jcoffey-dev is traveling from Thursday 1 October through Sunday 4 October. Issues and pull requests are welcome, and will get an answer after that. Thanks for your patience.
senderGroup, senderTenant and recipientGroup conditions now read and write group and tenant ids as JMAP ids ("b", "c"…), like legal hold scopes and the rest of the API, so the console can use its object pickers; plain numbers are still read. Held as numbers for matching. Unit test for both forms and a bad id; mail_rules_tests round-trips a tenant condition over JMAP.