Cachex Caching

Canonical FP bar: docs/fcis-engineering-rules.md — Functional Core, Imperative Shell: pure domain modules; side effects at edges. Workers and pipelines are edges: fetch IDs, call pure core, return tagged tuples.

RULES — Follow these with no exceptions

1. Set a TTL on every cached entry — never cache indefinitely unless the data is truly immutable 2. Enable stats: true — required to measure cache effectiveness via hit_rate 3. Use cache warmers for startup — pre-populate expensive data when the application starts 4. Use Cachex.fetch/3 for get-or-set — atomic cache-aside avoids the dogpile/race on concurrent misses 5. Invalidate with Cachex.del/2 after every mutation — stale entries outlive the source of truth otherwise 6. Handle the {:error, reason} tuple from every Cachex call — fall back to the database; a cache failure must never break the request 7. Bound the cache with :limit and an eviction policy — unbounded caches leak memory

End-to-End Workflow

Follow this sequence when adding caching to a feature: