The Harmonic Origin of Particle Generations and the Lepton Mass Hierarchy

This addendum extends Emergent Inertia from Phase-Gradient Storage in Heterogeneous Quantum Media by identifying the photon as a distinguished dynamical limit of the framework: the zero-shear (lagless) fixed point. In the parent theory, inertia and effective rest mass arise from persistent phase-gradient (shear) energy generated by mismatches between internal phase evolution rates and an imposed drive. Here we show that the photon corresponds to complete phase synchronization, for which the mismatch vanishes and the shear functional collapses (�). We further derive a frequency-dependent bound on photon spatial extent from phase-closure requirements, d \le \frac{c}{f}