[BUG] Claude code not expand inside tmux session

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Hi, I am trying to launch claude code inside a tmux session, but the CC panel is smaller than the tmux size. Can you help with this? Thank you!

<img width="2540" height="1336" alt="Image" src="https://github.com/user-attachments/assets/e204133d-d615-452c-b298-6d8700b1bb98" />

What Should Happen?

CC should fit inside tmux session

Error Messages/Logs

Steps to Reproduce

creating tmux session -> run claude code

Claude Model

None

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

2.1.119

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

_No response_