ExMCP.ACP.Adapters.Pi (ex_mcp v0.9.0)

ACP adapter for the Pi coding agent (badlogic/pi-mono).

Translates between ACP JSON-RPC and Pi's RPC NDJSON protocol. Pi runs as a subprocess in --mode rpc and communicates via JSONL on stdin/stdout.

Pi RPC Protocol

Input: JSONL on stdin: {"type":"prompt","id":"msg-1","message":"..."}
Output: JSONL on stdout with event types: message_update, agent_end, tool_execution_start/update/end, auto_compaction_start/end, etc.

ACP Mapping

Pi Event	ACP Message
`message_update` (text_delta)	`session/update` notification (text)
`message_update` (thinking_delta)	`session/update` notification (thinking)
`message_update` (tool_call)	`session/update` notification (tool_call)
`tool_execution_start/end`	`session/update` notification (tool_result)
`agent_end`	prompt response result
`auto_compaction_*`	`session/update` notification (status)

Features

Session persistence via --session <path> flag
Thinking level control (off/minimal/low/medium/high/xhigh)
Steering and follow-up message queuing
Image support with data-url prefix stripping
Tool execution streaming with progress updates
Context compaction (manual and auto)
Session forking and switching
Model switching mid-session

Configuration

config :arbor_ai, :acp_providers, %{
  pi: %{
    transport_mod: ExMCP.ACP.AdapterTransport,
    adapter: ExMCP.ACP.Adapters.Pi,
    adapter_opts: [
      cli_path: "pi",
      model: "anthropic/claude-sonnet-4-20250514",
      thinking_level: "medium",
      session_path: "/path/to/session.jsonl"
    ]
  }
}