cache-policy-designerlisted

Design caching as a correctness contract with a performance benefit. ## Workflow 1. **Inventory the cacheable object.** Name the response or value, authoritative source, readers, writers, sensitivity, size, cost to recompute, and consequence of serving it stale. 2. **Map every cache layer.** Trace browser, service worker, CDN, gateway, reverse proxy, framework, application, ORM, and database caches. Record which layer currently owns freshness and invalidation. 3. **Define identity and variation.** Specify the complete cache key: resource, tenant, user or authorization class, locale, encoding, version, query shape, and any header that changes representation. Remove unnecessary variants but never collapse security boundaries. 4. **Choose freshness semantics.** Set max age from the business freshness bound, not a convenient round number. Decide whether revalidation, `stale-while-revalidate`, or `stale-if-error` preserves acceptable behavior. 5. **Design invalidation.** Identify every write or event that changes the object. Choose purge, versioned keys, tag invalidation, write-through, or bounded expiration, and state how missed events heal. 6. **Control concurrency.** Prevent cold-key stampedes with request coalescing, locks with bounded leases, probabilistic early refresh, or jitter. Define behavior when the origin is slow or unavailable. 7. **Specify privacy and failure rules.** Mark values that must never enter a shared cache. Define fail-open versus fail-closed, negative c