/**
 * Tracks concurrent connections per key with a configurable limit.
 */
export declare class ConnectionCounter {
    readonly maxConnections: number;
    private readonly counts;
    constructor(maxConnections: number);
    acquire(key: string): boolean;
    release(key: string): void;
    /** Slots currently held for a key — for diagnosing an exhausted pool. */
    active(key: string): number;
}
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