Endpoint-Distance Strictness Reframed and Elasticity Kernel Closure: Dual Comparative Statics, the Unit-Length Elasticity Gap, and a Computer-Assisted K > 0

R25 corrects a normalization slip (b_n = d_n* should be b_n = t_n·d_n*), proves that the breadth-one endpoint distance d_n* strictly decreases, and reduces the strict decrease of the unit-length endpoint distance b_n to an elasticity-kernel positivity condition E > 0; R26 proves a ratio lemma, reduces the problem to K = 6(−s') − s·V_dd > 0, certified by an adaptive mpmath interval audit (28,244 boxes, 0 unresolved, minimum lower bound 6.339e-4), and concludes b_{n+1} < b_n, labelled computer-assisted and conditional on G0.