Shift+Enter does not work in Codex inside tmux

What version of Codex CLI is running?

codex-cli 0.117.0

What subscription do you have?

Business/Team

Which model were you using?

gpt-5.4

What platform is your computer?

Darwin 25.3.0 arm64 arm

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

Ghostty

What issue are you seeing?

Shift+Enter does not insert a newline in Codex when Codex is running inside tmux.

The same Shift+Enter shortcut works:

• in Codex outside tmux over the same SSH connection
• in other apps inside the same tmux session, including fish and Claude

So this appears to be specific to Codex running under tmux, not a general terminal or tmux key handling problem.

What steps can reproduce the bug?

1. SSH into a remote machine.
2. Start a tmux session.
3. Launch Codex inside tmux.
4. Focus the prompt input and press Shift+Enter.

I also verified tmux extended keys are enabled:
```tmux
set -s extended-keys on
set -s extended-keys-format csi-u
set -as terminal-features ",xterm-256color:extkeys"

 After reloading and reattaching, tmux reports:

 - version: 3.6a
 - client term: xterm-256color
 - client features: bpaste,ccolour,clipboard,cstyle,extkeys,focus,RGB,title
 - default terminal: tmux-256color

### What is the expected behavior?

Shift+Enter should insert a newline in Codex inside tmux, the same way it does when Codex is run outside tmux.

### Additional information

This is reproducible specifically in the ssh -> tmux -> Codex path.

In my setup:
-   ssh -> Codex: Shift+Enter works
-   ssh -> tmux -> Codex: Shift+Enter does not work
-   inside the same tmux session, Shift+Enter still works in fish and Claude

That suggests Codex is not recognizing the key sequence it receives under tmux, even when tmux extended key support is enabled.