Remark: Adaptive versus retained-coherent execution

In the restricted streaming model that retains every delivered carrier coherently until all three have arrived, peak occupancy is at least three. The batch unitary $U$, followed by terminal syndrome readout, attains it.

The adaptive streaming programme and this coherent programme implement the same complete channel $\mathcal{D}$. Their streaming peaks are two and three. For batch access both peaks are three, because the input itself already occupies three qubits.