Not a separate node type — an entity with isStub: true, representing something external to the corpus (JDK, npm packages, …). Exactly two traits contribute isStub, so exactly two things are stubbable.

Stub of	Trait	Shape	Why it must exist
a type	TType	TNamed + TType, optionally TChildOf; no children, no anchor	every corpus references types it does not declare
a module	TModule	TNamed + TModule + TWithChildren, definedIn: []	the import graph is module-level, so import java.util.List points at the package java:java.util; with no module stub the first-class import layer could never satisfy closure

A member (method, field) is deliberately not stubbable: an external member folds up to its declaring type’s stub. Fabricating a class named bill(Order) to close an endpoint is the one thing stub synthesis exists to prevent — an unresolvable member id is reported and left dangling instead.

A stub’s parent

The one non-degraded thing a stub type may hold is TChildOf — the external module it belongs to — and a stub module lists such types among its children. Two rules bound it, both extractor-side obligations:

1. A stub’s parent must itself be a stub. Attributing an external type to a corpus module would make it read as internal to every module-level analysis. Where the parent cannot honestly be named — a static-analysis artefact invented inside the corpus’s own package, or a primitive, which has no module at all — the stub stays parentless and is reported as unplaceable at module level.
2. Only the extractor may derive it. Ids are opaque to everything downstream; the extractor owns the id scheme and already knows the package.

Without this, an external type could not be folded to module level at all, and the tempting workaround — treating such a stub as its own module — silently changes the granularity of the result.

Membership

• Edges to stubs are kept; the internal-only view is obtained by filtering stubs out at analysis time — uniformly, for types and modules alike. That is what --internal-only does.
• Membership is decided by a whitelist of corpus-declared ids built in a first pass — never by package or name prefix. Spoon in noClasspath mode invents plausible FQNs, and a prefix filter would launder them into facts.

In each rendering

Rendering	How a stub appears
analyze node lists	external (stub)
DOT, PlantUML	dashed and grey node; <<stub>> stereotype in PlantUML
City	Building.isStub / District.isStub; a stub carries no anchor, so loc is unmeasured
Navigator	NavNode.isStub
Domain facts	no dossier is emitted for a stub type; external: true on the facts that reach one

Why stubs rather than dropped edges: Extracting without compiling.