Summary

• fix Slack mention gating for thread follow-ups when requireMention=true
• treat a thread reply as implicitly mentioned when either:
  • parent_user_id === botUserId (existing behavior), or
  • the thread session already exists in the session store (new behavior)
• add regression coverage in prepare.test.ts to ensure unmentioned follow-up thread replies are accepted once the thread session is active

Why

Slack thread roots started by humans often have parent_user_id != botUserId, which can cause follow-up no-mention messages in the same active thread session to be dropped despite prior interaction.

Validation

• corepack pnpm exec vitest run src/slack/monitor/message-handler/prepare.test.ts
  • 13 passed

Greptile Summary

Fixes Slack mention gating for thread follow-ups when requireMention=true. Previously, unmentioned thread replies from human-started threads could be dropped despite an active session. The PR adds a check for existing thread sessions (existingThreadSessionUpdatedAt) and treats replies in active thread sessions as implicitly mentioned.

• Moves storePath resolution and existingThreadSessionUpdatedAt check earlier in the flow (before mention gating logic)
• Updates implicitMention to include threadSessionHasHistory condition alongside existing parent_user_id === botUserId check
• Removes redundant ctx.botUserId check from implicitMention (still implicitly required via parent_user_id check)
• Adds regression test covering unmentioned follow-ups in active thread sessions with requireMention: true

Confidence Score: 4/5

• Safe to merge with minimal risk - focused fix for mention gating edge case with test coverage
• The changes are well-scoped, addressing a specific bug in thread mention gating. The logic is sound: checking for existing thread sessions prevents dropping follow-up messages in active conversations. Test coverage validates the fix. Minor concern: removing ctx.botUserId check from implicitMention could theoretically allow messages through when botUserId is undefined, but the parent_user_id === ctx.botUserId comparison already handles this safely (returns false when botUserId is undefined).
• No files require special attention

_{Last reviewed commit: b124544}

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