重构：简化流式架构，将 ReAct 循环移入 agent 节点

主要变更：
- 简化 agent_service：移除复杂双协程，只用 stream_mode=["updates"]
- stream_context：提供更清晰的 API (set_stream_queue/get_stream_queue)
- main_graph_builder：简化图结构，移除 tools 节点和条件边
- agent 节点：包含完整 ReAct 循环 + 流式 Tool Calling 拼接
- 前端：适配新的事件格式
- 添加测试文件：test_full_react_streaming.py, test_stream.py

tools/test/test_stream.py

@@ -0,0 +1,79 @@
+#!/usr/bin/env python3
+"""测试后端流式接口，看看是否真的有流式输出"""
+
+import asyncio
+import aiohttp
+import json
+
+BACKEND_URL = "http://localhost:8079/chat/stream"
+
+
+async def test_stream():
+    print("=" * 60)
+    print("🧪 测试后端流式接口")
+    print("=" * 60)
+
+    async with aiohttp.ClientSession() as session:
+        payload = {
+            "message": "你好，请简单介绍一下自己",
+            "thread_id": "test-thread-001",
+            "model": "zhipu",
+            "user_id": "test-user"
+        }
+
+        print(f"\n📤 发送请求: {json.dumps(payload, ensure_ascii=False)}")
+
+        try:
+            async with session.post(BACKEND_URL, json=payload) as response:
+                print(f"\n✅ 响应状态: {response.status}")
+                print(f"\n📥 开始接收流式响应...\n")
+
+                event_count = 0
+                token_count = 0
+
+                async for line in response.content:
+                    line = line.decode('utf-8').strip()
+                    if line:
+                        if line.startswith("data: "):
+                            data_str = line[6:]
+                            if data_str == "[DONE]":
+                                print("\n🏁 收到 [DONE] 事件")
+                                break
+                            
+                            try:
+                                event = json.loads(data_str)
+                                event_count += 1
+                                print(f"  [{event_count}] {event.get('type')}")
+                                
+                                if event.get('type') == 'llm_token' and 'token' in event:
+                                    token = event['token']
+                                    token_count += 1
+                                    print(f"      → token: {repr(token)}")
+                                
+                                if event.get('type') == 'node_start':
+                                    print(f"      → node: {event.get('node')}")
+                                
+                                if event.get('type') == 'tool_call_start':
+                                    print(f"      → tool: {event.get('tool')}")
+                                
+                                if event.get('type') == 'tool_call_end':
+                                    print(f"      → tool: {event.get('tool')}")
+                                
+                                if event.get('type') == 'error':
+                                    print(f"      ❌ 错误: {event.get('message')}")
+                                
+                            except Exception as e:
+                                print(f"  ❌ 解析失败: {e}, 原始数据: {repr(data_str)}")
+                        else:
+                            print(f"  📝 原始行: {repr(line)}")
+
+                print(f"\n📊 统计: {event_count} 个事件, {token_count} 个 token")
+
+        except Exception as e:
+            print(f"\n❌ 请求异常: {e}")
+            import traceback
+            print(f"📋 堆栈: {traceback.format_exc()}")
+
+
+if __name__ == "__main__":
+    asyncio.run(test_stream())