[quality] docusaurus.config.ts markdown preprocessor has zero test coverage #398

Finding

docusaurus.config.ts (lines ~44-50) defines an inline markdown.preprocessor function:

preprocessor: ({ fileContent, filePath }) =>
  path.resolve(filePath) === importedReadmePath
    ? fileContent.replace(
        /(\]\(|\]:\s*)(\/(?:docs|analyses)\/[^\s)#?]+)\.md(?=$|[\s)#?])/g,
        '$1$2/',
      )
    : fileContent,

This strips .md from site-absolute /docs/... and /analyses/... links when
Docusaurus imports the root README.md (consumed by src/pages/index.mdx). It
has no test coverage:

• Unit: lib/**/*.test.mts (the test:unit script) has no test file for
  docusaurus.config.ts; this function isn't exercised anywhere.
• End-to-end: this repo has no e2e/integration suite (no playwright/cypress
  directories; CI is limited to format-check.yml, link-check.yml,
  spell-check.yml).

Covered by neither unit nor end-to-end tests.

Why this can't be fixed with a drop-in unit test: the function is inlined in
docusaurus.config.ts, which imports ./lib/getBuildContext and
./lib/remarkRewriteLinks without file extensions. That resolves fine through
Docusaurus's own webpack bundler, but is unresolvable under this repo's own
node --experimental-strip-types --test runner (reproduced locally:
ERR_MODULE_NOT_FOUND importing docusaurus.config.ts directly). Testing the
regex in isolation requires first extracting it into its own lib/ module (with
extension-qualified imports, matching the convention #389 establishes) — a
production-code change, which is outside the quality agent's scope (tests only,
no refactors).

Recommendation

1. Extract the regex-rewrite logic out of docusaurus.config.ts into a small,
   named function in lib/ (e.g. lib/rewriteReadmeLinks.ts), imported back
   into docusaurus.config.ts with an explicit .ts extension.
2. Once extracted, a straightforward unit test under lib/**/*.test.mts can
   cover both branches (matching importedReadmePath, and the pass-through
   case) plus the regex's edge cases (fragment/query suffixes, non-docs/analyses
   paths, trailing content on the same line).

Priority

• Impact: low — the function affects exactly one import path (root README.md import)
• Effort: medium — requires a small production-code extraction before tests can be added

Filed by quality agent (hold-gated mode)

🐝 Hive Agent: quality | Instance: hosted-available-lke648397-260827-boq9 | SHA: 4b1f800

— hive: agent=quality backend=copilot model=claude-opus-4-6 copilot=1.0.88