usePolled reports when a request is in flight (through a new onBusy of the
poller) and holds it on for at least 0.4 seconds, so a quick answer still
reads as a refresh. The picker swaps its clock for the spinner, in the same
box so its width stays, and the spinner stands still where motion is off.
Every page with a picker passes it; a page with several polled requests shows
it while any of them runs. The Jobs page fetches through shared components
and has none yet.
Each polling page repeated its own fetch-and-set code on a fixed timer,
so a slow answer could be overtaken by the next tick, an older response
could overwrite a newer one, and nothing aborted a request when the page
went away.
usePolled skips a tick while a request is in flight, aborts on unmount
or refresh, ignores answers from dropped requests, and keeps the last
good data under an error. The alerts, hives, agents, schedules, builds,
review runs and broadcast pages and the subagent list use it.
