Agent 不是更长的 Prompt：从工具调用到受控执行循环

用户目标
  -> 模型决定下一步
  -> 生成结构化工具调用
  -> 应用校验并执行
  -> 工具结果返回模型
  -> 模型继续行动或给出最终回答

import { tool } from 'ai';
import { z } from 'zod';
 
const writeFile = tool({
  description: 'Write text content to a file in the sandbox',
  inputSchema: z.object({
    path: z.string().describe('Path relative to the sandbox root'),
    content: z.string().describe('Complete text to write'),
  }),
  execute: async ({ path, content }) => {
    return fileSystem.writeFile(path, content);
  },
});

{
  "toolName": "writeFile",
  "input": {
    "path": "todo.md",
    "content": "# Today\n\n- [ ] Review pull request\n- [ ] Write release notes"
  }
}

return {
  success: true,
  message: 'File written successfully: todo.md',
  path: 'todo.md',
};

import { stepCountIs, streamText } from 'ai';
 
const result = streamText({
  model,
  system: 'Use the sandboxed file tools to manage Markdown notes.',
  messages,
  tools: {
    writeFile,
    readFile,
    listDirectory,
    deletePath,
  },
  stopWhen: [stepCountIs(10)],
});

import {
  createAgentUIStreamResponse,
  InferAgentUIMessage,
  stepCountIs,
  ToolLoopAgent,
} from 'ai';
 
const agent = new ToolLoopAgent({
  model,
  instructions: 'Manage Markdown notes in the sandbox.',
  tools: { writeFile, readFile, listDirectory, deletePath },
  stopWhen: [stepCountIs(10)],
});
 
export type FileAgentMessage = InferAgentUIMessage<typeof agent>;
 
export const POST = async (req: Request) => {
  const { messages }: { messages: FileAgentMessage[] } = await req.json();
 
  return createAgentUIStreamResponse({
    agent,
    uiMessages: messages,
  });
};

{
  role: 'assistant',
  parts: [
    { type: 'step-start' },
    {
      type: 'tool-writeFile',
      toolCallId: 'call_123',
      state: 'output-available',
      input: {
        path: 'todo.md',
        content: '# Today\n\n- [ ] Review pull request',
      },
      output: {
        success: true,
        path: 'todo.md',
      },
    },
    { type: 'step-start' },
    {
      type: 'text',
      state: 'done',
      text: 'Created `todo.md` and verified its contents.',
    },
  ],
}

if (part.type === 'tool-writeFile') {
  if (part.state === 'input-streaming') {
    return <p>正在准备文件...</p>;
  }
 
  if (part.state === 'input-available') {
    return <p>正在写入 {part.input.path}...</p>;
  }
 
  if (part.state === 'output-available') {
    return <p>已创建 {part.output.path}</p>;
  }
}

import { experimental_createMCPClient as createMCPClient } from '@ai-sdk/mcp';
import { Experimental_StdioMCPTransport as StdioMCPTransport } from '@ai-sdk/mcp/mcp-stdio';
 
const transport = new StdioMCPTransport({
  command: 'docker',
  args: [
    'run',
    '-i',
    '--rm',
    '-e',
    'GITHUB_PERSONAL_ACCESS_TOKEN',
    'ghcr.io/github/github-mcp-server',
  ],
  env: {
    GITHUB_PERSONAL_ACCESS_TOKEN: process.env.GITHUB_PERSONAL_ACCESS_TOKEN!,
  },
});
 
const mcpClient = await createMCPClient({ transport });
const tools = await mcpClient.tools();

const mcpClient = await createMCPClient({
  transport: {
    type: 'http',
    url: 'https://api.githubcopilot.com/mcp',
    headers: {
      Authorization: `Bearer ${process.env.GITHUB_PERSONAL_ACCESS_TOKEN}`,
    },
  },
});

const sendEmail = tool({
  description: 'Send an email to a recipient',
  inputSchema: z.object({
    to: z.string(),
    subject: z.string(),
    body: z.string(),
  }),
  needsApproval: true,
  execute: async ({ to, subject, body }) => {
    return emailService.send({ to, subject, body });
  },
});

if (
  part.type === 'tool-sendEmail' &&
  part.state === 'approval-requested'
) {
  return (
    <EmailApproval
      email={part.input}
      onApprove={() =>
        addToolApprovalResponse({
          id: part.approval.id,
          approved: true,
        })
      }
      onReject={() =>
        addToolApprovalResponse({
          id: part.approval.id,
          approved: false,
        })
      }
    />
  );
}

const {
  messages,
  sendMessage,
  addToolApprovalResponse,
} = useChat<FileAgentMessage>({
  sendAutomaticallyWhen:
    lastAssistantMessageIsCompleteWithApprovalResponses,
});