Add Poseidon2 Goldilocks inline

[jay-clarke]

Summary

Adds a new jolt-inlines-poseidon2-goldilocks crate implementing the canonical 8-wide Poseidon2 permutation over the Goldilocks field as a Jolt inline.

Spec: specs/1570-poseidon2-goldilocks-inline.md

The inline exposes a small guest API:

• poseidon2_permute(&mut [u64; 8])
• RISC-V guest builds emit one custom inline instruction.
• Host builds use the standalone reference implementation.

The host side registers the inline with the Jolt tracer/prover through the existing register_inlines! path and adds a Poseidon2Goldilocks entry to InlineExtension.

Why

Poseidon2 over Goldilocks is commonly used inside proof systems for Merkle trees, commitments, and other ZK-native hashing paths. Running that permutation as ordinary guest Rust creates a much larger trace than an inline expansion. This adds a dedicated inline for the Plonky3-compatible Poseidon2-Goldilocks-8 instance.

Validation

• cargo check -p jolt-inlines-poseidon2-goldilocks
• cargo check -p jolt-inlines-poseidon2-goldilocks --features host
• cargo test -p jolt-inlines-poseidon2-goldilocks --features host
• cargo test -p jolt-riscv

The new tests cover:

• Goldilocks multiplication reduction against u128 arithmetic.
• Permutation parity with Plonky3's default Poseidon2Goldilocks<8>.
• Permutation parity with an explicitly constructed generic Plonky3 Poseidon2 path.
• Round-constant and internal-diagonal parity with Plonky3 constants.
• Deterministic sequence emission.
• Inline emulator execution against the host reference for fixed and randomized states.

Notes

The crate intentionally covers only the 8-wide Goldilocks instance. Other widths or fields can be added separately if they are useful.

[github-actions]

Warning

This PR has more than 500 changed lines and does not include a spec.

Large features and architectural changes benefit from a spec-driven workflow.
See CONTRIBUTING.md for details on how to create a spec.

If this PR is a bug fix, refactor, or doesn't warrant a spec, feel free to ignore this message.

[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	cargo/​p3-field@​0.5.3
	cargo/​p3-goldilocks@​0.5.3
	cargo/​p3-symmetric@​0.5.3
	cargo/​rand@​0.10.1
	cargo/​rand_core@​0.10.1
	cargo/​p3-poseidon2@​0.5.3

View full report