Returns flake is Flake & { entry: Entry } & {
entry: Property;
drain?: { mould: Model };
}
true if flake is a Property with a non-projected Model drain (or none); false
otherwise, including transform stages, Id / Type markers, query,
and projected branches
Checks whether a flake steps through a Property carrying a single-value Model template retrieval: a non-projected drain whose mould is a Model (or no drain).