/**
 * Nexus Connect — In-memory message broker.
 *
 * Maintains a pub/sub registry keyed by topic string.
 * Keeps the last published message per topic for late subscribers
 * (same semantics as RxJS BehaviorSubject).
 *
 * Designed to be a singleton per server process. In multi-process/Edge
 * environments, replace the singleton with a Redis/Upstash adapter.
 */
export interface ConnectMessage<T = unknown> {
    topic: string;
    data: T;
    id: string;
    ts: number;
}
type Subscriber<T> = (msg: ConnectMessage<T>) => void;
declare class MessageBroker {
    private subs;
    private cache;
    subscribe<T>(topic: string, fn: Subscriber<T>): () => void;
    publish<T>(topic: string, data: T): void;
    /** Number of active SSE listeners for a topic (useful for presence) */
    subscriberCount(topic: string): number;
    /** All currently active topics */
    topics(): string[];
}
/** Singleton broker shared across all channels in this server process. */
export declare const broker: MessageBroker;
export {};
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