Function mtp_refeed_shift 

pub fn mtp_refeed_shift() -> isize

2026-09-25: METRALE_MTP_REFEED_SHIFT: an offset added to every re-fed ring label, clamped to [-4, 4]; 0 (unset or unparseable) is the derived mapping. It exists to test that mapping: a run at +1 or -1 is compared with 0 by acceptance.