Definition: Complete channel interface

A prefix isometry is

Its accessible and inaccessible channels are

The system $Z_t$ contains every accessible quantum system and classical record. The system $F_t$ contains the residual source, excluded radiation, detector environments, stored-resource purifiers, and every other inaccessible output.

Fixed mixed preparations are purified explicitly before defining $W_t$; their purifiers are assigned to $Z_t$ or $F_t$, not omitted.