Speed of Light as a Function of Local Phase Density: A First-Principles Derivation in the Structured Resonance Framework

This paper derives the speed of light **c(ρₛ) = c₀ · cos(πρₛ / 2)** as a geometric consequence of local spacetime torsion, based on the structured resonance framework presented in *Principia Universalis*. It formally corrects earlier averaging approximations and provides a clean, testable derivation aligned with Euler’s identity *(e^{iπ} + 1 = 0)* and the Universal identity *(e^{i2π} = 1)*. A terrestrial example is included, along with practical guidance for experimental validation using fine-structure phase offsets near Earth’s surface.