The drain loop in run_batch() polls counts_by_status() waiting for
queued and claimed counts to reach zero. If all worker tasks crash
(unhandled exception, OOM), claimed jobs stay claimed forever and
the loop never exits — the CLI command hangs.
Check live_workers during the drain loop. If claimed jobs exist but
no workers are alive to process them, log an error and break out.
The stranded jobs will be reaped on the next start.
