feat: use postgres

gateway/docs/runbook.md

@@ -7,25 +7,28 @@ readiness, shutdown, and push or revoke incidents.
 
 Before starting the process, confirm:
 
-- `GATEWAY_SESSION_CACHE_REDIS_ADDR` points to the Redis deployment used for
-  session lookup and both internal event streams.
+- `GATEWAY_REDIS_MASTER_ADDR` and `GATEWAY_REDIS_PASSWORD` point to the Redis
+  deployment used for session lookup, replay reservations, session-events
+  consumption, and client-events fan-out. Optional read replicas may be
+  listed in `GATEWAY_REDIS_REPLICA_ADDRS` (currently unused; reserved for
+  future read-routing).
 - `GATEWAY_SESSION_EVENTS_REDIS_STREAM` and
-  `GATEWAY_CLIENT_EVENTS_REDIS_STREAM` reference existing Redis Stream keys or
-  the names publishers will use.
+  `GATEWAY_CLIENT_EVENTS_REDIS_STREAM` reference existing Redis Stream keys
+  or the names publishers will use.
 - `GATEWAY_RESPONSE_SIGNER_PRIVATE_KEY_PEM_PATH` points to a readable PKCS#8
   PEM-encoded Ed25519 private key.
-- the configured Redis ACL, DB, TLS, and key-prefix settings match the target
-  environment.
+- the configured Redis DB and key-prefix settings match the target
+  environment. Per `ARCHITECTURE.md §Persistence Backends`, Redis traffic is
+  password-protected and TLS is disabled by policy; the deprecated
+  `GATEWAY_REDIS_TLS_ENABLED` and `GATEWAY_REDIS_USERNAME` variables are no
+  longer accepted and cause a hard fail at startup.
 
-At startup the process performs bounded `PING` checks for:
+At startup the process opens one shared `*redis.Client` (instrumented via
+OpenTelemetry tracing and metrics) and performs one bounded `PING`. The
+session cache, replay store, session-events subscriber, and client-events
+subscriber all use that client.
 
-- the Redis-backed session cache adapter;
-- the replay store;
-- the session event subscriber;
-- the client event subscriber.
-
-Startup fails fast if any of those checks fail or if the signer key cannot be
-loaded.
+Startup fails fast if the ping fails or if the signer key cannot be loaded.
 
 Expected listener state after a healthy start: