Another tiny step in the right direction: I'm seeing requests to my code come through with the Role AccessibleText, but only when I have the screen reader turned on. And this is being requested of the items in the tree, not the tree itself.

This is good news. The punchline is that it was not returning the correct value for AccessibleText previously and now it is.

The screen reader still isn't reading off the entries of the selected item, but I know I fixed one problem with the code.