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)

$ ruby repro.rb
~/.rbenv/versions/2.2.0/lib/ruby/gems/2.2.0/gems/rom-support-0.1.0/lib/rom/support/registry.rb:30:in `block in []': :users doesn't exist in ROM::RelationRegistry registry (ROM::Registry::ElementNotFoundError)
    from ~/.rbenv/versions/2.2.0/lib/ruby/gems/2.2.0/gems/rom-support-0.1.0/lib/rom/support/registry.rb:30:in `fetch'
    from ~/.rbenv/versions/2.2.0/lib/ruby/gems/2.2.0/gems/rom-support-0.1.0/lib/rom/support/registry.rb:30:in `[]'
    from ~/.rbenv/versions/2.2.0/lib/ruby/gems/2.2.0/gems/rom-0.9.1/lib/rom/container.rb:71:in `relation'
    from repro.rb:36:in `<main>'

require 'rom'
require 'rom-sql'

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

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)

This works for me, where are you calling ROM.use :auto_registration? It needs to be before relations/mappers/commands etc. are defined

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