Some ideas after early work has landed to see how this ought to scale better:

• Make an isolated messages.cpp/h file
• Refactor responses so that they are easy to test JSON input/output (without "sending" anything via adapter sockets)
• Add unit tests
• Use a BSONObjBuilder to avoid directly constructing hard-to-maintain json strings
• Namespace everything under "debugger" (mongo::mozjs::Message etc is way to generic)
• Use the Request::toJSON to create specific request instances for better polymorphism: https://github.com/10gen/mongo/pull/48605#discussion_r2854774981