Paste/drop and attachment button previously used separate upload paths.
The button uploaded first then called insertFile (which replaced the
current selection), while paste inserted a blob preview first. This
caused the second image to overwrite the first when both were used.
Now both paths share the same flow via uploadAndInsertFile():
blob preview with uploading animation → background upload → replace URL.
- Extract shared uploadAndInsertFile() function
- Replace insertFile ref method with uploadFile (inserts at doc end)
- Simplify FileUploadButton to onSelect(file) — no more onUpload/onInsert
- Wire onUploadFile in comment edit mode (was missing, upload was no-op)
- Unify image border-radius CSS for both editing and readonly modes
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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