[BUG] Small images (2.2MB, 2396x1758) incorrectly rejected as 'too large'

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?

Standard macOS screenshots that are well within reasonable limits are being rejected with "Image was too large" error.

Image details:

• File size: 2.2 MB
• Dimensions: 2396 × 1758 pixels (~4.2 megapixels)

This is far below the documented API limits (~20MB, 8192×8192 pixels). The same user reports that some images work fine while others of similar size fail, suggesting inconsistent behavior.

This is distinct from #14099 (error persisting after /clear) and #15279 (UX improvement request).

What Should Happen?

Images of this size should be accepted without error. They worked as recently as the previous day.

Error Messages/Logs

⏺ Image was too large. Double press esc to go back and try again with a smaller image.

Steps to Reproduce

1. Take a standard macOS screenshot of a normal-sized window
2. Drop/paste the image into Claude Code
3. Error appears even though image is ~2MB and ~2400x1800 pixels

Claude Model

claude-opus-4-5-20251101

Is this a regression?

Yes, this worked in a previous version

Last Working Version

Worked as recently as the day before (version unknown, currently on 2.0.76)

Claude Code Version

2.0.76

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

Some images in the same conversation work fine while others of similar size fail, suggesting the size checking logic may be inconsistent or there's a race condition.