We define our API into the Rust via protobufs[0] and some codegen.
The wrapper around these is very lean, FFI-based[1], it's abstracted to a library so Android devs never need to know there's rust/codegen involved.
We then define a light Kotlin-based wrapper around the protobuf-generated API[2]. This is a candidate to move to Kotlin multiplatform in the near future (mostly for test speed improvements).