

Automated pipelines with no user present stall indefinitely waiting for notifications that never arrive. Current workaround: timeout-based file checkpoint after last received notification.

See also: #45581 (our original report, closing as duplicate)

Closing for now — inactive for too long. Please open a new issue if this is still relevant.

docs: cite the confirmed upstream root cause for the dropped asyncRewake

This issue has been automatically locked since it was closed and has not had any activity for 7 days. If you're experiencing a similar issue, please file a new issue and reference this one if it's relevant.

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stream-json: background-task notification doesn't wake idle session (race in runAsyncAgentLifecycle) #39632

Additional data from scheduled task session (v2.1.87, 2026-04-09)

Setup

Results: 3/13 notifications silently dropped (23%)

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stream-json: background-task notification doesn't wake idle session (race in runAsyncAgentLifecycle) #39632

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jungjoongi commented on Apr 9, 2026

Additional data from scheduled task session (v2.1.87, 2026-04-09)

Setup

Results: 3/13 notifications silently dropped (23%)

Impact

github-actions commented on May 23, 2026

github-actions commented on Jul 13, 2026

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