[Open Source] FCE — C++ in-memory code graph engine for RAG (10 languages, 10M symbols, ~50ns query)

Hi all, wanted to share an open-source project I've been working on. I’m a C++/Unreal Engine developer. Recently, I started building my own AI learning assistant to help me deep-dive into complex codebases. However, I quickly hit a wall: existing RAG pipelines were painfully slow for massive projects. I noticed most tools rely on Python + external DBs (SQLite, LanceDB, etc.). Every time I queried a symbol, I was paying a heavy tax for disk I/O and serialization overhead. So, I decided to build the engine I needed from scratch: FCE (Flat Code Engine