Function mtp_refeed_shift 

pub fn mtp_refeed_shift() -> isize

Deliberate off-by-N perturbation of the re-feed’s ring LABEL (ATLAS_MTP_REFEED_SHIFT, default 0 = the derived mapping).

This is a MAPPING-VALIDATION hatch, not a tuning knob. The label convention (label n holds hidden_{n-1}, so pair key k reads label k+1) cannot be falsified by any self-consistent checksum: the only independently-exercised consumer of the verify hidden buffer is save_hidden_for_mtp(num_accepted), which reads the SAME buffer at the SAME offset formula as the re-feed’s t = num_accepted write, and the sequence positions strictly between two propose positions are never observed by any other code path. So the mapping is tested BEHAVIOURALLY instead: shift every re-fed label by ±1 and measure acceptance. A uniform shift keeps the ring contiguous (delivery is unchanged) but hands pair key k the hidden of position k ± 1. If the derived mapping is right, shift = 0 must be the maximum of the three arms; if +1 or −1 wins, that arm IS the correct mapping. If all three are indistinguishable, the drafter’s KV-history rows do not carry enough signal for this lever to work at all — which is itself the answer.