Solana CT: SDK — confidential mint transaction building + proof-account approach (Sprint 1) #9381

Solana CT: SDK — Sprint 1

Build confidential transfer transaction construction in sdk-coin-sol. Uses the proof-account approach validated on Solana devnet.

Sprint 1 scope (this issue)

1. Confidential mint transaction building (proof-account approach):

   • Record program account for range proof (1000B BatchedRangeProofU128 exceeds 1056B tx size limit)
   • Context state accounts for equality + validity proofs
   • Tx sequence: create-record + write(1-2) + 3 verify + 1 confidentialMint (~5-6 txs per mint)
   • currentSupplyCiphertext = on-chain confidential_supply (identity = 64 zero bytes for fresh mint)

2. ConfigureConfidentialTransferAccount instruction:

   • One-time ATA setup — register ElGamal pubkey + AES key
   • Part of the token account configuration flow

3. Proof-account tx group sequencing (SendQ skeleton):

   • Group the 5-6 txs for a single mint/burn as one logical unit (create-record → write → 3 verify → confidentialMint)
   • SendQ must sequence these together; the indexer parses the group
   • This is the proof-account tx group — the required 5-6 tx sequence per mint/burn. This is NOT the same as transfer-splitting multi-tx (a single confidential transfer split across multiple txs because ZK proofs do not fit one tx) — that is an edge case deferred to the production scope doc.

Key details (validated on devnet)

• confidential_supply on fresh mint = identity ciphertext (64 zero bytes), NOT encryptU64(0)
• Record account is reusable across retries + closeable (closeAccount reclaims rent)
• Context state accounts are one-shot + closeable (closeContextStateProof reclaims rent)
• Proof gen inputs (supply key, auditor pubkey) come from KMS worker — SDK assembles instruction data, does NOT do proof crypto

Acceptance criteria

• Confidential mint tx builder produces valid instruction sequence (create-record → write → verify × 3 → confidentialMint)
• ConfigureConfidentialTransferAccount instruction builder
• Proof-account tx group sequencing skeleton (5-6 txs per mint/burn as one SendQ logical unit)
• Unit tests verify instruction data format matches expected Solana Token-2022 layout