Using MapFallbackToPage with a page called Index.cshtml leads to an ambiguious match

Repro

1. Create a new Server-Side Blazor app.
2. Rename Pages/_Host.cshtml -> Pages/Index.cshtml.
3. Navigate to /Index in the app.

This results in an ambiguous match from routing because a page named Index produces two endpoints. This isn’t ideal because it can be a useful pattern to place a page in the app route and then use fallback routing.

[iAlexanderMoon]

Well… I think I just ran into it this. Been pulling my hair out trying to figure out how I was getting 2 endpoints for a fallback to a razor page to serve a simple spa.

    app.UseEndpoints(endpoints =>
    {
        endpoints.MapRazorPages();    
        endpoints.MapFallbackToPage("/Index");
    });

If / is requested it doesn’t reach the fallback and is served… however… any request expected to be handled by the client hits the fallback and the following error is generated:

Microsoft.AspNetCore.Routing.Matching.AmbiguousMatchException: The request matched multiple endpoints. Matches: 
/Index
/Index

[glatzert]

We ran into this as well. We can alleviate the problem by using @page "/" on Index.cshtml. But it’s a lot of head-scratching.