[Fix] Automation scans stuck when Slack closeout lacks thread context

[roomote-roomote]

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

What changed

Channel-only Slack metadata (used by automations like CodeQL triage so rare blockers can still post_to_slack_channel) no longer turns the job into a full Slack conversation surface.

• Reply-satisfaction / closeout hooks now apply only when the job already has a thread or is a late-bound automation work-item run (automationWorkItemId).
• Channel is still exposed for channel posts.
• Standard-task surface classification matches: only thread-backed or late-bound execution tasks are treated as Slack-started.

Why this change was made

Scheduled CodeQL (and similar) scans carry a manager Slack channel without a root thread. That path was still enabling send_chat_reply closeout enforcement, so agents got stuck in a loop: closeout required, send_chat_reply 403'd for missing thread context, while post_to_slack_channel worked. Pre-creating a scan root message is not the right model for act-first silent scans.

Impact

Automation scans can finish cleanly when they should stay silent or only post optional channel blockers. Act execution tasks still late-bind a root on their first real closeout. Real Slack-originated threads are unchanged.

[roomote-roomote]

No code issues found. See task

_{Reviewed 14b3131}