[Bug] Daemon can never start again after its supervisor is left unreaped as a zombie

[mdumitrean]

Affected area

Agent core

What happened?

A daemon supervisor whose parent never reaps it — the parent CLI suspended with Ctrl+Z, or otherwise stopped — lingers as a zombie. A zombie still answers kill(pid, 0), and ps still reports its original start time, so both checks the supervisor ownership registry makes on the recorded owner pass: it reads the dead generation as the live owner and rejects every subsequent launch.

Error: Prime Agent daemon exited during startup (code 1).
DaemonSupervisorAlreadyRunningError: Daemon supervisor already owns
$TMPDIR/prime-agent-/daemon.sock

The state is permanent, not transient: the socket is long gone, so no client can connect either, and nothing ever clears the registry record. utils/child-process.ts already exported an isProcessAlive that excludes zombies, but six modules had each re-implemented a bare kill(pid, 0) probe and none of them used it.

Steps to reproduce

Deterministic:

npx vitest --run test/daemon-supervisor-ownership.test.ts
-t "reclaims an owner whose process is an unreaped zombie"

It parks a real unreaped child in an owner record and asserts acquisition reclaims it.

Manual:

1. Run a CLI command that starts the daemon, and leave that CLI process running — it is the supervisor's parent until it exits.
2. Suspend it with Ctrl+Z (SIGSTOP). A stopped parent never processes SIGCHLD, so it cannot reap.
3. Kill the supervisor it spawned. With its parent stopped it stays a zombie — ps -p -o stat= shows Z.
4. Run any further CLI command.

The probe behavior that makes it stick, checkable directly against that pid:

kill -0 # succeeds
ps -p -o lstart= # still prints the original start time

Expected behavior

• The ownership registry treats a zombie as dead and reclaims its record, so the next launch takes ownership instead of failing.
• A daemon whose supervisor was left unreaped can start again without manual intervention.
• Every liveness probe in the codebase agrees on what "alive" means, rather than each module deciding for itself.

Prime Agent version

9e49b73

Environment

macOS 26

Additional context

No response