[Fix] Next Slack question disappears when prompt delivery fails

[roomote-roomote]

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

What changed

Slack multi-question prompts now recover when the next question cannot be posted after the answer state has already advanced. Retrying the prior answer redelivers the pending question without advancing state again, while stable message IDs keep ambiguous delivery retries idempotent.

The next prompt is posted before the answered prompt is retired. If delivery fails, the old prompt keeps its controls and remains the visible retry path; after delivery succeeds, updating that old prompt remains best-effort.

Why this change was made

The Redis transition completes before Slack delivery. If posting fails, the durable current question is hidden and the prior prompt must remain actionable so the exact saved answer can retry delivery.

The recovery path deliberately preserves the advanced state rather than rolling it back, because a transport failure can occur after Slack accepted the post.

Impact

Users receive explicit retry guidance when their answer was saved but the next prompt was not delivered, and the button needed to perform that retry remains available. An exact retry can safely recover delivery; stale or different answers remain rejected and cannot mutate hidden state.

The Slack package suite, repository lint, fast typecheck, knip, and pre-push checks pass. No database schema or external protocol changed, and no browser proof applies to this backend-only behavior.

[roomote-community]

No new code issues found. See task

• packages/slack/src/handle-followup-answer.ts:221 Retiring the answered prompt before confirming the next prompt was posted removes the only retry control after delivery fails.

_{Reviewed de4a028}