V.T15 — Distance-Duration Duality

Operational distance and proper-time duration are dual readouts of the same structural quantity: duration is arc length along tau^1 between causally ordered depths (Delta t = sum p_k^{-1}), and distance is half the round-trip duration of a null intertwiner (d = c/2 * Delta t_{round-trip}). The ratio d/Delta t = c is exact.