P2-T2: Self-healing stale socket and PID file recovery

[SoundBlaster]

Description

Fixes a critical (P0) issue where a broker daemon crash leaves stale broker.sock and broker.pid files on disk. The proxy's _spawn_broker_if_needed previously checked only socket_path.exists() and skipped spawning if the socket file was present — even if nothing was listening. This silently blocked all future broker-mode sessions until the user manually deleted the files.

Changes:

• src/mcpbridge_wrapper/broker/proxy.py — Replace plain exists() guard with a connect-based liveness check. If socket.connect() raises OSError (covers ConnectionRefusedError, TOCTOU race, and non-socket files), both stale files are removed and spawn proceeds normally.
• src/mcpbridge_wrapper/broker/daemon.py — Register atexit.register(self._cleanup_files) after successful startup so socket/PID files are removed on abnormal interpreter exits (unhandled exceptions, sys.exit()), in addition to the existing SIGTERM/SIGINT handlers.

Tests:

• Updated test_spawn_noop_when_socket_exists to mock socket.connect() success (live broker scenario).
• Added TestBrokerProxyStaleSocket (3 tests): stale socket triggers spawn, stale files are removed, live socket skips spawn.
• Added TestBrokerDaemonAtExit (1 test): atexit.register called with _cleanup_files after start().

Type of Change

• Bug fix
• New feature
• Documentation update
• Refactoring
• CI/CD improvement

Quality Gates

• make test - All tests pass with ≥90% coverage (719 passed, 5 skipped; 91.78% coverage)
• make lint - No linting errors (ruff check src/ — all checks passed)
• make format - Code is properly formatted
• make typecheck - Type checking passes
• make doccheck - Documentation is synced with DocC (if docs changed)

Documentation Sync

• Documentation changes are synced with DocC catalog (or N/A) — no docs changed

Testing

• Added/updated tests for new functionality
• All tests pass locally
• Manually tested the changes

Checklist

• Code follows the project's style guidelines
• Self-review completed
• Comments added for complex code
• Documentation updated (if needed)
• No new warnings generated
• PR title is descriptive

[chatgpt-codex-connector]

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