Pachinko is the most chaos-amplifying machine you can draw: every peg is a curved surface, and a curved surface doubles a hair of difference on every bounce.
The top pair below is the control group: an ordinary floating-point particle solver, written the way everyone writes them, running the machine twice. Same hoppers, same balls, same schedule, same code. One difference only: pane A adds its contact forces in ascending order, pane B in descending order. That is not a bug we planted. It is exactly the difference two GPUs, two drivers, or two compiler versions introduce on their own. Floating-point addition is not associative: (a + b) + c and a + (b + c) round differently.
Four hoppers, four colours, one thousand balls, eleven bins. Watch a full drop, then read the bins: the same balls, released on the same clock, finish in different bins. The machine runs again on a loop, and the two panes never agree.
Below is the same machine built inside SunaEngine, the integer engine this site is about, running twice on your GPU. The balls are the engine's own powder, dyed per hopper, the pegs and bins are stamped from stone, and the release schedule is the exact schedule the control group uses.
It does not matter that pachinko amplifies chaos. Integer addition is associative, so the twin runs land every ball in the same bin, finish on the same 256-bit digest, and then do it all again, loop after loop, on any GPU, forever. Deterministic pachinko always ends the same way.
(The engine pair is its own build of the machine: same layout, same schedule, its own physics. The claim is not that it matches the float panes above. The claim is that it matches itself, provably, every single run.)
The front page's second demo scrubs a splash backwards and forwards through time. It can do that because a recorded session is just a starting state plus inputs, and replaying them lands on the same bits, verified, every time, by a 256-bit digest.
The bins above are why floating point cannot have that. A float replay is a new run, and a new run only agrees if every one of billions of additions re-rounds identically, on every machine, every driver, forever. OE-CAKE, the 2007 toy this engine honours, kept snapshots for undo: memories of states. It could never recompute the past, because in floating point the past does not recompute.
Determinism is not a benchmark number. It is the difference between a simulation you watched and a simulation you can prove.