Classic disk formation theory links galaxy disk sizes to the angular momentum of their host halos. Yet simulations find a weaker spin-size correlation than expected, raising the question of whether the connection is intrinsically weak or measured at the wrong time. I will address this using Lumina, a new large-volume radiation-hydrodynamic simulation based on IllustrisTNG, together with TNG100-1, spanning reionization to the present. We find that the size-spin correlation peaks at an earlier epoch, when disk material was acquiring angular momentum. Weighting halo spin history by star formation history roughly doubles the correlation and accounts for the signal carried by present-day spin. As halo spin evolves, disks retain a memory of a spin their halos no longer have. Models based on present-day halo properties may therefore underestimate the connection between disks and halos.
