static value + python script -- computed value flow
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entry inputs (seeded at the boundary):
  raw          = 72

static value literals (embedded in the workflow):
  Score.threshold  = 60

activities (assembled inputs -> script-computed outputs):
  Score [score]
      in : {'raw': 72, 'threshold': 60}
      out: {'margin': 12, 'passed': True}
  Report [report]
      in : {'n': 12, 'ok': True}
      out: {'text': 'PASS (margin=12)'}

whole-workflow outputs (returns):
  margin       = 12   <- Score.margin
  passed       = True   <- Score.passed
  summary      = 'PASS (margin=12)'   <- Report.text

contracts (checked at runtime -- all held):
  score.requires inputs.raw.view >= 0
  score.ensures  outputs.margin.view == inputs.raw.view - inputs.threshold.view
  score.ensures  outputs.passed.view == (inputs.raw.view >= inputs.threshold.view)
  report.ensures  outputs.text.view != ""
