[BUG] Cowork (macOS): attached image filenames not passed to Claude (works in Chat)

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?

Platform: Claude Desktop, Cowork (research preview), macOS. Plan: Max.

What's wrong:
In Cowork on macOS, when I attach images with the paperclip, the images themselves arrive, but their FILENAMES are no longer passed to Claude — Claude receives a nameless picture. This worked perfectly until ~24 hours ago and then suddenly broke. In regular Chat the filenames still work correctly, so the problem is specific to Cowork.

Why it blocks me:
My filenames carry essential information (the timeframe of each chart screenshot). Without filenames Claude cannot reliably identify the images, which breaks my entire analysis workflow. I am a paying Max subscriber and currently cannot use the product properly.

The folder workaround is NOT acceptable:
Images read from a local folder reach Claude at much lower quality (downscaled/compressed), so the fine chart details I need are lost. The same image attached through Cowork arrives at good quality. So I specifically need Cowork attachments WITH filenames — both the filename and the full image quality matter.

What I already tried:
Full reinstall of the desktop app on my MacBook (fresh download from the website, removed the old version, restarted). The problem persists, so it is not a local install issue.

Expected behavior:
Attached file filenames should be passed to Claude in Cowork, as they were before.

Is this a regression: Yes, worked before ~24 hours ago.

What Should Happen?

Attached image filenames should be passed to Claude in Cowork, exactly as they were before ~24 hours ago and as they still work in regular Chat. Claude should receive both the filename and the full-quality image from a paperclip attachment.

Error Messages/Logs

Steps to Reproduce

1. Open Claude Desktop on macOS, Cowork mode.
2. Open a project and attach an image file with the paperclip (a file that has a clear filename).
3. Ask Claude what the filename of the attached image is.
4. Claude cannot see any filename — it only receives a nameless image.
5. The same attachment in regular Chat (not Cowork) does pass the filename correctly.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

1.12603.1 (3df4fd) — Claude for Mac (Cowork)

Platform

Other

Operating System

macOS

Terminal/Shell

Other

Additional Information

Note: I am NOT using Claude Code or a terminal. This is the Claude desktop app, Cowork mode (research preview) on macOS. I am filing here because Cowork bugs are tracked in this repo. The "Terminal/Shell"/"Platform" fields do not really apply to my setup.