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_runtime_variables.py

@@ -79,6 +79,58 @@ class DynamicVariableTests(unittest.TestCase):
             "Bearer private",
         )
 
+    def test_optional_workflow_variable_renders_empty_but_remains_unset(self):
+        cfg = AssistantConfig(
+            type="workflow",
+            graph={
+                "specVersion": 3,
+                "settings": {"globalPrompt": "称呼 {{nickname}}"},
+                "nodes": [
+                    {
+                        "id": "start",
+                        "type": "start",
+                        "data": {"greeting": "您好 {{nickname}}"},
+                    }
+                ],
+                "edges": [],
+            },
+            greeting="",
+            dynamic_variable_definitions={
+                "nickname": {
+                    "type": "string",
+                    "required": False,
+                    "default": None,
+                }
+            },
+        )
+        prepared = prepare_dynamic_config(cfg, {}, assistant_id="asst_workflow")
+        store = DynamicVariableStore.from_config(prepared)
+
+        self.assertEqual(store.render("您好 {{nickname}}"), "您好 ")
+        self.assertNotIn("nickname", store.values)
+        with self.assertRaisesRegex(DynamicVariableError, "缺少动态变量"):
+            store.render("{{not_defined}}")
+
+    def test_exact_placeholder_keeps_action_argument_type(self):
+        store = DynamicVariableStore(
+            {"count": 3, "confirmed": True},
+            variable_types={"count": "number", "confirmed": "boolean"},
+        )
+
+        rendered = store.render_data(
+            {
+                "count": "{{count}}",
+                "confirmed": "{{confirmed}}",
+                "label": "数量 {{count}}",
+            }
+        )
+        self.assertEqual(rendered["count"], 3)
+        self.assertIs(rendered["confirmed"], True)
+        self.assertEqual(rendered["label"], "数量 3")
+
+        with self.assertRaisesRegex(DynamicVariableError, "类型应为 number"):
+            store.assign("count", "four")
+
     def test_tool_assignment_and_system_history(self):
         store = DynamicVariableStore(
             {