To enable the ResizingTool for a particular Node, set Part.resizable to true.
Optionally also set Part.resizeObjectName to the name of the element that you want the user to resize. I don’t think you want that in this case, so you don’t need to set that – it will default to resizing the whole Node.
But I think you will also want to save and restore the size of the Node. You can do that by adding a Binding on the GraphObject.desiredSize property. Make it a TwoWay Binding so that the user’s/ResizingTool’s changes to that property get saved in the model data.
So just insert two lines in that “Comment” template: