fix(gateway): resolve composite routes for websocket aliases

docs/COMPOSITE_GROUPS.md

@@ -63,6 +63,13 @@ payloads, and apply the configured `upstream_model` before dispatch.
 Codex model manifest requests reuse the existing OpenAI account selection and
 failover path within the Composite group.
 
+Responses WebSocket resolves the first `response.create` model in the
+`responses` route domain (including `any` routes). Only OpenAI and Grok targets
+are supported. The public model remains the admission and response identity;
+the route's upstream model is applied before channel/account mapping. Subsequent
+turns can repeat or omit the public model. Changing it requires reconnecting so
+the gateway can resolve the route and select an account again.
+
 ## Built-In Detection
 
 Composite routing detects common public model IDs and provider-prefixed IDs: