> Ensuring you maintain determinism across many platforms is where things get super nasty.

I learned that one the other day - I've been building a little RTS game with a replay mechanism, and replays in Safari broke where they worked in Chrome. Opus 5.5 fixed it by replacing calls to things like Math.sin() and Math.cos() with its own deterministic functions: https://gist.github.com/simonw/7df96ed7296c69b70a9990102cae0...