[BUG] mcp auth not automatically launching browser on Windows

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?

authentication to mcp on latest version of the Windows client does not automatically launch the browser.
2 things to note. LucidChart MCP automatically launches the browser to auth without needing to first select Authenticate, that happens without issue.
Any other MCP after this is launched does not open the browser eg Atlassian, DataDog, slack, SourceGraph

What Should Happen?

clicking authenticate should launch the browser

Error Messages/Logs

no errors, just no activity

Steps to Reproduce

update to latest claude 2.1.141 on Windows with GitBash, add an mcp server and no browser will open.

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.139

Claude Code Version

2.1.141

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

Bug Report: Claude Code v2.1.141 ΓÇö Browser launch broken on Windows Git Bash + SSH

Summary:
Claude Code auto-updated to v2.1.141 on 2026-05-14 and broke all browser-open flows (OAuth, MCP authentication) for users running in a Git Bash/MSYS2 session under an SSH/PLink context on Windows.

Environment:

• OS: Windows 11 Enterprise 10.0.26100
• Shell: Git Bash (MSYS2) via PLink/SSH (PLINK_PROTOCOL=ssh)
• BROWSER env var: unset
• DISPLAY env var: unset
• Claude Code: v2.1.141 (auto-updated 2026-05-14, binary at ~/.local/bin/claude.exe)

Behavior before v2.1.141: Browser opened automatically during OAuth/MCP auth flows.
Behavior after v2.1.141: Browser silently fails to open; user is dropped to a manual URL prompt.

Root cause: The update changed browser-open logic and no longer falls back to cmd.exe /c start when BROWSER is unset and DISPLAY is empty in this environment.

Workaround: Add to ~/.claude/settings.json:
{
"env": {
"BROWSER": "cmd.exe /c start \"\""
}
}
(The "" empty title argument is required by cmd.exe /c start when opening URLs.)

Steps to reproduce:

1. Run Claude Code in Git Bash under a PLink/SSH session on Windows
2. Trigger any OAuth/browser-open flow (e.g., MCP server authentication)
3. Browser does not open; manual URL prompt appears instead