Redshift without Expansion from Finite-Response Optical Propagation in ECSM

This preprint presents a finite-response redshift and optical-distance closure within the Emergent Condensate Superfluid Medium (ECSM) framework. Cosmological redshift is not interpreted as metric expansion, and photon-like signals are treated as coherent excitations of an underlying finite-response medium. The redshift coordinate is defined as Dz = ln(1+z), while luminosity and BAO observables are governed by a coherent optical propagation distance Dopt = Dz[1 + a Dz/(1+Dz)]. The saturating correction follows from a minimal finite-response optical-capacity equation dB/dDz = (1-B)/(1+Dz), giving B(Dz)=Dz/(1+Dz). Using the full Pantheon+ covariance matrix, the saturating ECSM optical model improves over the bare stationary redshift law by Δχ² ≈ 74.99 and selects a_SN = 0.203195. A BAO-only optical-capacity profile independently prefers a_BAO = 0.179343, with the supernova value lying inside the BAO-only 1σ interval. With a fixed to the supernova value, BAO is fit using one global scale parameter, S_BAO = 4518.09, giving χ²/dof = 0.732. The resulting BAO-anchored geometry remains compatible with redshift-space distortion growth data, giving χ²/dof = 0.305. A compact flat-ΛCDM baseline remains competitive, but the ECSM closure provides a non-expanding, internally consistent late-time redshift/optics interpretation across supernovae, BAO, and RSD.