Custom editor: undo change to editor property

I'm writing a custom editor to quickly define paths in the Scene view: basic functionality is to select a point in the path, move it around, add a line starting from the selected point and so on.

How can I add an Undo step when the user selects a different point in the path? This is exactly what the Unity Editor does when the selected GameObject changes.

Here is my code for the selection logic, in my editor class:

 // 'Curve' is my MonoBehaviour which defines a path in the game world.
 
 [SerializeField]
 private Curve curve_selected = null; // reference to the selected curve
 
 [SerializeField]
 private int point_selected_index = 0; // index of the selected point in the curve
 
 private Vector3 ShowPoint(Curve curve, int point_index)
 {
     Vector3 point = curve.GetControlPoint(point_index); // gets the point in world space
     
     Handles.color = Color.white;
     if (Handles.Button(point, Quaternion.identity, 0.04f, 0.06f, Handles.DotCap))
     {
         // point has been clicked in the Scene view: select it.
         //Undo.RecordObject(this, "Point Change"); // doesn't work! ('this' is the editor class)
         this.curve_selected = curve;
         this.point_selected_index = point_index;
         Repaint();
     }
     
     return point;
 }

My editor already supports Undo for changes to the path (i.e. the Curve script); since the reference to the selected point in the path is in my editor class (the 'curve_selected' and 'point_selected_index' fields), I've been unable to record the change to the editor.

I would be able to add the Undo step if I moved the reference to my path script, but it doesn't seem the right place to me: the point selection logic is only relevant in the Editor, not during gameplay.