How does one even copy their entire codebase? Are you saying you attach all the files? Or you use some script to copy all the text to your clipboard? Or something else?
I then structure my prompts around like so:
<project_code> ``` ``` </project_code>
<heroku_errors> " " </heroku_errors>
<task> " " </task>
I've been using this with Google Ai studio and it's worked phenomenally. 1 million tokens is A LOT of code, so I'd imagine this would work for lots n lots of project type programs.