fix: Ensure agent model takes precedence over starting_settings

- Move agent model assignment after starting_settings update
- This fixes P1 bug where agent's model was overridden
- Ensures proper precedence: agent model > starting_settings > run config
- Add test to verify fix for initial session scenario

Addresses feedback from chatgpt-codex-connector bot review

Author: pxkundu

src/agents/realtime/session.py

@@ -774,10 +774,6 @@ async def _get_updated_model_settings_from_agent(
         # Start with the merged base settings from run and model configuration.
         updated_settings = self._base_model_settings.copy()
 
-        # Use agent-specific model if specified
-        if agent.model is not None:
-            updated_settings["model_name"] = agent.model
-
         if agent.prompt is not None:
             updated_settings["prompt"] = agent.prompt
 
@@ -794,6 +790,11 @@ async def _get_updated_model_settings_from_agent(
         if starting_settings:
             updated_settings.update(starting_settings)
 
+        # Use agent-specific model if specified (applied last to ensure proper precedence)
+        # This ensures agent model > starting_settings > run config > defaults
+        if agent.model is not None:
+            updated_settings["model_name"] = agent.model
+
         disable_tracing = self._run_config.get("tracing_disabled", False)
         if disable_tracing:
             updated_settings["tracing"] = None

tests/realtime/test_agent_model.py

@@ -107,3 +107,27 @@ async def test_update_agent_with_different_model():
 
     # Verify the new model is in the session settings
     assert last_event.session_settings.get("model_name") == "gpt-4o-realtime-preview"
+
+
+@pytest.mark.asyncio
+async def test_agent_model_not_overridden_by_starting_settings():
+    """Test that agent's model is not overridden by starting_settings (fixes P1 bug)."""
+    from agents.realtime.config import RealtimeSessionModelSettings
+
+    model = _DummyModel()
+
+    # Agent with specific model
+    agent = RealtimeAgent(name="test_agent", instructions="Hello", model="gpt-4o-realtime-preview")
+
+    # Starting settings with different model (simulates model config)
+    starting_settings: RealtimeSessionModelSettings = {"model_name": "gpt-realtime"}
+
+    session = RealtimeSession(model, agent, None)
+
+    # Get model settings with starting_settings (this simulates initial session start)
+    model_settings = await session._get_updated_model_settings_from_agent(starting_settings, agent)
+
+    # Verify that agent's model takes precedence over starting_settings
+    assert model_settings["model_name"] == "gpt-4o-realtime-preview"
+    # Ensure it's not using the default from starting_settings
+    assert model_settings["model_name"] != "gpt-realtime"