feat: user service

gateway/docs/flows.md

@@ -52,6 +52,24 @@ sequenceDiagram
     Gateway-->>Client: ExecuteCommandResponse + signature
 ```
 
+## Direct Gateway -> User Self-Service Flow
+
+```mermaid
+sequenceDiagram
+    participant Client
+    participant Gateway
+    participant User as User Service
+
+    Client->>Gateway: ExecuteCommand(user.account.get | user.profile.update | user.settings.update)
+    Gateway->>Gateway: verify envelope + session + signature + replay
+    Gateway->>Gateway: decode FlatBuffers payload
+    Gateway->>User: trusted REST/JSON internal request
+    User-->>Gateway: JSON account aggregate or JSON error envelope
+    Gateway->>Gateway: encode FlatBuffers success or error payload
+    Gateway->>Gateway: sign response
+    Gateway-->>Client: ExecuteCommandResponse(result_code, payload_bytes, signature)
+```
+
 ## SubscribeEvents Lifecycle
 
 ```mermaid