Function machine_fields 

pub fn machine_fields(m: &MachineFacts) -> CapacityResponse

The wire’s box fields out of MachineFacts — and nothing else set, so a caller builds a response as CapacityResponse { ..., ..machine_fields(&m) } and both arms of answer fill these the same way (one implementation).

Absent, never zero. An Err fact leaves its fields None and puts the reason in machine_reason; machine_reason is never empty, because a caller that renders only the strings must still learn what was measured.