I would like to create a custom shortcut action for my countdown timer app that returns a variable containing the countdown time remaining. Returning parameters from custom shortcut actions is a new feature of iOS 13, but I've had no success in getting it working.
What I've Tried
I've defined my Intent and created an intents extension in Xcode 11 using the normal procedure. I have successfully donated actions to Siri/Shortcuts and gotten them to run properly both by interacting with Siri and by launching them from the Shortcuts app under iOS 13.1. Currently one of my actions has Siri report a string describing the time remaining and shows the clock ticking down in an IntentsUI extension. When run from Shortcuts, this action successfully shows the IntentsUI extension ViewController. I would like this action to pass out a parameter with the time remaining that can be used by other Shortcuts actions.
I have created an output parameter and assigned it to the intent response using the steps described at 29:51 of this WWDC 2019 video. This involves modifying the app's intentsdefinition file to define a variable, add it as a property to the intent response, and mark it as an output. Xcode's intents code generation successfully adds the output variable to my intent handling protocol and I am able to access and populate the output variable in my intent handler.
What doesn't work
Unfortunately, when I run the action in Shortcuts, it doesn't seem to provide the output variable. For example, if I add a "text" action below it, there is no line connecting my custom action to the text action. If I try to add a variable to a later action, the variable does not appear on the list of available variables, nor does it appear hanging from my action when I tap the "magic variables" button.
I know that other app devs have successfully implemented Shortcuts actions with output parameters, so I doesn't appear to be an Xcode 11 or iOS 13 bug (of which there are many). Any help/advice would be greatly appreciated.