/**
 * SSE (Server-Sent Events) connection pool for the sidecar server.
 *
 * Manages a set of SSE client connections with a configurable maximum
 * concurrent connection limit and an optional heartbeat interval.
 * Dead connections are automatically cleaned up during broadcast.
 *
 * @module sidecar/server/sse/pool
 */
import type { SidecarEvent } from "../../types.js";
/** Configuration options for the SSE connection pool. */
export interface SseConnectionPoolOptions {
    /** Heartbeat interval in milliseconds (default 30000). */
    heartbeatIntervalMs?: number;
    /** Maximum concurrent SSE connections (default 50). */
    maxClients?: number;
}
/** A single SSE connection handle. */
export interface SseConnection {
    id: string;
    controller: ReadableStreamDefaultController;
}
/**
 * Manages a pool of SSE client connections with broadcast,
 * heartbeat, and dead-connection cleanup.
 */
export declare class SseConnectionPool {
    #private;
    constructor(opts?: SseConnectionPoolOptions);
    /**
     * Register a new SSE client connection.
     *
     * @param controller - The stream controller for the SSE response.
     * @returns A unique connection ID.
     * @throws `[Hivemind]` error when the maximum connection count is reached.
     */
    addClient(controller: ReadableStreamDefaultController): string;
    /**
     * Deregister an SSE client connection.
     *
     * @param id - The connection ID returned by {@link addClient}.
     */
    removeClient(id: string): void;
    /** Returns the number of active SSE connections. */
    get clientCount(): number;
    /** Returns the maximum allowed SSE connections. */
    get maxClients(): number;
    /**
     * Broadcast a sidecar event to all connected SSE clients.
     *
     * The event is formatted as an SSE message (`event:` + `data:` lines).
     * If a client's stream controller throws during enqueue, the client
     * is considered dead and is automatically removed.
     *
     * @param event - The sidecar event to broadcast.
     */
    broadcast(event: SidecarEvent): void;
    /**
     * Start the heartbeat interval.
     *
     * Sends an `event: heartbeat` message to all connected clients at
     * the configured interval. Clears any previously running heartbeat
     * before starting a new one.
     */
    startHeartbeat(): void;
    /**
     * Stop the heartbeat interval and remove all connections.
     *
     * Each connection's controller is closed before removal.
     */
    stop(): void;
}
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