ZK proof replay attack in `ZkAuditVerifier.verifyAuditScoreProof`

[sitianjia]

I was auditing the ZK verification flow and noticed that verifyAuditScoreProof stores the proof hash after verification but never checks whether that hash was already used.

contracts/src/ZkAuditVerifier.sol around lines 144–157:

bytes32 proofHash = keccak256(abi.encodePacked(a[0], a[1], b[0][0], b[0][1], c[0], c[1]));
auditScoreProofs[tokenId][auditId] = AuditScoreProof({
    verified: true,
    score: score,
    verifiedAt: block.timestamp,
    proofHash: proofHash
});

There is no require(!usedProofs[proofHash], "PROOF_REPLAYED") guard. A valid proof for (tokenId=1, auditId=1) can be re-submitted to reset verifiedAt to the current block, making a stale audit appear freshly verified. Worse, if the public inputs are flexible enough, the same proof could be submitted for a different (tokenId, auditId) pair.

The fix is a global mapping(bytes32 => bool) private _usedProofHashes checked and set atomically on each submission.