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.

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