Challenge 2: Identify What's Generated — Possible Solution
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GENERATED ON THE CLIENT SIDE: a client stub class (e.g.
UserServiceClient) containing a method matching the one rpc definition
— calling it handles connecting to the server, serializing the request
message into Protobuf binary, sending it over HTTP/2, and
deserializing the response back into a usable object automatically.

GENERATED ON THE SERVER SIDE: a base/interface definition wiring up
the routing for that one method — accepting an incoming call, already
deserializing the request message, and expecting a callback/handler to
be registered for that specific method name.

WHAT A DEVELOPER STILL HAS TO WRITE BY HAND: exactly one thing — the
ACTUAL METHOD BODY implementing the real business logic on the server
side (e.g. querying a database, applying validation rules, deciding
what to return). Nothing about serialization, deserialization, request
routing, or the network transport itself needs to be written manually
— protoc's generated code handles all of that; the only genuinely new
code is the logic that decides WHAT the response should actually
contain.