import type { MessageStreamEvent } from "#protocol/message.js";
/** Remembers which session-stream events have already been consumed. */
export type EventDeduper = {
    /**
     * Records `event` and returns true when it is new — false when its id was
     * already admitted, so the caller should drop it.
     */
    admit(event: MessageStreamEvent): boolean;
    /** Number of ids currently remembered. */
    readonly size: number;
};
/**
 * Creates an {@link EventDeduper} keyed on the durable `meta.id`.
 *
 * Catches a reconnect that overlaps handled events, a rewind to an earlier
 * `startIndex`, and a saved log merged with the prefix a live stream replays.
 * A retried step is not a duplicate: it re-emits under new ids.
 *
 * The window is unbounded because a bounded one cannot survive a rewind past
 * its capacity — the oldest id is already evicted, so re-admitting it evicts
 * the next and the whole replay cascades back in. Callers here retain an
 * object per event anyway; one that retains nothing should bound its reads
 * with the `startIndex` cursor instead.
 */
export declare function createEventDeduper(): EventDeduper;