The admin page's download_worker_concurrency and log_level were stored but never reached the worker:
it read the env once at boot (worker.py) and never looked again. The worker now re-reads both every
10 s (_sync_knobs): extra loop threads start at once, surplus ones retire after their current job, and
a changed level is applied to the process. An unreadable database keeps what already runs.
peter
33dec56e45