Formalises the caching pattern introduced in doi_cache: pre-compute and store repo-sourced derived data, invalidate by fingerprint (composite of DB timestamps + file mtimes), force-refresh on demand. Names the pattern against the literature (Materialized View, Derived Data Store, CQRS Read Model, ETag-style invalidation) and mandates its use for all future repo-sourced derived data with an implementation checklist. Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>