Assumption: Identity-action semiclassical message baseline

For the selected fixed-background calculation:

1. the initial state of the message-independent field, source auxiliaries, and stored early systems does not depend on $x$;

2. the evolution of all decoder-accessible field and apparatus degrees of freedom acts as the identity on the internal message code, or factors through a subsystem whose complete accessible output is independent of that code;

3. no prompt reflected carrier, preparation record, or other message-dependent branch survives outside this factorization;

4. the discarded message and inaccessible auxiliaries are traced out without postselection.