FOLLOW-UP 4: Dual-protocol V3+V4 monitor and execution

Add Uniswap V3 support alongside the existing V4 monitor. One page, one UI, a "Protocol" field that selects V3, V4, or Both. Keep all existing V4 code unchanged — add V3 alongside it.

1. PROTOCOL SELECTOR (UI):

   • New field at top: "Protocol" with three options: V4 / V3 / Both (default: Both)
   • V4 = existing behavior unchanged
   • V3 = new V3 monitoring + execution
   • Both = scan both, show all pools in one table with a "V3" or "V4" tag column
   • Changing protocol restarts the monitor (same as changing pair)

2. V3 POOL DISCOVERY:

   • V3 Factory: 0x1f7d7550b1b028f7571e69a784071f0205fd2efa
   • V3 fee tiers: 100, 500, 3000, 10000
   • For the selected pair (token0, token1 sorted by BigInt), call factory.getPool(token0, token1, fee) for each of the 4 fees via eth_call
   • Return value 0x000...000 means no pool exists at that fee tier
   • Store the non-zero pool addresses for the pair
   • This is 4 eth_calls per pair change (not per poll)

3. V3 MONITORING (per poll):

   • eth_getLogs with address = [pool1, pool2, pool3, pool4] (array of the non-zero pool addresses), topics = [0xc42079f94a6350d7e6235f29174924f928cc2ac818eb64fed8004e115fbcca67], fromBlock/toBlock = window
   • This is ONE eth_getLogs call for all V3 pools of the pair (same as V4's singleton approach)
   • V3 Swap event: Swap(address indexed sender, address indexed recipient, int256 amount0, int256 amount1, uint160 sqrtPriceX96, uint128 liquidity, int24 tick)
   • Decode tick from the 7th data word (same position as V4)
   • Price = 1.0001^tick (same math as V4)
   • Staleness, window, and error handling: identical to V4 (same functions, same 30s/60s cadence)
   • For each active V3 pool, also call pool.liquidity() via eth_call (one per active pool). If liquidity == 0, mark "EMPTY" and exclude from spreads.

4. V3 DISPLAY:

   • Same pools table as V4, with an added "Protocol" column showing "V3" or "V4"
   • V3 fee display: 100 = "0.01%", 500 = "0.05%", 3000 = "0.30%", 10000 = "1.00%"
   • Spread table: identical logic. Pool A = lower price (buy), Pool B = higher price (sell). Works across protocols too (a V3 pool can be Pool A and a V4 pool can be Pool B in the same spread)
   • In "Both" mode, the spread table shows all pairwise combinations across V3 and V4 pools

5. V3 QUOTE:

   • For the selected spread's buy pool (V3), call pool.getAmountsIn(amountIn) via eth_call
   • This is a view function on the pool contract: function getAmountsIn(uint256 amountIn) external view returns (uint256 amountOut, uint256[] memory amountAtEachHop)
   • For a single-hop swap, amountAtEachHop[0] is the output
   • No router, no Permit2, no wallet needed. Same as V4's quote being free.
   • If amountOut == 0, show "Warning: no liquidity" and disable send (same as V4)
   • Apply the same 0.5% slippage (applySlippage) to get the bridge amount

6. V3 EXECUTION:

   • V3 SwapRouter02: 0xcaf681a66d020601342297493863e78c959e5cb2
   • Use multiswap for the two-leg arb: function multiswap(bytes calldata path, address recipient, uint256 deadline, uint256 amountIn, uint256 amountOutMinimum) external payable returns (uint256 amountOut)
   • Path format: [tokenIn, feeA, tokenMid, feeB, tokenOut] where each token is a 20-byte address and each fee is a 3-byte big-endian value. Total path length = 5 × 23 = 115 bytes
   • Example: selling USDG on pool A (fee 3000) to get PONS, then selling PONS on pool B (fee 10000) to get USDG: path = abi.encodePacked(USDG, uint24(3000), PONS, uint24(10000), USDG)
   • amountIn = input amount (currency1, e.g. 10000 for 0.01 USDG)
   • amountOutMinimum = quoted output minus slippage (the minimum USDG back)
   • recipient = connected wallet address
   • deadline = now + 20 minutes
   • This is a single transaction (both swaps atomic). If either leg fails, the whole tx reverts.

