The new _handle_clarify_sse_stream handler in #1355 holds clarify._lock and
then calls clarify.get_pending(sid) under the lock. get_pending also acquires
_lock internally — and clarify._lock is a non-reentrant threading.Lock(),
so the second acquisition deadlocks the SSE handler thread the moment any
client connects to /api/clarify/stream.
Existing tests pass because they only exercise sse_subscribe, sse_unsubscribe,
_clarify_sse_notify, and submit_pending directly — none of them invoke the
route handler. The deadlock would only manifest when a real EventSource opens
the connection.
Reproduced with a tiny harness that holds _lock and calls get_pending: the
worker thread is still blocked after a 2s timeout. With the fix, both empty
and populated queue cases complete in <1ms.
Fix: read clarify._gateway_queues / clarify._pending inline under the same
_lock acquisition, mirroring the approval SSE handler's pattern at
api/routes.py:2785-2793. No recursive lock; head-of-queue snapshot is
identical to what get_pending would have returned.
Added tests/test_pr1355_sse_handler_no_deadlock.py with three tests:
- behavioural: empty queue snapshot completes within 2s
- behavioural: populated queue snapshot returns the head entry
- source-level invariant: routes.py must not call get_clarify_pending()
inside `with _clarify_lock:` block (locks the regression in)
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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