Cache Key Discriminator Audit

Audits whether a cache key carries every discriminator the cached response actually depends on, so two requests that must not share a slot cannot collide. Ranks identity discriminators (tenant, user, authorization scope, plan tier) above presentation ones (locale, region, currency, feature flag), maps each missing discriminator to the data-exposure or wrong-content consequence it causes, classifies each key-and-value pair into a critical / high / medium severity band (including the Python lru_cache-on-an-instance-method trap), and writes the fix as a namespaced key builder plus the matching HTTP Vary header. Use when a cache key is being designed or changed, when a per-us…