Code tags are ground truth; implemented_in is generated
Decision. Code carries ID comment tags as ground truth. Markdown gets a
generated reverse index (gen-manifest.mjs). implemented_in never appears
in frontmatter — the schema omits it on purpose.
Why. File paths written into frontmatter rot on every rename; comment tags travel with the code through refactors. Hand-maintaining both directions guarantees drift, and a traceability graph that’s 80% accurate is worse than none.