Finite-Scale Realization Spectroscopy in a Reconstructed Dark Sector

This paper studies how action-level freedom that is invisible in one reconstructed dark-sector background becomes visible at finite scale. In the pressureless mixed scalar-fluid class, complete scalar linear response along a regular realized history depends on the realization through a single kinetic function K(N), with the apparent effective-mass freedom fixed by an explicit reconstruction identity. The corresponding transfer matrices satisfy an exact Duhamel identity, giving a one-function finite-scale realization fingerprint. The paper quantifies the finite-family response of 175 calibrated histories, identifies the exact linear null fibre M -> M + c F^2/2, and shows that its neighboring-family dynamical separation begins at quadratic rather than linear order. It also distinguishes retarded reduced dynamics from fundamental non-Markovianity by exhibiting a finite-dimensional instantaneous Markov closure.