Add workflow support and enhance runtime configuration in models and services

- Introduce RuntimeModelResource and RuntimeKnowledgeBase classes to manage workflow resources.
- Update AssistantConfig to include workflow_model_resources and workflow_knowledge_bases for better integration.
- Refactor validation and processing logic in routes and services to accommodate workflow types.
- Implement dynamic variable support for workflow assistants and enhance graph normalization.
- Add ToolExecutor for reusable tool execution across different assistant types.
- Update various services to ensure compatibility with new workflow features and improve error handling.

backend/tests/test_pipeline_knowledge.py

@@ -1,7 +1,11 @@
 import unittest
 
 from models import AssistantConfig
-from services.pipecat.pipeline import _knowledge_tool_description
+from services.pipecat.pipeline import (
+    KNOWLEDGE_CONTEXT_MARKER,
+    KnowledgeRetrievalProcessor,
+    _knowledge_tool_description,
+)
 
 
 class KnowledgeToolDescriptionTest(unittest.TestCase):
@@ -33,6 +37,25 @@ class KnowledgeToolDescriptionTest(unittest.TestCase):
         self.assertNotIn("\n  ", description)
         self.assertLess(len(description), 1000)
 
+    def test_workflow_knowledge_uses_system_role(self):
+        processor = KnowledgeRetrievalProcessor(None)
+        messages = [
+            {"role": "assistant", "content": "你好"},
+            {
+                "role": "developer",
+                "content": f"{KNOWLEDGE_CONTEXT_MARKER}\n旧检索结果",
+            },
+        ]
+
+        processor._set_context(
+            messages,
+            f"{KNOWLEDGE_CONTEXT_MARKER}\n新检索结果",
+        )
+
+        self.assertEqual(messages[0]["role"], "system")
+        self.assertIn("新检索结果", messages[0]["content"])
+        self.assertFalse(any(message["role"] == "developer" for message in messages))
+
 
 if __name__ == "__main__":
     unittest.main()