Bug Report: Claude Desktop re-registers itself as the default file handler on every launch

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?

Claude Desktop silently reclaims default-app status for common file types (PDF, DOCX, PNG, CSV, etc.) every time the app is launched, overriding whatever default app the user has explicitly set in Windows Settings. There is no visible toggle in Claude Desktop's own Settings to control this — the only related option present is "Open links in built-in browser," which governs hyperlinks clicked inside chats, not OS-level file-type associations.

Steps to Reproduce
Fully quit Claude Desktop (system tray → Quit/Exit, not just closing the window).
With Claude closed, go to Windows Settings → Apps → Default apps, and set a different app (e.g. Adobe Acrobat, Photos) as the default for a file type such as .pdf.
Confirm the change took effect by double-clicking a file of that type from File Explorer — it opens in the chosen app.
Relaunch Claude Desktop.
Without touching any settings, double-click the same file type again.
Expected Behavior

The file opens in the app selected in step 2.

Actual Behavior

The file immediately reopens in Claude Desktop, attached to a new chat — with no user action, no prompt, and no way to opt out. This happens every time Claude Desktop is (re)started, not just after an update or reinstall.

Impact

Users who want Claude Desktop's "attach and discuss a file" capability available when they choose it still need a working default viewer for everyday file opening. This silently and repeatedly removes that choice, and manually resetting defaults in Windows Settings provides no lasting fix since Claude reclaims them on its very next launch.

Environment
OS: Windows (please confirm exact build via Settings → System → About)
Claude Desktop version: please confirm via Help → About or the bottom of Settings
Architecture: x64
Requested Fix

Gate any default-app / file-type registration behind an explicit, persisted user opt-in — the same fix requested in #53864 for the native messaging host — and/or add a visible toggle in Settings to stop Claude Desktop from claiming file-type defaults at launch.

What Should Happen?

Requested Fix

Gate any default-app / file-type registration behind an explicit, persisted user opt-in — the same fix requested in #53864 for the native messaging host — and/or add a visible toggle in Settings to stop Claude Desktop from claiming file-type defaults at launch.

Error Messages/Logs

Steps to Reproduce

Steps to Reproduce
Fully quit Claude Desktop (system tray → Quit/Exit, not just closing the window).
With Claude closed, go to Windows Settings → Apps → Default apps, and set a different app (e.g. Adobe Acrobat, Photos) as the default for a file type such as .pdf.
Confirm the change took effect by double-clicking a file of that type from File Explorer — it opens in the chosen app.
Relaunch Claude Desktop.
Without touching any settings, double-click the same file type again.

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

1.49585.0

Platform

Other

Operating System

Windows

Terminal/Shell

Other

Additional Information

_No response_