Stitch MCP (stitch.googleapis.com) fails with 'Incompatible auth server: does not support dynamic client registration'

Description

When using the Stitch MCP server (stitch.googleapis.com/mcp) configured with an API key header, Claude Code throws:

Incompatible auth server: does not support dynamic client registration

Configuration

In ~/.claude.json:

{
  "mcpServers": {
    "stitch": {
      "type": "http",
      "url": "https://stitch.googleapis.com/mcp",
      "headers": {
        "X-Goog-Api-Key": "<api-key>"
      }
    }
  }
}

Expected behavior

Claude Code should use the provided API key header for authentication instead of attempting OAuth dynamic client registration.

Actual behavior

Claude Code ignores the headers config and attempts OAuth discovery, which fails because Google Stitch does not support dynamic client registration.

Steps to reproduce

1. Add the Stitch MCP server to ~/.claude.json with an X-Goog-Api-Key header
2. Try to call any mcp__stitch__* tool
3. Error: Incompatible auth server: does not support dynamic client registration

Environment

• Claude Code version: latest
• OS: macOS