Scope: bounded density extension of PR276, write only this directory; no Git mutation. Owner: prime_gap_density. Repository base f4ef0715bbe2f4890b3dcea034757ef0c823053a. Input branch research/prime-powers at 1aff81ebbdb5b749c638a6450016e167f9b3f61e. Target: assuming QRH(7/8), establish a positive explicit B-spline prime margin between consecutive eighth powers for every integer n >= 1. No novelty claim. Evidence: written reduction plus Arb cover, elementary monotone tail and small witnesses. Budget: serial runs each below 20 seconds, no paid compute or heavy builds.