Scroll back on the terminal stopped working.

### What happened?

[ACTION REQUIRED] 📎 PLEASE ATTACH THE EXPORTED CHAT HISTORY JSON FILE TO THIS ISSUE IF YOU FEEL COMFORTABLE SHARING IT.

### What did you expect to happen?

I needed to scroll back to what the CLI said to do, but scrolling back is failing. I tried ^Q in case it got a ^S

### Client information

* **CLI Version:** 0.55.1
* **Git Commit:** 41327e407
* **Session ID:** 7ab73382-a898-4b36-ab30-3949b98b595c
* **Operating System:** linux v24.12.0
* **Sandbox Environment:** no sandbox
* **Model Version:** auto
* **Auth Type:** gemini-api-key
* **Memory Usage:** 973.7 MB
* **Terminal Name:** Unknown
* **Terminal Background:** #0c0c0c
* **Kitty Keyboard Protocol:** Unsupported

### Login information

_No response_

### Anything else we need to know?

_No response_

Reproduce the scrollback failure with CLI version 0.55.1 on Linux, including the reported ^S/^Q possibility, then trace the terminal input and scrollback entry points. No source file or test is named in the issue; done means the terminal can reliably scroll back to earlier CLI output without disrupting input.

Written by the indexing model from the issue text.