fix(shell-snapshot): detach snapshot from tty

[kfiramar]

Summary

• fix a macOS Terminal.app input regression when shell_snapshot is enabled by isolating the snapshot subprocess from the interactive TTY
• prevent snapshot shells/.zshrc from flipping terminal modes while the TUI is in raw mode
• add CODEX_SHELL_SNAPSHOT so users can guard tty-touching rc logic if needed

Bug Details

When shell_snapshot is enabled, Codex spawns a login shell (zsh -lc) and sources ~/.zshrc to capture aliases/functions/env. On some setups (e.g., Terminal.app + a .zshrc that runs stty/tput or emits escape sequences), the snapshot shell writes to the live TTY and changes terminal modes. While the Codex TUI is in raw mode, this breaks input handling: Enter/backspace stop working and raw escape sequences like ^[[O appear (often after alt-tab). Disabling shell_snapshot avoids the issue.

Repro Steps (macOS)

1. Enable shell_snapshot (TUI /experimental → “Shell snapshot”, or set [features].shell_snapshot = true in ~/.codex/config.toml and restart).

2. Create a minimal zshrc that touches the tty:

   mkdir -p /tmp/codex-tty-repro
   cat > /tmp/codex-tty-repro/.zshrc <<'EOF'
   stty sane 2>/dev/null
   EOF

3. Launch Codex with that rc:

   ZDOTDIR=/tmp/codex-tty-repro codex

4. When the TUI appears, input is broken (Enter/Backspace don’t work). After alt‑tabbing, you may see raw escape sequences like ^[[O.

5. Confirm that disabling snapshot restores input:

   ZDOTDIR=/tmp/codex-tty-repro codex --disable shell_snapshot

Why It Failed Before

The snapshot subprocess inherited the controlling TTY and ran .zshrc while the TUI was in raw mode. Any tty mode changes or escape output from the snapshot shell hit the live terminal, which flips the terminal state out of raw mode and effectively “breaks” input handling for the running TUI. The failure is config-dependent, so it only shows up when shell_snapshot is enabled and .zshrc (or a plugin) touches the TTY.

Fix

Detach the snapshot subprocess from the controlling terminal and avoid inheriting stdin:

• stdin set to /dev/null
• setsid() before exec on Unix
• env CODEX_SHELL_SNAPSHOT=1 for rc guards

This keeps snapshot output capture intact while preventing tty side effects.

Testing

• not run (missing just tool in environment)

Issue

• Input broken in TUI when shell_snapshot is enabled (macOS Terminal.app) #9383

[github-actions]

All contributors have signed the CLA ✍️ ✅
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[kfiramar]

I have read the CLA Document and I hereby sign the CLA

[etraut-openai]

@codex review

[etraut-openai]

Thanks for the contribution.

Please fix the CI failure — a simple formatting issue. Just ask codex to run formatting tool locally. You can ignore the Bazel failures.

[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: 7ab0ff888a

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[kfiramar]

@codex review

[chatgpt-codex-connector]

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[kfiramar]

@etraut-openai Feel free to run the formatting CI and the review again

[kfiramar]

@etraut-openai Do you know if there's a plan to merge it soon?

[etraut-openai]

@kfiramar, it's a national holiday in the U.S. today (MLK Day), so most Codex team members are on vacation. We'll try to get it merged later this week.

[etraut-openai]

@kfiramar, thanks for the contribution. We've made other changes recently that address this issue, so this PR is no longer needed.