iTerm2: Ctrl+C exit can intermittently leave terminal stuck in CSI-u mode and print `9;5:3u`

What version of Codex CLI is running?

codex-cli 0.125.0

What subscription do you have?

_No response_

Which model were you using?

_No response_

What platform is your computer?

macOS 26.4.1 / Darwin 25.4.0 arm64

What terminal emulator and version are you using (if applicable)?

iTerm2 3.6.10

Relevant environment:

SHELL=/bin/zsh
TERM=xterm-256color
TERM_PROGRAM=iTerm.app
TERM_PROGRAM_VERSION=3.6.10

What issue are you seeing?

When running Codex CLI in iTerm2 on macOS, pressing Ctrl+C to exit Codex can intermittently leave the parent terminal input state corrupted. I have not found a stable reproduction pattern yet, and it does not happen on every Ctrl+C exit. However, the failure has occurred after exiting Codex with Ctrl+C.

After Codex exits, the shell can receive or display a raw CSI-u style keyboard sequence such as:

9;5:3u

This looks like Codex enables enhanced keyboard reporting / CSI-u / modifyOtherKeys style input, but does not always fully restore the terminal state on the Ctrl+C exit path. After Codex exits, the parent shell should be back in normal text input mode instead of still emitting raw enhanced-keyboard fragments.

This appears related in shape to #16517, but the environment and trigger are different:

• terminal emulator: iTerm2, not Ghostty
• trigger observed so far: local Ctrl+C exit from Codex, not an abnormal SSH disconnect
• reproducibility: intermittent; I do not yet know the exact timing or state needed to trigger it
• observed raw fragment: 9;5:3u

What steps can reproduce the bug?

I do not currently have a fully deterministic reproduction sequence. The observed trigger path is:

1. Open iTerm2 on macOS.
2. Start codex.
3. While the Codex TUI is active, press Ctrl+C to exit.
4. Return to the same iTerm2 tab/window's shell.
5. Continue typing or pressing keys.

Observed intermittent result:

the shell can receive or display raw CSI-u style text such as:

9;5:3u

What is the expected behavior?

Codex should restore the terminal keyboard/input state on Ctrl+C / SIGINT exit paths, including disabling or popping any enhanced keyboard / CSI-u / modifyOtherKeys modes it enabled.

After Codex exits, the parent shell should immediately behave normally, without requiring the user to run reset, stty sane, or manual terminal control sequences.

Additional information

A possible manual recovery command is:

printf '\033[<u\033[>4;0m' && stty sane && reset

The fact that this kind of reset helps suggests the issue may be related to keyboard enhancement flags / CSI-u / modifyOtherKeys state not being reliably restored.

Suggested area to inspect: the Codex TUI cleanup path for SIGINT, early return, panic, task cancellation, and any other abnormal or semi-abnormal exits. In particular, please check whether keyboard enhancement flags are always restored symmetrically with the setup path.