this should hopefully get resolved with the 4.0 release.

Docusaurus 3.10.1 + future.v4 = broken build. Two fixes:

1. Drop invalid config.format='detect' from per-plugin docs config -- 3.10's schema rejects it. Site-level
   markdown.format='detect' already covers it.

2. Polyfill the {#id} heading anchors and <!-- --> comments in upstream .mdx from _remotes/. Under v4-strict
   MDX, both blow up micromark before Docusaurus's built-in heading-id plugin gets a turn. Can't fix the files
   (_remotes/ is upstream, gets clobbered on every build-docs.sh). MDX wontfix'd it, Docusaurus can't-repro'd it.
   Site-level markdown.preprocessor rewrites the source pre-tokenization; companion remark plugin promotes the
   placeholder into a real <h2 id="..."> so Docusaurus's anchor validator sees it. Same shape Docusaurus's own MDX2
   migration used.

Refs:

• Unable to parse custom heading ids mdx-js/mdx#2485 -- wontfix from MDX
• Bug: MDX/Acorn error triggered by text{ pattern in LaTeX arguments facebook/docusaurus#11235 -- can't-repro from Docusaurus
• docs: remove problematic mdx2 anchor id docs for MDX 2 migration facebook/docusaurus#8788 -- precedent for the polyfill pattern