Compose row gains a 📎 attach button that uploads the file via /api/blob
and calls mesh.send-content for the selected peer. Received content_ref
bubbles render as a caption+filename card with either an inline image
preview or a Download button that calls mesh.fetch-content and swaps in
the returned local_url.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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