Start cfg.Workers goroutines in New that drain one rotation of live jobs in
submit order, each taking the next job with a pending target and none in flight,
so targets alternate across jobs and each job stays serial. One target per fetch
under the Close-cancelled context: panic recovers into ErrInternal (never
echoed), ErrRetryLater retries after RetryWait (bounded by RetryFor), otherwise
the target is stored done/failed and the hooks fire. Terminal status is set once
per job; cancelling a running job stores the in-flight target without overwriting
cancelled and leaves later targets pending.
Co-Authored-By: ornith-1.5-35b-a3b <ornith-1.5-35b-a3b@llama.cpp.invalid>
kyleandornith-1.5-35b-a3b
816a76fe5b