Effective Metric Plasticity in the Cosmic Web: A Conservative Prediction of the Geometric Relay Programme

This note introduces a conservative and testable prediction of the Geometric Relay Programme: effective metric plasticity in the cosmic web. The central claim is not macroscopic spacetime navigation, but a weaker observational hypothesis: in low-density environments such as voids, filament edges, and halo–filament transition regions, baryonic, lensing, dynamical, and timing distance estimators may exhibit structured residual mismatches. The paper defines an effective plasticity index and proposes that the signal should be suppressed in dense, baryonically locked environments and enhanced in low-density regions where the relay field is less constrained by matter. A minimal toy reproducibility script is provided. It does not fit Euclid or other observational data; it only reproduces the qualitative hierarchy predicted by the model: |Pi_eff|_void > |Pi_eff|_filament > |Pi_eff|_cluster. This deposit is intended as a theoretical prediction note and reproducibility package for future comparison with Euclid, Rubin/LSST, SKA/FRB, weak lensing, galaxy clustering, and standard-siren distance data.