Can't get Rake Routes to work with 3.2 Engine

here is the app routes file

# config/routes.rb
Rails.application.routes.draw do

  root :to => "home#index"
  mount ReactiveRecord::Engine => "reactive_record"

end

here is the engine.rb file

# reactive_record/lib/reactive_record/engine.rb
module ReactiveRecord
  class Engine < Rails::Engine
    isolate_namespace ReactiveRecord
    config.generators do |g|
      g.test_framework      :rspec,        :fixture => false
      g.fixture_replacement :factory_girl, :dir => 'spec/factories'
      g.assets false
      g.helper false
    end
  end
end

here is the engines routes file:

# reactive_record/config/routes.rb
ReactiveRecord::Engine.routes.draw do
  root to: "reactive_record#fetch"
end

rake routes says:

           root     /                    home#index
reactive_record     /reactive_record     ReactiveRecord::Engine

Routes for ReactiveRecord::Engine:

no routes are listed for the engine, and if i visit localhost:3000/reactive_record I get a 404.

Everything else is working fine. I.e. all the code in the gem is working and accessible.

Thanks in advance, I;m sure I;m missing something trivial