A Pre-Registered Fork for the Cosmological Constant: Either Dark Energy Evolves, or ρ_Λ ≈ (0.2–0.4)·m₁⁴

Abstract

The observed dark-energy density satisfies ρ_Λ^{1/4} = 2.24 meV, within an order of magnitude of the neutrino mass splittings — a coincidence with a mechanism lineage (mass-varying neutrinos, neutrino condensates) but no accepted explanation. We present a falsifiable fork derived from a lattice-measured mechanism in which geometry's infrared window is referenced by the lightest massive structured species. The mechanism's two faces — the timing of the window's closure against the cosmic thermal edge, and the magnitude of the unabsorbed residue left at the closing edge — are individually quantitative and mutually inconsistent for a single lightest mass: the timing face fits current DESI w(z) data with m₁ ≈ 0.25–0.35 meV, while the magnitude face reproduces the observed ρ_Λ with m₁ ≈ 2.8–3.5 meV. The inconsistency is structural, so exactly one face survives, and near-term data decides which. Both branches predict an effectively hierarchical neutrino spectrum with Σm_ν ≈ 59–63 meV — directly in the path of current cosmological neutrino-mass measurements — and sub-percent transient dark-energy excesses at the heavier mass eigenstates' closure epochs. Thresholds, both branches' numbers, and all kill conditions were frozen before DR3-class data existed; the present DR2 significance (3.1σ) adjudicates as unresolved under the frozen rule, so the fork is genuinely open at registration. A complete reproduction package, including the mechanical adjudication script, accompanies this deposit.