- treat `EPERM` from `signal(0)` as “process exists” on Unix
- classify malformed PID files as invalid and auto-remove them during read
- keep cached `pidData` only for transient races and downgrade `running` to `stopped` when the tracked process is gone
- refresh PID data on WebSocket proxy requests and reject stale cached gateway state
- add regression tests for invalid PID files, status downgrade, on-demand PID loading, and stale proxy rejection
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