When doing POST /api/hosts, one can pass the image_id to the controller (see https://theforeman.org/api/2.4/apidoc/v2/hosts/create.html) and a user would expect that this image is used when one passes provision_method = image

But the actual deployment code looks at compute_attributes[image_id] instead: https://github.com/theforeman/foreman/blob/2b5ff89b21f797c37ca2bd73c941ce3dc677de03/app/models/concerns/orchestration/compute.rb#L240-L262

  def find_image
    return nil if compute_attributes.nil?
    image_uuid = compute_attributes[:image_id] || compute_attributes[:image_ref]
    return nil if image_uuid.blank?
    Image.find_by(:uuid => image_uuid, :compute_resource_id => compute_resource_id)
  end

  def validate_compute_provisioning
    return true if compute_attributes.nil?
    if image_build?
      return true if (compute_attributes[:image_id] || compute_attributes[:image_ref]).blank?
      img = find_image
      if img
        self.image = img
      else
        failure(_("Selected image does not belong to %s") % compute_resource)
        false
      end
    else
      # don't send the image information to the compute resource unless using the image provisioning method
      [:image_id, :image_ref].each { |image_key| compute_attributes.delete(image_key) }
    end
  end

Even worse, the image id it expects is actually the image uuid which is something completely different.

This is super confusing for users and results in API clients (hammer, Ansible) needing custom code to find the UUID and inject it in the right place.
This seems backwards, as we can just deduce all this from the actual image id the user (could) provide.