ROM Relation setup difficulty

inject.rb

require 'domain'
require 'persist/rom'
require 'persist/users_relation'

rom = ROM.env
p rom

Domain::Repository::User.delegate = rom.relation(:users).as(:user)

persist-rom.rb

require 'rom'

ROM.use(:auto_registration)
ROM.setup(:sql, 'postgres://localhost/apphf_dev')
ROM.finalize

persist-users_relation.rb

require 'persist/rom'
require 'rom-sql'

module Persist
  class UsersRelation < ROM::Relation[:sql]
    register_as :users
    dataset :users
  end
end

repro.rb

require 'rubygems'
gem 'rom-sql'

ROM.setup(:sql, 'postgres://localhost/apphf_dev')

class UsersRelation < ROM::Relation[:sql]
  dataset :users
end

class User
end

class UserEntityMapper < ROM::Mapper
  relation :users
  model User
end

rom = ROM.finalize.env

user_relation = rom.relation(:users)
mapped_user_relation = user_relation.as(:users)

Yes, I'm doing it as my first line of ROM code, in persist-rom.rb.