// ── Relationship ─────────────────────────────────────
/**
 * A relationship definition — like a component, but represents a directed
 * link between two entities.
 *
 * @example
 * ```ts
 * const ChildOf = defineRelationship();
 * world.relate(child, ChildOf, parent);
 * ```
 */
export interface RelationshipDef {
  /** Unique symbol used as the storage key. */
  readonly _key: symbol;
}

/**
 * Define a named relationship between entities.
 */
export function defineRelationship(): RelationshipDef {
  return { _key: Symbol() };
}