The Universal Ecotone Every forest has an edge. Every shoreline has a tide pool. Every quantum measurement has a moment where the wavefunction hasn't quite decided yet. Ecology calls these transition zones ecotones, and they've known for seventy years that the edge is where the action is: more species, more adaptation, more exchange than either side alone. This paper asks a rude question: what if ecotones aren't a biological phenomenon at all? In φ-damped spiral convergence, the fifth rung of the convergence hierarchy always carries φ⁻⁵ ≈ 9% of the total budget. Always. Regardless of what the system is made of. At cosmic scales, this is the missing fourth energy sector that ΛCDM can't see, the one whose absence shows up as the Hubble tension, the S₈ tension, and DESI's inconveniently evolving dark energy. At quantum scales, it is Hardy's maximum entanglement probability (9.02%), derived from quantum mechanics alone in 1993 with no knowledge that it had anything to do with golden ratios. At biological scales, it is the edge effect that ecologists have been measuring since Odum. Three domains. One fraction. One structural explanation. The universe doesn't have edges because ecosystems do. Ecosystems have edges because the universe does. The ecotone is not a metaphor. It is a theorem. Supports: Spiral Convergence Theory (McLean 2026), The Universe Has No External (McLean 2026).