Unable to mount instances instead of class definitions

Grape seems to mostly work when you mount an instance of a class instead of the class definition itself. However, it doesn't actually and uses the instance to find the class definition. This has the side effect that configured classes don't work correctly, and any properties set on them aren't set on the actual controller

As an example:

class DebugController < Grape::API
    format :json

    def initialize(name)
        @name = name
    end

    desc "No-op that confirms that the service is working"
    get '/ping' do
        {
            :ping => @name
        }
    end
end

class API < Grape::API
    format :json

    mount DebugController.new("Test") => "/api/debug"
end

In the above application, when the controller for "/api/debug/ping" is called, the value for "@name" is Nil and not "Test", because the DebugController instance that was passed to mount isn't actually the instance that is used.

Start by tracing Grape's mount handling for the DebugController.new("Test") instance and the /api/debug/ping request in the issue example. Verify which object handles the request and whether @name remains "Test"; done means mounted instances retain their instance state instead of being replaced by a new class-based controller.