feat: AG-UI 协议对齐与路由导航功能

- 前端: 添加 SSE 流式支持、stateSnapshot 事件、路由导航工具
- 前端: 实现工具调用审批流程，支持 pending 状态展示
- 后端: Agent 状态管理与会话持久化相关重构
- 文档: 新增 agent-agui-full-alignance 设计文档
- 测试: 补充相关单元测试和集成测试

backend/tests/unit/v1/agent/test_router_guards.py

@@ -0,0 +1,33 @@
+from __future__ import annotations
+
+import pytest
+
+from v1.agent import router as agent_router
+
+
+@pytest.mark.asyncio
+async def test_allow_run_request_fails_closed_when_redis_unavailable(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    async def _raise_redis_error():
+        raise RuntimeError("redis unavailable")
+
+    monkeypatch.setattr(agent_router, "get_or_init_redis_client", _raise_redis_error)
+
+    allowed = await agent_router._allow_run_request(user_id="user-1")
+
+    assert allowed is False
+
+
+@pytest.mark.asyncio
+async def test_acquire_sse_slot_fails_closed_when_redis_unavailable(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    async def _raise_redis_error():
+        raise RuntimeError("redis unavailable")
+
+    monkeypatch.setattr(agent_router, "get_or_init_redis_client", _raise_redis_error)
+
+    allowed = await agent_router._acquire_sse_slot(user_id="user-1")
+
+    assert allowed is False