fix(backend): system prompt override (planning agent) (#12893)

enterprise/experiments/experiment_manager.py

@@ -28,9 +28,11 @@ class SaaSExperimentManager(ExperimentManager):
             return agent
 
         if EXPERIMENT_SYSTEM_PROMPT_EXPERIMENT:
-            agent = agent.model_copy(
-                update={'system_prompt_filename': 'system_prompt_long_horizon.j2'}
-            )
+            # Skip experiment for planning agents which require their specialized prompt
+            if agent.system_prompt_filename != 'system_prompt_planning.j2':
+                agent = agent.model_copy(
+                    update={'system_prompt_filename': 'system_prompt_long_horizon.j2'}
+                )
 
         return agent
 

enterprise/tests/unit/experiments/test_saas_experiment_manager.py

@@ -126,3 +126,24 @@ def test_run_agent_variant_tests_v1_calls_handler_and_sets_system_prompt(monkeyp
     # Should be a different instance than the original (copied after handler runs)
     assert result is not agent
     assert result.system_prompt_filename == 'system_prompt_long_horizon.j2'
+
+
+@patch('experiments.experiment_manager.ENABLE_EXPERIMENT_MANAGER', True)
+@patch('experiments.experiment_manager.EXPERIMENT_SYSTEM_PROMPT_EXPERIMENT', True)
+def test_run_agent_variant_tests_v1_preserves_planning_agent_system_prompt():
+    """Planning agents should retain their specialized system prompt and not be overwritten by the experiment."""
+    # Arrange
+    planning_agent = make_agent().model_copy(
+        update={'system_prompt_filename': 'system_prompt_planning.j2'}
+    )
+    conv_id = uuid4()
+
+    # Act
+    result: Agent = SaaSExperimentManager.run_agent_variant_tests__v1(
+        user_id='user-planning',
+        conversation_id=conv_id,
+        agent=planning_agent,
+    )
+
+    # Assert
+    assert result.system_prompt_filename == 'system_prompt_planning.j2'