Time-Symmetric Quantum Darwinism VII: Ontological Invariance of the Asymptotic de Sitter Horizon Filter (Equivalence of Two-State Retrocausality, All-at-Once Action Principles, and Many-Worlds Horizon Attrition)

Any self-contained quantum cosmology that avoids the infinite regress of an external observer must close the informational loop between the primordial vacuum state |Ψ₀⟩ and the asymptotic future de Sitter event horizon (I⁺ at R_H = √(3/Λ) ≈ 16.5 Gly). In previous works (Papers I–VI), this closure was formulated using the Aharonov–Bergmann–Lebowitz Two-State Vector Formalism (TSVF) paired with forward Quantum Darwinism. A natural question arises: do the physical predictions of this model depend on adopting TSVF as a literal ontology of backward-evolving quantum states? In this paper, we prove an Ontological Equivalence Theorem: the asymptotic boundary filter operator Π_I⁺ and all of its empirical consequences are strictly invariant across four major interpretations of quantum mechanics: (1) Two-State Retrocausality (TSVF), (2) Lagrangian "All-at-Once" Block-Universe Action Principles, (3) Everettian Many-Worlds (via Thermal Horizon Attrition), and (4) Hawking–Hertog / dS/CFT Holography. In particular, we prove that in a strictly forward-evolving Everettian multiverse with Λ > 0, Gibbons–Hawking thermal radiation (T_GH) acts as an asymptotic "cosmic woodchipper" that thermally scrambles and recoheres any branch whose coherent horizon imprint falls below the Page threshold (f_A < 1/2). Consequently, regardless of whether one views the mechanism as a retrocausal handshake, a 4D standing-wave cavity, or the survival of the sole non-recohered Everettian branch, the exact same parameter-free observational signatures emerge: the 60° (S_1/2) CMB large-angle cutoff, the β = 1.2336 × 10⁻³ (369.82 km/s) kinematic quadrupole–octupole alignment, the Λ_min link-budget pinch, and single-anchor exclusivity within our causal patch.