implement feedback loop

dotnet/AipsRT/Model/Whiteboard/WhiteboardManager.cs

@@ -32,6 +32,18 @@ public class WhiteboardManager
         _whiteboards.TryRemove(whiteboardId, out _);
     }
 
+    public async Task RefreshWhiteboard(Guid whiteboardId)
+    {
+        var whiteboard = GetWhiteboard(whiteboardId);
+
+        if (whiteboard == null)
+        {
+            RemoveWhiteboard(whiteboardId);
+        }
+        
+        await AddWhiteboard(whiteboardId);
+    }
+
     public Whiteboard? GetWhiteboard(Guid whiteboardId)
     {
         return _whiteboards.GetValueOrDefault(whiteboardId);