›_ Codex Issues
Codex Issues / #21699

Shift+Enter is not recognized inside tmux because Codex does not enable modifyOtherKeys / Ext 2

Resolved 💬 3 comments Opened May 8, 2026 by odlove Closed May 10, 2026

What version of Codex CLI is running?

codex-cli 0.129.0

What subscription do you have?

plus

Which model were you using?

_No response_

What platform is your computer?

_No response_

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

_No response_

What issue are you seeing?

Problem

Inside tmux, Shift+Enter is received by Codex as plain Enter, so it submits instead of inserting a newline.

The same terminal/tmux setup works in Neovim.

Environment

  • Terminal: kitty 0.46.2
  • tmux: 3.6a
  • tmux config:
  • extended-keys on
  • extended-keys-format csi-u
  • xterm-keys on
  • terminal-features includes xterm*:extkeys
  • Codex: codex-cli 0.129.0

Reproduction

  1. Start Codex inside tmux.
  2. Run /keymap debug.
  3. Press Shift+Enter.
  4. Codex reports plain Enter / no shift modifier.
  5. tmux reports the Codex pane as VT10x.

Commands used:

tmux list-panes -a -F '#{pane_id} #{pane_current_command} #{pane_key_mode}'

Observed:

%0 codex VT10x

Compare with Neovim in the same tmux server:

%3 nvim Ext 2

Workaround / validation

Manually enabling xterm modifyOtherKeys mode 2 for the Codex pane fixes it:

printf '\e[>4;2m' > /dev/pts/0

After that, the Codex pane changes to Ext 2, and Shift+Enter is reported correctly.

Suspected cause

Codex currently enables crossterm/kitty keyboard enhancement in
codex-rs/tui/src/tui/keyboard_modes.rs:

pub(super) fn enable_keyboard_enhancement() {
    if keyboard_enhancement_disabled() {
        return;
    }

    let _ = execute!(
        stdout(),
        PushKeyboardEnhancementFlags(
            KeyboardEnhancementFlags::DISAMBIGUATE_ESCAPE_CODES
                | KeyboardEnhancementFlags::REPORT_EVENT_TYPES
                | KeyboardEnhancementFlags::REPORT_ALTERNATE_KEYS
        )
    );
}

but it does not send xterm/tmux modifyOtherKeys mode 2:

ESC [ > 4 ; 2 m

Codex already sends the corresponding reset on exit in
codex-rs/tui/src/tui/keyboard_modes.rs:

pub(super) fn reset_keyboard_reporting_after_exit() {
    let _ = execute!(
        stdout(),
        PopKeyboardEnhancementFlags,
        ResetKeyboardEnhancementFlags,
        DisableModifyOtherKeys
    );
}

impl Command for DisableModifyOtherKeys {
    fn write_ansi(&self, f: &mut impl fmt::Write) -> fmt::Result {
        f.write_str("\x1b[>4;0m")
    }
}
ESC [ > 4 ; 0 m

via DisableModifyOtherKeys, but there is no matching enable path.

Expected behavior

Codex should request an extended key mode compatible with tmux so Shift+Enter is distinguishable from Enter.

Related

What steps can reproduce the bug?

/

What is the expected behavior?

_No response_

Additional information

_No response_

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