I have written a Siri Intents extension (#1) with a corresponding IntentsUI extension (#2). Both are working.
To debug the Intents extension (#1), I can just cmd-R for the Intents Extension scheme (with the scheme executable set to "Ask On Launch"), it runs and attaches to the debugger, as expected (also answered here).
After the Intents extension (#1) completes, the Intents UI extension (#2) runs and displays, again as expected, but it does NOT attach to the debugger.
I thought maybe I could use the same type of scheme setup for the IntentsUI extension (#2) as with Intents extension (#1), but this fails to launch at all.
I see no way to get the IntentsUI extension (#2) to attach in the debugger and allow stepping through the code.