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

Adapter for Codex CLI (OpenAI) using codex app-server persistent mode.

Translates between ACP JSON-RPC and Codex's app-server JSON-RPC protocol. The app-server runs as a persistent subprocess communicating over NDJSON on stdin/stdout, with a JSON-RPC initialize handshake.

Ported from nshkrdotcom/codex_sdk's AppServer.Connection pattern.

Codex App-Server Protocol

Command: codex app-server
Handshake: initialize request → response → initialized notification
Session: thread/start → turn/start → notifications → turn/completed
Notifications: NDJSON events for items, text deltas, reasoning, tool calls, etc.

ACP Mapping

ACP Message	Codex JSON-RPC
`session/new`	`thread/start` request
`session/load`	`thread/start` with threadId (resume)
`session/prompt`	`turn/start` request
`session/cancel`	`turn/interrupt` request
`item/agentMessage/delta`	`session/update` (text)
`item/reasoning/textDelta`	`session/update` (thinking)
`item/completed` (tool)	`session/update` (tool_call/tool_result)
`item/commandExecution/*`	`session/update` (tool_output)
`turn/completed`	prompt response result

Features

Initialize handshake with post_connect/1
Text and thinking streaming
Tool call and tool result notifications
Command execution output streaming
Token usage tracking
Turn interrupt/cancel support
Image content in prompts

Limitations

No session listing (Codex doesn't expose session enumeration)
No mode switching (static approval policy at session start)
No model switching mid-session (set at thread/start)
No authentication flow (relies on user's local auth)