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.
Registry calls (x:Account, x:Domain and the rest of the x: types) were
always sent under urn:stalwart:jmap. inbuxa advertises the same registry
as urn:inbuxa:jmap:registry, so the capability now comes from the connected
server: Session::registry_urn() picks urn:inbuxa:jmap:registry when the
session advertises it, else urn:stalwart:jmap, so Stalwart servers still
work as a source. A request carrying an x: call against a server that
advertises neither fails with a MissingCapability error naming both,
treated like any other connection-level failure, instead of sending a
capability the server never offered.