Function exit_class 

pub fn exit_class(code: &str) -> ExitClass

The exit class of code, or ExitClass::Unregistered when the registry does not know it.

Codes reach this from outside the registry — assay_core::validate forwards policy-engine verdict codes verbatim, and an unexpected trace error is reported as a bare E_UNKNOWN. Those are unregistered rather than misclassified, and the caller decides what that means.