[maximilliangrand]

ConnectionPool.aclose() can return while an ordinary get() is still opening a connection. The close invalidates the in-flight attempt, so _connect() closes that result and retries after shutdown has already returned, leaving the replacement connection open. An acquisition draining a retired connection has the same race.

Serialize invalidation and draining in aclose() with the existing connection lock. This waits for the acquisition to finish before closing its connection. Prewarm cancellation still happens before taking the lock, and the pool can still be reused after closing.

The regressions cover blocked handshakes and blocked drains, exact-once closure, reuse, and cancellation of an in-flight prewarm. Both acquisition cases fail before the fix; all 19 pool tests pass with it. A separate loopback TCP reproduction leaves one live socket before the fix and none afterward.

Validation:

• On base 049aea8, uv run --no-sync pytest tests/test_connection_pool.py --unit -q: 19 passed.
• make check passed: Ruff formatting/lint and mypy across all 737 source files. Local commands used the checkout's core/plugin roots in PYTHONPATH to work around an editable-install import issue on macOS.
• Independent review and four additional cancellation/concurrent-close probes passed.

The full local unit/audio-EOT suite was not repeated after rebasing. The earlier Python 3.14 run passed 6,096 tests but encountered twelve NumPy buffer-resize failures and nine missing-livekit-server setup errors, reproduced on the unchanged base, plus one audio-decoder cancellation failure that passed in isolation on both trees. Fresh PR CI will validate the updated head.

No live provider credentials were used. Implementation and independent review were AI-assisted.

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.

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