refactor(jolt-field): Land Solinas field from akita-field in jolt-field

[Acentelles]

Summary

This PR does two things toward a single audited field implementation:

1. Lands the Solinas field stack from akita-field in jolt-field: the 32-, 64-, and 128-bit prime fields, the FpExt2/FpExt4/FpExt8 extension towers, NEON/AVX2/AVX-512 packed backends, unreduced accumulator paths, tests, fuzz coverage, and benchmarks. One implementation, one Rust type identity: Akita consumes jolt-field directly, with no dependency back except a temporary feature-gated bootstrap adapter (see Changes).
2. Consolidates the resulting trait surface per specs/consolidate-field-traits.md. The import brought the crate to 46 public traits across 82 files, with 15 one-trait-per-file micro-files at the root. The consolidation reduces this to 22 public traits in four root trait modules (algebra.rs, canonical.rs, accumulator.rs, field.rs) plus the feature-gated backend modules, switches Solinas wire serialization to serde + bincode, and adopts the explicit arkworks/bn254.rs per-type layout. This is a refactor of trait boundaries, not arithmetic.

Akita source	jolt-field destination (post-consolidation)
crates/akita-field/src/traits.rs	src/algebra.rs, src/canonical.rs, src/accumulator.rs, src/field.rs, src/solinas_traits.rs
crates/akita-field/src/prime/	src/prime/
crates/akita-field/src/ext/	src/ext/
crates/akita-field/src/packed/	src/packed/
crates/akita-field/src/unreduced/	src/unreduced/
crates/akita-field/src/fft.rs	Not imported in final form: removed in the consolidation (zero consumers in this workspace)
crates/akita-field/src/parallel.rs	src/parallel.rs
crates/akita-pcs/benches/field_arith.rs and field_arith/	benches/solinas_field_arith.rs and benches/solinas_field_arith/
Akita field arithmetic fuzz coverage	fuzz/fuzz_targets/solinas_field_arith.rs

Changes

Solinas import

• Add solinas and parallel features to jolt-field while retaining the existing BN254 default.
• Import the complete Akita Solinas implementation (prime fields, extension towers, packed backends, unreduced/wide accumulators, parallel helpers).
• Keep Akita proof and field serialization concerns out of the shared crate: no AkitaSerialize, no Akita validation policy or protocol framing. Add FieldError for backend-independent input and shape failures; Akita converts it at its repository boundary.
• Keep src/akita.rs and the akita feature as a temporary, feature-gated bootstrap so the adapter stays buildable until the Akita cutover; both are removed in the final migration PR. akita-config/akita-field are optional dependencies behind that feature only.
• Update jolt-akita to the current Akita runtime ring dimension, opening claim, setup, commitment, and batching APIs.
• Move the Solinas Criterion benchmark into jolt-field, add a Solinas arithmetic fuzz target, and record file-level source provenance.
• Add a CI feature matrix for backend-free, BN254-only, Solinas-only, and combined builds, plus scripts/check-shared-field-identity.sh.

Trait consolidation (spec phases 1–5)

• Phase 1 — delete dead surface. Remove traits with no generic consumer in this workspace or Akita: both signed-accumulator families (SignedScalarAccumulator/WithSmallScalarAccumulator, SignedProductAccumulator/WithSignedProductAccumulator), ExtensionCoeff, ScaleI32, BalancedDigitLookup (now a free function), and SmoothFftField together with the 1,100-line fft.rs.
• Phase 2 — one accumulator trait. Merge AdditiveAccumulator + RingAccumulator into a single Accumulator.
• Phase 3 — root traits and wire format. FieldCore absorbs Invertible and RandomSampling; FromPrimitiveInt absorbs MulPow2 and MulPrimitiveInt; a new CanonicalRepr replaces the seven byte/introspection/challenge traits (CanonicalBytes, ReducingBytes, FixedByteSize, FixedBytes<N>, CanonicalU64, CanonicalBitLength, TranscriptChallenge). Solinas wire serialization becomes serde + bincode, matching the existing serde implementations on arkworks/bn254.rs; Fiat-Shamir transcript bytes keep the explicit canonical little-endian encoding and never go through bincode.
• Phase 4 — extension cluster. ExtField<F> absorbs LiftBase, MulBase, and FrobeniusExtField; FpExt4MulBackend + FpExt8MulBackend merge into one ExtMulBackend; PackedField absorbs PackedValue; the degree-4 mul/square schedule now exists in exactly one place, shared between scalar and packed backends.
• Phase 5 — per-type layout. Everything a concrete type implements is visible in that type's file, as an explicit impl or a one-line shared-macro invocation; the three native_algebra.rs side-files are replaced by one shared macro module.

