Constant MAX_PREFIX_IN_BRANCHES 

pub const MAX_PREFIX_IN_BRANCHES: usize = 10;

Hard ceiling on the element count of the (at most one) IN prefix pin — the number of prefix branches one ranked / having-range request may fan out into.

Each element is one full secondary walk and one proof branch, each carrying up to limit committed entries plus boundary commitments, so worst-case proof size is MAX_PREFIX_IN_BRANCHES × MAX_RANKED_LIMIT entries (≈100–150 KB at the ceiling). A hard rejection rather than a clamp, for the same reason as the limit: the branch set is bound into the branched proof envelope and re-checked by the verifier.