> The signing process doesn't recursively traverse the bytes of the commit to pull them into GPG, like you would expect.

No I wouldn't expect this. If by recursive you mean traversing the entirety of git history, that would be prohibitively expensive performance-wise (imagine rehashing the entire multi-gigabyte history of the Linux kernel every time to sign and verify a commit) and destroy git functionality such as shallow clones and blob-less clones.

If you by recursive you are only referring to the current working directory, as I lay out here https://news.ycombinator.com/item?id=49930048 it doesn't work. Indeed, without attestation of parent commits, a malicious attacker can actively frame any pre-existing vulnerability as someone else's handiwork by simply inserting a new commit that purports to be the parent of another commit that does not contain the vulnerability, which then makes the original commit look like the source of the vulnerability.

"I didn't introduce the vulnerability, he did! Look I can even prove it with my signed commit!"