Gravitational Closure Geometry and the Physical Meaning of the Aether Maximum Mass: A QMU Interpretation of Schwarzschild Closure, Rotational Compression, and Propagation Boundaries

The Aether maximum mass ($m_a$) occupies a central role within the Quantum Measurement Units (QMU) framework of the Aether Physics Model (APM). Previous work demonstrated that the Planck system factorizes into an electron--Aether bridge structure in which the Planck mass becomes the circularly normalized geometric mean between the electron mass and the Aether maximum mass. The present paper develops the physical interpretation of $m_a$ itself. Using QMU ledger identities, the Schwarzschild radius corresponding to $m_a$ is shown to equal the Compton propagation length: \[\frac{Gm_a}{c^2}=\lambda_C\] This identity implies that $m_a$ represents the maximum rotational propagation mass permitted within Compton-scale geometry before full gravitational closure occurs. The analysis reinterprets gravitational collapse as rotational propagation compression rather than as a purely geometric coordinate singularity. Within this framework, Schwarzschild closure corresponds to the loss of outward propagation degrees of freedom as rotational phase geometry collapses toward the Compton boundary. The results suggest that black-hole horizons represent closure-locked propagation geometries rather than infinitely dense points. The Planck system consequently emerges not as a primitive foundation of physics, but as a crossover layer between localized electron closure and maximum Aether closure. The paper develops the Schwarzschild--Compton closure relation: \[r_s=\lambda_C\] for the Aether maximum mass and argues that gravitational closure is fundamentally associated with propagation-boundary compression rather than purely coordinate-based singularity formation. Additional analysis explores: rotational propagation compression, loxodromic closure geometry, black-hole horizons as closure-locked propagation states, Planck geometry as a transition layer, ultraviolet closure limits, and observational consequences for scalar gravitational-wave searches and rotational horizon structure. The framework proposes that many conventional singularities arise from SI projection breakdown rather than from physically infinite density. Within QMU, the Planck system becomes a relational bridge between minimum stable electron closure and maximum gravitational propagation closure.