Polish pass hardening the queue and closing plan gaps.
- Task state machine gains `running`: the first heartbeat moves a task from
leased to running (migrations 0006/0007 add the enum value and extend the
lease-integrity check). verifyLease, ExpireLease, the reaper SQL, and job
progress all treat leased and running alike.
- Worker liveness: a heartbeat from a registered worker (UUID worker_id) bumps
its last_heartbeat_at online; a second background reaper marks workers offline
after WORKER_OFFLINE_AFTER of silence (RunReaper generalized to RunPeriodic).
- Request-size limits: JSON bodies capped at 1 MiB; dataset/artifact uploads
capped at MAX_UPLOAD_BYTES (default 1 GiB) via http.MaxBytesReader.
- Tests cover the running transition, liveness + offline reaper (unit over
memstore and integration over Postgres).
Efremenko Arhip
3b41455b20