Oversized image attachment puts Claude.ai desktop session in unrecoverable state

Summary

On the Claude.ai desktop app, attaching an image larger than the 2000px multi-image dimension limit puts the session into an unrecoverable state. The API returns:

An image in the conversation exceeds the dimension limit for many-image requests (2000px). Start a new session with fewer images.

The offending image stays in the conversation transcript, so every subsequent send re-includes it and fails identically. The only escape is starting a new session, which loses all prior context.

Steps to reproduce

1. In a multi-image turn, attach at least one image larger than 2000px on the long edge.
2. Send. The turn fails with the dimension error.
3. Try any follow-up message. It fails identically because the offending image is still in the conversation history.

Expected behaviour

Any one of the following would resolve it:

• Down-scale images client-side before they enter the transcript.
• Validate dimensions at attach-time, not send-time, so the user can replace the attachment before the message is committed.
• Offer a "drop failing attachments and retry" affordance on the dimension error.
• Allow editing or removing attachments from a previous turn.

Impact

Loss of in-progress work and conversation context. Especially impactful in long investigative sessions where rebuilding context with the assistant is expensive. A real session named "Convert unsubscribe flow to list-scoped only" (24-26 April 2026) was killed mid-investigation by this trap state.

Environment

Claude.ai desktop app on macOS.

Note

Filing here at anthropics/claude-code because there isn't a public issue tracker for the Claude.ai desktop app. Please redirect if there's a more appropriate venue.