[kghbln]

Fixes #132

Every <gallery mode="carousel"> fails with a TypeError, so the page does not render. CarouselGallery::toHTML() passed on the carousel component's parser function result, [ $html, 'isHTML' => true, 'noparse' => true ], but MediaWiki's <gallery> tag hook must return a string, as declared from MediaWiki 1.43 to master. toHTML() now returns the HTML only, the same unwrapping Collapse already applies to its button's result. A tag hook's output is HTML the parser does not parse again, which is what the two flags ask for in a parser function. CarouselGalleryTest asserted the array and now expects the HTML. {{#bootstrap_carousel:}} is unchanged.

Human input

Goal and shape: Claude's finding and fix, at @kghbln's request. @kghbln first asked whether {{#bootstrap_carousel:}} breaks too (it does not) and whether an extension should hook into core's <gallery> tag at all; Claude answered that the gallery mode is the intended extension point and worth keeping.

Outcome: not reviewed by a human yet. Left for you: the diff, and a <gallery mode="carousel"> on a test wiki, which no wiki has rendered with this change yet.

Claude's calls

• Not discussed with @kghbln: the HTML is unwrapped in CarouselGallery; the release note goes under a new 6.1.2 heading.
• Considered by Claude, omitted: a test that parses <gallery mode="carousel"> through MediaWiki's parser. Without a local MediaWiki it could not be seen failing first, and the changed unit test already pins the string result.
• Not verified: the tests did not run locally, so CI is their first run.
• Where your judgment helps: whether Carousel should return HTML for the parser function and the gallery mode alike.

Not in this PR

Core keeps only the <gallery> attributes that are valid on ul, so fade has no effect in the gallery mode even after this fix. Not filed yet.

Verification evidence

• MediaWiki 1.43.11, PHP 8.3, BootstrapComponents 6.1.1: action=parse of <gallery mode="carousel"> with captions, without captions, with fade and with style returned internal_api_error_TypeError; a <gallery> without the mode and {{#bootstrap_carousel:}} parsed.
• MediaWiki REL1_43 to master declare CoreTagHooks::gallery(): string. REL1_43's Parser::renderImageGallery() returns what toHTML() returns and passes the tag's attributes through Sanitizer::validateTagAttributes( $params, 'ul' ).
• CI on the extension's master (5af4f23) passes CarouselGalleryTest against MediaWiki 1.43 through MediaWiki master while the test expects the array.
• php -l on both changed PHP files.

_{AI-authored — Claude Code, Opus 5.5 (max), on a Professional Wiki account}