Theory of Self-Purification in Digital Ecosystems via Cost-Mediated Information Propagation Control — Structural Suppression of Infodemics through Basic Attention Credits and Nonlinear Feedback —

This paper proposes a censorship-free information governance protocol that structurally suppresses infodemics by introducing cost-mediated information propagation. By assigning finite Transmission Cost Credits and applying nonlinear costs based on propagation impact, influence, and data size, the system enforces sender responsibility without evaluating content. Logarithmic attenuation and temporal decay prevent information monopolization, enabling a self-purifying digital ecosystem applicable from social networks to space civilization communication systems.