pi-acp

ACP (Agent Client Protocol) adapter for pi coding agent.

pi-acp embeds pi directly via the @mariozechner/pi-coding-agent SDK and exposes it as an ACP agent over stdio. Each ACP session owns one in-process AgentSession.

Status

Active development. ACP compliance is improving steadily. Development is centered around Zed editor support; other ACP clients may have varying levels of compatibility.

Features

• Streams assistant output as ACP agent_message_chunk
• Streams thinking output as ACP agent_thought_chunk
• Maps pi tool execution to ACP tool_call / tool_call_update
  • Descriptive tool titles (Read src/index.ts, Run ls -la, Edit config.ts)
  • Tool call locations surfaced for follow-along features in clients like Zed
  • For edit and write, emits ACP structured diffs (oldText/newText)
  • Tool kinds: read, edit, execute (bash), other
• Session configuration via ACP configOptions
  • Model selector (category: model)
  • Thinking level selector (category: thought_level)
  • Also advertises modes and models for backward compatibility
  • session/set_config_option for changing model or thinking level
  • config_option_update emitted when configuration changes
• Session persistence and lifecycle
  • Multiple concurrent sessions supported
  • pi manages sessions in ~/.pi/agent/sessions/...
  • session/list with title fallback from first user message
  • session/load replays structured history (text, thinking, tool calls)
  • unstable_closeSession, unstable_resumeSession, unstable_forkSession
  • Sessions can be resumed in both pi CLI and ACP clients
• Usage and cost tracking
  • usage_update emitted after each agent turn with context size and cost
  • PromptResponse.usage includes per-turn token counts
• Slash commands
  • File-based prompt templates from ~/.pi/agent/prompts/ and <cwd>/.pi/prompts/
  • Extension commands from pi extensions
  • Skill commands (appear as /skill:skill-name)
  • Built-in adapter commands (see below)
• Authentication via Terminal Auth (ACP Registry support)
• Startup info block with pi version and context (configurable via quietStartup setting)

Prerequisites

• Node.js 20+
• pi installed globally: npm install -g @mariozechner/pi-coding-agent
• Configure pi for your model providers/API keys

Install

ACP Registry (Zed)

Launch the registry with zed: acp registry and select pi ACP:

"agent_servers": {
  "pi-acp": {
    "type": "registry"
  }
}

npx (no global install)

"agent_servers": {
  "pi": {
    "type": "custom",
    "command": "npx",
    "args": ["-y", "@victor-software-house/pi-acp"],
    "env": {}
  }
}

Global install

npm install -g @victor-software-house/pi-acp

"agent_servers": {
  "pi": {
    "type": "custom",
    "command": "pi-acp",
    "args": [],
    "env": {}
  }
}

From source

bun install
bun run build

"agent_servers": {
  "pi": {
    "type": "custom",
    "command": "node",
    "args": ["/path/to/pi-acp/dist/index.js"],
    "env": {}
  }
}

Built-in commands

• /compact [instructions...] -- compact session context
• /autocompact on|off|toggle -- toggle automatic compaction
• /export -- export session to HTML
• /session -- show session stats (tokens, messages, cost)
• /name <name> -- set session display name
• /steering all|one-at-a-time -- set steering message delivery mode
• /follow-up all|one-at-a-time -- set follow-up message delivery mode
• /changelog -- show pi changelog

Authentication

Terminal Auth for the ACP Registry:

pi-acp --terminal-login

Zed shows an Authenticate banner that launches this automatically.

Development

bun install
bun run dev          # run from src
bun run build        # tsdown -> dist/index.mjs
bun run typecheck    # tsc --noEmit
bun run lint         # biome + oxlint
bun test             # 26 tests

Project layout:

src/
  index.ts                  # stdio entry point
  env.d.ts                  # ProcessEnv augmentation
  acp/
    agent.ts                # PiAcpAgent (ACP Agent interface)
    session.ts              # PiAcpSession (wraps AgentSession, translates events)
    auth.ts                 # AuthMethod builder
    auth-required.ts        # auth error detection
    pi-settings.ts          # settings reader (Zod schema)
    translate/
      pi-messages.ts        # pi message text extraction
      pi-tools.ts           # pi tool result text extraction (Zod schema)
      prompt.ts             # ACP ContentBlock -> pi message
  pi-auth/
    status.ts               # auth detection (Zod schema)
test/
  helpers/fakes.ts          # test doubles
  unit/                     # unit tests
  component/                # integration tests

Limitations

MUST-level gaps

• MCP servers -- accepted in session/new and session/load params but not wired through to pi. ACP requires agents to connect to all provided MCP servers. This is the main compliance gap (upstream pi SDK limitation).

SHOULD-level gaps

• session/request_permission -- pi does not request permission from ACP clients before tool execution.

Not implemented (MAY / client capabilities)

• agent_plan -- plan updates not emitted before tool execution. pi has no equivalent planning surface.
• ACP filesystem delegation (fs/read_text_file, fs/write_text_file) -- pi reads/writes locally. Not advertised.
• ACP terminal delegation (terminal/*) -- pi executes commands locally. Not advertised.

Design decisions

• pi does not have real session modes (ask/architect/code). The modes field exposes thinking levels for backward compatibility with clients that do not support configOptions.
• configOptions is the preferred configuration mechanism. Zed uses it exclusively when present.
• pi-acp uses direct filesystem access rather than delegating reads/writes to the ACP client. This means pi reads on-disk file versions, not unsaved editor buffers.

See docs/engineering/acp-conformance.md for detailed conformance status.

Release

Releases are automated via semantic-release on pushes to main. The pipeline runs typecheck, lint, tests, and npm pack --dry-run before publishing. npm trusted publishing (OIDC) is used -- no long-lived npm tokens.

Commit messages must follow Conventional Commits. Commitlint enforces this locally via lefthook and in CI.

License

MIT (see LICENSE).

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Inspired by svkozak/pi-acp.