worker.py (~1090 L) mixed the PARENT supervisor (claim + supervise + the process
loop) with the CHILD pipeline (the yt-dlp/ffmpeg download+edit that runs in the
spawned subprocess). Extract them:
worker.py 1090 -> 475 parent: claim/supervise/loop
downloads/pipeline.py (new 592) the child pipeline (_download/_process_edit +
hooks/progress/ffmpeg helpers + _Aborted)
downloads/jobdb.py (new 73) the short-lived-session helpers both sides
share (_set_job/_job_status/_touch_job/
_requeue_if_running/_reset_asset_pending +
the staging-dir paths)
The graph is one-directional (runner -> pipeline -> jobdb; worker -> jobdb; no
worker<->pipeline edge) — the parent never calls the child directly, it spawns
runner.py as a subprocess. Consumers rewired: runner import, and two tests follow
the moved symbols (_media_info/_produced_file -> pipeline; the ffmpeg-callback
patches target pipeline where the names are looked up).
Pure code motion, verbatim bodies. ruff clean, full lane 363 pass (unchanged).
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