This work introduces the GS–L–RS framework, a fully mechanical substrate that replaces geometric curvature and abstract quantum fields with tension, coupling, and resonance in a single unified fabric. The GS field defines global tension and produces gravity through spatial gradients. The Loose‑String (L) field governs local resistance and generates effective mass. The RS sector contains the resonant modes that appear as particles and radiation. Together, these three components form a coherent physical system capable of reproducing gravitational behavior, particle families, cosmological expansion, and the observable structure of the universe. The paper derives the field equations for each component, constructs the unified Lagrangian, and presents testable predictions that distinguish the framework from conventional theories. Cosmogenesis is modeled as a catastrophic bull‑whip excitation of the primordial substrate, fracturing the uniform tension into the GS, L, and RS fields and initiating expansion through mechanical relaxation rather than geometric postulate. This manuscript establishes the foundational substrate for future work, including the development of the GRD (Gravitational Relaxation Dynamics) extension, which will connect GS tension gradients to curvature analogues and observational gravitational phenomena.