- worker.py: wrap the watchdog loop so a failure in it (e.g. a transient DB error in
_job_liveness) still hard-kills the child + fails the job, instead of leaving the child
running unsupervised — the exact wedge the feature prevents (#1).
- worker.py: _touch_job heartbeat bumps updated_at at each extraction attempt, so a slow /
multi-client-set fallback extraction (which writes no progress, and re-writes identical
values so ORM onupdate does not fire) is not false-killed as "stalled" (#2).
- edit.py: extract escalate_kill (terminate->wait->kill escalation); _stop and worker's
_stop_child (process-group variant) now share it (#3).
- worker.py: document the edit path's second, tighter run_ffmpeg watchdog and that the
supervisor is POSIX/Linux-container-only (#4, #6).
- tests: a long download stays alive while progress is fresh, and a watchdog-loop error
still stops the child (#1, #5).
Defense-in-depth after the ReDoS incident. The heavy work (yt-dlp download / ffmpeg edit)
now runs in a child process (app.downloads.runner) supervised by the worker thread, not in
the thread itself. A thread can't be killed and a C-level spin can't even be cooperatively
cancelled, so one wedged download used to pin a core, hold the GIL and freeze the whole
queue; a child process can be SIGTERM/SIGKILLed.
The supervisor kills the child (and its process group, so ffmpeg grandchildren die too)
when: a route pauses/cancels the job, it makes no progress for download_stall_timeout_seconds
(150s), it runs past download_wall_clock_max_seconds (2h), the worker is shutting down, or
the child crashes without setting state. On a kill it frees the asset and fails the job with
a retryable network error (stalls are not auto-requeued). A clean exit is left alone — the
child already wrote the terminal state, including a cooperative pause via the progress hook.
- config.py: stall / wall-clock / supervisor-poll / kill-grace settings.
- worker.py: _run_supervised + _spawn_download_child / _job_liveness / _stop_child /
_cleanup_staging; _process_job claims the asset, then hands the heavy work to the child.
- app/downloads/runner.py: the child entrypoint.
- docker-compose.localdev.yml: init:true on the worker so tini (PID 1) reaps orphaned
ffmpeg grandchildren left by a hard-kill (the worker reaps its own direct children).
- tests: watchdog decision logic + SIGTERM->SIGKILL escalation (fake proc, no real subprocess).
peter