The request; its lease is held until the returned promise settles.
Data or metadata pool.
Urgency class, or a FetchPriorityCell whose class
may be raised while the request waits. Defaults to demand.
Optionalorigin: string
The request's origin, which picks the data-lane width (multiplexed origins get the wide lane). Omitted = the default width.
Optionalsignal: AbortSignal
The caller's abort signal: aborting while the request still
waits for a slot rejects it with the signal's reason and frees its queue
place. Once started, fn owns the signal.
p-limit-style gate: never lets more than the lane's width run concurrently.