fix: a swap split across steps the user pays for shows every amount it spends (closes #625)

The swap's Amount line gave only the first swap step's amount. It now
gives the total the steps take of Token In: the amount of the step that
sets the input side plus each later take of it by a step the user pays.
A take of another token, one after an amount that is not a quantity, or
one of unknown amount gets lines of its own. A step that may take what
the decoder did not read, such as a V3_SWAP_EXACT_OUT or an
EXECUTE_SUB_PLAN, gets one line saying so and leaves no figure. A
PERMIT2_PERMIT names Token In; its amount stands only in the plain shape
of Uniswap's own routes.

Model: opus-5-5

src/shared/uniswap.js

@@ -335,7 +335,8 @@ const UNNAMED_CURRENCY = "Unknown (not named in the calldata)";
 // commands this decoder does not read. That action names both of its
 // currencies, and those commands may name one, so saying the calldata did not
 // name it would be false. The Paid to line uses it too, when a step may pay an
-// address this decoder did not read.
+// address this decoder did not read, and so do the lines for what a step
+// takes from the sender, when this decoder does not know it.
 const UNDECODED_CURRENCY = "Unknown (could not be decoded)";
 
 // The Paid to line for each token paid to the router, the swap's output or
@@ -356,6 +357,11 @@ function present(value) {
     return value !== null && value !== undefined;
 }
 
+// Whether `a` and `b` are both known and the same address.
+function sameAddress(a, b) {
+    return present(a) && present(b) && a.toLowerCase() === b.toLowerCase();
+}
+
 // Uniswap V4 spells "use the whole open delta" as an amount of zero:
 // v4-periphery `src/libraries/ActionConstants.sol` declares
 // `uint128 internal constant OPEN_DELTA = 0` ("used to signal that an action
@@ -566,6 +572,7 @@ function decodeV2SwapExactIn(input) {
 // Decode V2_SWAP_EXACT_OUT (command 0x09) input bytes.
 // ABI: (address recipient, uint256 amountOut, uint256 amountInMax,
 //        address[] path, bool payerIsUser)
+// With `payerIsUser` false the router pays the input from its own balance.
 function decodeV2SwapExactOut(input) {
     try {
         const d = coder.decode(
@@ -578,6 +585,7 @@ function decodeV2SwapExactOut(input) {
             amountInMax: d[2],
             tokenIn: d[3][0],
             tokenOut: d[3][d[3].length - 1],
+            payerIsUser: d[4],
         };
     } catch {
         return null;
@@ -901,10 +909,15 @@ function totalAmount(amounts) {
 // and its recipient as written, MSG_SENDER for a TAKE_ALL. TAKE_PORTION takes
 // a share of the currency, so it does not name the output side as TAKE does.
 // `recipientUnread` is set when the step has a payout this decoder did not
-// read. `settledFromRouter` is every SETTLE that the router pays from its own
-// balance (`payerIsUser` false), as its currency and the amount it pays: a
-// quantity, CONTRACT_BALANCE (all the router holds), or null when this
-// decoder cannot tell (see below).
+// read, and `settleUnread` when it has a SETTLE or SETTLE_ALL this decoder
+// did not read. `settledFromRouter` is every SETTLE that the router pays from
+// its own balance (`payerIsUser` false), as its currency and the amount it
+// pays: a quantity, CONTRACT_BALANCE (all the router holds), or null when
+// this decoder cannot tell (see below). `paidByUser` is what the user pays
+// the step, once per currency, as that currency and the amount: the total of
+// every SETTLE paid by the user (`payerIsUser` true) and every SETTLE_ALL,
+// which V4Router always has the user pay, of that currency, or null when
+// this decoder cannot tell what one of them pays.
 function decodeV4Swap(input) {
     try {
         const d = coder.decode(["bytes", "bytes[]"], input);
@@ -914,16 +927,18 @@ function decodeV4Swap(input) {
         let settleToken = null;
         let takeToken = null;
         const takes = [];
-        // Every SETTLE paid from the router, as its currency, its amount as
-        // written and its index among the step's actions.
-        const routerSettles = [];
-        // The currency of every SETTLE and SETTLE_ALL.
-        const settledCurrencies = [];
+        // Every SETTLE and SETTLE_ALL, as its currency, its amount as
+        // written, whether the user pays it, and its index among the step's
+        // actions. A SETTLE_ALL pays what a SETTLE of OPEN_DELTA (zero) paid
+        // by the user pays, all the step still owes of its currency, so it
+        // is kept as one; its maxAmount only caps that.
+        const settles = [];
         // The index of the step's last swap action, read or not, or -1.
         let lastSwapAction = -1;
         // Set when an action of the step could not be read.
         let actionUnread = false;
         let recipientUnread = false;
+        let settleUnread = false;
         // The step's swap actions that could be read, as decodeV4SwapAction()
         // reads them.
         const swaps = [];
@@ -942,19 +957,22 @@ function decodeV4Swap(input) {
                         params[i],
                     );
                     settleToken = s[0];
-                    settledCurrencies.push(s[0]);
-                    if (!s[2]) {
-                        routerSettles.push({
-                            currency: s[0],
-                            amount: s[1],
-                            index: i,
-                        });
-                    }
+                    settles.push({
+                        currency: s[0],
+                        amount: s[1],
+                        payerIsUser: s[2],
+                        index: i,
+                    });
                 } else if (actionId === V4_SETTLE_ALL) {
                     // SETTLE_ALL: (address currency, uint256 maxAmount)
                     const s = coder.decode(["address", "uint256"], params[i]);
                     settleToken = s[0];
-                    settledCurrencies.push(s[0]);
+                    settles.push({
+                        currency: s[0],
+                        amount: 0n,
+                        payerIsUser: true,
+                        index: i,
+                    });
                 } else if (actionId === V4_TAKE) {
                     // TAKE: (address currency, address recipient, uint256 amount)
                     const t = coder.decode(
@@ -996,7 +1014,8 @@ function decodeV4Swap(input) {
             } catch {
                 // Skip sub-actions we can't decode. A TAKE, TAKE_ALL or
                 // TAKE_PORTION among them is a payout this decoder did not
-                // read.
+                // read, and a SETTLE or SETTLE_ALL may take from the user
+                // what it did not read: the router still runs both.
                 actionUnread = true;
                 if (
                     actionId === V4_TAKE ||
@@ -1005,25 +1024,29 @@ function decodeV4Swap(input) {
                 ) {
                     recipientUnread = true;
                 }
+                if (actionId === V4_SETTLE || actionId === V4_SETTLE_ALL) {
+                    settleUnread = true;
+                }
             }
         }
 
