HTTP caching

Arqen does not automatically cache every GET response. Applications must opt in because user- and tenant-scoped responses must not become public cache entries.

use arqen::http::HttpCachePolicy;

let policy = HttpCachePolicy::public("\"catalog-v42\"", 300);

The cache middleware adds ETag, Cache-Control, and Vary: Accept-Encoding. A matching If-None-Match request receives 304 Not Modified without a response body. Use HttpCachePolicy::private for authenticated responses and omit the policy for personalized data unless the application has stronger cache isolation.