Unified Survival-Constraint (USC) Framework v1: A Geometric Foundation for the Dark Sector

The central result is the derivation of the observed order of magnitude of the cosmological constant (Λ ≈ 10⁻⁵² m⁻²) via entropy suppression at a CPT-symmetric boundary, rather than through parameter fitting. This preprint introduces USC v1, a unified dark sector framework via entropy suppression at the Janus boundary. The key innovation is the entropy-suppression duality mechanism (S₍chaos₎⁻¹ ≈ 10⁻¹²²), which simultaneously resolves the vacuum catastrophe and generates warm dark matter (m₀ ≈ 10 keV). The Janus boundary (Lⱼ ≈ 360 Mpc) replaces the Big Bang singularity with a CPT-symmetric junction at conformal past infinity. Horizon entropy S₍chaos₎ ≈ 10¹²² geometrically dilutes Planck-scale boundary stiffness, naturally explaining the cosmological constant scale without fine-tuning. Predictions include partial Hubble tension relief (H₀ ≈ 71 km s⁻¹ Mpc⁻¹), reduced structure growth (S₈ ≈ 0.78), and small-scale structure resolution via a free-streaming cutoff (λ_FS ≈ 700 kpc). All predictions are falsifiable by upcoming surveys (Euclid, Roman, CMB-S4, Lyman-α forest) within the next decade. Framework Development: The entropy-suppression duality mechanism underlying USC was developed prior to January 2026; USC v1 was finalized and publicly released in January 2026. This version establishes the conceptual foundation and scale-setting relations. The framework assumes General Relativity with linear perturbations; phenomenological elements (activation potentials, coupling gates) are explicitly labeled as placeholders. Full numerical derivations (including a precision cosmological-constant calculation from S₍chaos₎ ≈ (L_H / L_Pl)²), Boltzmann code implementation, and precision cosmological fits are deferred to USC v2/v3.