The artifact pane from main loads and previews files through the streamed
artifact route like the file card, so its hook takes only the artifact id.
attach_file keeps media types and gains present, which marks image and
file blocks for the pane.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MRtGG9ARfqqhma3t85Ro2u