[BUG] Image attachment causing UTF-8 surrogate error

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?

Windows 11
Version 2.1.197
Image attachment causing UTF-8 surrogate error
Plain text works but images do not

<img width="889" height="485" alt="Image" src="https://github.com/user-attachments/assets/177c4981-3c7f-4b2a-82b4-a8f5abb64873" />

What Should Happen?

when ever I am attaching an image it is showing me error as 'API Error: 400 The request body is not valid JSON: str is not valid UTF-8: surrogates not allowed: line 1 column 1 (char 0)' in Claude code. After explaining it is not able to resolve the issue only image is working in my complex project.

Error Messages/Logs

API Error: 400 The request body is not valid JSON: str is not valid UTF-8: surrogates not allowed: line 1 column 1 (char 0)

Steps to Reproduce

include any image in claude code.

Claude Model

Sonnet (default)

Is this a regression?

No, this never worked

Last Working Version

2.1.187

Claude Code Version

2.1.197

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

_No response_