Image too large for vision: silent failure or unhelpful error

Problem

When using the Read tool to view a large/tall screenshot (e.g., a 10-screen scrolling capture of App Store Connect), one of two things happens:

1. Silent failure: The image is "read" but text is unreadable because aggressive downscaling made it too small to parse. No error is shown — Claude just can't see anything useful and the user doesn't know why.

1. Late, unhelpful error: On very large files, an error eventually surfaces, but only after the user has already spent time capturing and providing the image.

Expected behavior

• Clear, immediate error when an image exceeds usable dimensions or file size
• Error message should explain why it failed (e.g., "Image is too tall — text will be unreadable after resizing. Try splitting into smaller screenshots.")
• Ideally, suggest the workaround (crop/split) in the error message itself

Context

User captured a 10-screen-tall scrolling screenshot of Apple Developer portal. First attempts silently produced no useful output. Later attempt with the full image hit a size limit but the error didn't explain what happened or what to do about it.

This is especially painful because:

• The user has to re-capture everything as individual screenshots
• There's no documentation of image size/resolution limits
• Claude itself couldn't answer "how big can images be" when asked

Suggested fix

1. Detect oversized/over-tall images before processing
2. Return a clear error: dimensions, file size, and the limits
3. Suggest splitting into smaller images or using PDF with pages parameter