When I turn a geo node into a HDA, it doesn't display the handles when I switch to the Handles Tool. Individual Move, Rotate, Scale tools display fine.
For comparison I created a Pighead HDA (which is a geo HDA as well) but it has those general purpose handles working.

With the Pighead selected, I see that when I press and hold on the Handles Tool, it shows some options there:

But when I do that with my own tool, there's nothing there:

How can I make handles appear?