Variational Backbone and Regime Closures XX (Expansion): Cosmic Expansion as the Readout of Background Compression The clock–cone degeneracy, the critical surface at the horizon, and the de Sitter tail

This paper studies the VBRC readout of cosmological background evolution. Part XVI showed that, in the mixed gate, conservative retained propagation on a non-frozen dissipative background acquires derived friction, with the background-measure component appearing as Hubble friction. The VBRC-internal origin of that evolving background measure was left open. The present Part closes that flag at the structural level by declaring one principal identification gate and deriving its consequences. The identification gate states that the evolving background measure is read through the Part II background-formation compression. Cosmic expansion is therefore not a direct output of Part II alone. It is the retained expansion readout obtained when Part II compression is combined with the declared expansion gate and the associated future-volume and clock-readout gates. Within this grammar, three consequences follow. First, local time-cone drift is absorbed into the declared time-readout factor, so the internal invariant record of background relaxation is not the relaxation itself but the two-time ratio between emission and reception, namely redshift. Second, the mixed-gate critical surface is read at the horizon: modes crossing it stop oscillating as they leave the readable patch. Third, the compression flow relaxes toward its softest summary-sector mode, producing a late-time constant Hubble rate read as a de Sitter tail. The resulting co-readout family extends the earlier relation between the horizon acceleration scale and the cosmological constant to a threefold readout of one unread zero mode: late-time Hubble rate, Lambda, and the horizon acceleration scale. Retaining the softest two modes gives a closed-form effective dark-energy equation of state with no phantom crossing, while the spectral gap controls the deviation from w = -1. In the de Sitter horizon instance, the same small zero-mode response that gives a small Lambda and a rank-one galactic footprint also forces the present dark-energy behavior to remain close to LambdaCDM. The claim discipline is explicit. The principal expansion gate is declared, not derived from Part II alone. Its preferred grounding is the geometric future-volume split, with a weaker thermodynamic balance route kept as secondary. No Friedmann-level data fitting is performed, and the numerical value of H0 is not predicted; it remains the declared primary clock. The structural outputs are the monotone arrow of H, late-time constancy, the one-object status of late-time Hubble rate, Lambda, and horizon acceleration, a two-mode w(z) with no phantom crossing, and the rank-one-Lambda lock tying a rank-one horizon footprint to w close to -1 today.