Papers I–XII established the Vacuum Folding Dynamics (VFD) framework, deriving twelve standard-model observables from the vacuum micro-state density σf, constructing electromagnetic coupling channels, and designing a laboratory detection strategy. One key question remained open (Paper XII, §7. 2 v): the dynamical evolution of σf through cosmological history and its observable imprints. In the present paper we address this question in three stages. First, we derive the cosmological field equation for σf in a Friedmann–Lemaître–Robertson–Walker background, showing that the chameleon mass mₑff (ρ) tracks the cosmic mean density through radiation domination, matter domination, and Λ-domination. Second, we integrate this equation numerically from z = 10¹⁰ (post-BBN) to z = 0, demonstrating that σf remains deeply frozen (mₑff >> H) throughout the entire cosmological history: the ratio mₑff/H grows monotonically from ~10¹³ at BBN to ~10³⁰ today. The chameleon contribution to mₑff becomes sub-dominant below z ~ 3×10⁹, after which mₑff ≈ m₀; the transition from radiation- to matter-dominated expansion at zₑq ≈ 3400 leaves mₑff essentially unchanged. Third, we compute the perturbative imprints of σf on the cosmic microwave background (CMB) and matter power spectrum, finding: (a) a scale-dependent modification of the ISW effect at ℓ ≤ 30 with amplitude ΔC_ℓ/C_ℓ ~ 10⁻¹⁰⁸, (b) an oscillatory feature in the matter transfer function at the Compton scale k_σ ~ 10²⁶ Mpc⁻¹, utterly inaccessible to cosmological probes, and (c) a characteristic oscillation frequency f_σ ~ 2. 4×10¹¹ Hz today (redshifted to ~7×10⁷ Hz when sourced at matter–radiation equality). All three signatures are astronomically below current observational sensitivity, confirming that VFD is cosmologically inert. The numerical cosmology confirms that the ρ → 0 analytic limit used in Papers I–IX is an excellent approximation (relative deviation < 10⁻³²) in the late-universe vacuum, validating the foundational derivations.
Daniel Leonforte (2026) studied this question.