Codex CLI does not interpolate ${CLAUDE_PLUGIN_ROOT} in plugin .mcp.json args, breaking imessage MCP

Summary

The imessage plugin from anthropics/claude-plugins-official ships a .mcp.json that references ${CLAUDE_PLUGIN_ROOT} — a placeholder Claude Code interpolates with the plugin install dir. Codex CLI passes the literal string through to the spawned process, so bun run --cwd ${CLAUDE_PLUGIN_ROOT} ... fails with ENOENT: Could not change directory to "${CLAUDE_PLUGIN_ROOT}".

Reproduction

1. codex plugin marketplace add claude-plugins-official https://github.com/anthropics/claude-plugins-official.git
2. Enable imessage@claude-plugins-official
3. Launch Codex — startup log shows: MCP client for \imessage\ failed to start: MCP startup failed: handshaking with MCP server failed: connection closed: initialize response

\codex mcp list\ confirms the literal placeholder:

\\\
imessage bun run --cwd \${CLAUDE_PLUGIN_ROOT} --shell=bun --silent start
\\\

Expected

Codex CLI should interpolate \\${CLAUDE_PLUGIN_ROOT}\ (and likely \\${CLAUDE_PLUGIN_DATA}\, etc.) in \.mcp.json\ \args[]\ and \command\ per the Claude Code plugin spec, since plugins shared between marketplaces rely on this idiom.

Workaround

Register a custom MCP via \codex mcp add\ with the absolute install path; or edit cache \.mcp.json\ (reverts on plugin re-extract).

Affected versions

Codex CLI (current GA as of 2026-04-25), claude-plugins-official imessage 0.1.0.