fix: stabilize admin ui and agent chat model fallback

backend-fastapi/ai_platform/services/agent_service.py

@@ -75,7 +75,8 @@ class AgentService:
             流式事件
         """
         # 检查模型是否支持 Function Calling
-        supports_function_call = await self._check_model_supports_function_call(agent.model_id)
+        model_id = await self._resolve_agent_model_id(agent)
+        supports_function_call = await self._check_model_supports_function_call(model_id)
         
         if supports_function_call:
             async for event in self._chat_autonomous_function_calling(agent, conversation, user_message, attachments):
@@ -94,6 +95,43 @@ class AgentService:
         )
         model = result.scalar_one_or_none()
         return model.supports_function_call if model else False
+
+    async def _resolve_agent_model_id(self, agent: Agent) -> Optional[str]:
+        if not self._db:
+            return str(agent.model_id) if agent.model_id else None
+
+        if agent.model_id:
+            result = await self._db.execute(
+                select(LLMModel).where(
+                    LLMModel.id == agent.model_id,
+                    LLMModel.is_deleted == False,
+                    LLMModel.is_active == True,
+                )
+            )
+            if result.scalar_one_or_none():
+                return str(agent.model_id)
+
+        result = await self._db.execute(
+            select(LLMModel)
+            .where(
+                LLMModel.is_deleted == False,
+                LLMModel.is_active == True,
+                LLMModel.model_type == "chat",
+            )
+            .order_by(LLMModel.sort.desc(), LLMModel.sys_create_datetime.desc())
+        )
+        model = result.scalars().first()
+        if not model:
+            return None
+
+        agent.model_id = model.id
+        await self._db.flush()
+        logger.info(
+            "Agent %s has no active model, fallback to default chat model %s",
+            getattr(agent, "code", agent.id),
+            model.id,
+        )
+        return str(model.id)
     
     async def _chat_autonomous_function_calling(
         self,
@@ -214,6 +252,9 @@ class AgentService:
             
             # 检查是否启用流式输出
             enable_streaming = getattr(agent, 'enable_streaming', True)
+            model_id = await self._resolve_agent_model_id(agent)
+            if not model_id:
+                raise ValueError('未找到可用的 chat 模型，请先在模型配置中启用一个模型')
             
             total_tokens = 0
             final_answer = ''
@@ -222,7 +263,7 @@ class AgentService:
                 # 流式输出
                 accumulated_content = ''
                 async for chunk in self.llm_service.chat_stream(
-                    model_id=str(agent.model_id),
+                    model_id=model_id,
                     messages=messages,
                     temperature=agent.temperature or 0.7,
                     max_tokens=agent.max_tokens or 2048,
@@ -241,7 +282,7 @@ class AgentService:
             else:
                 # 非流式输出
                 response = await self.llm_service.chat_async(
-                    model_id=str(agent.model_id),
+                    model_id=model_id,
                     messages=messages,
                     temperature=agent.temperature or 0.7,
                     max_tokens=agent.max_tokens or 2048,