Make wrapToolCall asynchronous for error handling (#1374)

## Overview
Make wrapToolCall asynchronous for error handling

## Type of change

Fix bug

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Author: liuqiang1357

src/oss/langchain/agents.mdx

@@ -341,9 +341,9 @@ import { createAgent, createMiddleware, ToolMessage } from "langchain";
 
 const handleToolErrors = createMiddleware({
   name: "HandleToolErrors",
-  wrapToolCall: (request, handler) => {
+  wrapToolCall: async (request, handler) => {
     try {
-      return handler(request);
+      return await handler(request);
     } catch (error) {
       // Return a custom error message to the model
       return new ToolMessage({