Make managed server port allocation atomic - #204
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Jul 14, 2026
## Summary Follow-up to the post-merge review of #204. - `_await_bound_port` now lets the reader thread do the parsing and relies on `thread.join(timeout)`: the engine's death closes stdout and ends the thread, so the queue, the manual deadline loop and the `process.poll()` check were three error paths for the same condition. Same guarantees, a third less code. - A non-numeric `VOLCA_PORT=` value now raises the same clear `RuntimeError` as an out-of-range one, instead of leaking a bare `ValueError`. Covered by a new test parameter. - The `--port` help text and the changelog now say that port 0 binds the loopback interface only — Warp's `openFreePort` binds 127.0.0.1, unlike the fixed-port path which listens on all interfaces. Without this note the narrower bind is a silent behavior difference. ## Verification - pyvolca: 233 passed, 7 skipped - pyright on `server.py`: 0 errors, 0 warnings
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Summary
openFreePortServer(port="auto")to pyvolca while preserving existingport=0semanticsWhy
The canonical converter previously probed and released a free port before starting VoLCA. Another local process could claim that port and impersonate the engine. This change removes the TOCTOU at its source.
Verification
openFreePort/runSettingsSocketintegration type-checked locally