Hi Eric !
Fun challenging question, I did a quick test on an idea and concluding it can be done with some coding, and assuming two other conditions:
User is logged in to WP
The Q2 field is in another page of the form, or different form from the Q1 form.
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But I’m guessing there is some other trick the experts here know that will solve this for you, as time will tell…
If no one else responds with a better answer, and my two requirements are acceptable for your use case, I’ll do some more digging and update this thread with my “hack” solution.
My solution leveraged the user table to cache the input field values recorded for the user’s “next page” event.
But I assume the same entry value is available to a filter function when handling pre-render of the second page of the form - then it would need to be inserted into the default value of the field element.
It would be nice if there was an easier way for your use case. Sorry I can’t be of much help.