Only the truth is load-bearing
The cache makes her fast; the durable store makes her correct. If the cache dies, everything falls back to the store, so she gets slower, never wrong.
Redis holds Alix's state for speed, but it is never load-bearing: if it fails, everything falls back to PostgreSQL, and a test suite proves her correctness doesn't depend on the cache. Only the durable, verifiable store is allowed to be load-bearing.