Notion MCP OAuth fails with "Missing or incomplete Client ID" for non-admin users

Bug Description

The Notion MCP integration OAuth flow fails with error "Missing or incomplete Client ID"
when attempting to authenticate as a non-admin user in Claude Code, despite working
correctly in Claude Desktop.

## Environment

• Claude Code version: 1.0.69
• Platform: macOS Darwin 24.5.0
• MCP Server: notion (https://mcp.notion.com/mcp)

## Steps to Reproduce

1. Install Notion MCP: claude mcp add --transport http notion https://mcp.notion.com/mcp
2. Run /mcp command to authenticate
3. Select "notion" from the list
4. Browser opens with OAuth URL
5. Error appears: "Something went wrong - Missing or incomplete Client ID"

## Expected Behavior
OAuth authentication should complete successfully for non-admin Notion users, as it does in
Claude Desktop.

## Actual Behavior
OAuth fails with client ID error. The generated OAuth URLs contain different client IDs:

• First attempt: client_id=1f8d872b-594c-80a4-b2f4-00370af2b13f
• Second attempt (via /mcp): client_id=gHRJRHcy8HD3JxIY

Both are rejected by Notion's OAuth endpoint.

## Additional Context

• User is not a Notion workspace admin
• Same integration works correctly in Claude Desktop app
• Personal integration tokens cannot be created without workspace admin access
• This prevents non-admin users from using Notion MCP in Claude Code entirely

## Workaround
Currently none available for non-admin users.