I didn't look at the implementation but sounds similar to something I two years ago recursively summarize the documentation based on structure (domain/page/section) and then ask the model to walk the hierarchy based on summaries.

My motivation back then I had 8k context length to work with so I had to be very conservative about what I include. I still used vectors to narrow down the entry points and then use LLM to drill down or pick the most relevant ones and the search threads were separate, would summarize the response based on the tree path they took and then main thread would combine it.