添加调试日志，排查Task was destroyed问题

backend/app/agent/agent_service.py

@@ -151,9 +151,13 @@ class AIAgentService:
         # ========================================
 
         # ========== React 循环路径 ==========
+        info(f"🚀 开始执行 React 图，模型: {model_name}")
         current_node = None
         tool_calls_in_progress = {}
 
+        try:
+            info(f"📡 开始调用 graph.astream()...")
+            chunk_count = 0
             async for chunk in graph.astream(
                 input_state,
                 config=config,
@@ -161,12 +165,15 @@ class AIAgentService:
                 version="v2",
                 subgraphs=True
             ):
+                chunk_count += 1
                 chunk_type = chunk["type"]
+                info(f"📦 收到第 {chunk_count} 个chunk, type: {chunk_type}")
                 processed_event = {}
 
                 if chunk_type == "messages":
                     message_chunk, metadata = chunk["data"]
                     node_name = metadata.get("langgraph_node", "unknown")
+                    info(f"📨 处理消息chunk, node: {node_name}")
 
                     # 检测节点变化，发送节点开始事件
                     if node_name != current_node:
@@ -223,6 +230,7 @@ class AIAgentService:
                         }
 
                 elif chunk_type == "updates":
+                    info(f"🔄 处理updates chunk")
                     updates_data = chunk["data"]
                     serialized_data = self._serialize_value(updates_data)
 
@@ -260,6 +268,7 @@ class AIAgentService:
                     }
 
                 elif chunk_type == "custom":
+                    info(f"🎯 处理custom chunk")
                     serialized_data = self._serialize_value(chunk["data"])
                     processed_event = {
                         "type": "custom",
@@ -269,6 +278,14 @@ class AIAgentService:
                 if processed_event:
                     yield processed_event
 
+            info(f"✅ graph.astream() 完成，共 {chunk_count} 个chunks")
+
+        except Exception as e:
+            error(f"❌ 执行 React 图时出错: {e}")
+            import traceback
+            error(f"📋 堆栈: {traceback.format_exc()}")
+            raise
+
         # 发送结束事件
         if current_node:
             yield {