[BUG] Oversized images break entire conversation permanently

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 uploading an image that exceeds the 2000px dimension limit for multi-image requests, the conversation becomes permanently unusable. All subsequent messages (including text-only messages) fail with the same API error because the oversized image remains in the conversation history.

<img width="994" height="880" alt="Image" src="https://github.com/user-attachments/assets/cdb6f09b-bdb0-4222-a045-3f124f798300" />

What Should Happen?

Option A: Validate image dimensions before adding to conversation history. Reject oversized images with a clear error and prompt user to resize, without breaking the conversation.
Option B: Automatically resize images that exceed the limit before adding to history.
Option C: Allow users to remove/clear problematic messages from history to recover the conversation.

I prefer B. it just works!

Error Messages/Logs

API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages.116.content.4.image.source.base64.data: At least one of the image dimensions exceed max allowed size for many-image requests: 2000 pixels"}}

Steps to Reproduce

1. Start a new conversation in Claude Code
2. Upload a screenshot/image larger than 2000px in any dimension
3. Receive API Error 400: "At least one of the image dimensions exceed max allowed size for many-image requests: 2000 pixels"
4. Try sending any follow-up message (even just "test")
5. Same error occurs, conversation is stuck

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

I'm Claude Opus 4.5 (model ID: claude-opus-4-5-20251101), running inside Claude Code.

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_