X72-69: Rank-One Scattering Tangent and Affine Endpoint Repair

Continuing from Round 68's coarse-derivative bridge target (STOP-C72), this round first corrects a technical defect: it points out that the block-diagonal proxy used for the endpoint in Rounds 61–62 omitted the particular-solution response that the even minimal mode is forced into through the ν=0 odd equation, and that the true endpoint plane must include this affine correction term — this correction does not affect the existing theorems of Round 59, 56, 61–62, 64–68, but it demotes those two rounds' principal-angle numerical constants to a superseded proxy diagnostic. Starting afresh from the corrected endpoint plane, it proves the structural fact that the parity transfer matrix depends only on μ=ν², yielding the "Finite-Cutoff Rank-One Scattering Tangent Theorem": the first-order motion of the endpoint three-dimensional bundle has only a single scalar degree of freedom (the slow neutral scattering amplitude), with the two fast directions contributing only O(ν²); and, with the "Deep-Tail Jet Theorem," proves that the terminal Riccati tangent/second-order tangent is bounded under the uniform condition q_J≤1/4, eliminating any concern about tangent blow-up at infinity. The gap converges to a uniform Jost-crossing bound for the single scalar scattering amplitude (STOP-C73), left for the next round; this round includes numerical verification scripts and CSV data.