SIGNAL
Precise answers from optimization solvers are not the same as correct ones, and a new structural result makes that gap impossible to ignore for 2D manufacturing layout. A class of compact encodings designed to fit cutting-stock problems onto quantum annealing chips provably cannot represent one basic operation: fitting one rectangular piece inside another. Containment, the geometric relation that turns nesting into nesting rather than tiling, is a longest-path constraint on a chain, and bounded-degree penalty terms cannot enforce it once the chain exceeds the solver's interaction order. The consequence is mechanical, not statistical. The sequence-pair formulation looks compact because its variable count is independent of plate resolution, but that compactness is borrowed from geometry the formulation cannot enforce. The arXiv:2609.20853 study confirms it empirically: a hybrid solver returns a configuration with its energy tied to thirteen decimal places, then overflows the plate. The same paper gives practitioners a usable rule. When geometry is rich and containment matters, reach for coordinate-based set-packing, whose ground state is a feasible layout by construction. When plate resolution is the bottleneck, sequence-pair has structural limits worth naming before benchmark numbers get read as geometric success. The field's long-standing "which QUBO to pick" question now has a documented answer, and the answer is the bound, not the chip.