The Mittermeier RG Attractor as the Essential Renormalization-Group Skeleton of MAT: Closed Two-Threshold Normal Forms from the Euler-Mascheroni Constant γE, the Plastic Constant ρ, and π; locked three-channel architecture built from a geometric residue channel, an amplitude channel, and a vacuum channel; downstream vacuum hierarchy, closure-first cosmology, and microscopic lift

Modern renormalization-group approaches to quantum gravity are controlled by compact structural backbones that preserve their defining relations across representations. The present paper identifies the Mittermeier Attractor as such a backbone inside Mittermeier Attractor Theory (MAT). Its central claim is that the synchronized vacuum flow is not an isolated one-channel ansatz, but the exact observation-facing reduction of a locked three-channel (3C) architecture built from a geometric residue channel, an amplitude channel, and a vacuum channel. E (u) = ξ (u), φ̂₀ (u), λ̂_π (u) The starting point is a closed ultraviolet datum fixed by the plastic constant, which in MAT determines the Planck-boundary constant and the metrological branch rather than entering as a free phenomenological insertion. κM = e^ (-2) /ρ, ρ³ = ρ + 1, αM = κM/14 From this datum one obtains a closed two-threshold vacuum normal form, an exact integrated vacuum chart, and an exact particle-bridge representation in which the same flow can be written entirely in terms of the internal fine-structure constant coupling αM. The theorem-level result of the paper is that the synchronized vacuum law is reconstructed identically from the resummed Cluster-A (residue channel) and Cluster-B (amplitude channel). The attractor therefore carries not only the local beta law, but also the exact back-integration that turns that local law into a global vacuum trajectory with a late-time readout. This reconstruction fixes the main analytic structure of the flow in closed form: the infrared plateau, the canonical late-k scaling, the global monotonicity condition, the unique inflection-point structure, and the universal infrared tail law. It also changes the explanatory order of MAT. Quantities that previously appeared as separate late-time outputs are reorganized as consequences of one auditable upstream skeleton. The literature benchmark readout Λₒbs = 2. 9 × 10^-122 together with the calibrated closure-first branch Λ*₀ = 2. 8169986378639677 × 10^-122 enters as a reverse consistency check, showing that the same Attractor structure locks not only upstream but also downstream. The result established here is: a closed renormalization-group skeleton with hard invariants, exact 3C emergence, exact back-integration, and a reproducible audit trail. What is not claimed is a unique microscopic ultraviolet completion or a complete phenomenological solution of the cosmological-constant problem.