FEAT-0004resolvedships in mvp

Implementation manifest

Code carries ID tags as ground truth; markdown gets a generated reverse index. Never hand-maintain both directions.

File paths written into frontmatter rot; comment tags travel with code through refactors. So the direction of truth is fixed: one tag per feature, at its entry point —

// FEAT-0012: usage-based billing — spec: /features/billing

gen-manifest.mjs greps the tree at build time and writes the implemented_in reverse index. It’s a “start here” pointer, not a coverage map — per-function tagging dies of tedium and poisons trust in the whole graph, so it’s banned.