import type { Logger } from "pino";
import type { EventBus } from "../events/event-bus.js";
/** Fixed per-connection outgoing buffer size (design.md D28; task 5.6b). */
export declare const DEFAULT_CONNECTION_BUFFER_CAPACITY = 100;
/** Keep-alive interval, comfortably under a typical proxy idle timeout. */
export declare const DEFAULT_KEEPALIVE_MS = 15000;
/**
 * Manages every open SSE connection for the realtime event stream.
 *
 * Subscribes to the shared {@link EventBus} exactly once and fans each event
 * out to every open connection, isolating a connection whose write fails
 * (design.md's Multiple Concurrent Clients requirement; task 5.6) and
 * bounding what accumulates for a connection that stops reading without
 * erroring — a genuinely different failure from a write error (design.md D28;
 * task 5.6b).
 *
 * Per design.md D32/R21, every log call reachable from delivering an event —
 * fan-out, overflow, the fell-behind signal, serialisation, failing-client
 * isolation — MUST go through `deliveryLogger` (the stdout-only instance from
 * `engine.ts`), never through `lifecycleLogger`. Only connection accepted/
 * closed logging uses `lifecycleLogger` (the primary logger), so an operator
 * diagnosing a stalled dashboard can still find stream activity in the log
 * view. This is enforced by {@link assertLogCycleIsClosed}, not by review.
 */
export declare class EventStreamHub {
    private readonly deliveryLogger;
    private readonly lifecycleLogger;
    private readonly bufferCapacity;
    private readonly keepAliveMs;
    private nextConnectionId;
    private readonly connections;
    private readonly unsubscribeFromBus;
    constructor(bus: EventBus, deliveryLogger: Logger, lifecycleLogger: Logger, bufferCapacity?: number, keepAliveMs?: number);
    /** Number of currently open connections. */
    get connectionCount(): number;
    /** Open a new SSE connection and return its Response. */
    open(): Response;
    /** Release every connection and the hub's own bus subscription. */
    stop(): void;
    private broadcast;
    private isBackedUp;
    private deliver;
    private bufferEvent;
    private drain;
    private closeConnection;
}
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