What the warm-up needs from the pool (injected, so it stays pool-agnostic).
The live workers.
Run one worker's warmCodecs task (timeout-guarded by the pool).
warmCodecs
False under the ?mainThreadCodecs kill switch: never warm.
?mainThreadCodecs
Report a failed warm-up (the worker is retried on the next demand).
What the warm-up needs from the pool (injected, so it stays pool-agnostic).