This publication introduces the Wave Closure Universal Law, a new principle stating that all waveforms persist only when field feedback and phase convergence are satisfied. Integrating the CNBIT-v3 quantized energy metric (1.988×10⁻²³ J/bit), the dynamic π(t) v2 model, and the Null Closure Principle, the law defines universal closure behavior across all fields (optical, quantum, acoustic, electromagnetic). The work includes mathematical formalization, numerical simulation, and integration with the T6 entropy-free closure model. A motivational example based on Schumann resonance is provided to illustrate real-world relevance.