[BUG] [VSCode Extension] MCP Authenticate button does not open browser on macOS

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?

Bug Description

Clicking the "Authenticate" button for remote MCP servers (e.g. claude.ai Atlassian Rovo) in the /mcp panel does not open a browser window on macOS. The UI shows "Completing authentication in browser..." indefinitely, but no browser opens.

Steps to Reproduce

1. Open Claude Code VSCode extension
2. Type /mcp in the chat input
3. Select a remote MCP server that requires auth (e.g. "claude.ai Atlassian Rovo")
4. Click the Authenticate button

Expected Behavior

A browser window opens with the OAuth authentication page.

Actual Behavior

The UI transitions to "Completing authentication in browser..." and stays there. No browser window opens.

Additional Context

• open https://claude.ai works fine in the VSCode terminal, so browser itself is not blocked
• Extension log shows authenticate_mcp_server request is received, but no URL is opened afterward — only get_mcp_servers polling continues
• Log entry: Received message from webview: {"type":"authenticate_mcp_server","serverName":"claude.ai Atlassian Rovo"} with no subsequent openExternal call logged

Environment

• OS: macOS
• VSCode version: 1.113.0
• Claude Code extension version: 2.1.90

What Should Happen?

Clicking the "Authenticate" button should open a browser window with the OAuth login page for the MCP server (e.g. Atlassian login page via claude.ai).

Error Messages/Logs

MCP server "claude.ai Atlassian Rovo": Skipping connection (cached needs-auth)

Steps to Reproduce

1. Open a project in VSCode with the Claude Code extension installed
2. Type /mcp in the Claude Code chat input and press Enter
3. The MCP servers panel opens — select "claude.ai Atlassian Rovo"
4. Click the "Authenticate" button
5. UI shows "Completing authentication in browser..." but no browser window opens

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.90 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_