Purity boundary cards
Recall the practical checks for pure functions and effect boundaries.
REPLAY What does REPLAY check before you call a function pure? Recall the six boundary questions. Purity check REPLAY asks whether the function reads only explicit inputs, avoids effects, returns a value, and yields the same answer for equal inputs. Pure core or effectful shell? Compare Pure core computes from explicit values; effectful shell reads, writes, schedules, logs, retries, and publishes around that calculation. Keep the business rule in the pure core and let the shell gather and publish. Objection: "A little mutation is faster and simpler." Use this when a teammate is mutating shared state inside a rule you…
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