[BUG] Bug Report: Performance Degradation (Frame Drops) During Code Editing in v2.0.50

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

Claude CLI version: 2.0.50 (native installation)
Operating System: Windows 11 + WSL2 (Ubuntu)
Terminal: Windows Terminal / WSL bash
Project Location: /mnt/d/ (Windows filesystem accessed via WSL)

Bug Description
Starting from version 2.0.50, severe frame drops occur when Claude Code begins editing files. The issue appears as soon as the real-time diff counter is displayed below the input prompt (e.g., 1 file +4234 -4388).
The lag is similar to frame drops in video games - the terminal becomes unresponsive and choppy during the entire code modification process.

What Should Happen?

Expected Behavior
Code editing should be smooth without noticeable lag, as it was in version 2.0.49.
Actual Behavior

Severe frame drops and terminal lag when editing files
The lag persists throughout the entire code modification process
Terminal becomes choppy and unresponsive

Workaround
Downgrading to v2.0.49 completely resolves the issue:

rm ~/.local/bin/claude
ln -s ~/.local/share/claude/versions/2.0.49 ~/.local/bin/claude

After rollback, code editing is smooth again with no performance issues.

### Additional Context

- The issue may be related to the new real-time diff display feature introduced in v2.0.50
- Problem is more pronounced on WSL2 with Windows filesystem (`/mnt/d/`), possibly due to cross-filesystem I/O overhead combined with the new diff tracking feature
- `claude doctor` output shows no errors

### Diagnostic Output

$ claude doctor
Diagnostics
└ Currently running: native (2.0.50)
└ Path: /home/username/.local/bin/claude
└ Config install method: native
└ Auto-updates: default (true)
└ Search: OK (bundled)

Error Messages/Logs

Steps to Reproduce

1. Run Claude Code v2.0.50 in WSL2 environment
2. Navigate to a project on Windows filesystem (/mnt/d/...)
3. Request Claude to modify any code file
4. Observe the diff counter appearing below the prompt (e.g., 1 file +4234 -4388)
5. Notice severe lag/frame drops during the editing process

Claude Model

Sonnet (default)

Is this a regression?

No, this never worked

Last Working Version

2.0.50

Claude Code Version

native (2.0.50)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

WSL (Windows Subsystem for Linux)

Additional Information

_No response_