Ask Cursor to write usage and mocking documentation for the most important injected dependencies, then include that documentation in your context. I’ve got a large tree of such documentation in my docs folder specifically for guiding AI. Cursor’s Notebook feature can bundle together contexts.

I use Cursor to work on a Rust Qt app that uses the main branch of cxx-qt so it’s definitely not in the training data, but Claude figures out how to write correct Rust code based on the included documentation no problem, including the dependency injection I do through QmlEngine.