kill(pid, 0) succeeds for zombie processes, causing the gateway lock
to treat a zombie lock owner as alive. Read /proc/<pid>/status on
Linux to check for 'Z' (zombie) state before reporting the process
as alive. This prevents the lock from being held indefinitely by a
zombie process during gateway restart.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>