Row 3: the radiation and readout analogy

If $R=S\otimes A$, the post-readout accessible factor is $K\otimes A$, while $B$ remains outside the observer's access. An unconditioned readout on $S$ leaves the marginal on $B$ unchanged. A conditional residual can change. For example, reading one half of $(|00⟩+|11⟩)/\sqrt{2}$ prepares the other half in $|z⟩$ on branch $z$, although its average state remains $I/2$.

The instrument (eq:enter) does not derive (eq:hawking-temperature) or (eq:hawking-occupation). Producing bits does not establish an outgoing energy flux. A selected thermal state or occupation law is not a specification of a complete input–output channel or its physical complement. This is the spectrum/interface distinction emphasized in En07-C CheungEn07C,Hawking1975.