Both early-outs return without touching the generator: p <= 0 false, p >= 1
true, otherwise exactly one word compared with a strict <. The zero-cost cases
decide stream alignment wherever a caller's probability climbs -- the spy
counter-mission adds 0.2f per failed turn and stops drawing entirely from the
fifth. A model without the early-outs drifts one word from there on, for ever.
NaN takes neither early-out in the original, so it draws and returns false;
reproduced rather than smoothed over.
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