How to use this with multiple projects using the HostingStartup attribute?

[YodasMyDad]

Have a look here for info on the new HostingStartup attribute

https://docs.microsoft.com/en-us/aspnet/core/fundamentals/host/platform-specific-configuration?view=aspnetcore-2.2

In short, I have several projects within a solution that all use this as (to me) it's a great way to add startup code to separate projects. I have a X.Core project where I'd like to setup the framework like below.

        // Add the Commanding Framework
        var adapter = new CommandingDependencyResolverAdapter(
            (fromType, toInstance) => services.AddSingleton(fromType, toInstance),
            (fromType, toType) => services.AddTransient(fromType, toType),
            resolveTo => _serviceProvider.GetService(resolveTo));
        var registry = adapter.AddCommanding();

Then need a way of getting the ICommandRegistry via the IWebHostBuilder builder I guess, so I can register query handlers from the other projects.