AT Transparency Logs: accountable record collections

atproto lets us delete and modify records, which for social media is definitely good. But there are cases where you'd like to instead ensure everyone is seeing the same append-only set of records, forever: software releases, for example. That's what tlogs are for! tlogs are the technology that makes Certificate Transparency, the Go Checksum Database, Sigstore and Sigsum possible. atproto gives us everything we need to make a tlog: canonically hashed records and a global mechanism to access them. We can even make the tlog configuration in-protocol, letting multiple tlog operators work like any other AppView.