Circuit-level equivariance is code-dependent: obstruction in the surface code, exactness in the honeycomb Floquet code, and consequences for neural decoders

Whether exact (twisted) equivariance survives at circuit level is a property of the code: obstructed for surface-code extraction circuits (999 spacetime maps, 1,728 schedules, with a mirror-axis impossibility lemma), exact for the honeycomb Floquet code, whose C3 rotation mixes the logical qubits (GL(2,F2)). The exactly-tied decoder flips the honeycomb task from unlearnable to learned (≥256× sample-efficiency separation; noise-rate sweep included). Solver released as the demsym package (pip install demsym); every number traces to a logged run via a 116-check audit. Code: github.com/dwatces/equivariant-quantum-ml