Vercel MCP (mcp.vercel.com) OAuth flow never triggers - silent failure

Description

Adding the Vercel MCP server via claude mcp add vercel --transport http "https://mcp.vercel.com/mcp" results in a silent connection failure. No browser OAuth flow is ever triggered, and the server shows as ✗ Failed to connect in claude mcp list.

Steps to Reproduce

1. claude mcp add vercel --transport http "https://mcp.vercel.com/mcp"
2. Restart Claude Code
3. Run claude mcp list

Expected Behavior

A browser window opens prompting OAuth authorization with Vercel.

Actual Behavior

Silent failure — no browser window, no error message, server shows as failed.

Environment

• Claude Code version: 2.1.92
• OS: macOS Darwin 25.3.0
• The Vercel MCP endpoint correctly returns OAuth metadata at /.well-known/oauth-protected-resource and /.well-known/oauth-authorization-server

Related Issues

• #36307 - HTTP MCP servers with OAuth never trigger browser auth flow
• #11585 - MCP servers requiring OAuth don't expose tools
• #26917 - HTTP MCP servers requiring OAuth silently fail