The handler now automatically attaches user blocks for all handles found in the thread before sending to the agent, and detaches them in a finally block after processing completes. - Add handle_to_block_label() to convert handles to block labels - Add attach_user_blocks_for_thread() to attach/create user blocks - Add detach_user_blocks_for_thread() to clean up after processing - Wire into process_mention() with proper error handling 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>