import { type JoinKeyType } from './JoinKeys.js';
export type { JoinKeyType };
export interface CardinalityIndex {
    /**
     * How many distinct actors share this key value in the window.
     *
     * Zero means the value was never seen, or was seen only on rows that carry no client address
     * — either way there is no evidence that it identifies anybody.
     */
    cardinality(type: JoinKeyType, value: string): number;
}
/**
 * Count distinct actors behind each join-key value across a window.
 *
 * This is the evidence for Invariant 2. Some keys identify a person and some identify a crowd,
 * and the difference is not knowable from the key's name: REQUEST_ID is reliably 1:1, while a
 * community guest USER_ID was measured at 1:1371 in a single hour. Expanding through the second
 * turns one actor's timeline into every anonymous visitor's, attributed to one actor.
 *
 * Actors are counted as distinct client IPs rather than rows on purpose. Rows measure how busy a
 * key was; IPs measure how many people stand behind it. A single actor making ten thousand
 * requests must stay expandable, and ten actors sharing one key must not.
 *
 * The index only measures. Refusing to expand, and recording why, belongs to the engine — a
 * timeline that was quietly bounded is as misleading as one that was over-attributed.
 */
export declare function buildCardinalityIndex(rows: ReadonlyArray<Record<string, unknown>>): CardinalityIndex;
//# sourceMappingURL=CardinalityIndex.d.ts.map