The empty-resources guard refused every empty body as a likely mistake,
with no way to say emptiness was meant — so the control plane could
never tell a node to drop its last resource. The envelope gains
owns_nothing: with it, an empty declaration is applied (the node drops
what the mesh owned); without it, empty is still refused, so a
truncated or mis-composed body cannot silently strip a machine. One
test, both directions.