[s6pa1rta3n-lab]

Summary

Implements ZK-011 (Wave 1): Add explicit domain separation tags to note commitments.

Closes #255

Cryptographic Specification

• Domain Tag: "commitment_domain_v1"
• ASCII Hex (20 bytes): 636f6d6d69746d656e745f646f6d61696e5f7631
• Field Representation (left-padded to 32 bytes):
  0x000000000000000000000000636f6d6d69746d656e745f646f6d61696e5f7631
• Hash Function: Poseidon2 4-element sponge hash
  poseidon2_hash_4(COMMITMENT_DOMAIN_SEP, nullifier, secret, pool_id)

Scope of Changes

• Noir Circuits (circuits/lib/src/hash/commitment.nr):
  • Defined COMMITMENT_DOMAIN_SEP constant.
  • Implemented 4-element sponge hashing with the domain separator prepended.
  • Added unit tests for domain separator non-zero validation, deterministic hashing, and cross-domain isolation against nullifiers, Merkle pairs, and legacy undomain-separated hashes.
• Commitment Circuit (circuits/commitment/src/main.nr):
  • Added negative regression tests rejecting legacy undomain-separated hashes and nullifier hashes.
• Vectors & Fixtures:
  • Updated scripts/generate_commitment_vectors.mjs to prepend COMMITMENT_DOMAIN_SEP_HEX.
  • Regenerated test vectors and fixtures across artifacts/zk/commitment_vectors.json, artifacts/zk/v1/commitment_vectors.json, and circuits/commitment/src/fixtures.nr.
  • Baseline constraints updated (withdraw: 1596, commitment: 6).
• TypeScript SDK (sdk/src/):
  • Defined and exported COMMITMENT_DOMAIN_SEP_HEX and COMMITMENT_DOMAIN_SEP in zk_constants.ts and index.ts.
  • Updated computeNoteCommitmentField in poseidon.ts to prepend the domain separator and validate canonical BN254 field inputs.
  • Added full test suite in sdk/test/commitment_domain.test.ts verifying format, determinism, cross-domain isolation, and test vector conformance.

Validation

• node scripts/zk_ticket_check.mjs --issue-key ZK-011 --run -> All checks passed
• nargo check --workspace -> Clean compilation
• nargo test --workspace -> All 131 Noir tests passed
• node scripts/check_circuit_constraints.mjs -> ACIR opcode baselines verified
• npm run build in sdk -> Clean build (exit code 0)
• SDK Jest tests (commitment_domain.test.ts, commitment_corpus.test.ts, note_commitment_denomination.test.ts) -> 49/49 tests passed

Payout Routing

• EVM (Base/Arbitrum/Polygon/ETH): 0xF46C9F6d70C50BF81ef3588AB523a90a594a2F89
• Stellar: GCL6OXAMLD75BMTINA6EMRUDWK5THQUSHMYNLSNBCJAPZJHNYJTUNIBC