copilot-cli

GitHub Copilot CLI Integration

This document describes the Agent Client Protocol (ACP) used by GitHub Copilot CLI and how to integrate it with Overseer.

Overview

GitHub Copilot CLI is a command-line AI coding agent that can be integrated into Overseer using the Agent Client Protocol (ACP) - an open standard for agent-editor communication. ACP uses JSON-RPC 2.0 over stdio, similar to how Codex is already integrated.

References:

• About Copilot CLI
• ACP Server Reference
• ACP Protocol Specification

Starting Copilot in ACP Mode

# stdio mode (recommended for IDE integration)
copilot --acp --stdio

# TCP mode (for remote/network access)
copilot --acp --port 3000

Protocol Basics

• Transport: JSON-RPC 2.0 over stdio (NDJSON - newline-delimited JSON)
• Encoding: UTF-8
• Message types:
  • Methods: Request-response pairs (have id)
  • Notifications: One-way messages (no id)
• File paths: Must be absolute
• Line numbers: 1-based indexing

Message Flow

Client (Overseer)                    Agent (copilot --acp --stdio)
  |                                      |
  |-- initialize ----------------------->|
  |<-- result (capabilities) ------------|
  |                                      |
  |-- session/new ---------------------->|
  |<-- result (sessionId) ---------------|
  |                                      |
  |-- session/prompt ------------------->|
  |<-- session/update (streaming) -------|  (notifications)
  |<-- session/request_permission -------|  (approval request)
  |-- result (selected option) --------->|
  |<-- session/update (tool updates) ----|
  |<-- result (stopReason) --------------|

Initialization

Request: initialize

{
  "jsonrpc": "2.0",
  "method": "initialize",
  "id": 1,
  "params": {
    "protocolVersion": 1,
    "clientInfo": {
      "name": "overseer",
      "title": "Overseer",
      "version": "1.0.0"
    },
    "clientCapabilities": {
      "fs": {
        "readTextFile": true,
        "writeTextFile": true
      },
      "terminal": true
    }
  }
}