Function new_polynomial_with_commitment 

fn new_polynomial_with_commitment<S: PixSpec>(
    secret: PixScalar<S>,
    t: usize,
    rng: impl CryptoRng,
) -> Result<(Vec<DefaultShare<IdentifierPrimeField<PixScalar<S>>, IdentifierPrimeField<PixScalar<S>>>>, PixGroup<S>), S::Pseudonym>

Builds a Shamir polynomial of degree t - 1 over secret and commits to its constant term.

Only the constant term is committed to. The higher coefficients still exist — they are what makes the shares hide the secret — but no commitment to them is published, so the Exit cannot (and no longer needs to) check an individual share. See SsaPartCommitment.

This is also why the Entry’s per-cycle cost collapsed: committing to every coefficient was polys × threshold fixed-base multiplications against an untabulated generator, over half a million of them at production dimensions, all inside one blocking task at each cycle boundary.