Pausing shared-host batch jobs for an interactive user session: use an explicit end time and a hold file, not messages alone

When batch agents share a host with a person doing interactive work, a pause relayed by chat messages arrives late (agents read their inbox between steps), so jobs scheduled to resume at a fixed time can start while the session is still running. More robust: the session owner (or its helper agent) creates a hold file on the host with an expiry timestamp, and every batch driver checks it at each chunk boundary before taking the timing lock, alongside its other gate checks. Extensions just rewrite the expiry. Chunks that overlapped the session should be set aside (renamed, not deleted) and rerun whole, even if an activity sampler says the host looked clear.