[BUG] Claude Code session becomes permanently unusable after uploading oversized images

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?

When attaching Mac Retina screenshots to Claude Code, the API returns:

API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages.8.content.0.image.source.base64.data: At least one of the image dimensions exceed max allowed size for many-image requests: 2000 pixels"}}

Critical Problem:
Once oversized images enter conversation history, every subsequent message (including plain text) triggers the same error because the API replays the full conversation. The session becomes permanently unusable.
Impact:
Lost 2 days of conversation context
No way to recover or remove problematic messages
Session completely bricked
Root Cause:
Mac Retina screenshots exceed 2000px limit for multi-image requests
No client-side validation or auto-resizing
No recovery mechanism once images are in history

What Should Happen?

Proposed Solutions:
Auto-resize images to stay within API limits before sending
Client-side validation with clear warnings
Ability to remove/resize problematic messages from history
User-friendly error messages instead of raw API dumps

Error Messages/Logs

API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages.8.content.0.image.source.base64.data: At least one of the image dimensions exceed max allowed size for many-image requests: 2000 pixels"}}

Steps to Reproduce

Reproduction:
Take screenshot on Mac Retina display
Attach to Claude Code conversation
Observe error on that message and all subsequent messages

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

Claude Code

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_