Characteristic Transport of Gravitational Information in a Finite-Capacity Vacuum

We derive the transport law governing the propagation of gravitational information in a vacuum with finite response capacity. Starting from a nonlinear saturating kinetic structure, we obtain the characteristic metric controlling high-frequency perturbations and derive a unique state-dependent propagation speed. We prove strict hyperbolicity, absence of ghost modes, and strictly subluminal propagation across the full physical domain. In the saturation limit, the characteristic cone narrows continuously, leading to causal freezing without loss of hyperbolicity. The resulting relaxation time is shown to be a geometric functional of the saturation profile rather than a free parameter. The framework is explicitly falsifiable and provides no-escape experimental criteria based on independent observables, including phase-noise modulation, cross-coherence, and non-Gaussian statistics under controlled excitation. This work closes the derivation of the effective transport law previously introduced and establishes transport speed as an emergent property of the vacuum state rather than a universal constant.