Keep the comment card off its passage and share one composer and author row

Open comment cards sit in a wide gutter beside the passage or directly
below it (above when there is no room), never over the text being
discussed. New comments use the reply field's inset send button and drop
the duplicate Cancel. Authors show Chat's face and display name.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>