A yt-dlp process can stall with the OS process alive but no progress — a
wedged TLS handshake, an unresponsive server, a dead socket mid-fragment.
Before, that job hung forever, holding a concurrency slot until the user
noticed and cancelled.
Now each Job tracks last_activity (bumped on any stdout/stderr line or
progress message). poll() runs check_watchdog(): a Running job silent for
HANG_TIMEOUT (5 min) gets SIGKILLed by pid via libc::kill. The threshold
sits well above any legitimate quiet gap — yt-dlp prints a line per
download chunk, polls every 30s under --wait-for-video, and our longest
sleep is ~30s — so 5 min of total silence is a real stall.
To capture the pid, spawn_job + enqueue_transcode now spawn the child
*before* the reader thread (the thread still owns it for the blocking
wait()). A watchdog kill sets watchdog_killed, and drain() forces the
resulting failure to NetworkError (retryable) instead of the Other that
classify() would return for an output-less kill — so the existing
auto-retry path re-queues it (a hang is transient).
Non-Unix builds keep the flagging but can't force-kill (no portable
pid-kill; Windows isn't first-class). JobState gains Debug for tests.
2 tests: watchdog kill → retryable class; normal failures still
classify from the log. 98 pass.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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