Using Xcode 10b5, I finally figured out how to find the auto-generated source code for the Intents.intentdefinition file for a custom intent. However, said source is deeply buried inside Xcode folders. Specifically, this is the directory that Xcode points to if you click the right arrow from the inspector:
/Library/Developer/Xcode/DerivedData/MyApp-[...]/Build/Intermediates.noindex/MyApp.build/Debug-iphonesimulator/MyFramework.build/DerivedSources/IntentDefinitionGenerated/Intents/MyIntent.h
So, I've tried a crazy number of syntax variations for the #import on that. Things like:
#import <MyFramework/MyIntent.h>
#import "MyIntent.h"
---many other variations---
Nothing working. I'm about ready to give up and just copy/paste the header into my code. Surely there is a "proper" way to import this auto-generated header as that would be the whole point of auto-generating it?