Allit Geoid Truth Projection (AGTP-1): Implementation-Grade Mathematical, Inverse, Differential-Distortion, and Reproducibility Supplement

This record is an implementation-grade technical supplement to the original Allit Geoid Truth Projection (AGTP-1) v1.0 publication, DOI 10.5281/zenodo.22385043. It closes specific implementation and reproducibility gaps identified during external GIS-oriented review without changing the underlying AGTP-1 local projection geometry. The supplement publishes explicit WGS 84 forward and inverse equations, numerical convergence rules, finite-precision seam semantics, a reversible packed 2D representation, an analytic Jacobian and equal-area proof, Gaussian first-fundamental-form and Tissot distortion derivations, a dependency-free reference implementation, automated 100-cycle round-trip tests, PROJ cross-validation, conformance vectors, and a reproducible land-weighted benchmark with bundled point inputs and source-data hashes. AGTP-1 remains an interrupted small-scale equal-area world-mapping research framework and is not a navigation or local-surveying projection.