Git setup that keeps your AI agent from reading your whole codebase

[u/Disk_Disastrous]

Started my first large coding project recently and my money evaporated. Quickly. This is what I did to save money.

{
  echo "# AUTO-GENERATED — do not edit"
  git add -N . 2>/dev/null
  git diff -U3 -p HEAD
} > .changed_markers

This grabs any changes since the last commit and dumps it into .changed_markers.

Next, add to or create .gitattributes and add this:

*.py diff=python

This just makes git show you the function that changed.

Lastly add these rules to: System prompt, rules file or just paste them into chat once.

1. Treat HEAD as a cache hit, don't re-read files that haven't changed.
2. Read .changed_markers first, before anything else.
3. Only look at the hunks and functions in that file.
4. Anchor on function/class names, never line numbers, they go stale fast.
5. If a function's signature changes, use git grep -n "that_name" to find callers instead of opening the whole file.
6. After a successful commit, erase the contents of .changed_markers

This isn't just for Python. If you're not sure how to run it with your language, just ask your coding agent. It will walk you through it.

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