check / check (push) Waiting to run
Acquire read vaultik.pid, checked whether that PID was alive, then wrote its own, so two writers started together could both pass the check and both run. The lock is now an flock on vaultik.pid, held while the file stays open; the kernel drops it when the process exits, so the stale-PID check is gone. Release empties the file instead of deleting it. Deleting it would let a process that opened the old file a moment earlier lock it while another creates and locks a new one. The new concurrent test fails against the old code only when the race is hit, not on every run; against the fix it cannot admit two callers. Model: opus-5-5