Emergent Inertia Addendum: Photons as Lagless Phase-Locked Structures

Description This addendum extends the Emergent Inertia framework by analyzing the photon as a distinguished dynamical limit of phase-gradient mechanics. In the parent theory, inertia and effective mass arise from persistent phase-gradient (shear) energy generated by mismatches between internal phase evolution rates and an external drive. Here we show that the photon occupies the unique zero-shear fixed point of the theory: all internal modes synchronize at the invariant speed �, eliminating phase lag and stored shear energy. The photon’s apparent masslessness is therefore reinterpreted as laglessness, rather than as a primitive ontological property. We further derive a frequency-dependent coherence bound on spatial extent, �, demonstrating that photons are not pointlike objects but phase-locked coherence structures whose effective size scales inversely with energy. Configurations exceeding this bound accumulate phase mismatch, acquire shear, and dynamically exit the light-speed sector. This addendum unifies massive and massless states under a single dynamical principle, reframing the invariant speed of light as a coherence condition rather than a postulate. The results provide a structural interpretation of photon propagation consistent with classical wave mechanics, quantum phase-space formalism, and relativistic limits, while remaining fully compatible with the parent Emergent Inertia framework.