[BUG] Google Drive upload fails for .docx files with "Internal Error" on Desktop v1.3109.0 — .md uploads work

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 v1.3109.0 on macOS. Google Drive upload button appears on all generated files (new in this release). Clicking the Drive icon on .md files uploads successfully. Clicking the Drive icon on .docx files fails every time with toast error: "Google Drive rejected the upload: Internal Error" Reproduction:

Ask Claude to produce both a .docx and a .md version of a document in the same response
Click the Google Drive icon on the .md file → succeeds
Click the Google Drive icon on the .docx file → fails with Internal Error

Environment:

Claude Desktop v1.3109.0
macOS (MacBook Pro M5 Pro)
Google Drive connector installed and functional for other operations
Reproducible across multiple files, multiple threads, after full app restart

Expected: .docx uploads to Drive like .md does.
Actual: .docx upload fails every time with "Google Drive rejected the upload: Internal Error." The .md path to the same Drive account succeeds, confirming auth and destination are fine. Failure is specific to the .docx upload path.

What Should Happen?

Clicking the Google Drive icon on a generated .docx file should upload it to Google Drive, the same way clicking the Drive icon on a .md file currently does. Both file types use the same connector and auth path; only the .docx path currently fails.

Error Messages/Logs

Toast error message (user-facing):
Google Drive rejected the upload: Internal Error

No logs available from the Desktop app UI. Error appears as a dismissible banner in the chat window after clicking the Drive icon on a .docx file.

Steps to Reproduce

1. In Claude Desktop v1.3109.0, ask Claude to produce both a .docx and a .md version of any document in the same response (e.g., a PRD or technical doc).
2. Two output file cards appear in the chat, each with a Google Drive icon and a Download button.
3. Click the Google Drive icon on the .md file → uploads successfully to Google Drive.
4. Click the Google Drive icon on the .docx file → fails every time with toast error: "Google Drive rejected the upload: Internal Error"

Reproducible across multiple files, multiple threads, after full app quit/relaunch. Google Drive connector is installed and functional for other operations (read, search, etc.).

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

Pre-v1.3109.0 Claude Desktop

Claude Code Version

2.1.84 (Claude Code) — but note: this bug is in Claude Desktop v1.3109.0, not the Claude Code CLI. The CLI version is unrelated to this bug.

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

IMPORTANT CONTEXT: This is a Claude Desktop bug, NOT a Claude Code CLI bug. The form required a Claude Code CLI version (2.1.84), but that is unrelated to this issue. The actual affected app is:

• Claude Desktop v1.3109.0 (updated this morning from the prior build, which resolved the Cowork "process exited with code 1" issue)
• macOS, MacBook Pro M5 Pro

UI change observed in v1.3109.0:
Previously, generated .docx files showed a Google Drive icon (upload to Drive) and generated .md files showed a Download button. After the v1.3109.0 update, all file cards now show both a Google Drive icon AND a Download button, regardless of file type.

Bug:

• Clicking the Google Drive icon on .md files → uploads successfully to Google Drive
• Clicking the Google Drive icon on .docx files → fails every time with toast error: "Google Drive rejected the upload: Internal Error"

Scope of testing:

• Multiple .docx files across multiple threads — all fail
• Full app quit/relaunch did not resolve
• Sign out / sign back in not yet attempted
• Other Google Drive connector operations work normally (search, read, metadata)
• Google Drive account has storage available; uploads via drive.google.com work normally
• Google Drive is NOT experiencing an outage (.md uploads to the same Drive account succeed)

Workaround:
Click the Download button on the .docx, then drag the file into Drive manually via Finder or drive.google.com.

Likely root cause hypothesis (for triage):
The .docx upload path may be sending the wrong MIME type, setting an unintended "convert to Google Docs format" flag, or sending a malformed multipart request that Google Drive rejects with a 500. The .md path evidently uses a different code path that works correctly.

<img width="478" height="56" alt="Image" src="https://github.com/user-attachments/assets/3b476803-5747-4e21-aca2-6314297b3458" />