[BUG] Fullscreen TUI mode has janky/non-smooth scrolling

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?

With "tui": "fullscreen" enabled in settings.json, scrolling through conversation history is noticeably janky — it jumps in large chunks rather than scrolling smoothly line-by-line like in the default TUI mode.

What Should Happen?

Scrolling should be smooth and proportional to scroll input, similar to the default TUI mode.

Error Messages/Logs

Steps to Reproduce

1. Set "tui": "fullscreen" in settings.json
2. Have a conversation long enough to require scrolling
3. Scroll up/down through the conversation history
4. Observe: scrolling is choppy/jumpy compared to the default TUI mode

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.118 - @anthropic-ai/claude-code

Platform

Other

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

I switched to fullscreen mode to work around the scrollback duplication that happens in default mode when resizing the terminal window (see also the duplicate frames in scrollback when resizing: https://github.com/anthropics/claude-code/issues?q=is%3Aissue+scrollback+resize). Fullscreen mode fixes that problem, but introduces this scrolling regression.

Ideally both issues would be resolved so we don't have to pick between clean scrollback and smooth scrolling.

Btw: I'm sorry I haven't tested the very latest version! My installation is controlled by my company and I don't have a choice over which version to use.