Holds: counted, labelled work-in-progress that refreshes without input

[dmythro]

Why

Some work has no input for minutes (a payment awaited on a terminal, an upload, a background job the page is watching) and must never be interrupted by an idle timeout.

Proposal

const release = keeper.hold('checkout')   // counted, labelled
release()

• An open hold counts as activity for the planner: the session is refreshed with no input at all.
• Expose holds (count + labels) in state for debugging.
• React: useSessionHold(active: boolean, label?: string) acquires while active is true and releases on change/unmount.