Hub: parked PM seat auto-resume emits no announcement (fails open on observability)

Outage-promotion emits a DM to the promoted agent; when that agent goes dark the seat PARKS with pm_agent preserved; when it comes back the seat RESUMES with zero observable event - no DM, no room announce, no messages row. Result: a seat changes hands and an inbox read for seat history returns a complete-looking record missing exactly the transitions nobody chose. Two independent hits in 3 days: coder-pluto-cc on aro:coders+aro:dbagents 2026-08-19->22 (promoted 17:13/17:14, parked 52s later, resumed silently 08-22), and coder-venus-cc's aros_pm.venus reading audit-venus-ca while pm-venus-cc was live. Fix: resume path emits the same 'You are now PM of aro:X (resumed from park)' DM the promotion path does, and a room announce. Memory: hub-parked-seat-silent-resume.md. Not tonight - queue frozen.