BN254 is untouched by the consolidation: Fr's serde and byte encodings, the Fiat-Shamir stream, and static dispatch are unchanged (spec invariants 1 and 6). MontgomeryConstants is retained pending confirmation that no out-of-tree GPU/Metal consumer exists (spec OPEN item; 22 traits become 21 when resolved).

Testing

• muldiv e2e passes in --features host and --features host,zk after the consolidation.
• jolt-field feature matrix passes: backend-free (--no-default-features), BN254-only, Solinas-only, combined, and Solinas-plus-parallel.
• mersenne61_compat (in jolt-sumcheck) compiles and passes against jolt-field --no-default-features with bounds updated to the merged traits: the slim hierarchy remains implementable without arkworks.
• New bincode round-trip tests for Fp32/Fp64/Fp128/FpExt2/FpExt4/FpExt8; serialized-size tests assert each element encodes to exactly NUM_BYTES bytes and a Vec of $n$ elements to $n \cdot \texttt{NUM BYTES}$ plus one length prefix.
• A compile test verifies the merged CanonicalRepr challenge derivation matches the previous TranscriptChallenge behavior on Fr (identical bytes in, identical element out).
• The solinas_field_arith fuzz target and both Criterion benches build; bench results before/after the consolidation are within noise.
• scripts/check-shared-field-identity.sh reports one jolt-field identity and no akita-field in the integrated dependency graph.
• Byte-for-byte comparison of a standard-mode muldiv proof against a main-built proof: identical in all 63,371 bytes, proving is deterministic run-to-run, and the main-built verifier accepts the branch-built proof. (Reproduction note: cfg(test) builds randomize the Dory URS per process via DoryGlobals::configure_test_cache_root, so cross-process comparison requires pinning both builds to a shared URS cache.)

Security Considerations

This change touches security-sensitive field arithmetic used by the PCS and therefore affects the trusted audit surface for prover and verifier correctness. The intended arithmetic change is zero across both stages: moduli, canonical representations, extension bases, reduction algorithms, and packed kernel behavior are preserved, and architecture-specific arithmetic kernels (NEON, AVX2, AVX-512) are moved without semantic modification.

For the import stage, 22 of the imported files are byte-for-byte copies of their Akita sources and 38 are adapted imports; the main semantic adaptations are removal of Akita serialization bounds and replacement of protocol-level AkitaError with the narrower FieldError. The consolidation stage then rewrites trait boundaries only: merges are compile-time renames, #[inline] discipline is carried over onto both trait methods and impls, and all dispatch remains static. The net effect is a smaller audit surface: 46 public traits become 22, and the crate root drops from 15 trait micro-files to 4 trait modules.

Breaking Changes

• Removes akita-field from Jolt's dependency graph (jolt-field keeps optional akita-* dependencies behind the temporary akita bootstrap feature only).
• Deletes or merges 24 public traits; downstream code generic over the old names (Invertible, RandomSampling, CanonicalBytes, TranscriptChallenge, LiftBase, MulBase, FrobeniusExtField, AdditiveAccumulator, PackedValue, ...) must rebind to the survivors (FieldCore, CanonicalRepr, ExtField, Accumulator, PackedField, ...). Akita adapts at its next pin bump.
• Removes fft.rs and SmoothFftField from jolt-field.
• Solinas types' wire format is now serde + bincode (BN254/Fr encodings unchanged).

[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
	p3-baby-bear@​0.5.3
	p3-mersenne-31@​0.5.3

View full report

[Acentelles]

Once LayerZero-Labs/akita#307 is merged, we can remove the temporary akita-field compatibility dependency from jolt-field and change jolt-akita from the temporary jolt-field/akita feature to jolt-field/solinas.