## Why
Codex 0.131 started enabling tmux `modifyOtherKeys` mode 2 when the
active tmux session reported `extended-keys-format csi-u`, and also when
that format could not be queried. The fallback was meant to help
compatible tmux panes enter extended-key mode, but it breaks iTerm2
control-mode sessions on older tmux.
Issue #23711 reproduces with:
```bash
ssh -t ubuntu@192.168.68.149 'tmux -CC new -A -s main'
```
On tmux 3.2a, `extended-keys-format` is not available. With mode 2
enabled, `Ctrl-C` is delivered as `^[[27;5;99~` instead of the normal
interrupt/control key path, so Codex does not handle it. Running with
`CODEX_TUI_DISABLE_KEYBOARD_ENHANCEMENT=1` restores `Ctrl-C`, which
points at keyboard mode setup rather than chat input routing.
## What Changed
- Only request `modifyOtherKeys` mode 2 when tmux explicitly reports
`extended-keys-format csi-u`.
- Treat an unknown or unavailable tmux extended-key format as
unsupported for this mode.
- Update the keyboard mode unit coverage so `None` no longer opts into
`modifyOtherKeys`.
This preserves the explicit modern tmux `csi-u` path from #21943 while
avoiding the unsafe fallback on older or unqueryable tmux setups.
## How to Test
Regression path from #23711:
1. Start iTerm2 tmux integration against an older tmux host:
```bash
ssh -t ubuntu@192.168.68.149 'tmux -CC new -A -s main'
```
2. Start patched Codex.
3. Run `/keymap debug`, press a regular key, then press `Ctrl-C`.
4. Confirm `Ctrl-C` closes the inspector and Codex remains responsive
without `CODEX_TUI_DISABLE_KEYBOARD_ENHANCEMENT=1`.
5. Confirm `Shift+Enter` still inserts a newline in the same session.
Modern tmux compatibility path:
1. Start an ordinary tmux 3.6a server with explicit `csi-u`:
```bash
tmux -L codex-csiu -f /dev/null new-session -d -s repro
tmux -L codex-csiu set-option -g extended-keys on
tmux -L codex-csiu set-option -g extended-keys-format csi-u
tmux -L codex-csiu attach -t repro
```
2. Start patched Codex.
3. From another terminal, confirm the Codex pane reports `mode=Ext 2`:
```bash
tmux -L codex-csiu list-panes -a -F '#{pane_id} mode=#{pane_key_mode}
cmd=#{pane_current_command}'
```
4. Type `one`, press `Shift+Enter`, type `two`, and confirm the composer
shows two lines without submitting.
5. Press `Ctrl-C` and confirm Codex handles it normally.
Targeted tests:
- `./tools/argument-comment-lint/run.py -p codex-tui -- --lib`
- `just test -p codex-tui` runs the new keyboard mode test successfully;
the full run currently reports two unrelated guardian feature-flag test
failures:
-
`app::tests::update_feature_flags_disabling_guardian_clears_manual_review_policy_without_history`
-
`app::tests::update_feature_flags_disabling_guardian_clears_review_policy_and_restores_default`
No documentation update is needed.
Felipe CouryandGitHub
8a4a537e44