/**
 * Token Refresh Mutex
 *
 * Implements a "Singleflight" pattern for token refreshes.
 * Ensures that for a given user, only ONE token refresh request happens at a time.
 * All other concurrent requests for that user will await the same refresh promise.
 */
export declare class TokenRefreshMutex {
    private refreshPromises;
    /**
     * Execute a refresh function with a lock for the given userId.
     * If a refresh is already in progress for this user, returns the existing promise.
     *
     * @param userId The user ID to lock on
     * @param refreshFn The actual refresh logic to execute
     */
    withLock<T>(userId: string, refreshFn: () => Promise<T>): Promise<T>;
}
export declare const tokenMutex: TokenRefreshMutex;
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