feat(ADM-018): completed feature

work/artifacts/F-027/documenter.md

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+# Documenter — F-027 Caching layer with explicit contracts
+
+## Summary
+Cache module exposes a read-through wrapper, registered contracts and metrics. PostgreSQL remains the source of truth; the cache is best-effort and degrades to the loader when the adapter is unavailable.
+
+## Public API notes
+
+| Route | Access | Result |
+|---|---|---|
+| GET /cache/contracts | admin | Returns registered contracts (key, TTL, source, invalidation) |
+| GET /cache/metrics | authenticated | Returns hits/misses/invalidations/hitRatio |
+
+## Contracts (v1)
+- `product:{slug}` 300s invalidated by ProductUpdated
+- `category:{slug}` 300s invalidated by CategoryUpdated
+- `nav:tree` 600s invalidated by NavigationInvalidated
+- `search:popular` 60s invalidated by SearchInvalidated
+
+## Evidence
+- `work/artifacts/F-027/architect.md`
+- `work/artifacts/F-027/implementer.md`
+- `work/artifacts/F-027/reviewer.json`
+- `work/artifacts/F-027/security.json`
+- `work/artifacts/F-027/qa.json`