/** Engine-neutral: the registry is shared across connectors, so each connector narrows at its own call site. */
export type TRelationBuilder = (opts: {
    source: unknown;
    relations: unknown;
}) => {
    relations?: unknown;
} | undefined;
export declare class RelationBuilderRegistry {
    static readonly SINGLETON_REAL_KEY = "relation-builder";
    /** Realm-anchored like the other cross-package registries: connectors installs into one copy of this package and the `@repository` mixin resolves from the other, which throws "no relation builder is registered". */
    private static slot;
    static set(opts: {
        builder: TRelationBuilder;
    }): void;
    static resolve(): TRelationBuilder | undefined;
}
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