RFC: Codex Integration

[thatjosh]

Summary

This RFC proposes adding first-party Codex CLI governance to AGT as a new package, agent-governance-codex-cli. It's a thin host adapter over the existing Claude Code governance core. Codex's hook system (SessionStart, UserPromptSubmit, PreToolUse) mirrors Claude Code's contract, so the governance logic is reused unchanged and only host wiring is new, following the same derivation used for the OpenCode integration (#2658). I originally fork and extended it to govern my own Codex agent, so it's already implemented and verified, with policy deny/allow/audit working e2e. I'm happy to contribute it back upstream and help maintain this going forward.

Working fork: https://github.com/thatjosh/agent-governance-toolkit

Motivation

AGT ships governance integrations for Claude Code, Copilot CLI, OpenCode, and Antigravity, but not for the OpenAI Codex CLI, which is becoming more popular with GPT 5.6.

Detailed Design

Codex's hook system (SessionStart, UserPromptSubmit, PreToolUse) mirrors Claude Code's contract, so the governance logic is reused unchanged and only host wiring is new, following the same derivation used for the OpenCode integration (#2658).

Enforcement surface

Codex event	AGT behavior
SessionStart	inject governance context
UserPromptSubmit	prompt inspection, fail-closed block
PreToolUse	allow / deny / ask via policy

Decision mapping onto Codex's hook response schema:

// policy deny  ->
{ "hookSpecificOutput": { "hookEventName": "PreToolUse",
    "permissionDecision": "deny", "permissionDecisionReason": "…AGT policy…" } }
// policy review -> "permissionDecision": "ask"
// policy allow  -> no permissionDecision

Alternatives Considered

N/A

Security Implications

Trust model / cryptographic boundaries are unchanged. This package does not modify the policy engine, trust scoring, cryptographic choices, or the audit format. It reuses the existing Claude Code governance core unchanged and only translates Codex's hook payloads
to and from that core.

Migration / Backward Compatibility

No response

Scope

Single package

Target Placement

Integration (integrations/ directory)

Prior Art

#2658

Checklist

• I have searched existing issues and RFCs for duplicates
• I have read the ADR index (adr/index.md) for related decisions
• I am willing to implement this RFC or help review an implementation

[github-actions]

Welcome to the Agent Governance Toolkit! Thanks for opening your first issue.
A maintainer will review this shortly. Check our Contributing Guide.
For security issues, use private vulnerability reporting.

[github-actions]

🤖 AI Agent: contributor-guide

AI-generated review output. Treat it as untrusted analysis and verify before acting.

Welcome, and thank you for your contribution! This issue relates to a proposed new package, agent-governance-codex-cli, for Codex CLI governance. It seems to align with existing integrations like Claude Code and OpenCode.

Please review our CONTRIBUTING.md for guidance on submitting RFCs and implementations. Let us know if you need any help!