Core contracts

Contract	Defined in	Purpose
EngineContract	contract/types.ts	Injected text, icon, colour-role, and legibility capabilities
FamilyDefinition	family/types.ts	Typed family authoring surface
GraphIR	family/types.ts	Shared normalized semantics
PlacementSpec	family/types.ts	Choice of configured or bespoke placement
MeasuredGraph	measure/measure-graph.ts	Content with exact extents
Placement	place/types.ts	Coordinates, route hints, and routing ownership
RoutedGraph	route/route-placement.ts	Final connectors and label positions
MaterializedGraph	materialize/materialize-graph.ts	Unframed neutral NGD elements
NGD	ngd/types.ts	Fully resolved renderer-independent scene graph

Routing ownership

type RoutingOwnership = { kind: 'shared' } | { kind: 'authored' } | { kind: 'hybrid'; edgeIds: ReadonlySet<string> };

This union prevents ambiguous booleans and makes routePlacement() exhaustive.

Output vocabulary

NgdElement is a discriminated union of node, group, edge, vector, and label. Structured vector primitives are path, rectangle, circle, or text; all paints are semantic roles. Consumers can switch exhaustively without importing engine internals.