plate chain (Int carried alongside an Object)
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boundary inputs             : {'start': {'view': 42}, 'sample': {'spot': 'loader.stage', 'view': {'barcode': 'ABC'}}}

per-step values (device model: next = current + 1, plate carried through):
  S1.next  = 43
  S1.plate = {'barcode': 'ABC'}
  S2.next  = 44
  S2.plate = {'barcode': 'ABC'}

whole-workflow outputs      : {'result': 44, 'plate_final': {'barcode': 'ABC'}}
