[DGD] Is self nesting ALWAYS a bug?

[Shentino]

Me and someone else who I am choosing to keep anonymous at this time just
got into a huge debate of whether cyclic containment is ever a legitimate
circumstance.

Personally I think that allowing an object to contain itself, even
indirectly (or similiarly, be a detail of its container, or be contained by
its own detail) will cause no end of anomalies, infinite loops, logical
absurdities, and whatnot.

But based on runtime overhead, there are concerns over whether a trace-up is
a good investment of ticks just to prevent this.

Opinions?

Kotaka btw has self containment outlawed at the core, and not even an
administrator is allowed to override it.  This is in large part due to the
fact that kotaka's world saves are based upon cascading the save downwards.
Phantasmal, however, is flat and based on object numbers.

I'm thinking though that cache-hot roots would minimize a good part of the
overhead.