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

General relativity rests on the foundational assertion of the equivalence principle: that gravitational and non-gravitational acceleration are locally indistinguishable. This paper demonstrates, from the first principles of Quantum-Geometry Dynamics (QGD), that this indistinguishability is an artefact of single-mass approximations and fails for rigidly connected multi-mass systems. Under QGD, the two forms of acceleration are governed by strictly divergent physical mechanisms. Gravitational acceleration strictly reorients the intrinsic momentum vectors of a body's existing preons⁺, leaving its absolute mass exactly invariant ($\Delta m_a = 0$). In contrast, non-gravitational acceleration proceeds via the propulsive absorption of new preons⁺ emitted by an external agent, actively increasing the accelerated body's mass as thrust is sustained ($\Delta m_a = m_F$). By introducing a two-mass suspension protocol into Einstein’s original thought experiment, this paper shows that these divergent mechanisms yield a macroscopic, locally measurable discriminator. Releasing a suspended mass inside a non-gravitationally propelled chamber removes a mass sink from a rigidly connected system, instantly redistributing the absorbed momentum flux and producing a sudden spike in acceleration (a "jolt"). Because gravity involves no flux absorption, the exact same protocol run in a gravitational field yields no such spike. Finally, the paper introduces a novel falsifiable prediction—that non-gravitationally accelerated bodies retain a measurable mass excess—while recovering the core kinematics of relativity as effective, scale-dependent approximations rather than evidence for a curved spacetime continuum.