Method subscribe

ui/src/protocol/message-processor.ts:969–981

* Subscribe to surface changes

(surfaceId: string, listener: (surface: Surface) => void)

   * Subscribe to surface changes
   */
  subscribe(surfaceId: string, listener: (surface: Surface) => void): () => void {
    let listeners = this.listeners.get(surfaceId);
    if (!listeners) {
      listeners = new Set();
      this.listeners.set(surfaceId, listeners);
    }
    listeners.add(listener);

    // Return unsubscribe function
    return () => {
      listeners?.delete(listener);
    };
  }

  /**
   * Notify listeners of surface changes