"since Touchgram functions inside iMessage, It probably doesn't suffer from chicken-and-egg issues of larynx"

Exactly!

I was originally working on a cross-platform version using a similar game engine (Cocos2D-X in C++, rather than Apple's SpriteKit in Swift). A mentor advised me in 2018 to try to get it working either inside Facebook Messenger or Apple iMessage. The only platform with a rich enough API is iMessage. Apple take care of the notification side, because Touchgrams arrive like any other message. They also provide streamlined installation - if you don't have Touchgram installed and I send you one, Aple put the install link right there in the message bubble.

One of the things that informed my attitude to building "on top" of platforms, especially if you're trying to add extended capabilities, was https://www.gamedeveloper.com/business/a-story-of-gamelayers-inc-

which was also turned into a book https://www.amazon.com/Story-GameLayers-inside-internet-startup-ebook/dp/B005PDH410