import type { UsageSnapshot } from "./affinity.js";
export interface UsageCacheOptions {
    ttlMs?: number;
    timeoutMs?: number;
    now?: () => number;
}
export interface UsageCache {
    /** Current snapshot, refreshing in the background when stale. */
    get(): UsageSnapshot | undefined;
    /** Await a fresh snapshot, bounded by `timeoutMs`. */
    refresh(): Promise<UsageSnapshot | undefined>;
}
/**
 * Wrap a usage fetcher in a TTL cache.
 *
 * The first call returns `undefined` rather than waiting: routing proceeds
 * without usage data and the snapshot is ready for the next request. This keeps
 * the very first request of a session as fast as an unrouted one.
 */
export declare function createUsageCache(fetchUsage: () => Promise<Record<string, number | undefined>>, options?: UsageCacheOptions): UsageCache;