Function mtp_refeed_debug 

pub fn mtp_refeed_debug() -> bool

ATLAS_MTP_REFEED_DEBUG=1: fingerprint every hidden that enters and leaves the catch-up ring, so the pair-key -> hidden mapping can be read off the serve log instead of argued about. Costs a D2H of one hidden row (h * 2 bytes) plus a stream sync per event — NEVER enable it in a timed leg. See mtp_refeed_shift for why the fingerprints alone cannot falsify the mapping, and what they DO establish (the ring’s slot arithmetic and the pair-key bookkeeping round-trip).