[BUG] Desktop built-in browser pane: downloads saved as <guid>.tmp, download filename and extension ignored

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report
• [x] I am using the latest version of Claude Desktop

What's Wrong?

Product: Claude Desktop, built-in browser pane (the one the agent drives). Windows. Not the CLI.

If the agent clicks a download link in the built-in browser pane (an <a> with a download attribute that points to a PDF), the file is saved to the Downloads folder as <guid>.tmp. The filename from the download attribute and the .pdf extension are ignored, and the file is never renamed. The agent isn't told where the file went or what it's called.

I reproduced this once on purpose. Older files in Downloads have the same <guid>.tmp pattern from earlier months, so it isn't a one-off.

What Should Happen?

The file should be saved under its download name and extension, like a normal browser does, or the agent should get the saved path back. A .tmp that is never renamed looks like a failed or partial download.

Error Messages/Logs

None shown. The only symptom is the file in Downloads named like <guid>.tmp, which is a valid PDF once renamed.

Steps to Reproduce

1. In a Claude Desktop agent session, open a page in the built-in browser pane that has a link like <a href="/file.pdf" download="report.pdf">.
2. Have the agent click the link.
3. Open the Downloads folder: the file is <guid>.tmp, not report.pdf.

Claude Model

Not sure / Multiple models

Is this a regression?

I don't know

Claude Desktop Version

2.31226.1 (current); first seen on the build before

Operating System

Windows 11 Pro (build 26300)

Related

#96800 (file upload in the built-in browser pane).