Remark: External drive

The Schrödinger-picture Hamiltonian is $H(t)=H_0+g_j(t)S_j$ during a pulse. The conservation claim concerns $H_0$, not a time-independent total Hamiltonian including a switching apparatus. No autonomous controller, clock, or work-storage system is constructed. On the prepared one-excitation sector, free evolution adds a common phase, so it does not change the derived channels. The decoder is likewise an allowed CPTP laboratory operation, not a separately energy-priced apparatus.