I don't get your problem. :) It's not worth copying large codebases because an LLM can't handle it; the context window is too small. For things like that, it's better to use Claude Code, Codex, Antigravity (I use Codex) or other extensions connected to development environments (like Kilo Code, for example).

If you only want to develop small steps or individual small functions at a time, then it's worth copying only that code snippet and properly explaining what you want.