[BUG] Read tool crashes on PNGs with large transparent areas (400 "Could not process image")

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?

Summary:
The Read tool fails with a 400 error when attempting to read PNG images containing large transparent areas. This appears to be an issue with the image processing
API, not Claude Code itself.

Impact:

• CRITICAL: After this error occurs, ALL subsequent messages in the conversation fail with the same 400 error, even simple text messages without tool calls
• Entire conversation context is lost, requiring complete restart
• No error recovery mechanism available

Environment:

• Claude Code Version: 2.0.37
• Platform: WSL2 (Linux 6.6.87.1-microsoft-standard-WSL2)
• Model: claude-sonnet-4-5-20250929

Reproduction:

1. Create a screenshot with significant transparent areas (tested with Greenshot)
2. Attempt to read the PNG file using the Read tool
3. Error occurs: API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"Could not process image"}}
4. All subsequent messages fail, conversation is unrecoverable

Test Results:

• ✅ PNG screenshots without transparency: SUCCESS
• ✅ JPEG images: SUCCESS
• ✅ Windows Snipping Tool PNGs: SUCCESS
• ✅ Screenshot of the failing image (re-rendered): SUCCESS
• ❌ Greenshot PNG with ~50% transparent area: CONSISTENT FAILURE

Failing Image Characteristics:

• Dimensions: 1762 x 1181 pixels
• Size: 64KB
• Format: PNG (8-bit/color RGBA, non-interlaced)
• Content: Browser screenshot with bottom half transparent
• Tool: Greenshot

Expected Behavior:
Either the image should be read successfully, or the error should be recoverable without corrupting the entire conversation state.

Additional Context:
This tool worked perfectly for months on thousands of screenshots before suddenly failing. The issue appears to be triggered by specific PNG encoding/transparency
patterns rather than file size or tool used.

What Should Happen?

<img width="1762" height="1181" alt="Image" src="https://github.com/user-attachments/assets/90a2379f-a957-4c13-9f15-05733203cece" />

Error Messages/Logs

Steps to Reproduce

Ask Claude to read the image file attached to this issue, CrashesClaude.png

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.0.37

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

WSL (Windows Subsystem for Linux)

Additional Information

_No response_