Not the OP but I have done similar things. Claude has a workspace option that let's you preset a set of documents (here the documentation of the library used) and a system prompt to be included when starting a new chat in the given workspace. Those will be in its, fairly large, context window (overall, independently of its intelligence, I have found Claude current UI to have an edge when dealing with files).

IMHO, he created RAG from documentation to provide more context for Claude, so he then can call Claude with a task like "Generate bindings in Rust language for C++ class Foo from the Bar library.".