Function select_spotcheck_indices 

pub fn select_spotcheck_indices(
    nonce: &[u8; 32],
    path: &SubtreePath,
    k: u32,
) -> Vec<u32>

Pick k distinct nonce-derived leaf positions within the selected subtree.

Returned as indices into path.real_leaf_count() (0-based within the subtree). DETERMINISTIC from the nonce.

NOT used for the live round-2 sample. Deriving the byte-challenge sample from the round-1 nonce is unsound: the structural root check binds only (key, bytes_hash) (both public), not nonced_hash, so a responder that knows the nonce at proof-build time could fabricate nonced_hash on every un-sampled leaf and fetch only the predictable sample. The auditor therefore chooses the round-2 sample with fresh CSPRNG randomness after receiving the proof (storage_commitment_audit::random_spotcheck_leaves). This deterministic helper is retained only for tests/observers that need a reproducible selection.