The preprint arXiv:2605.16488 advances a thermostat paradigm in which black-hole feedback sets an entropy ceiling rather than continuously powering outflows, allowing buoyant gas to reach the virial radius without further energy input. FLAMINGO cosmological hydrodynamical simulations, run in large volumes with both isotropic thermal and jet-mode AGN feedback, demonstrate that outflow entropy at the virial radius becomes mass-independent under thermal injection but scales with heated solid angle for jets. This picture directly challenges the canonical 'maintenance-mode' engine framework used in most semi-analytic models and subgrid prescriptions. A critical transition mass near 10^13.5-14 solar masses is identified where virial shocks overwhelm the ceiling, predicting a late-time rejuvenation of star formation supported by emerging low-redshift SFR and morphological data. As a 2026 preprint the work remains unpeer-reviewed and relies on the specific subgrid implementations and resolution limits of FLAMINGO (approximately 1 kpc softening in the highest-resolution runs). The analysis notably under-connects to the observed bimodality in group-scale X-ray profiles and to the entropy-core measurements from Chandra and XMM-Newton that already hint at mass-independent floors. Synthesizing this with Schaye et al. (2023) on FLAMINGO calibration and the earlier virial-shock theory of Dekel & Birnboim (2006) reveals that the thermostat naturally explains why quenching efficiency plateaus above group scales without invoking ever-rising AGN energy budgets, a tension missed in current IllustrisTNG and EAGLE feedback tuning. If confirmed, the model forces a re-derivation of preventive feedback recipes in next-generation simulations, shifting emphasis from cumulative energy injection to the geometry and timing of entropy injection.