feat: backend service

gateway/docs/redis-config.md

@@ -1,43 +1,33 @@
 # Decision: Redis configuration shape
 
-PG_PLAN.md §7. Captures the standing rules adopted by Edge Gateway when it
-joined the project-wide Redis topology defined in
-`ARCHITECTURE.md §Persistence Backends`.
+Captures the standing rules adopted by Edge Gateway when it joined the
+project-wide Redis topology described in `ARCHITECTURE.md`.
 
 ## Context
 
-Gateway intentionally stays Redis-only. All gateway state Redis serves is
-TTL-bounded or runtime-coordination state:
+Gateway intentionally stays Redis-light. The only Redis state served by
+gateway is the replay reservation namespace (short-lived `SETNX` per
+authenticated request, bounded by
+`GATEWAY_REPLAY_REDIS_RESERVE_TIMEOUT`). Session lookup goes through
+backend's REST surface, and inbound events are delivered through the
+gRPC `Push.SubscribePush` consumer (see
+`gateway/internal/backendclient`).
 
-- the session cache is a read-through projection of authsession's
-  source-of-truth session records (rebuildable via re-authentication);
-- the replay store is a short-lived `SETNX` reservation namespace per
-  authenticated request (`GATEWAY_REPLAY_REDIS_RESERVE_TIMEOUT`);
-- the session-events stream is a runtime fan-out of session lifecycle
-  updates;
-- the client-events stream is a runtime push fan-out.
-
-Stage 7 brought gateway in line with the steady-state rules established in
-Stage 0: every Galaxy service uses one master plus zero-or-more replicas
-with a mandatory password, no TLS, and no Redis ACL username; the connection
-is configured by the shared `pkg/redisconn` helper.
+The shared rule is: every Galaxy service uses one master plus
+zero-or-more replicas with a mandatory password, no TLS, and no Redis
+ACL username; the connection is configured by the shared
+`pkg/redisconn` helper.
 
 ## Decisions
 
 ### One shared `*redis.Client` owned by the runtime
 
 `cmd/gateway/main.go` constructs a single `*redis.Client` via
-`internal/redisclient.NewClient`, attaches OpenTelemetry tracing and metrics
-via `internal/redisclient.InstrumentClient`, performs one bounded `PING`
-via `internal/redisclient.Ping`, and registers `client.Close` for shutdown.
-The session cache, replay store, session-events subscriber, and
-client-events subscriber all receive this same client.
-
-Adapters no longer build or own a Redis client. Their `Config` structs hold
-only behavior settings (key prefix, stream name, per-subsystem timeouts).
-Adapter constructors take `(*redis.Client, …)`. The stream subscribers'
-`Close`/`Shutdown` methods became no-ops; the runtime's context cancellation
-unblocks the `XRead` loop and the runtime closes the shared client.
+`internal/redisclient.NewClient`, attaches OpenTelemetry tracing and
+metrics via `internal/redisclient.InstrumentClient`, performs one
+bounded `PING` via `internal/redisclient.Ping`, and registers
+`client.Close` for shutdown. The replay store is the only adapter
+backed by Redis.
 
 ### One env-var prefix for the connection
 
@@ -51,17 +41,10 @@ Connection topology is loaded from a single `GATEWAY_REDIS_*` group via
 - `GATEWAY_REDIS_DB` (default `0`)
 - `GATEWAY_REDIS_OPERATION_TIMEOUT` (default `250ms`)
 
-Per-subsystem behavior env vars keep their existing prefixes — they do not
-describe connection topology, only namespace and timing:
+Per-subsystem behavior env vars (namespace and timing only):
 
-- `GATEWAY_SESSION_CACHE_REDIS_KEY_PREFIX`,
-  `GATEWAY_SESSION_CACHE_REDIS_LOOKUP_TIMEOUT`
 - `GATEWAY_REPLAY_REDIS_KEY_PREFIX`,
   `GATEWAY_REPLAY_REDIS_RESERVE_TIMEOUT`
-- `GATEWAY_SESSION_EVENTS_REDIS_STREAM`,
-  `GATEWAY_SESSION_EVENTS_REDIS_READ_BLOCK_TIMEOUT`
-- `GATEWAY_CLIENT_EVENTS_REDIS_STREAM`,
-  `GATEWAY_CLIENT_EVENTS_REDIS_READ_BLOCK_TIMEOUT`
 
 ### Retired env vars (hard removal)
 
@@ -96,11 +79,8 @@ downstream dashboards will start populating without further changes.
 
 ## Consequences
 
-- Gateway test code that previously constructed a Redis client per adapter
-  must now construct one client and pass it to every adapter under test
-  (see `internal/session/redis_test.go`, `internal/replay/redis_test.go`,
-  `internal/events/subscriber_test.go`,
-  `internal/events/client_subscriber_test.go`).
+- Gateway test code constructs one shared client and passes it to the
+  replay-store adapter under test (see `internal/replay/redis_test.go`).
 - Operators must set `GATEWAY_REDIS_PASSWORD`. A passwordless local Redis
   is still acceptable as long as a placeholder password is supplied to the
   binary; Redis without `requirepass` accepts AUTH unconditionally.