[BUG] Severe rendering issue on Windows: white input bar and broken output (ConPTY)

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?

Environment:

• OS: Windows 10 / Windows 11
• Shell: PowerShell, Windows Terminal, cmd.exe
• Claude Code version: 2.0.73
• Terminal backend: ConPTY

Problem:
Claude Code UI rendering breaks on Windows:

• Input bar becomes an extremely long white block
• Output text is clipped or misaligned
• Cursor position is incorrect
• Screen repaint fails after resizing or split view

This happens consistently on Windows and is not recoverable without restarting the session.
It appears to be a ConPTY / Windows terminal rendering issue.

Workaround:
Using cmd.exe is slightly more stable, but the issue still occurs.

Expected:
Stable TUI rendering across Windows terminals.

This seems to be a Windows-specific bug and cannot be fixed by user configuration.

What Should Happen?

Claude Code should render a stable and usable TUI on Windows terminals.

Specifically:

• The input bar should remain a normal single-line height and not expand into a large white block.
• Output text should render fully without clipping, truncation, or misalignment.
• Cursor position should correctly match user input.
• Screen repainting should work correctly after output updates, without requiring a restart.

The application should behave consistently across Windows terminals (cmd.exe, PowerShell, Windows Terminal) without rendering corruption.

Error Messages/Logs

Steps to Reproduce

1. Run Claude Code on Windows (cmd.exe, PowerShell, or Windows Terminal).
2. Start a new Claude Code session.
3. Interact normally (enter prompts, receive multiple outputs).
4. After several interactions or longer outputs, observe the UI state.

Result:

• The input bar turns into a large white block.
• Output text becomes clipped or misaligned.
• Cursor position is incorrect.
• The UI does not recover unless the session is restarted.

This issue occurs consistently on Windows across different terminal applications.

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.0.73

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

PowerShell

Additional Information

_No response_