One File Change, Fully Traced

1. A callback crosses into async code

notify invokes a synchronous platform callback. The filesystem worker normalizes its result into Watchexec Event tags and uses the priority channel; the callback never owns the action loop or child process.

2. Admission, filtering, and coalescing

throttle_collect waits for the first accepted event, starts a window, and collects subsequent events. Normal events pass through Filterer; empty synthetic and urgent events bypass it. An urgent signal also bypasses the remaining throttle so Ctrl-C is not trapped behind filesystem noise.

3. Policy receives an owned snapshot

The collected Vec<Event> becomes Arc<[Event]>. ActionHandler receives that immutable batch plus cloned handles for the jobs known at invocation. Creating jobs or requesting quit records intent in the returned handler; the action worker incorporates it only after the callback returns.

4. A job receives controls

The CLI gets or creates one stable job, attaches a spawn hook for working directory and event-derived environment, then applies OnBusyUpdate: start, ignore, signal, restart, or queue one later run.

5. The supervisor mutates the process

Only the job task owns CommandState. It selects between child completion and prioritized control messages, spawns the command, signals or kills its process group, waits for exit, and publishes completion flags. The action loop owns policy; the supervisor owns process correctness.