fix: WETH paid to the user before an UNWRAP_WETH reads as WETH (closes #607)

An UNWRAP_WETH made Token Out ETH whenever the output side was WETH,
though the router unwraps only the WETH it holds. decode() now records
where the step that set the output side paid its output, and an
UNWRAP_WETH makes the output ETH only when that step paid WETH to the
router and the router still holds WETH. When that step paid only part
of its WETH to the router, or made a payout the decoder cannot read,
the output reads ETH with no minimum, since the calldata states none
for the ETH. A BALANCE_CHECK_ERC20 pays nobody, so it is never read as
unwrapped. README Display Consistency says the same.

Model: opus-5-5

README.md

@@ -1250,20 +1250,23 @@ Decoding). So a step whose USDT-for-USDC swap action could not be read, with a
 A V4 step with no swap action sets only the sides its `SETTLE`, `SETTLE_ALL`,
 `TAKE` or `TAKE_ALL` names.
 
-An `UNWRAP_WETH` step makes `Token Out` ETH only when the output side is WETH,
-on mainnet or Sepolia, that the router holds when the step runs (Transaction
-Decoding below gives what the router holds), or when no step set the output
-side; a WETH `Min. received` figure then reads in ETH. A later step that sets
-the output side sets it anew. The router unwraps only the WETH it holds, so a
-swap that pays its WETH to the user and then unwraps shows WETH. The decoder
-follows what the router holds by token, not by step: a swap that pays part of
-its WETH to the user and part to the router, and then unwraps, shows ETH with
-the minimum of the step that set the output side. Otherwise `Token Out` and
-`Min. received` keep the output side's own token and figure, whether the swap
-was paid in ETH or in a token: a V2 exact-out swap that buys USDC and then
-unwraps the WETH it did not spend shows USDC. The token permission warning on
-the signature screen has its own amount wording, including `Unknown`; the
-SignApproval section below describes it.
+An `UNWRAP_WETH` step makes `Token Out` ETH only when no step set the output
+side, or when the output side is WETH, on mainnet or Sepolia, that the step that
+set it paid to the router and that the router still holds when the `UNWRAP_WETH`
+runs (Transaction Decoding below gives what the router holds). The router
+unwraps only the WETH it holds, so WETH that step paid to the user, or to anyone
+else, stays WETH: a swap that pays the router WETH, then a swap that pays the
+user WETH, then an unwrap, shows WETH with the second swap's minimum. The
+minimum reads in ETH when that step paid all its WETH to the router. When it
+paid only part of it to the router, as a V4 step does that `TAKE`s some of its
+WETH to the user and the rest to the router, or paid the router WETH beside a
+payout the decoder cannot read, the swap shows ETH with no minimum, since the
+calldata states none for the ETH. A later step that sets the output side sets it
+anew. Otherwise `Token Out` and `Min. received` keep the output side's own token
+and figure, whether the swap was paid in ETH or in a token: a V2 exact-out swap
+that buys USDC and then unwraps the WETH it did not spend shows USDC. The token
+permission warning on the signature screen has its own amount wording, including
+`Unknown`; the SignApproval section below describes it.
 
 The swap's `Deadline` line is the router's deadline as a UTC date and time, e.g.
 `2026-02-27 08:25:51`. A JavaScript date reaches only to 275760-09-13 00:00:00

src/shared/uniswap.js

@@ -1223,6 +1223,11 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
         // which the router holds; cleared whenever the output side is set
         // again.
         let outputUnwrapped = false;
+        // Where the step that set the output side paid its output: the
+        // recipient of a swap step, as written, or of each TAKE and
+        // TAKE_PORTION of it in a V4 step, with null for a payout of that
+        // step this decoder did not read. A BALANCE_CHECK_ERC20 pays nobody.
+        let outputRecipients = [];
         let hasV2OrV3ExactOut = false;
         let swapUndecoded = false;
         let hasSubPlan = false;
@@ -1259,12 +1264,13 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
             if (!present(token) && !present(amount)) return;
             setInput(token, amount);
         };
-        const setOutput = (token, amount) => {
+        const setOutput = (token, amount, recipients) => {
             if (!present(token) && !present(amount)) return;
             outputToken = present(token) ? token : null;
             minOutput = present(amount) ? amount : null;
             outputEstablished = true;
             outputUnwrapped = false;
+            outputRecipients = recipients;
         };
 
