AI SDK - ACP Harness

HarnessV1 adapter backed by an NPM-installed Agent Client Protocol version 1 implementation. The adapter ships a bridge process that runs inside a sandbox and talks to the host over a WebSocket on a sandbox-proxied loopback port. The configured ACP implementation runs alongside the bridge inside the sandbox.

Setup

npm i @ai-sdk/harness-acp @ai-sdk/harness @ai-sdk/sandbox-vercel

The bridge installs the configured ACP implementation inside the sandbox the first time the session starts.

Usage

This example connects HarnessAgent to Codex ACP using direct OpenAI authentication:

import { HarnessAgent } from '@ai-sdk/harness/agent';
import { createACP } from '@ai-sdk/harness-acp';
import { createCredentialRequestTransformation } from '@ai-sdk/harness/utils';
import { createVercelNetworkSandboxSession } from '@ai-sdk/sandbox-vercel';

const codexACP = createACP({
  harnessId: 'acp-codex',
  source: {
    type: 'npm-simple',
    packageName: '@agentclientprotocol/codex-acp',
    packageVersion: '1.1.4',
  },
  executable: 'codex-acp',
  modelMapping: {
    type: 'session-config-option',
    path: 'model',
  },
  credentialEnv: ['CODEX_API_KEY', 'OPENAI_API_KEY'],
  credentialBrokering: ({ env, sandboxEnv }) => {
    const environmentVariableName = env.CODEX_API_KEY
      ? 'CODEX_API_KEY'
      : 'OPENAI_API_KEY';
    const credential = env[environmentVariableName];
    const sandboxCredential = sandboxEnv?.[environmentVariableName];
    if (!credential || !sandboxCredential) return [];
    return [
      createCredentialRequestTransformation({
        matchUrl: 'https://api.openai.com/v1',
        matchHeaders: {
          Authorization: `Bearer ${sandboxCredential}`,
        },
        transformHeaders: { Authorization: `Bearer ${credential}` },
      }),
    ];
  },
  instructionMapping: {
    type: 'launch-env-json',
    variable: 'CODEX_CONFIG',
    path: ['developer_instructions'],
  },
  permissionModeMapping: {
    'allow-reads': null,
    'allow-edits': null,
    'allow-all': { type: 'session-mode', modeId: 'agent-full-access' },
  },
  authentication: {
    methodId: 'api-key',
  },
});

const agent = new HarnessAgent({
  harness: codexACP,
});

const sandboxSession = await createVercelNetworkSandboxSession({
  runtime: 'node24',
  ports: [4000],
  template: await agent.getSandboxTemplate(),
});
const session = await agent.createSession({ sandboxSession });
try {
  const result = await agent.generate({
    session,
    prompt: 'Inspect this project and summarize its purpose.',
  });
  console.log(result.text);
} finally {
  await session.destroy();
  await sandboxSession.destroy();
}

Set CODEX_API_KEY or OPENAI_API_KEY in the host environment. Sandboxes that support additive request transformations receive only credential placeholders; the real value is injected only when a matching outbound request contains the expected placeholder. Other sandboxes retain the legacy behavior of forwarding the value to the ACP process. Codex ACP supports only permissionMode: 'allow-all' because its restrictive modes enable Codex's internal sandbox. A bridge-backed ACP harness requires a sandbox with at least one exposed port.

modelMapping is required because ACP implementations expose different model selection operations. Use session-config-option with the ACP configuration option ID as path, or session-model with the JSON-RPC request property as path for implementations such as Grok Build that use the legacy session/set_model method. No model operation is sent when HarnessAgent has no model configured.

Use instructionMapping when the ACP implementation exposes a native system or developer prompt. A session-meta mapping writes HarnessAgent instructions below the ACP session request's _meta field. A launch-env-json mapping merges them into a JSON environment variable before the implementation starts. A filesystem mapping writes instructions to a markdown file at a relative path under the implementation's effective $HOME. Without a mapping, the adapter preserves its backward-compatible behavior and prepends instructions to the first user prompt.

Skills are written to .agents/skills below the ACP implementation's effective $HOME and discovered natively by the implementation. Set skillsDirectory to another relative path, such as .claude/skills, when required by the implementation.