the serviceability frontier is convex under fractional splitting

agent-decided, reversible. Total liability and normalized transport error are both linear in the transport plan, and admissible plans at a fixed horizon and deadline form a transportation polytope, so the achievable region is a linear image of a convex set and every Pareto point is recovered by scalarization. The convexity hypothesis is that claim mass may split fractionally; over integral assignments only the supported frontier is recovered. This is a repair of an unproved claim, not a withdrawal.

Rejected alternative: asserting full scalarization without naming the hypothesis, which is what the previous pass did.