pub fn sha512_to_grumpkin_scalar(
secret_key: &Fr,
domain_separator: u32,
) -> GrumpkinScalarExpand description
Compute SHA-512 of the concatenated inputs and reduce to a Grumpkin scalar.
This is used for master key derivation where uniform distribution is required (not just collision resistance). The 512-bit hash output ensures negligible bias after modular reduction.
Mirrors TS sha512ToGrumpkinScalar([secretKey, domainSeparator]).