A button that grabs every page into a cache: owner-only POST /_fill
(cache id in the body; target private|public; action start|stop),
advanced by DO alarms a few pages per step, progress stored in the DO
(new, additive state) so it survives eviction, cached pages skipped,
a rerun rejoins the running job, failures recorded and logged once.
The created page gets the button; the public page shows progress.
startFill/fillStatus/stopFill on PagedCache are JSDoc'd stubs; 13
specs are describe.skip until it lands (alarms driven by
runDurableObjectAlarm, eviction by evictDurableObject).
Generated-by: Claude Opus 5.5
