I spoke with someone at the IRS who checked and said they never received my return. I've re-submitted it, three months late.
So, big thanks to Intuit for that April 9 email telling me the IRS had received my return!
Thanks also to the drones and/or bots who took time to copy and paste irrelevant boilerplate non-answers to my original question. It was no substitute for an actual customer service process, but since I'm never going to use Intuit or TurboTax again there's no point in worrying about it. Lesson learned!
