Instrument 003 · does the map help?
Two particles enter with almost the same spin — a hair apart, ε. The rule is deterministic; you hold the whole map ahead of time. With the scatterer off, they remain close in this square billiard. Switch it on and watch their sampled paths separate. Each path is determined by the rule, while the coarse read can lose their distinction at finite precision. Run the comparison rather than treating the map alone as the result.