A node type declaration can no longer write itself as an instance

A recent fix retyped the three built-in declarations that had been filed under the type they describe — User, Virtual User and Partition — so they stopped showing up in their own nodeType: queries. That cleaned up the three known cases, but nothing stopped the same mistake from being written again later: a repair, a package install, or a hand-authored edit could still create a new declaration that files itself under its own type, and the portal's user directory would go right back to handing out a description-of-a-person where it expected an actual person.

Creating or updating a node now checks that rule directly: a node whose content describes a type can no longer also file itself under that same type. The write is refused with a message naming the node and the type it claims, rather than surfacing later as a silent lookup failure. This closes the underlying class of bug rather than the three instances of it that were already fixed.

The rule is deliberately narrow. A node that describes a type while being filed under some unrelated type is still allowed — a package root that is a space, and whose content happens to also describe a type, is a real and shipping shape. Refusing that would have made those packages impossible to install, which is a worse outcome than the mismatch it would have prevented.