Slack reactions were placed around handle_message(), which returns
immediately after spawning a background task. This caused the 👀
→ ✅ swap to happen before any real work began.
Fix: implement on_processing_start / on_processing_complete callbacks
(matching Discord/Telegram) so reactions bracket actual _message_handler
work driven by the base class.
Also fixes missing stop_typing() for Slack's assistant thread status
indicator, which left 'is thinking...' stuck in the UI after processing
completed.
- Add _reacting_message_ids set for DM/@mention-only gating
- Add _active_status_threads dict for stop_typing lookup
- Update test_reactions_in_message_flow for new callback pattern
- Add test_reactions_failure_outcome and test_reactions_skipped_for_non_dm_non_mention
70a33708e7