Cosmological Horizon Redundancy as a Physical Mechanism for Cross-Perspective Links in Relational Quantum Mechanics

In Carlo Rovelli's Relational Quantum Mechanics (RQM), physical states are defined strictly relative to interacting systems rather than as observer-independent absolutes. To prevent macroscopic observers from fragmenting into isolated informational islands in extended Wigner's friend scenarios, recent formulations by Adlam and Rovelli introduce the postulate of Cross-Perspective Links (CPL) within an all-at-once block history framework. In this brief foundational note, we examine whether Cross-Perspective Links require an independent metaphysical axiom or if they emerge naturally from environmental redundancy in de Sitter spacetime. Because all causal worldlines within a given patch share the asymptotic de Sitter horizon (I+) as a common radiative sink, any macroscopic interaction whose cumulative radiative imprint exceeds the Page scrambling threshold (f_A > 1/2) establishes a permanent, shared boundary record. Within a two-state boundary formulation, this common horizon anchor enforces intersubjective agreement among all internal observers via the Aharonov-Bergmann-Lebowitz (ABL) rule without requiring an extra postulate. Finally, we discuss how observer-dependent de Sitter horizons provide a natural relational ontology for patch-relative classicality across multiple causal diamonds.