QAOA-XORSAT: Exact QAOA Performance on D-Regular Max-k-XORSAT

First public release. Exact QAOA on Max-3-XORSAT (k=3, D=4) through p=10, doubling the previous state of the art (p<=5). Three novel techniques: Walsh-Hadamard factorisation (65,000x speedup for k=3), manual adjoint differentiation (12x faster than ForwardDiff), and a generic fold engine parametrised by a cost algebra. 714 tests, 100% coverage. Runs on commodity hardware (Apple M4 Max, 64GB).