Structural Walls and Observable Horizons in Reduced Inverse Geometry

This initial draft formulates a reduced inverse-geometric framework separating two distinct limits of observability: structural walls, defined by rank loss of the reduced Jacobian, and observable horizons, defined by covariance-dependent Fisher-threshold suppression. The paper proves that covariance whitening deforms the operational Fisher geometry while preserving the structural rank stratification, rank(Σ-1/2J)=rank(J). It then uses this distinction to build a two-domain dictionary connecting reduced dynamical-decoupling spectroscopy and reheating reconstruction in cosmology. The work is intended as a bridge/framework paper rather than a comprehensive review of the model-specific results in the separate ratio-map, DD, reheating, formulation-switching, and cusp/swallowtail precursor papers.