[BUG] Cowork file preview panel shows blank content (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?

Description
File preview panel in Cowork opens with the correct header/toolbar
but the content area is completely blank/white. The same file types
(PDF, etc.) preview correctly in Chat mode.

Steps to reproduce

1. Open a Cowork session
2. Generate or open any file (PDF, DOCX, etc.)
3. Click the file link — preview panel opens on the right
4. Header shows filename and Adobe Acrobat dropdown, but content is blank

Expected behavior
File content should render in the preview panel

Environment

• Claude Desktop version: 1.1.5749
• Plan: Max
• macOS: Sequoia 15.7.3
• Mac: MacBook Pro 16-inch 2023, M2 Max, 32GB RAM

Troubleshooting tried

• Updated app to latest version (1.1.5749)
• Restarted Mac
• Tested in a fresh Cowork session — same issue
• Confirmed preview works fine in Chat mode

<img width="1138" height="1109" alt="Image" src="https://github.com/user-attachments/assets/f552ad5e-5647-4405-b511-a11d05f30d88" />

What Should Happen?

File content (PDF, DOCX, HTML, etc.) should render and be visible in the Cowork preview panel, the same way it does in Chat mode.

Error Messages/Logs

Steps to Reproduce

1. Open any Cowork session
2. Ask Claude to create a file (e.g. "create a 1 page lorem ipsum PDF")
3. Click the file link in the response
4. Preview panel opens on the right — header/toolbar shows but content area is blank

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

N/A

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Other

Additional Information

This bug occurs in Claude Desktop (Cowork mode), not the API or CLI. The bug report template doesn't have a Claude Desktop option for Platform.