[BUG] Cowork (Windows): Screenshot/image uploads fail silently — regression since ~March 30, 2026

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?

Screenshot and image uploads in Cowork sessions (Claude Desktop, Windows) have been consistently failing since approximately March 30, 2026. Uploading screenshots is central to my Cowork workflow — I use it to feed account pages, documents, and visual information into Claude so it can process and act on the data. Without working uploads, the product is effectively unusable for my use case.
The failure is silent or shows a generic error. Logging out and back in does not help. The issue has persisted across multiple sessions over more than a week (tested April 2, 3, 6, and 7).
This appears to affect multiple users across platforms. Issue #41242 documents a size-dependent upload failure starting the same date (March 30) where even a 70KB PNG fails while a 28KB PNG succeeds — suggesting the upload pipeline has an extremely low size threshold. Normal screenshots far exceed 70KB.
(Ironically, I cannot attach a screenshot of the error because the bug prevents screenshot uploads.)
Related issues: #39580 (API 400 on multi-image paste), #41242 (ECONNRESET + size-dependent upload failure, Windows), #42651 (plugin upload fails in Cowork, closed as duplicate), #39539 (Dispatch photo uploads silently fail), #37609 (screenshot via remote session, closed as duplicate)

What Should Happen?

Screenshots and images should upload successfully in Cowork sessions, as they did reliably before late March 2026. Claude should be able to receive and process uploaded images within the conversation.

Error Messages/Logs

No detailed error logs available from Cowork UI. The upload either fails silently (image never appears in conversation) or shows a generic failure message. See #41242 for detailed API error logs from a similar failure pattern on the same date, including ECONNRESET and size-dependent behavior.

Steps to Reproduce

Open Claude Desktop on Windows (v1.1.9310 or later)
Start a Cowork session (research preview)
Take a screenshot (e.g., Win+Shift+S or Snipping Tool)
Paste or upload the screenshot into the Cowork conversation
Upload fails — image either never appears or a generic error is shown
Retry does not help. Logging out and back in does not help.
Issue reproduces consistently across sessions and days (tested April 2, 3, 6, 7)

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

Before March 30, 2026

Claude Code Version

https://github.com/anthropics/claude-code/issues/new?template=bug_report.yml

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Other

Additional Information

Claude Desktop (Windows) — Cowork mode (research preview)