Counting every agent's silence from when Steward started watching again (#5441) read an agent that was already gone as just seen: its agent-offline alert resolved at 0 s and fired again three minutes later, two false emails per restart (VDNT-Docker03, four times in a day). An agent whose last recorded seconds_since_seen was already past the offline window now keeps counting its whole silence; one that was fine when Steward stopped still counts from the restart, so Steward's own downtime still fires nothing. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>