>we'd likely use some form of nanotechnology to recompose waste into food. But again, without "creating" matter, simply rearranging it.
Nanotech isn't magic. The process would still require energy and would create more waste than can be possibly recovered, and diminishing returns would be inevitable. There's no perfect system possible here, entropy can't be cheated.
In any case, if we want to discuss a realistic implementation of this (which is probably at least a century away), we'd likely use some form of nanotechnology to recompose waste into food. But again, without "creating" matter, simply rearranging it.