Testnet DX feedback from building a lending dApp on Arc: USYC stub, oracle gap, gasless/EVM docs #107

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1. ZhiyuCircle

   added

   need-triage

   on Jun 2, 2026
2. osr21 commented on Jun 19, 2026

   

   osr21

   on Jun 19, 2026

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   Adding: exact EIP-712 domain values for USDC and EURC + memo precompile for labeling

   Great writeup. Adding two more concrete findings from Arc Swap that are directly relevant to point 3 (EIP-2612/EIP-3009 domain documentation):

   Exact EIP-712 domain for USDC and EURC on Arc Testnet

   Both USDC and EURC use version "2", which is not obvious and not documented. Using version "1" produces an invalid signature that reverts without a helpful error:

   // USDC — Arc Testnet
   const usdcDomain = {
     name: "USDC",
     version: "2",           // ← must be "2", not "1"
     chainId: 5042002n,
     verifyingContract: "0x3600000000000000000000000000000000000000",
   };
   
   // EURC — Arc Testnet
   const eurcDomain = {
     name: "EURC",
     version: "2",           // ← same — must be "2"
     chainId: 5042002n,
     verifyingContract: "0x89B50855Aa3bE2F677cD6303Cec089B5F319D72a",
   };

   You can verify programmatically via eip712Domain() (ERC-5267) on either contract — but having it documented saves builders from having to discover it empirically.

   Memo precompile for labeling on-chain operations (Arc v0.7.2)

   Relevant to any DApp wanting audit trails for lending actions (supply, borrow, repay, liquidate): Arc v0.7.2 activated a memo precompile at 0x5294E9927c3306DcBaDb03fe70b92e01cCede505 (confirmed live on testnet as of 2026-06-18). It accepts arbitrary UTF-8 bytes and writes them as an on-chain label attached to the transaction:

   // Fire-and-forget after every lending action — non-fatal if it fails
   walletClient.writeContract({
     address: "0x5294E9927c3306DcBaDb03fe70b92e01cCede505",
     abi: [{ name: "memo", type: "function", stateMutability: "nonpayable",
             inputs: [{ name: "data", type: "bytes" }], outputs: [] }],
     functionName: "memo",
     args: [toHex(Buffer.from(`ArcLend: supply ${amount} USDC @ block ${blockNumber}`, "utf8"))],
     gas: 100_000n,
   }).catch(() => {}); // non-fatal

   This makes liquidation events and supply/borrow actions human-readable on Arcscan without needing a custom indexer.
3. osr21 commented on Jul 2, 2026

   

   osr21

   on Jul 2, 2026

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   Oracle gap update — Stork live on Arc Testnet; adapter errors + evmVersion follow-up

   Circling back on items #2 and #4 from the original issue with findings from deploying the oracle infrastructure for ArcLend.

   ---

   Item #2: Stork is now live on Arc Testnet (but feed data not yet published)

   As of July 1 2026 (Chainlink Scale announcement), five oracle providers are now listed in the Arc docs: Chainlink, Chronicle, Pyth, RedStone, and Stork.

   Stork Verifier on Arc Testnet: 0xacC0a0cF13571d30B4b8637996F5D6D774d4fd62
   Interface: getTemporalNumericValueUnsafeV1(bytes32 feedId) → {uint64 timestampNs, int192 quantizedValue} (1e18-scaled USD price)

   We deployed a full adapter stack for ArcLend:

   Contract	Address	Purpose
   StorkChainlinkAdapter (USDC/USD)	0x704CBB1d1ff44Ec569b402ee08D2e14a7bC43bc2	Wraps Stork → AggregatorV3Interface
   StorkChainlinkAdapter (EURC/USD)	0xD1ba670BBA1E445eA8633489935294d939291957	Same for EURC
   ChainlinkAdapter	0x30c4C225F3441151d85F0410EdF7848F3ec6A3A1	Aggregates feeds → IPriceOracle for the pool
   LiquidationUpkeep	0x046c32ee269550D4d0B7f649D2790124Ff99F1aa	Chainlink ACE-compatible liquidation automation

   Errors found during integration:

   1. All Stork feed IDs revert — getTemporalNumericValueUnsafeV1 returns execution reverted for every encoding tried: keccak256("USDCUSD"), keccak256("USDC/USD"), ASCII right-padded bytes32, keccak256("BTCUSD"), keccak256("ETHUSD"). The verifier IS deployed (342-byte proxy) but publishers have not yet pushed data to Arc Testnet — timing issue, not a feed ID encoding bug.

   2. Feed ID encoding is keccak256 — bytes32 id = keccak256(abi.encodePacked("USDCUSD")), not ASCII right-padded. Worth documenting officially alongside the verifier address.

   3. Hot-swap works without protocol redeploy — LendingPool.setOracle(adapter) activates new price feeds atomically. No migration needed when Stork goes live.

   Current state: Protocol runs on MockPriceOracle with admin-set prices. The adapters are deployed and wired — a single setOracle() call activates live prices once publishers push data.

   ---

   Item #4: evmVersion: "cancun" confirmed (note on PR #151)

   PR #151 documents --evm-version paris for Foundry. That's correct for contracts without OZ 5.1+. However OZ ≥ 5.1 requires cancun — EIP712 and ECDSA emit the mcopy opcode (EIP-5656), absent in shanghai/paris. Solc 0.8.24 defaults to shanghai and fails silently.

   Any contract inheriting EIP712, ECDSA, or ERC4626 from OZ ≥ 5.1 (gasless routers, permit vaults, etc.):

   • Hardhat: evmVersion: "cancun" in hardhat.config.js
   • Foundry: --evm-version cancun in forge commands

   Arc Testnet executes Cancun opcodes correctly.
4. ZhiyuCircle

   added

   documentationImprovements or additions to documentationImprovements or additions to documentation

   ecosystemComponent: ecosystemComponent: ecosystem

   on Jul 23, 2026