Add input validation to WS connect method

Author: seratch

src/agents/realtime/openai_realtime.py

@@ -208,15 +208,25 @@ async def connect(self, options: RealtimeModelConfig) -> None:
 
         self._playback_tracker = options.get("playback_tracker", None)
 
-        self.model = model_settings.get("model_name", self.model)
+        call_id = options.get("call_id")
+        model_name = model_settings.get("model_name")
+        if call_id and model_name:
+            error_message = (
+                "Cannot specify both `call_id` and `model_name` "
+                "when attaching to an existing realtime call."
+            )
+            raise UserError(error_message)
+
+        if model_name:
+            self.model = model_name
+
         api_key = await get_api_key(options.get("api_key"))
 
         if "tracing" in model_settings:
             self._tracing_config = model_settings["tracing"]
         else:
             self._tracing_config = "auto"
 
-        call_id = options.get("call_id")
         if call_id:
             url = options.get("url", f"wss://api.openai.com/v1/realtime?call_id={call_id}")
         else:

tests/realtime/test_openai_realtime.py

@@ -53,6 +53,18 @@ async def test_connect_missing_api_key_raises_error(self, model):
             with pytest.raises(UserError, match="API key is required"):
                 await model.connect(config)
 
+    @pytest.mark.asyncio
+    async def test_connect_with_call_id_and_model_raises_error(self, model):
+        """Test that specifying both call_id and model raises UserError."""
+        config = {
+            "api_key": "test-api-key-123",
+            "call_id": "call-123",
+            "initial_model_settings": {"model_name": "gpt-4o-realtime-preview"},
+        }
+
+        with pytest.raises(UserError, match="Cannot specify both `call_id` and `model_name`"):
+            await model.connect(config)
+
     @pytest.mark.asyncio
     async def test_connect_with_string_api_key(self, model, mock_websocket):
         """Test successful connection with string API key."""