I wrote a simple implementation to do this in ChatGPT via local plugin [0]. Obviously it doesn’t hit the “fully private” requirement but I imagine it would be relatively straightforward to integrate into a local LLM. The question is whether a local LLM would be as good at grabbing enough context and nuance from the project to answer meaningfully as GPT-4 is able to do with plugins.

[0] https://github.com/samrawal/chatgpt-localfiles