Indistinguishable in Principle, Distinguishable in Practice: Einstein's Equivalence Principle Reassessed, and the Predictions of Relativity Recovered from Quantum-Geometry Dynamics

P45 in the Quantum-Geometry Dynamics (QGD) / Minimally Physically Derivable Theories (MPDT) paper series. General relativity's foundational commitment — the equivalence principle — has been treated as secure since Einstein's 1907 uniformly-accelerated-frame argument, on the strength of an indistinguishability between gravitational and non-gravitational acceleration that was asserted, not derived. This paper shows, from the axioms of Quantum-Geometry Dynamics, that the indistinguishability does not hold in general: gravitational acceleration is exactly independent of the accelerated body's mass (P11 Ch. 7), while non-gravitational acceleration is inversely proportional to mass and additionally depends on the relative velocity between the accelerated body and its propulsive agent (P11 Ch. 12) — two structurally distinct mechanisms that coincide only for a single mass at a single instant, the special case Einstein's thought experiment happens to consider. A two-mass protocol run inside Einstein's own rooms distinguishes them by ordinary measurement. The paper's second part derives the confirmed predictions of special and general relativity — the constancy of the speed of light, velocity and gravitational time dilation, the deflection of starlight, the precession of Mercury's perihelion, and the orbital decay of compact binaries — directly from QGD's two axioms, without a physical time dimension, a spacetime metric, or gravitational waves. General relativity's numerical successes are explained as a consequence of its geodesic formalism tracking the same instantaneous gravitational vectors QGD computes directly. Companion to P11 (Quantum-Geometry Dynamics: An Axiomatic Approach to Physics, DOI 10.5281/zenodo.195846