Summary

Consolidates and hardens the threading fixes from #23320 and #23513:

• respect configured replyToMode when Slack auto-populates top-level thread_ts
• only force thread continuity for genuine thread replies (isThreadReply=true)
• ignore inline replyToId directive tags when replyToMode is off
• keep inline replyToId behavior when replyToMode is all/first
• add targeted regression tests and changelog entry

Why

Two separate leaks existed:

1. auto-created top-level thread_ts could make replyToMode=off behave like all
2. inline reply directive tags could force thread replies even when replyToMode=off

Both violate user threading preference and produce inconsistent Slack behavior.

Validation

• pnpm test -- src/slack/threading.test.ts src/slack/monitor.tool-result.test.ts
• pnpm exec oxfmt --check src/slack/monitor/replies.ts src/slack/monitor/message-handler/dispatch.ts src/slack/threading.ts src/slack/threading.test.ts src/slack/monitor.tool-result.test.ts CHANGELOG.md
• pnpm exec oxlint src/slack/monitor/replies.ts src/slack/monitor/message-handler/dispatch.ts src/slack/threading.ts src/slack/threading.test.ts src/slack/monitor.tool-result.test.ts

Fixes: #5470
Fixes: #16080
Supersedes: #23320, #23513

Greptile Summary

Hardens Slack threading logic to respect the configured replyToMode setting by fixing two distinct leaks where threading was forced against user preference.

Key changes:

• src/slack/threading.ts:51-55: Changed replyThreadTs resolution to only use incomingThreadTs when isThreadReply=true, preventing auto-created top-level thread_ts from forcing threading when replyToMode=off
• src/slack/monitor/replies.ts:22-24: Added replyToMode guard to ignore inline replyToId directive tags when mode is off
• src/slack/monitor/replies.ts:97-99: Simplified effective mode logic by removing chatType distinction and only forcing all mode for genuine thread replies (isThreadReply=true)
• src/slack/monitor/message-handler/dispatch.ts:189: Propagated replyToMode to deliverReplies to enable the inline directive filtering

The changes preserve correct threading for genuine user thread replies (detected via parent_user_id or mismatched thread_ts !== ts) while preventing Slack's auto-populated thread_ts on top-level messages from overriding user configuration.

Confidence Score: 5/5

• This PR is safe to merge with minimal risk
• The changes are well-scoped, logically sound, and backed by comprehensive test coverage. The fix addresses real user-facing bugs without introducing breaking changes. The threading logic simplification removes unnecessary complexity (chatType parameter) while preserving correctness for all edge cases. Tests explicitly cover both the regression scenarios and expected behavior for off, first, and all modes.
• No files require special attention

_{Last reviewed commit: 6f6aab4}