Keep links and inline formatting in image captions

[semsevens]

Problem

When a figure is standardized (createFigureWithCaption in src/elements/images.ts), the caption goes through extractUniqueCaptionContent, which collects the caption's text nodes and joins them with spaces. Every element is dropped, so links in captions disappear:

<figcaption class="image-caption"><span>…You can find the source code </span><a href="https://…/notebook.ipynb">here</a><span>.</span></figcaption>

becomes …You can find the source code here. This is how Substack renders captions, so every Substack post with linked captions loses them (a real post I clipped lost 12). It also reaches Obsidian Web Clipper users.

A second, smaller issue in the same path: the joined text is passed back through parseHTML, so escaped markup in a caption (<img src=x>) is turned back into a real element. With the current code the new fixture's Figure 4 comes out as ![](https://www.example.com/article/x).

Fix

extractUniqueCaptionContent is replaced by appendUniqueCaptionContent, which copies the caption into the new <figcaption> as DOM nodes instead of building an HTML string:

• repeated text is still skipped, which was the original purpose of the function;
• links are kept, and their href is checked with isDangerousUrl. Inline formatting (em, i, strong, b, code, sub, sup) is kept as clean elements with no attributes;
• other wrappers (spans, divs) are unwrapped, with a space at block boundaries so that <div>A</div><div>B</div> doesn't become AB;
• text stays text, and there's no parseHTML/innerHTML round trip.

Tests

• New fixture elements--figcaption-inline-formatting covers a Substack-style caption, emphasis + inline code + a relative link, a caption split across block elements, escaped markup, and a javascript: link that keeps its text but loses its href. It fails on main and passes with the fix.
• issues--227-noscript-lazy-images expected output updated: its captions contain <a href="https://example.com/source1">Source One</a> and <a href="https://example.com/source2">Source Two</a>, which were flattened before and are now kept as links.
• npm test and npm run test:jsdom: 773/773. lint:unused and lint:innerhtml pass, and npm run size is within budget.

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