[Fix] Slack repeats pull request status after session closeout

[roomote-roomote]

​Opened on behalf of @mrubens. Follow up by mentioning @roomote-roomote, in the web UI, or in Slack.

What changed

Fast/session-backed tasks are no longer included in the generic Slack pull-request terminal notification fan-out. Their parent session remains responsible for the terminal closeout and reaction, while direct and legacy Slack tasks keep the existing standalone status delivery.

Task classification and run-derived Slack delivery use each task's latest run, matching the existing Fast terminal-event path. Focused tests cover current session-backed and legacy tasks whose histories contain the opposite run type.

Why this change was made

The generic webhook path treated inherited Fast child Slack coordinates as direct notification destinations. That posted a canned pull-request status after the parent session had already received the same lifecycle event.

Impact

Slack conversations currently backed by Fast sessions no longer receive redundant standalone messages such as a pull request being merged or closed. Tasks whose latest run is direct or legacy continue to receive their existing status post and terminal reactions, even after an older Fast run.

[roomote-community]

No code issues found. See task

• apps/api/src/handlers/github/notifyPullRequestTerminalStatus.ts:840-844 now classifies each task from its latest run, preserving direct Slack delivery after an earlier Fast run.

_{Reviewed 04724ec}

[roomote-roomote]

Fixed the outstanding review issue in 04724ec1: Slack classification and run-derived delivery now use each task's latest run, with mixed Fast/direct history coverage. The review thread is resolved, and the follow-up Roomote review found no code issues.

The escaped <platform_event> acknowledgement is a separate Fast child-message relay issue, not this PR terminal webhook path. Recommended follow-up scope: suppress child messages with purpose ack before relayFastAgentChildChatReply wraps them as parent platform events, because the launch kickoff already owns acknowledgement.