Abstract

We specify an observation boundary for a finite linearly typed quantum interface with destructive computational-basis readout and primitive classical geometric labels. Geometric rules inspect declared labels; coupling rules inspect declared matter observables; control and resource checks are part of the interface. Under spectator-blind control, arbitrary extensions with the same accessible reduced state preserve geometric traces and accessible matter states. A restricted coherent implementation of destructive readout agrees with immediate readout on their common record–matter output.

For a channel $T$, coarse effects $E_w$, and aggregated fine effects ${\Pi }_w$, record compatibility is equivalent to $T^{\ast }(E_w)={\Pi }_w$. The exact unassisted worst-case total-variation error is a maximum of operator norms over outcome events. Exact record compatibility extends to untouched entangled references, but does not determine residual instruments. For sharp measurements and a coarse Lüders instrument, full compatibility is characterized exactly by the removal of fine coherence within each coarse outcome. A compositional criterion identifies when continuations preserve agreement on a declared observable algebra.

One complete four-face adjacency exchange illustrates the interface. It is induced by a prescribed slicing of a fixed conical spacetime and has explicit charts, edge laws, a compact collar, a transition stratum, an exact guard, location transport, and a decoder-correct finite reversible implementation. The general interface results are independent of this example. A separate dictionary proves three linear observation rules for distributional comparisons without assuming any particular renormalized composite.