/** One in-flight acknowledgement and one latest pending intent per conversation. */
export declare class ConversationReadAckQueue {
    private readonly intervalMillis;
    private pending;
    private running;
    private activeSequence;
    private lastStarted;
    private flushPending;
    private closing;
    constructor(intervalMillis?: number);
    /** Already observed messages remain read when leaving; flush that one accepted intent. */
    close(): void;
    enqueue(sequence: number, run: () => Promise<void>): Promise<void>;
}
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