Follow-ups for thumb-style image embeds (invalid figure nesting, missing-file caption, media module)

[JeroenDeDauw]

Follow-ups from #2 / #12 (opt-in thumb framed embeds with visible captions). None blocks the shipped feature; grouped for tracking. Severity is low — everything below renders correctly and is security-clean.

1. Invalid <p><figure> nesting for standalone thumbs (most notable)

[[File:X|thumb|Caption]] on its own line renders as <p><figure typeof="mw:File/Thumb">...</figure></p>. <figure> is flow content, invalid inside a phrasing-only <p>; browsers auto-close the paragraph, so it displays fine but ships invalid HTML5 and leaves a stray empty <p>. This is the common case (a thumb on its own line). The HTML is set directly on ParserOutput and not run through RemexHtml/Tidy. The fix is to promote a solitary block-level embed out of its CommonMark paragraph.

2. Missing file + thumb drops the caption

[[File:Missing.png|thumb|Important caption]] falls through to the upload red link (missingFileHtml), which uses only alt text, so the caption is discarded. Wikitext renders a framed broken-thumb box with the caption.

3. Non-inline media + thumb ignores the keyword

Audio/PDF with thumb renders as a plain file-page link (the !allowInlineDisplay() guard precedes the thumb branch). Consistent with the current minimal subset, but a divergence from wikitext.

4. mediawiki.page.media module not loaded

Linker::makeThumbLink2() only registers the client-side media module when passed a $parser; the renderer passes none, so the magnify affordance is absent. Server-rendered frame and caption are unaffected.

Also deferred from #2: frame/frameless, alignment (left/right/center), border.

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Filed by Claude Code (Opus 4.8 (max)) at Jeroen De Dauw's direction, from the code review of #12. Jeroen sets direction and reviews. Identified with Claude Code.

[JeroenDeDauw]

Sub-items 1, 2 and 4 are fixed by #43 (merged; recorded in the not-yet-tagged 1.2.0 release notes). Remaining here: sub-item 3 (non-inline media with thumb) and the deferred frame/frameless/alignment/border keywords, so the issue stays open.

One edge noted while fixing sub-item 1, staying out of scope for now: two thumb embeds on consecutive lines with no blank line between them form a single CommonMark paragraph and still render the invalid <p><figure> nesting. A blank line between the embeds avoids it.

_{AI-authored — Claude Code, Fable 5 (max); delegated wrap-up of @JeroenDeDauw's fix-and-merge ask; posted unattended.}

[JeroenDeDauw]

Sub-item 3 rests on a false premise, so there is nothing actionable left here and this can close.

thumb on non-inline media is not a divergence from wikitext — core behaves identically. Parser::makeImage()
routes every image, thumb included, through Linker::makeImageLink() (Parser.php:5595), whose first
substantive step is:

if ( $file && !$file->allowInlineDisplay() ) {
	wfDebug( __METHOD__ . ': ' . $title->getPrefixedDBkey() . ' does not allow inline display' );
	return self::link( $title );
}

That is Linker.php:343 (allowInlineDisplay() being an alias for canRender()), and the thumb branch calling
makeThumbLink2() sits at Linker.php:447, after the guard. So in wikitext, [[File:Audio.ogg|thumb|Caption]]
for a file no installed handler can render returns a plain link to the file page and drops thumb on the floor —
exactly what MediaWikiFileEmbedRenderer::renderEmbed() does. The guard preceding the thumb branch is the wikitext
behaviour, not a deviation from it. Implementing sub-item 3 would create a divergence.

Where a handler can render the media (TimedMediaHandler for audio/video, PdfHandler for PDF), allowInlineDisplay()
is true on both paths and thumb frames it — again the same on both.

The one real difference favours us: we label the fallback link with the caption, where core falls back to the page
title, so we preserve slightly more.

Sub-items 1, 2 and 4 are fixed and go out in 1.2.0. The deferred frame/frameless/alignment/border keywords move
to #45, which also records a related find from this check: an unrecognised keyword falls through to the caption, so
[[File:Cat.png|thumb|left]] currently renders a thumbnail captioned "left".

_{AI-authored — Claude Code, Opus 4.8 (max); @JeroenDeDauw asked whether sub-item 3 was worth doing before tagging 1.2.0; not yet human-reviewed; claim verified by reading MediaWiki 1.43 core (Linker::makeImageLink, Parser::makeImage, File::allowInlineDisplay) against our renderer, not reproduced in a browser.}