Enhance conversation history and runtime variable management

- Update ConversationRecorder to include source and nodeId metadata in transcripts for better context tracking.
- Introduce optional variable handling in DynamicVariableStore, allowing for unset variables to be rendered as empty without raising errors.
- Refactor WorkflowBrain to apply turn configurations and manage interaction policies dynamically, improving agent responsiveness.
- Implement tests to ensure proper handling of updated session variables and workflow metadata in various scenarios.

backend/tests/test_workflow_v3.py

@@ -170,6 +170,11 @@ class WorkflowGraphTests(unittest.TestCase):
                 "knowledgeMode": "on_demand",
                 "knowledgeTopN": 8,
                 "knowledgeScoreThreshold": 0.4,
+                "enableInterrupt": False,
+                "turnConfig": {
+                    "bargeIn": {"strategy": "transcription"},
+                    "turnDetection": {"strategy": "silence", "silenceTimeoutSecs": 1.2},
+                },
             }
         )
         engine = WorkflowEngine(graph)
@@ -177,6 +182,11 @@ class WorkflowGraphTests(unittest.TestCase):
         self.assertEqual(inherited.llm_resource_id, "llm_global")
         self.assertEqual(inherited.tool_ids, ("tool_global",))
         self.assertEqual(inherited.knowledge_mode, "on_demand")
+        self.assertFalse(inherited.enable_interrupt)
+        self.assertEqual(
+            inherited.turn_config["bargeIn"]["strategy"],
+            "transcription",
+        )
 
         engine.data("agent").update(
             {
@@ -184,12 +194,22 @@ class WorkflowGraphTests(unittest.TestCase):
                 "llmResourceId": "llm_agent",
                 "toolIds": ["tool_agent"],
                 "knowledgeBaseId": "",
+                "enableInterrupt": True,
+                "turnConfig": {
+                    "bargeIn": {"strategy": "vad"},
+                    "turnDetection": {"strategy": "smart_turn"},
+                },
             }
         )
         custom = engine.agent_stage_config("agent")
         self.assertEqual(custom.llm_resource_id, "llm_agent")
         self.assertEqual(custom.tool_ids, ("tool_agent",))
         self.assertEqual(custom.knowledge_mode, "disabled")
+        self.assertTrue(custom.enable_interrupt)
+        self.assertEqual(
+            custom.turn_config["turnDetection"]["strategy"],
+            "smart_turn",
+        )
 
     def test_start_agent_and_handoff_may_have_no_outgoing_edge(self):
         terminal_graphs = [