The cosmological constant problem, characterized by a 10^122 discrepancy between theoretical vacuum energy and observed cosmic expansion, fundamentally relies on integrating quantum fields down to the theoretical Planck length (10^-35 meters). This paper proposes that the Planck baseline is a mathematical extrapolation devoid of physical geometry. By applying the General Theory of Correspondence, we establish the true geometric floor of spacetime at 10^-31 meters. Using standard energy-length proportionality, we demonstrate that a 10^-31 meter spatial boundary mathematically correlates to exactly 1.97 x 10^15 GeV. This explicitly identifies the structural floor of the universe as the established Grand Unified Theory (GUT) scale. Furthermore, we demonstrate that this precise geometric limit acts as a master constant, simultaneously resolving the historical proton decay paradox by structurally preventing continuous quantum tunneling, and perfectly predicting the observed neutrino mass spectrum via the Seesaw Mechanism.