Question: Having a contract refer to previous values

[badBlackShark]

I have a very particular case, where I have a set of mappers (where only one should apply), the selection of which depends on a value earlier in the path. Here an example that I hope is not too convoluted:

class Embedded < Remap::Base
  contract do
    # Check somehow that `values.get(:d)` is true
  end

  define do
    map(:b, to: :test)
    to(:static).then { 'd is true' }
  end
end

class Test < Remap::Base
  define do
    map [:a] do
      each do
        map(:c, to: :something)
        embed Embedded
      end
    end
  end
end

Test.call({ a: [{ b: 1, c: 2 }, { b: 3, c: 4 }], d: true })

Is there a way to reference not the input of the mapper, but what came before it in the contract?