export interface PruneOptions {
    root: string;
    now: Date;
    retentionDays: number;
    /** Oldest snapshots are dropped past this, across every instance together. */
    maxTotalBytes?: number;
}
export interface PruneResult {
    removed: string[];
    /** Dated entries that were not plain directories, so were left untouched. */
    skipped: string[];
    keptBytes: number;
    /** The cap is still exceeded by the snapshots nothing is allowed to delete. */
    overCap: boolean;
}
/**
 * Prunes the backup root to a rolling window and a total-size cap. It runs on
 * every backup, including one where a target failed - a run that cannot write
 * is exactly when an unbounded pile of old snapshots would fill the disk.
 *
 * The cap never fails the run: it removes what it is allowed to remove and
 * reports the shortfall.
 */
export declare function pruneSnapshots(options: PruneOptions): PruneResult;
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