A target-adapted causal route

Choose two regular spatial ports $x_A,x_B$ whose straight developed connecting segment lies in a convex part of the laboratory. Let its length be $L>0$. Install $n+1$ sites

each with an equal-dimensional payload register $S_j$. Initialize $S_1,\dots ,S_n$ in the same blank state $\omega$.

At hop $j$, use the admitted communication channel that exchanges the contents of $S_{j-1}$ and $S_j$ over duration $L/(nc)$. Its two transfer directions have causal ports; it is not an instantaneous spatially extended gate.