feat(mcp): 增强MCP服务器异常处理和错误描述

- 添加_iter_leaf_exceptions函数用于处理嵌套异常组
- 实现_describe_mcp_exception函数提供详细的MCP服务器错误信息
- 改进connect_mcp_servers中的错误处理，使用更精确的错误描述
- 在日志记录中包含更具体的错误详情

feat(outlook): 优化Outlook集成异常处理

- 添加_iter_leaf_exceptions函数用于异常处理
- 创建_coerce_outlook_mcp_exception函数统一异常转换
- 改进_call_outlook_mcp_tool中的异常捕获和处理
- 对认证令牌获取和MCP调用添加专门的超时和HTTP错误处理

feat(web): 改进Web会话定时任务结果记录

- 实现_record_cron_result_for_web_session函数
- 为Web模式下的独立定时任务执行结果提供持久化存储
- 支持将定时任务响应消息添加到目标会话中
- 确保前端可以显示定时任务执行结果

app-instance/backend/nanobot/agent/tools/mcp.py

@@ -19,6 +19,37 @@ from nanobot.agent.tools.base import Tool
 from nanobot.agent.tools.registry import ToolRegistry
 
 
+def _iter_leaf_exceptions(exc: BaseException) -> list[BaseException]:
+    if isinstance(exc, BaseExceptionGroup):
+        leaves: list[BaseException] = []
+        for sub_exc in exc.exceptions:
+            leaves.extend(_iter_leaf_exceptions(sub_exc))
+        return leaves
+    return [exc]
+
+
+def _describe_mcp_exception(exc: BaseException, *, server_name: str, url: str | None = None) -> str:
+    leaves = _iter_leaf_exceptions(exc)
+    target = f" ({url})" if url else ""
+
+    for leaf in leaves:
+        if isinstance(leaf, httpx.TimeoutException):
+            return f"MCP server '{server_name}' timed out while waiting for a response{target}"
+        if isinstance(leaf, httpx.ConnectError):
+            return f"MCP server '{server_name}' is unreachable{target}"
+        if isinstance(leaf, httpx.HTTPStatusError):
+            return f"MCP server '{server_name}' returned HTTP {leaf.response.status_code}{target}"
+        if isinstance(leaf, httpx.HTTPError):
+            detail = str(leaf).strip() or leaf.__class__.__name__
+            return f"MCP server '{server_name}' HTTP error{target}: {detail}"
+
+    detail_source = leaves[0] if leaves else exc
+    detail = str(detail_source).strip() or detail_source.__class__.__name__
+    if isinstance(exc, BaseExceptionGroup):
+        return f"MCP server '{server_name}' failed: {detail_source.__class__.__name__}: {detail}"
+    return detail
+
+
 class MCPToolWrapper(Tool):
     """把单个 MCP server tool 包装成 nanobot Tool。"""
 
@@ -340,7 +371,12 @@ async def connect_mcp_servers(
             )
         except Exception as e:
             # 单个 server 失败不影响其他 server 继续连；错误写进 report 供 UI 展示。
+            error_detail = _describe_mcp_exception(
+                e,
+                server_name=name,
+                url=str(getattr(cfg, "url", "") or "").strip() or None,
+            )
             report[name]["status"] = "error"
-            report[name]["last_error"] = str(e)
-            logger.error("MCP server '{}': failed to connect: {}", name, e)
+            report[name]["last_error"] = error_detail
+            logger.error("MCP server '{}': failed to connect: {}", name, error_detail)
     return report