Regularizing Relativistic Singularities through a C ∞ -Smooth Extension of the d'Alembert Invariance: Resolving the Hubble Tension and the Non-Zero Photon Mass

We derive a $C^\infty$-smooth extension of classical relativity that regularizes the singularities of Special Relativity (SRT) by replacing the divergent Lorentz factor with a structurally complete boost. Unlike the metric truncation inherent in SRT, our \textbf{Asymptotic Lorentz Relativity (ALR)} framework provides the "missing information" necessary for a non-singular description of the light speed limit. This regularization was achieved by restoring the full d'Alembert form invariance across all velocity regimes.