Rails Concern class_macro with params from inherited class

Question

This is probably a really easy question but I'd like to have a concern which adds a validation whose parameters depend on methods in the derived class. For instance, I'd like to have a concern SlugHelpers as follows

module SlugHelpers
  extend ActiveSupport::Concern


  included do
     validates :slug, uniqueness: { case_sensitive: false, message: "Slug must be unique", scope: slug_scope }, presence: true,

  end

  class_methods do
    def slug_scope
      []
    end
  end

end

But then have a model Post which overrides slug_scope, e.g.,

class Post < ApplicationRecord
  include SlugHelpers

  def self.slug_scope
     [:stream_id, :stream_type]
  end

I want the slug_scope defined in Post to override the slug_scope used in the included do (though I might be calling that wrong, maybe I need self.class.slug_scope) but as written I think that this won't work (isn't the included do executed before the derived class defines its methods)?

Can I do this somehow using prepended do? Or is the way I wrote this roughly correct? I know that included modules are entered into inheritance chain before the derived class but I'm obviously kinda confused about when/where code in an included do block gets executed.