7. V3 APPROVAL:

   • V3 uses standard ERC20 approve to SwapRouter02 (NOT Permit2)
   • Before first V3 swap: ERC20.approve(0xcaf681a66d020601342297493863e78c959e5cb2, amount) for the input token
   • The page should check existing allowance to SwapRouter02 before requesting approval
   • Add a "APPROVE V3 ROUTER" button (separate from "APPROVE PERMIT2")
   • When Protocol = V4: show Permit2 approve button (existing)
   • When Protocol = V3: show V3 Router approve button
   • When Protocol = Both: show both
   • Approval limit: same 100x test amount as V4

8. V3 vs V4 ROUTING LOGIC:

   • When a spread is selected, check which protocol each pool belongs to:
     • Both V3: use multiswap (single tx, one approval to SwapRouter02)
     • Both V4: use existing buildCalldata (two V4_SWAP commands, Permit2)
     • Mixed (one V3, one V4): use TWO separate transactions:
       • Tx 1: V3 swap on the V3 pool (multiswap single hop, or exactInputSingle)
       • Tx 2: V4 swap on the V4 pool (existing buildCalldata single swap)
     • For mixed: the page shows "2 transactions required" warning and executes sequentially (Tx 1 receipt confirmed before Tx 2)
   • Auto mode in mixed mode: only fires when both legs are the same protocol (to keep it atomic). Mixed spreads are manual-only.

9. KEEP UNCHANGED:

   • All V4 code: encoder, Permit2 flow, V4 quote, V4 execution, buildCalldata, buildAtomicCalldata
   • Pool monitor architecture (30s poll, 60s retry, window, staleness, slot0/extsload)
   • UI layout (add Protocol field, add Protocol column to tables, add V3 approve button)
   • Wallet transfer section
   • Activity log, button locking, 20-min deadline
   • All existing tests continue to pass

10. V3 ADDRESSES: V3 Factory: 0x1f7d7550b1b028f7571e69a784071f0205fd2efa

    V3 SwapRouter02: 0xcaf681a66d020601342297493863e78c959e5cb2

    V4 PoolManager: 0x8366a39CC670B4001A1121B8F6A443A643e40951

    V4 Universal Router: 0x8876789976dEcBfCbBbe364623C63652db8C0904

    Permit2: 0x000000000022D473030F116dDEE9F6B43aC78BA3

    WETH: 0x0Bd7D308f8E1639FAb988df18A8011f41EAcAD73 (18 decimals)

    USDG: 0x5fc5360D0400a0Fd4f2af552ADD042D716F1d168 (6 decimals)

    PONS: 0x39dbed3a2bd333467115de45665cc57f813c4571 (18 decimals)

    RPC: https://rpc.mainnet.chain.robinhood.com

    Chain ID: 4663

11. V3 SWAP EVENT TOPIC: 0xc42079f94a6350d7e6235f29174924f928cc2ac818eb64fed8004e115fbcca67

    (keccak256("Swap(address,address,int256,int256,uint160,uint128,int24)"))

12. TEST PAIRS (for verification): PONS/WETH: should show 2 V3 pools (fee 3000 and fee 10000) with ~0.6% spread

    CASHCAT/WETH: should show 2 V3 pools with ~1.0% spread

    WETH/USDG: should show at least 1 V3 pool (fee 500, $567M 24h vol)

    PONS/USDG: V4 pool (fee 3000/60) already confirmed active

DELIVERABLE: Updated index.html + js/v4-arb-encoder.js (rename to js/arb-encoder.js if you prefer, but keep the same file path for deployment). Same repo.