[BUG] Terminal viewport jitter / aggressive auto-scrolling during task execution

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?

• The terminal UI is unstable while Claude is running tasks; the viewport hitches and jumps instead of staying anchored.

• The screen rapidly flickers up and down while Claude is "thinking" or generating output.

• I am frequently thrown back to an upper part of the terminal buffer automatically, which cuts off the live text.

• It feels like the auto-scroll is fighting with the manual scroll position, creating a stuttering/hitching effect.

What Should Happen?

The terminal should remain anchored to the current line of output.

I should be able to read the live progress without the screen jumping or flickering to previous parts of the session.

Error Messages/Logs

There are no explicit error codes generated for this issue.

This is a visual/UI regression where terminal output becomes misformatted or corrupted during high-frequency updates; visual/UI regression in the terminal rendering.

Steps to Reproduce

The terminal should remain stable and anchored to the current line of output as Claude works.

Manual scrolling should not be overridden by the auto-scrolling mechanism unless new output is actively being generated at the bottom.

Claude Model

Not sure / Multiple models

Is this a regression?

No, this never worked

Last Working Version

None, this issue occurred from the beginning/this never worked

Claude Code Version

2.1.17 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_