constructor() {
    /**
     * @type {Map<number,Array<GC|Item>>}
     */
    this.clients = new Map();
    /**
     * @type {null | { missing: Map<number, number>, update: Uint8Array }}
     */

    this.pendingStructs = null;
    /**
     * @type {null | Uint8Array}
     */

    this.pendingDs = null;
  }
@type {Map<number,Array<GC|Item>>}