The standard cosmological model explains current observations at the cost of postulating that 95% of the universe's content is unknown (Dark Matter and Dark Energy) and of numerically tuning a set of free parameters, while accumulating growing observational tensions (Hubble, early maturity of high-redshift galaxies). In this work we propose Geometric Response Cosmology (GRC), a framework where global linear expansion (Rₕ = ct) is not a dynamical solution governed by energy content but an intrinsic kinematic property of the substrate. This single premise produces a complete reinterpretation of the cosmological apparatus. Time ceases to be a dimension: it is the substrate's update process generated by the expansion itself, so that the limit c emerges as the medium's re-writing speed and time dilation as the lag of matter with respect to that update, preserving relativistic predictions without a four-dimensional block universe. The Hubble parameter is computed geometrically, H₀ = c/Rₕ = 1/t₀, and the horizon problem is solved by permanent causal connection, without inflation. On local dynamics, we propose a gravitational extension in the low-acceleration regime whose critical scale derives from the expansion, a₀ = cH₀/2π, reproducing galactic rotation phenomenology without non-baryonic dark matter. The framework dissolves the Hubble and JWST tensions structurally, declares its scope (BBN and CMB not derived in its current state), and proposes its own validation observables. We present GRC as a structurally parsimonious cosmological alternative whose detailed analysis is only beginning.