"Principle-Locked H² Vacuum and Late-Time Cosmology: Conservation, Local GR, and Future Asymptotics"

We present a background-level modification in which the late-time vacuum contribution obeys ρΛ = (3c²/8πG)H² with a principle-locked prefactor derived along two independent routes (a four–form variational construction and a horizon thermodynamic balance). The framework introduces no new propagating degrees of freedom, preserves local General Relativity and standard matter conservation, and admits an early-time exact match to ΛCDM. Departures are confined to a slow, monotonic late-time drift, leading to testable predictions for the Hubble rate, structure growth, and redshift drift. The scenario is structurally economical, falsifiable, and consistent with both local gravity tests and early-Universe