MCP OAuth no longer auto-opens browser on Windows (v2.1.140)

Summary

Running /mcp to reconnect an OAuth MCP server prints "A browser window will open for authentication" but no browser tab opens. The URL is shown for manual copy (press c), which works, but the auto-launch step is broken. This used to work in earlier versions.

Environment

• Claude Code: v2.1.140 (Opus 4.7, 1M context)
• OS: Windows 11 Pro (10.0.26200)
• Shell: PowerShell

Repro

1. Run /mcp against an OAuth-based MCP server
2. CLI prints "A browser window will open for authentication" and the auth URL
3. No browser tab opens; have to press c and paste manually

What I tried

• Closed all browser windows and retried — same behavior
• Full reboot pending

Related

• #42548
• #36307

Happy to provide more details or logs.