[BUG] 2.1.84 introduced ConEmu output constantly "scrolling to top" and interleaving output

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?

Both the input line and the output frequently "scrolls to top" and both whitespace and non-printed chars (after newline) are not blanked out, causing unreadable interleaved output. This only started after I auto-updated to 2.1.84.

This is occurring for me on Windows 11 with Cmder. I have tried changing TERM from winpty to xterm-256color and also disabling loading clink, and those didn't help. At this point my best guess about the issue is that it's because of ConEmu, because plain cmd works fine.

What Should Happen?

Claude Code should not scroll to the top after every input and output.

Error Messages/Logs

Steps to Reproduce

1. install Cmder with default settings
2. launch the default {cmd::Cmder} (or {cmd::Cmder as Admin}) task
3. run claude

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.81 or 2.1.83 (unsure)

Claude Code Version

2.1.84

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Other

Additional Information

Example of a PTY-related code analysis followed by printing a README:

<img width="1146" height="442" alt="Image" src="https://github.com/user-attachments/assets/40e35598-2b22-40ca-b9b1-0dd9528631d0" />