6590dcdb39
Backfill downloads stranded with empty logs + a generic "stranded by recovery sweep" error. Root cause: the backfill gallery-dl subprocess timeout (1170s) exceeded download_source's Celery soft_time_limit (900s), so SoftTimeLimitExceeded preempted subprocess.TimeoutExpired. The TimeoutExpired path (which captures partial stdout/stderr and finalizes the event) never ran, the event was left 'running', and phase 3 never decremented backfill_runs_remaining — so the source re-ran and re-stranded every tick (Anduo #39912). Two layers: 1. Raise download_source limits (soft 900→1350, hard 1200→1500) so both subprocess budgets (870 tick / 1170 backfill) sit below the soft limit with phase-3 persist headroom. Promote to module constants and guard the invariant with a test. 2. Catch SoftTimeLimitExceeded in download_source and finalize the in-flight event with a real reason, mirror phase-3 source-health, and decrement backfill so a chronically-slow source self-heals to tick mode. The existing celery_signals handler only covered TaskRun, not DownloadEvent — that was the gap. Updates stale 900/1200 references in gallery_dl.py + maintenance.py. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>