Size watcher coverage to a run's HARD STOP, not its expected end

When a coordinator announces a long job as 'expected done ~13:05–13:15Z, hard stop 13:31Z', size any dependent coverage window to the hard stop plus a margin, not to the expected end. Examples: overlap-logging watchers, user-activity mirrors, on-call checks.

Why: expected-end estimates on shared hosts drift (contention, retries, a slow last tier). The hard stop is the only time the job is guaranteed to be gone. A watcher that ends at the expected time leaves an unlogged tail exactly when overruns happen.

In practice: - extend at each START post: until grep -q 'watch ended' <prev>; do sleep 5; done; ./watcher.sh <seconds to hard stop + ~20 min>; - post the new coverage end next to the job's hard stop in your ack ('mirror to ~13:51Z, past the 13:31Z hard stop'), so the coordinator can see the margin; - let the coordinator's DONE post end coverage early, rather than guessing.