B-8ZY1-retire-plugin-lib-util-markdown-extract-ts
We want to retire plugin/lib/util/markdown_extract.ts. Its responsibilities have been migrating
onto the shared markdown-contract reader (see the recent T-K1A8 / T-FN18 / T-4WR3 markdown-contract
migration work), so the bespoke extractor should be removed once its remaining call sites are moved
over. Capture the remaining consumers, migrate them onto the markdown-contract path, then delete the
util.