         // What the steps take from the sender beyond the amount of the step
@@ -1510,7 +1516,7 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
                         // does. It pays nobody.
                         const minBalance = allowedToFail ? 0n : b.minBalance;
                         if (!(minBalance === 0n && present(minOutput))) {
-                            setOutput(b.token, minBalance);
+                            setOutput(b.token, minBalance, []);
                         }
                     }
                 } else if (command === "V3_SWAP_EXACT_IN") {
@@ -1524,7 +1530,7 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
                         // Always update output: in multi-step swaps (V3 → V4),
                         // the last swap step determines the final output token
                         // and minimum received amount.
-                        setOutput(s.tokenOut, s.amountOutMin);
+                        setOutput(s.tokenOut, s.amountOutMin, [s.recipient]);
                         if (!s.payerIsUser) {
                             spendFromRouter(s.tokenIn, s.amountIn);
                         }
@@ -1544,7 +1550,7 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
                         } else if (s.payerIsUser) {
                             addUserPaid(s.tokenIn, s.amountIn);
                         }
-                        setOutput(s.tokenOut, s.amountOutMin);
+                        setOutput(s.tokenOut, s.amountOutMin, [s.recipient]);
                         if (!s.payerIsUser) {
                             spendFromRouter(s.tokenIn, s.amountIn);
                         }
@@ -1575,7 +1581,7 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
                         } else if (s.payerIsUser) {
                             addUserPaid(s.tokenIn, s.amountInMax);
                         }
-                        setOutput(s.tokenOut, s.amountOut);
+                        setOutput(s.tokenOut, s.amountOut, [s.recipient]);
                         if (!isHop(i, s.tokenOut, s.recipient)) {
                             addPayee(s.recipient, s.tokenOut);
                         }
@@ -1733,6 +1739,14 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
                         (p) => p.currency === v4.tokenIn,
                     );
                     const amountIn = paidIn ? paidIn.amount : v4?.amountIn;
+                    // Where the step pays its output, if it sets the output
+                    // side (see outputRecipients).
+                    const takeRecipients = v4
+                        ? v4.takes
+                              .filter((t) => t.currency === v4.tokenOut)
+                              .map((t) => t.recipient)
+                              .concat(v4.recipientUnread ? [null] : [])
+                        : [];
                     if (v4 && v4.hasSwapAction) {
                         // A step with a swap action always sets the output
                         // side, as the last swap step wins, and sets the
@@ -1750,13 +1764,14 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
                         minOutput = v4.amountOutMin;
                         outputEstablished = true;
                         outputUnwrapped = false;
+                        outputRecipients = takeRecipients;
                     } else if (v4) {
                         // A step with no swap action sets only the sides its
                         // SETTLE, SETTLE_ALL, TAKE or TAKE_ALL names:
                         // setInputOnce() and setOutput() leave alone a side
                         // whose two halves are both unstated.
                         setInputOnce(v4.tokenIn, amountIn);
-                        setOutput(v4.tokenOut, v4.amountOutMin);
+                        setOutput(v4.tokenOut, v4.amountOutMin, takeRecipients);
                     }
                     // Every V4 step, with a swap action or without, takes
                     // from the sender what the user pays it (an amount an
@@ -1778,16 +1793,27 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
                     }
                 } else if (command === "UNWRAP_WETH") {
                     hasUnwrapWeth = true;
-                    // The router unwraps all the WETH it holds, the output
-                    // side's included when it is WETH the router holds, even
-                    // when the recipient cannot be read. WETH a step paid to
-                    // anyone else is not unwrapped.
+                    // The router unwraps all the WETH it holds, even when the
+                    // recipient cannot be read. The output side's WETH is
+                    // among it when the step that set the output side paid it
+                    // to the router and the router still holds WETH. WETH
+                    // that step paid to the user, or to anyone else, stays
+                    // WETH, so when that step also paid some of its output
+                    // elsewhere, or made a payout this decoder did not read,
+                    // only part of it may be unwrapped. The calldata then
+                    // states no minimum for the ETH, and the output side keeps
+                    // no figure.
+                    const toRouter = (r) => present(r) && isRouter(r);
                     if (
                         present(outputToken) &&
                         WETH_ADDRESSES.includes(outputToken.toLowerCase()) &&
-                        heldByRouter.has(outputToken.toLowerCase())
+                        heldByRouter.has(outputToken.toLowerCase()) &&
+                        outputRecipients.some(toRouter)
                     ) {
                         outputUnwrapped = true;
+                        if (!outputRecipients.every(toRouter)) {
+                            minOutput = null;
+                        }
                     }
                     const u = decodeUnwrapWeth(inputs[i]);
                     if (u) {

