How can a Trailblazer Operation with Paperdragon process an image sequentially?

In a Trailblazer operation that uses Paperdragon to process an image, code like this is typical:

def process(params)
  validate(params) do |f| 
    f.image!(f.upload) do |v| 
      v.process!(:original)
      v.process!(:version_a) { |job| job.something... }
      v.process!(:version_b) { |job| job.something... }
      v.process!(:version_c) { |job| job.something... }
      end 
    end 
  end 
end 

which would create four versions from an uploaded image that is accessible as upload on the operation's contract.

I would like to do a few things to :original resulting in :edited and then use :edited as the baseline for :verson_a, :version_b and :version_c. How can I achieve that with Paperdragon?

You can run a second processing block using a version created by the first as its input:

def process(params)
  validate(params) do |f| 
    f.image!(f.upload) do |v| 
      v.process!(:original)
      v.process!(:edited) { |job| job.thumb!(crop) }
      end 
    end 
    f.image!(f.file(:edited)) do |v| 
      v.process!(:version_a) { |job| job.something... }
      v.process!(:version_b) { |job| job.something... }
      v.process!(:version_c) { |job| job.something... }
    end                                                                           
    f.save
  end 
end

where file is a method on the contract:

def file(version)
  File.new(Dragonfly.app.datastore.server_root+image[version.to_sym].url)
end