qector-two-stage-css

Two-stage CSS decoding for QECTOR (manual chapter 12). Independent X and Z decoders assume P(X, Z) = P(X) P(Z); depolarising noise violates this. Two-stage decoding removes the cross-talk explicitly. Load for any question about depolarising noise, CSS sector coupling, feedforward X->Z syndrome updates, or the Theorem 13 joint-faithfulness guarantee.