Random numbers

Decided

D-0067, settled by the language’s author: part of spec §18. Older text cites it as 18.67.

One generator per thread, reached as Random::… with no instance, chosen by the user over a value-type generator: game code wants a number, not a generator to pass around. SplitMix64 (one u64 of state) rather than PCG or xoshiro, for its size and simplicity; seeded from the clocks unless Random::seed is called. Random::range<T: Number> covers every number kind through the new Number trait, which Integer and Float both require. Integer ranges are [lo, hi), as floats are. A separate seedable stream — a replay that must not share state with gameplay — can come later as a value type (§14.4)