`provekit/backend/goldilocks/src/field`: GoldilocksField` (base-committed) can subsume this once it binds

[recmo]

On 2026-07-13 in 61744fa “Merge pull request #470 from worldfnd/feat/base-field-witness-commit”:

GoldilocksField(base-committed) can subsume this once it binds challenges directly — needs (1) a base transcript codec so base challenges can be drawn from Fiat-Shamir (theFieldHash Sourcebyte bridge), and (2) k-fold repetition, since a singleField64` challenge is only ~64-bit sound.

/// `Field64_3` extension.
///
/// Serves challenge-bearing circuits, where an extension challenge cannot be
/// stored in a base-field (`Field64`) witness slot; committing in the extension
/// keeps 128-bit soundness.
// TODO: `GoldilocksField` (base-committed) can subsume this once it binds
// challenges directly — needs (1) a base transcript codec so base challenges can
// be drawn from Fiat-Shamir (the `FieldHash` `Source` byte bridge), and (2)
// k-fold repetition, since a single `Field64` challenge is only ~64-bit sound.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct GoldilocksEfField;

impl ProofField for GoldilocksEfField {
    type Embedding = Identity<Field64_3>;

From provekit/backend/goldilocks/src/field.rs:33