The legacy caching bundle at sources/legacy-caching/dist/ was
gitignored by sources/.gitignore, so CI never included it. Fix by:
- Copying the bundle into sources/dist/legacy-caching/ during build
- Updating the loader path to resolve from dist/legacy-caching/
- Adding legacy module build steps to build-dist action and
ci-update-dist workflow
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>