[BUG] Every character typed in the Claude Code TUI causes a line of chat history to disappear

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?

Every character typed in the Claude Code TUI causes a line of chat history to disappear from the display. The chat content is being progressively hidden line-by-line as I type, making it impossible to read the conversation while composing messages.

Resizing the terminal window temporarily restores all content, proving the data is still there and the terminal can render it correctly, but as soon as I start typing again, the lines disappear one-by-one with each keystroke.

What Should Happen?

The chat history should remain fully visible and stable while typing new messages. Previous conversation lines should not disappear or be affected by input events.

Error Messages/Logs

Steps to Reproduce

1. Launch Claude Code in macOS Terminal.app: claude
2. Start any conversation with Claude
3. Wait for Claude to respond (creating several lines of chat history)
4. Begin typing a new message in the input area
5. Observe: With each character typed, one line of previous chat history disappears from the top of the display
6. Continue typing: Lines continue to disappear sequentially
7. Resize the terminal window: All content returns temporarily
8. Type another character: Lines start disappearing again immediately

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.0.26

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

Previous issue https://github.com/anthropics/claude-code/issues/10045 was incorrectly closed even though it is still happening in the latest version.

Terminal sizes tested:

• 80x24 (default): Issue occurs
• 269x66 (maximum screen size): Issue occurs identically
• Size does not appear to be a factor

Workarounds attempted that did NOT help:

• CTRL+L refresh: No effect
• Increasing terminal size: No improvement
• Different terminal sizes: Same behavior at all sizes

Temporary workaround that works:

• Resizing the terminal window restores content temporarily, but typing resumes the bug immediately

Technical observation:
The fact that resizing fixes it temporarily suggests the full screen redraw logic is correct, but the incremental rendering logic (triggered by input events) has a bug where it miscalculates the display buffer position by approximately one line per keystroke.

This appears to be an issue with cursor position tracking or screen buffer management during input handling, likely introduced in a recent refactor of the TUI rendering code.