Actually, should we just fall through to this case? Shouldn't GetTypeVersionByID just fail if it gets a 0 as normal?

Maybe but honestly I'd prefer that we never lookup 0 which is specifically the constant descpb.InvalidDescriptorID. The thing here isn't that id is 0 but that it's 0 - 100000 which wraps around.

cockroach/pkg/sql/catalog/typedesc/type_desc.go

Lines 148 to 152 in 448663c

	// UserDefinedTypeOIDToID converts a user defined type OID into a
	// descriptor ID.
	func UserDefinedTypeOIDToID(oid oid.Oid) descpb.ID {
	return descpb.ID(oid) - oidext.CockroachPredefinedOIDMax
	}

My feeling is that typedesc.UserDefinedTypeOIDToID should be panicking here if ooid is less than 100000. I'm inclined to do something like above the id := ...:

if ooid < oidext.CockroachPredefinedOIDMax {
    return false, nil
}

We can't assert because users can provide arbitary values for this join. I'm going to do that instead.