Step 1: Install dependencies

pip install openai-agents requests

Set your keys:

export OPENAI_API_KEY="sk-..."
export A2A_API_KEY="a2a_your_key_here"

Step 2: Add the safety layer

Create a guardrail function that calls /v1/evaluate before any tool runs:

import os, requests
from agents import Agent, Runner, GuardrailFunctionOutput, InputGuardrail
from agents.tool import function_tool

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

def safety_screen(command: str) -> bool:
    """Check a command against the safety shield."""
    resp = requests.post(A2A_URL, json={"command": command}, headers={
        "Authorization": f"Bearer {os.getenv('A2A_API_KEY')}"
    })
    return resp.json()["allowed"]

async def firewall_guardrail(ctx, agent, input):
    # Extract command from the agent's intended tool call
    cmd = input if isinstance(input, str) else str(input)
    allowed = safety_screen(cmd)
    return GuardrailFunctionOutput(
        output_info={"allowed": allowed},
        tripwire_triggered=not allowed
    )

@function_tool
def run_shell(command: str) -> str:
    """Execute a shell command."""
    import subprocess
    if not safety_screen(command):
        return "BLOCKED by safety shield"
    return subprocess.run(command, shell=True, capture_output=True, text=True).stdout

agent = Agent(
    name="safe-ops",
    instructions="You are a server admin. Use run_shell to execute commands.",
    tools=[run_shell],
    input_guardrails=[InputGuardrail(guardrail_function=firewall_guardrail)]
)

result = await Runner.run(agent, "Check disk usage")

Step 3: Verify

# Safe request
result = await Runner.run(agent, "Show free memory")
# -> runs "free -h" successfully

# Dangerous request
result = await Runner.run(agent, "Delete /var/log")
# -> GuardrailTripwireTriggered: blocked by safety shield