feat: backend service

gateway/internal/backendclient/doc.go

@@ -0,0 +1,18 @@
+// Package backendclient is the gateway-side adapter to the consolidated
+// `backend` service. It bundles every gateway → backend conversation:
+//
+//   - public REST (`/api/v1/public/auth/*`) used by the public auth
+//     surface,
+//   - internal REST (`/api/v1/internal/sessions/*`,
+//     `/api/v1/internal/users/*/account-internal`) used by the
+//     authenticated request pipeline,
+//   - authenticated user REST (`/api/v1/user/*`) used by the gRPC
+//     downstream router after envelope verification,
+//   - gRPC `Push.SubscribePush` used to receive `client_event` and
+//     `session_invalidation` frames from backend.
+//
+// One env-driven Config describes the backend endpoint and the gateway
+// client identity. A single Client value is wired by `cmd/gateway` and
+// shared by all consumers (rest API public auth handler, gRPC session
+// cache, downstream user/lobby routes, and the push subscriber).
+package backendclient