grpc/grpc-java ? reverse-engineered prompt

Build me a Java gRPC library and framework that lets developers define services in protobuf and generate client and server code that works over HTTP 2.

I want it to support modern Java, plus Android clients too, with a lighter option for protobuf if needed. Include a simple quick start example, a server, a client, and a small test service so I can see how the pieces fit together. The library should make it easy to create typed stubs, connect through channels, and plug in different transports, with sensible defaults for common use cases.

Please also make sure it feels like a real project I can build and run locally, with documentation, tests, and clear setup instructions. If you need to check current docs or best practices online, go ahead and look them up.