I can prove all contributions to stagex are by humans because we all belong to a 25 year old web of trust with 5444 endorser keys including most redhat, debian, ubuntu, and fedora maintainers, with all of our own maintainer keys in smartcards we tap to sign every review and commit, and we do background checks on every new maintainer.
I am completely serious. We have always had a working proof of human system called Web of Trust and while everyone loves to hate on PGP (in spite of it using modern ECC crypto these days) it is the only widely deployed spec that solves this problem.
https://kron.fi/en/posts/stagex-web-of-trust/