fix(queue): harden drain threads against BaseException

[chazmaniandinkle]

Problem

SpeechQueue._drain() (server.py) and ChannelQueue._drain() (output_queue.py) both have an except Exception guard around the job runner, but Python's BaseException hierarchy includes subclasses that don't inherit from Exception:

• SystemExit (from sys.exit() or process lifecycle)
• KeyboardInterrupt (from signal handling)
• MemoryError (OOM during TTS synthesis)
• GeneratorExit (from a TTS generator being closed)

When any of these escape the inner handler, the drain thread exits with _draining / _running still True. Every subsequent enqueue() / submit() call sees the flag and skips starting a new drain thread, so jobs pile up in the queue indefinitely:

• SpeechQueue.depth (reported in diagnostics()["queue_depth"]) grows without bound
• active_jobs stays at 0
• Audio stops playing

This is the root cause of the reported queue_depth=16, active_jobs=0 stale counter bug.

The code already documents the hazard (server.py lines 643–647):

A failure here must not kill the drain thread: if it does, _draining stays True and subsequent enqueues never start a new drain, so jobs accumulate in the queue with no processor.

Commit d3009a7 added the except Exception guard, which handles the common case (KeyError, ValueError, etc.), but left the BaseException gap.

Fix

Wrap each drain loop in try/finally. The finally block unconditionally resets the flag (_draining or _running) and clears the active-job pointer under the lock, so any exit path — normal or abnormal — leaves the queue in a consistent, restartable state.

KeyboardInterrupt and SystemExit are re-raised after cleanup so the process can still respond to signals normally.

Tests

• tests/test_speech_queue.py — new class TestDrainBaseExceptionResilience:

  • test_drain_resets_draining_after_system_exit
  • test_drain_resets_draining_after_memory_error
  • test_drain_accepts_new_jobs_after_base_exception_kill (end-to-end: queue resumes after thread death)

• tests/test_output_queue.py (new file) — covers ChannelQueue and OutputQueueManager:

  • Normal drain behavior (submit, depth, order, exception resilience)
  • TestChannelQueueBaseExceptionResilience: same three regression cases for ChannelQueue
  • OutputQueueManager: channel isolation, cancel, drop_queue

All 35 new + existing tests pass.