Add a visible caption (<figcaption>) under images, editable from the
image bubble-menu and persisted across all formats: native Yjs/JSON,
HTML export, and Markdown.
- image node: new plain-text `caption` attribute (parse/render
`data-caption` on <img>, emitted only when set) + `setImageCaption`
command. The node stays an atom; the schema shape is unchanged, so the
server's generateHTML/generateJSON path round-trips it for free.
- resize node-view: re-parent the resizable wrapper into a <figure> and
render the caption in a <figcaption> BELOW it, outside nodeView.wrapper
(so onCommit's offsetHeight measurement and the left/right resize
handles still cover the image only). This path also drives read-only /
share rendering. React placeholder view renders the caption too.
- bubble-menu: new useCaptionControl panel modeled on useAltTextControl
(own icon, Caption strings, softer sanitizer, ~500 char limit).
- markdown lossless round-trip: a captioned image is emitted as a raw
<img data-caption> wrapped in a block <div> (same trick as <video>) in
both the editor-ext turndown rule and the MCP converter; caption-less
images stay clean . Import restores the caption via the
shared markdownToHtml + parseHTML.
- styles + i18n keys; tests for the schema attr round-trip, markdown
round-trip (editor-ext) and the MCP converter.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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