What is current state of the art workflow when working with legacy code across multiple languages?

This would be a 100 kLOC legacy project written in C++, Python, and jQuery era Javascript circa 2010. Original devs have long left. I would rather avoid C++ as much as possible.

I've been Github Copilot (in VS Code) user since June of 2021 and still use it heavily, but the "more powerful intellisence" approach is limiting me on legacy projects.

Presumably I need to provide more context on larger projects.

I can get pretty far with just ChatGPT plus and feeding bits and pieces of project. However that seems like using the wrong tool.

Codex seems better for building things but not sure about grokking existing things.

Would Cursor be more suitable for just dumping the whole project (all languages) basically 4 different sub projects and then selectively activating what to include in queries?