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.
Pick agents from a grid of their icons (running or all), type the text, send.
The page posts the names and the text to the controller and shows what
happened to each agent, with a retry that selects just the ones that failed.
The selection rules and the controller's answer are read by plain functions
with tests.
