Codex

This page documents how Happier integrates with Codex and what Codex-specific behavior matters for day-to-day usage.

Install Codex

If you use hstack, you can install Codex with the providers installer:

hstack providers install codex
codex --version

Or install manually, then restart Happier:

npm install -g @openai/codex
codex --version

Modes: MCP vs ACP (and local-control)

Happier can run Codex using different backends depending on what’s available and what features you enable:

• Codex MCP: Happier connects to Codex via MCP over stdio.
• Codex ACP (experimental): Happier runs Codex through the Agent Client Protocol (ACP). Some agents expose “session modes” (for example “plan” vs “code”).
• Local-control: Happier can switch a session into a “local control” mode that mirrors Codex activity (useful when moving control from the app back to your terminal).

Permissions

Happier uses a provider-agnostic permission mode (default, read-only, safe-yolo, yolo, plan) and applies it to Codex in the best available way.

For the full user guide (CLI flags, UI picker, defaults, apply timing), see:

• Permissions

What permission modes mean in Codex

Codex enforcement is a combination of:

• Happier tool-approval gating (what Happier will auto-approve vs deny vs prompt for), and
• provider-native sandbox/policy (what the Codex backend enforces internally).

Important notes:

• read-only is enforced by Happier by denying write-like actions (edits/patches/exec) when Happier is the approver.
• safe-yolo and yolo control whether Happier prompts vs auto-approves actions it can approve.
• Codex backends may have sandbox policies that are fixed at session start. Changing permission mode mid-session can still update Happier’s approval behavior, but it may not change Codex’s internal sandbox until you start a new Codex session.

Plan mode

plan is shown only when the current Codex backend/session advertises a compatible session mode.

If plan is not supported for the current session, Happier will fall back to default and the UI will show that in the “Effective policy” line.

Switching and permission persistence

When you change permission mode:

• it is stored canonically in session metadata, and
• it follows you when you open the same session on another device or switch local ↔ remote.

If you choose Apply timing: next prompt in the app:

• the selection applies to the next message you send (as message metadata), and
• it becomes session-wide only after that message is committed.