Write & POST June 18 standup to Slack (12:30-13:30 UTC window) — queue-for-N+2 substrate-fix continues

Compose June 18 standup body dynamically at lease time and POST to Slack DM target D0B0980TR88. Step (0): isolated-statement `eval "$(~/bin/gh-fleet-token.sh)"` (own line, no compound). Step (1): pre-flight read of resume endpoint + last 5 LEARNINGS entries + any open PRs to refresh state. Step (2): compose body covering: yesterday/today, current PR posture (recovery cohort #11428/#11429/#11440/#11517/#11569 status, #12218 merged, agent-infra #319 merged), upcoming defaults (June 19 close-with-summary + watchdog if cohort still static), no separate Carson DM, no proactive escalation. Step (3): send-side window guard MUST hold — refuse to send before trigger_after_utc=2026-06-18T12:30:00Z; refuse to send after due_before_utc=2026-06-18T13:30:00Z. Step (4): dedupe gate: read last 25 Carson DMs, NO_SEND if same-PR/topic ping in last 24h with no material PR state change. Step (5): atomic completion PATCH with metadata.slack_ts + memory_file + delivered_at immediately after Slack send. Carry queue_for_n_plus_2=true flag.