Nature is lazy and reuses her inventions.Electrons and positrons are made from light — pair creation can be watched directly in a cloud chamber.The geometric scaffold that holds a stationary half-photon in a temporal loop is reused to make neutrinos when that half-photon is shed. The same scaffold, when three leptons form a closing ring in the presence of a diverging magnetic field and a molecular hydrogen scaffold, catalytically produces a neutron. The reaction is exothermic and yields additional rest mass from the energy of stretched spacetime. This paper characterises that process — Coronal Lepton Fusion — and identifies it as the engine of continuous creation driving the expansion of the universe. The process is directly observable at the poles of Jupiter, in Earth's auroral thermosphere, and in solar coronal heating events. The predicted isotopic signature — anomalous deuterium enrichment, with a specific ratio between water and methane — was confirmed by the March 2026 measurements of interstellar comet 3I/ATLAS, timestamped prior to those observations. CLF is the only identified mechanism capable of providing the energy density required to halt climate change and to power self-fuelling interstellar drives. The tabletop experiment that confirms or refutes the mechanism costs £15,000 and takes three months. It has not been run.