> 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.