Structural Plenitude Theory (SPT v1.3 – Part I): The Structural Flux Paradigm and Thermal Coupling in a Viscoelastic Substrate

This work presents SPT v1.3 – Part I, introducing the Structural Flux Paradigm, a thermodynamically consistent extension of the Structural Plenitude Theory (SPT). In this formulation, heat, radiation, momentum, and energy transfer are no longer treated as independent or purely radiative processes. Instead, they are described as substrate-mediated fluxes governed by the viscoelastic state of the vacuum (Pleroma). Thermal exchange is reinterpreted as a problem of structural coupling efficiency, where unsuccessful coupling results in residual radiative dissipation (ℛ) rather than heat absorption. This paper establishes the conceptual and mathematical foundations of structural impedance, redefining: thermal coupling, latitudinal temperature asymmetries, failed thermodynamic anchoring, and radiative excess phenomena. No new ontological postulates are introduced. The work strictly extends previous SPT formulations by adding a dynamic and thermodynamic framework, preparing the theory for quantitative modeling and observational tests developed in subsequent parts of v1.3. This document is part of a frozen, multi-part v1.3 release, where each part receives an independent DOI for traceability and version control.