A GPL tool that processes data doesn't virally transfer the license to its output. Copyrighted ffmpeg code isn't incorporated into the video output. The LLM didn't just conjure up equivalent behavior to git without ingesting the code and transforming it as new output. There is no other behavioral description that would reproduce all needed functionality.

> There is no other behavioral description that would reproduce all needed functionality.

Tests often are exactly the information necessary to understand exactly what the output should be. See https://github.com/git/git/blob/master/t/t0000-basic.sh for an example of how detailed these tests are.

It would be reasonable to point an LLM at these and use them with a basic knowledge of git to produce a rust version of git in a non-infringing manner.

If you did this manually it would take a long time.