Don's 2025 reference implementation of RR differs in some details from the 2023 specification jointly authored by Joseph and Don. Also the GitLab README file about RR describes the reference implementation, but its most recent update is January 2025: https://gitlab.com/xalgorithms-alliance/rule-networking-software/prod-impl/-/blob/master/README.md

Andrew, I think the best way two begin is for you to take a look at Don's current Rust implementation and related it to his README, and also compare this with the RR sequence diagram:
https://gitlab.com/xalgorithms-alliance/rule-networking-software/prod-impl/-/tree/master

https://gitlab.com/xalgorithms-alliance/data-with-direction-specification/dwds-documents/-/tree/master/rr-sequence-diagram
https://xalgorithms.org/white-paper

Along the way, it will be optimal if you use this Redmine worksite to document whatever gap or error you come across, or even just anything you find is a headscratcher needing better explanation. You can assign such issues to me or to Don, depending whose topic it seems to be.