Two jobs on the same shared asset (same video+format queued twice, or by two
users) starved the worker pool: worker A downloads the asset; worker B claims the
sibling job, finds the asset `downloading`, requeues it, sleep(2)s, and re-claims
it on the next tick — burning a whole worker slot behind one in-flight asset for
the entire download (at concurrency=2, the queue stalls).
Fix: the claim SQL now excludes any job whose asset is already `downloading`
(`NOT EXISTS … media_assets.status='downloading'`), so a competing sibling simply
waits until the asset settles and the workers pick up unrelated jobs meanwhile.
The `_process_job` busy/lost-race branches drop their `time.sleep(2)` — the
exclusion keeps a requeued job out of the claim window, so there's no spin.
TDD: the new test failed on the old claim (claimed the sibling), passes now.
Full lane green, ruff clean.
peter
7d89bc8b8e