Gauss-Riemann Spectral Calculus: Riemann-Original Integral and Series Interfaces

This four-preprint package develops the Riemann-original integral and series interface branch of Gauss-Riemann Spectral Calculus (GRSC). The papers organize Riemann-original measure-relation grammar, observation remainders, finite integral readings, spectral-tail bridges, Lean and numerical interfaces, terminal benchmark tables, and a float-error audit. The package is presented as a public route and benchmark artifact, not as a complete Riemann integration theory or theorem-level analytic closure.