Claim PUB-persistent-scaffold-causal-algebra--thm-two-row

Exact statement

Theorem 8.1 (Unexposed two-row sewing). Fix $d$ , $k\geq1$ , and a behaviorally reduced old prefix. Consider two unexposed acyclic two-row extensions with the same consumer label, the same valid nonmissing path-demanding consumer coordinates, and literal agreement as missing or $\mathsf{SELF}$ on every other consumer coordinate. If corresponding path demands have the same final old residual behavior, the blocks are connected by endpoint detours, causal-garbage moves, continuation-aware routing crossings, and dedicated relation exchanges. Every common suffix is preserved.