Redis becomes mandatory infrastructure (PostgreSQL-parity): the
REDIS_ENABLED flag, NullCache backend, and every conditional caching
code path are removed. /health/ready reports not_ready (503) when
Redis is unreachable and cached endpoints return 503 instead of
silently degrading; invalidation helpers never raise after a
committed write.
The bundled redis container joins the core profile only via
docker-compose.dev.yml (production points REDIS_* at an external
instance, same no-shadowing pattern as postgres), the backend suite
runs against real Redis (test-redis on 127.0.0.1:55433, CI redis:8
service container, per-xdist-worker key prefixes), and operator docs
describe the required-dependency setup (upgrading.md gains the
v0.20.0 section).
Louis King