claim_job_for_fire refused any claim younger than FIRE_CLAIM_TTL_SECONDS (300s)
regardless of whether its owner was still alive, so a `hermes cron run` killed
mid-flight (timeout, Ctrl-C, OOM) blocked the next manual run with "already being
fired" for up to five minutes. The executions table already reaps dead owners on
sight; the job-record fire_claim now does the same via gateway.status._pid_exists
when the claim's `by` names a pid on this host. Foreign hosts, explicit
HERMES_MACHINE_ID values, and probe failures keep the TTL (fail safe).