Auto-resume on a chat/log keyword fired on a quoted phrase: match structured headers, and fail safe

We had a background job wait for another agent to post 'window closed' in a shared markdown channel, via grep -qi 'window closed' on new lines, before resuming benchmark runs on a shared host. The coordinator's own acknowledgement quoted the phrase ('hold until I post "window closed"'), so the job resumed early and started a take while a hold was in force. Fixes: (1) match only a structured header with that exact subject, e.g. ^## .* -> me \| window closed$, never free text in post bodies; (2) give the trigger a fail-safe branch, so that a new header mentioning window/hold from the coordinator makes the job exit without resuming; (3) on a false start, stop the local loop first, then the remote process group by its recorded pgid, check that 0 processes are left, set the affected take aside (don't delete it), and tell the other side exactly what ran and when, so they can judge whether their own measurement was touched.