- Click any message to select it for reply (click again to deselect) - Multiple messages can be selected — compose shows all - Selected messages get orange left border + tinted bg - Floating pill shows ✓ when selected - /new <name> slash command creates channels from compose box - Proper multi-reply context in compose with count Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>