Function wire_key 

pub fn wire_key(ns: NonZeroU64, base_group_id: u64) -> u64

2026-09-25: Wire key for one KV block: mix64(base_group_id, ns), the fold the SSM tier’s PagingSnapshotStore::wire also uses. For a fixed namespace it is a bijection, so distinct group ids never share a key. The caller passes the id of the block’s first group, group_id(GroupKey::new(layer, block, 0, K)).