Micro-Dynamics of Topological Valves in Open Cosmological Systems: Kerr-Vaidya Flux and the Gravitational Derivation of the Cosmological Constant

Building upon the thermodynamic framework of open cosmological systems previously proposed [Frisina, Zenodo 2026], we perform a rigorous derivation of the metric transition occurring at the event horizon of a saturated black hole. We model the Parent Singularity using a Kerr-Vaidya metric to incorporate both the angular momentum necessary for chiral baryogenesis and the time-dependent accretion flux driving the internal expansion. By solving the Israel Junction Conditions at a stretched horizon located at proper distance δ ~ l_Pl, we demonstrate that the horizon acts as a dissipative membrane. The junction stress-energy tensor absorbs the angular momentum jump, thermalizing the rotational energy into the reheat temperature of the nascent Baby Universe (FLRW interior).Furthermore, we provide an "exploded" derivation of the Time Dilation Factor Gamma. We calculate that for astrophysical black holes, Gamma ~ 10^47, whereas a parent of cosmological horizon scale yields Gamma ~ 10^60, resulting in a renormalization of the input Planck-density flux into a low-energy effective Cosmological Constant Lambda ~ 10^-122 M_Pl^2. This offers a parsimonious geometric resolution to the Cosmological Constant problem, deriving the observed magnitude solely from the bulk-brane temporal scaling hierarchy, without invoking anthropic selection or fine-tuned scalar potentials.