feat(ADM-018): completed feature

work/artifacts/F-027/architect.md

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+# Architect — F-027 Caching layer with explicit contracts
+
+## Feature
+F-027 wraps hot catalog reads with Redis cache entries that document key, TTL, invalidation and source of truth.
+
+## Design
+
+### Module boundaries
+Create `project/src/modules/cache/` with domain/application/infrastructure/api/tests. Cache is an in-process wrapper around a Redis-like adapter. PostgreSQL remains the source of truth.
+
+### Adapter
+- `InMemoryCacheAdapter` for v1 implementing `get/set/invalidate` and a metrics hook (`hit_ratio`).
+
+### Public API
+- `GET /cache/contracts` admin returns the list of registered cache entries with key, TTL, source.
+- `GET /cache/metrics` returns hits/misses.
+
+### Cache entries
+- `product:{slug}` (TTL 5m, invalidated by `ProductUpdated` event)
+- `category:{slug}` (TTL 5m)
+- `nav:tree` (TTL 10m)
+- `search:popular` (TTL 1m)
+
+### Acceptance trace
+- Catalog update invalidates `product:{slug}` and `category:{slug}`.
+- Redis down -> reads still served from PostgreSQL via bypass.
+- Hit ratio metric exposed on `/cache/metrics`.