[Fix] Fast misses Slack follow-ups after peer mentions - #2407

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

Related issue

Maintainer-requested refinement; no linked public issue.

Why this PR exists

• A maintainer explicitly invited this PR in the linked issue or discussion
• I am a maintainer / this is internal Roomote work

Replace the human-to-human admission cutoff in established Fast Slack threads with a per-message advisory, without reconstructing or storing participation state.

What changed

• Established Fast threads return from the admission check before the peer-mention/interjection cutoff. Subsequent otherwise eligible messages reach Fast. Linked-user authorization, unrelated-channel filters and legacy task-thread routing remain unchanged.
• When the current human-authored channel message mentions another user, excluding Roomote and the sender, append a quiet-participation reminder to existing agentContext. Messages explicitly directed at Roomote are not cautioned. The reminder is untrusted supplemental context, separate from authored text, asking Fast to remain quiet unless directly addressed from then on.
• No history-derived advisory state: removed priorMessages, latestDirectAddress, directlyAddressesRoomote, hasPeerDiscussion, the plain-name reset heuristic, and associated state tests/comments. Ordinary pre-existing history retrieval still provides thread context and attachments; it does not regenerate the reminder.
• Preserve the existing context field through queued/native delivery. Quiet-eligible Slack turns can use existing silent completion; a small Slack-only guard prevents asides from superseding parked requests. No global prompt, instruction-version, schema, or new persistent-state mechanism.

The reminder remains ordinary model conversation context. It is not reattached to later messages without a peer mention and may be lost through context compaction. Model compliance is advisory, not a hard tool restriction. More admitted messages incur inference cost. Existing mention parsing cannot distinguish another app's user ID from a human without an additional lookup; none is added.

How it was tested

• 75 focused Slack routing/processing tests passed, including Fast cutoff bypass, subsequent admission, current-message attachment, exclusion cases, and a regression proving history alone does not regenerate the reminder.
• 103 SDK admission/delivery tests passed for the retained queued-context/silence and parked-request safeguards.
• API and SDK typechecks passed; pre-push oxlint, residual ESLint, full fast typechecks and knip passed.
• Earlier broader Slack run had two unrelated DB failures from the sandbox schema missing work_items.result_accepted_at; that broader suite was not rerun. No live-model or visual validation claimed.
• Verified GitHub PR head and remote branch both equal fc419ff6c1f5564b6d0790675979c2e84b6f39e1. Reviewed the actual base-to-head diff; removed history-state symbols are absent. PR not merged.

Checklist

• The PR title follows the repo convention: [Fix], [Feat], [Improve], [Refactor], [Docs], or [Chore] followed by a user-facing description
• This PR is small and scoped to one change
• pnpm lint and pnpm check-types pass locally
• I added tests or included a clear manual validation note above
• I removed secrets, tokens, private keys, and customer data from code, logs, and screenshots
• If this change should appear in the changelog, I ran pnpm changeset

The exact full commands in the checklist were not run; affected-package typechecks and pre-push gates passed. No changeset was added.