Finding a vulnerability by looking at the diff that fixed it is very different than just looking through the code.
"How likely is this diff a patch for an existing vulnerability?"
Seems to be an easier question to answer than
"Are there any new vulnerabilities introduced by this diff?"
In other words identifying that a patch is for a vulnerability is typically easier than finding the vulnerability in the first place.
Scanning every commit doesnt automatically make everyone in the world patch immediately, vulns can still be found from commits and diffs and used against those who havent patched yet.
Do you assume ai will just stop at a certain level? Or is it possible that it will keep increasing in intelligence? If the latter, then isnt it possible that even if you are auto checking all your commits, next week a more advanced ai model might be released that finds vulns in your old commits, even though they were checked by (an inferior) ai?
Blinding saying that auto checking commits will make you safe from ai based attacks and vulnerability free is just madness.