Relational Gravity v1.2.1: Technical Addendum

This Technical Addendum presents the scalar-field implementation of the coherence–curvature relation in Relational Gravity. It formalizes the informational sector, derives the stress–energy tensor, outlines stability and Einstein limits, and provides first internal consistency checks against DESI DR2 BAO using an RG–CLASS–Cobaya pipeline. All empirical comparisons are strictly background-level and intended as numerical validation only; no statistical preference over ΛCDM is implied. This document is a technical supplement to “Relational Gravity v1.0” and prepares the ground for forthcoming perturbation-level and joint likelihood analyses.