Based on excellent analysis from user, implemented comprehensive fixes:
1. ZMQ Socket Cleanup:
- Set LINGER=0 on all ZMQ sockets (client and server)
- Use try-finally blocks to ensure socket.close() and context.term()
- Prevents blocking on exit when ZMQ contexts have pending operations
2. Global Test Cleanup:
- Added tests/conftest.py with session-scoped cleanup fixture
- Cleans up leftover ZMQ contexts and child processes after all tests
- Lists remaining threads for debugging
3. CI Improvements:
- Apply timeout to ALL Python versions on Linux (not just 3.13)
- Increased timeout to 180s for better reliability
- Added process cleanup (pkill) on timeout
4. Dependencies:
- Added psutil>=5.9.0 to test dependencies for process management
Root cause: Python 3.9/3.13 are more sensitive to cleanup timing during
interpreter shutdown. ZMQ's default LINGER=-1 was blocking exit, and
atexit handlers were unreliable for cleanup.
This should resolve the 'all tests pass but CI hangs' issue.
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