tests/uniswapRecipient.test.js

@@ -270,18 +270,28 @@ const SWAP_USDT_FOR_ETH = [
         [[[ZERO, USDT, 500, 10, ZERO], false, USDT_2000, ONE_WETH, "0x"]],
     ),
 ];
+const SWAP_USDT_FOR_WETH = [
+    0x06, // SWAP_EXACT_IN_SINGLE
+    coder.encode(
+        [
+            "tuple(tuple(address,address,uint24,int24,address),bool,uint128,uint128,bytes)",
+        ],
+        [[[USDT, WETH, 500, 10, ZERO], true, USDT_2000, ONE_WETH, "0x"]],
+    ),
+];
 // SWAP_EXACT_IN_SINGLE with no parameters, which cannot be read.
 const UNREADABLE_SWAP = [0x06, "0x"];
 const SETTLE_USDT = [
     0x0b,
     coder.encode(["address", "uint256", "bool"], [USDT, 0n, true]),
 ];
-function take(currency, recipient) {
+// A TAKE of `amount`, by default zero: the open delta, all the step owes.
+function take(currency, recipient, amount = 0n) {
     return [
         0x0e,
         coder.encode(
             ["address", "address", "uint256"],
-            [currency, recipient, 0n],
+            [currency, recipient, amount],
         ),
     ];
 }
@@ -594,9 +604,9 @@ describe("an UNWRAP_WETH makes the output ETH only when the router holds it", ()
     });
 
     // The user receives the first step's WETH as WETH and the second's as
-    // ETH. The second step sets the output side, and the router holds its
-    // WETH, so the output reads as ETH with the second step's minimum.
-    test("a swap paying part of its WETH to the user and the rest to the router, then an UNWRAP_WETH, reads as ETH", () => {
+    // ETH. The second step sets the output side and pays its WETH to the
+    // router, so the output reads as ETH with the second step's minimum.
+    test("two swaps, the second paying its WETH to the router, then an UNWRAP_WETH, reads as ETH", () => {
         const result = decode(
             execute(
                 swapToWeth(MSG_SENDER),
@@ -611,6 +621,69 @@ describe("an UNWRAP_WETH makes the output ETH only when the router holds it", ()
         expect(detail(result, "Min. received").value).toBe("0.5000 ETH");
     });
 
+    // The same two swaps the other way round. The user receives the first
+    // step's WETH as ETH and the second's as WETH. The second step sets the
+    // output side and pays its WETH to the user, so the output reads as WETH
+    // with the second step's minimum, though the router holds the first's.
+    test("two swaps, the second paying its WETH to the user, then an UNWRAP_WETH, reads as WETH", () => {
+        const result = decode(
+            execute(
+                v2Swap(0x08, ADDRESS_THIS, USDC_1990, ONE_WETH / 2n, [
+                    USDC,
+                    WETH,
+                ]),
+                swapToWeth(MSG_SENDER),
+                unwrapWeth(MSG_SENDER),
+            ),
+        );
+        expect(result.name).toBe("Swap USDC → WETH");
+        expect(detail(result, "Min. received").value).toBe("1.0000 WETH");
+    });
+
+    // One V4 step buys at least 1 WETH and TAKEs 0.6 WETH to the user and the
+    // rest to the router. The user receives 0.6 WETH and the rest as ETH, so
+    // neither minimum is shown: the calldata states none for the ETH.
+    test("one V4 step paying part of its WETH to the user and the rest to the router, then an UNWRAP_WETH, reads as ETH with no minimum", () => {
+        const result = decode(
+            execute(
+                v4Swap(
+                    SWAP_USDT_FOR_WETH,
+                    SETTLE_USDT,
+                    take(WETH, MSG_SENDER, (ONE_WETH * 6n) / 10n),
+                    take(WETH, ADDRESS_THIS),
+                ),
+                unwrapWeth(MSG_SENDER),
+            ),
+        );
+        expect(result.name).toBe("Swap USDT → ETH");
+        expect(labels(result)).toEqual([
+            "Protocol",
+            "Token In",
+            "Amount",
+            "Token Out",
+            "Steps",
+            "Deadline",
+        ]);
+    });
+
+    // A TAKE the decoder cannot read may pay part of the WETH to the user.
+    test("one V4 step paying WETH to the router beside a TAKE that cannot be read, then an UNWRAP_WETH, reads as ETH with no minimum", () => {
+        const result = decode(
+            execute(
+                v4Swap(
+                    SWAP_USDT_FOR_WETH,
+                    SETTLE_USDT,
+                    withDirtyWord(take(WETH, MSG_SENDER), 1),
+                    take(WETH, ADDRESS_THIS),
+                ),
+                unwrapWeth(MSG_SENDER),
+            ),
+        );
+        expect(result.name).toBe("Swap USDT → ETH");
+        expect(detail(result, "Min. received")).toBeUndefined();
+        expect(detail(result, "Min. paid out")).toBeUndefined();
+    });
+
     // A step after the UNWRAP_WETH that sets the output side sets it anew.
     test("a swap paying WETH to the user after an UNWRAP_WETH of an earlier swap's WETH reads as WETH", () => {
         const result = decode(