Function transition 

pub fn transition(from: State, on: Outcome, ctx: &TransitionCtx) -> State

lifecycle state machine The transition table, mirroring conformance/state_machine.yaml row for row. yaml_and_code_agree_row_for_row in the tests parses that file and cross-checks every transition, so a row commented out THERE is a failing test HERE — and an unhandled Outcome variant here is a compile error. Both languages check against the same file so they cannot drift.