Defining one callback several times in the same class behaves different in ActiveRecord and ResourceController.
While in ActiveRecord the callbacks are enqueued, they overwrite each other in ResourceController.

ActiveRecord - a common practice

class Post < ActiveRecord::Base
  does 'post/behavior'
  before_validation :do_something
end

module Post::BehaviorTrait
  as_trait do
    before_validation :do_something_else
  end
end

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do_something_else and do_something are executed before validation in exactly this order

ResourceController - here you have to be careful

class PostController
  include ResourceController::Controller
  does 'post_controller/behavior'
  index.before { do_something }
end

module PostController::BehaviorTrait
  as_trait do
    index.before { do_something_else }
  end
end

Only do_something is executed before index because the callback defined in the trait is overwritten.