Step 1: Install dependencies

npm install ai @ai-sdk/openai

Set your keys in .env:

OPENAI_API_KEY=sk-...
A2A_API_KEY=a2a_your_key_here

Step 2: Add the safety layer

Create a tool wrapper that calls /v1/evaluate before executing any tool:

import { generateText, tool } from "ai";
import { openai } from "@ai-sdk/openai";
import { execSync } from "child_process";
import { z } from "zod";

const A2A_URL = "https://a2ainfrastructure.com/v1/evaluate";

async function safetyScreen(command: string): Promise<boolean> {
  const resp = await fetch(A2A_URL, {
    method: "POST",
    headers: {
      "Content-Type": "application/json",
      "Authorization": `Bearer ${process.env.A2A_API_KEY}`,
    },
    body: JSON.stringify({ command }),
  });
  const result = await resp.json();
  return result.allowed;
}

const shellTool = tool({
  description: "Execute a shell command",
  parameters: z.object({
    command: z.string().describe("The shell command to run"),
  }),
  execute: async ({ command }) => {
    const allowed = await safetyScreen(command);
    if (!allowed) {
      return { error: "Blocked by safety shield" };
    }
    const output = execSync(command, { encoding: "utf-8" });
    return { output };
  },
});

const { text } = await generateText({
  model: openai("gpt-4o"),
  tools: { shell: shellTool },
  maxSteps: 5,
  prompt: "Check disk usage on this machine",
});

Step 3: Verify

// Safe prompt -> tool executes normally
prompt: "List files in /tmp"
// -> shell tool runs "ls /tmp", returns listing

// Dangerous prompt -> tool blocked
prompt: "Delete everything in /var"
// -> shell tool returns { error: "Blocked by safety shield" }
// -> model explains the command was blocked for safety