chore: add system instruction to enhance compliance with function call

app/services/chat/message_converter.py

@@ -1,14 +1,16 @@
 # app/services/chat/message_converter.py
 
 from abc import ABC, abstractmethod
-from typing import List, Dict, Any
+from typing import Any, Dict, List, Optional
+
+SUPPORTED_ROLES = ["user", "model", "system"]
 
 
 class MessageConverter(ABC):
     """消息转换器基类"""
 
     @abstractmethod
-    def convert(self, messages: List[Dict[str, Any]]) -> List[Dict[str, Any]]:
+    def convert(self, messages: List[Dict[str, Any]]) -> tuple[List[Dict[str, Any]], Optional[Dict[str, Any]]]:
         pass
 
 
@@ -30,16 +32,19 @@ def _convert_image(image_url: str) -> Dict[str, Any]:
 class OpenAIMessageConverter(MessageConverter):
     """OpenAI消息格式转换器"""
 
-    def convert(self, messages: List[Dict[str, Any]]) -> List[Dict[str, Any]]:
+    def convert(self, messages: List[Dict[str, Any]]) -> tuple[List[Dict[str, Any]], Optional[Dict[str, Any]]]:
         converted_messages = []
-        for msg in messages:
-            role = "user" if msg["role"] == "user" else "model"
-            parts = []
+        system_instruction = None
 
-            if isinstance(msg["content"], str):
-                # 请求 gemini 接口时如果包含 content 字段但内容为空时会返回 400 错误，所以需要判断是否为空
-                if msg["content"]:
-                    parts.append({"text": msg["content"]})
+        for msg in messages:
+            role = msg.get("role", "")
+            if role not in SUPPORTED_ROLES:
+                role = "model"
+
+            parts = []
+            if isinstance(msg["content"], str) and msg["content"]:
+                # 请求 gemini 接口时如果包含 content 字段但内容为空时会返回 400 错误，所以需要判断是否为空并移除
+                parts.append({"text": msg["content"]})
             elif isinstance(msg["content"], list):
                 for content in msg["content"]:
                     if isinstance(content, str) and content:
@@ -50,6 +55,10 @@ class OpenAIMessageConverter(MessageConverter):
                         elif content["type"] == "image_url":
                             parts.append(_convert_image(content["image_url"]["url"]))
 
-            converted_messages.append({"role": role, "parts": parts})
+            if parts:
+                if role == "system":
+                    system_instruction = {"role": "system", "parts": parts}
+                else:
+                    converted_messages.append({"role": role, "parts": parts})
 
-        return converted_messages
+        return converted_messages, system_instruction