-        // What each SETTLE paid from the router pays. A quantity or
-        // CONTRACT_BALANCE pays as written. A SETTLE of OPEN_DELTA (zero)
-        // pays whatever the step still owes of its currency when it runs.
-        // That is what the step's swap actions state they spend of it only
-        // in the plain shape of Uniswap's own routes, so only then is it
-        // given that amount: every action in the step was read; every swap
-        // action names the currency it spends and the one it buys (an
-        // exact-in action with an empty path swaps nothing); the SETTLE is
-        // the step's only SETTLE or SETTLE_ALL of its currency and comes
-        // after every swap action; no swap action buys that currency; and
-        // the swap actions that spend it state a quantity together (see
-        // totalAmount()). Otherwise it is given null.
-        const settledFromRouter = routerSettles.map((s) => {
-            if (s.amount !== 0n) {
-                return { currency: s.currency, amount: s.amount };
-            }
+        // What a SETTLE or SETTLE_ALL pays. A SETTLE of any amount but
+        // OPEN_DELTA (zero) pays as written: a quantity, or, for
+        // CONTRACT_BALANCE, as much as the router holds. A SETTLE of
+        // OPEN_DELTA, and a SETTLE_ALL, pay whatever the step still owes of
+        // the currency when they run. That is what the step's swap actions
+        // state they spend of it only in the plain shape of Uniswap's own
+        // routes, so only then is it given that amount: every action in the
+        // step was read; every swap action names the currency it spends and
+        // the one it buys (an exact-in action with an empty path swaps
+        // nothing); it is the step's only SETTLE or SETTLE_ALL of its
+        // currency and comes after every swap action; no swap action buys
+        // that currency and nothing in the step takes it (a TAKE of a stated
+        // amount adds to what the step owes); and the swap actions that spend
+        // it state a quantity together (see totalAmount()). Otherwise it is
+        // given null.
+        const pays = (s) => {
+            if (s.amount !== 0n) return s.amount;
             const stated = totalAmount(
                 swaps
                     .filter((w) => w.tokenIn === s.currency)
@@ -1032,16 +1055,30 @@ function decodeV4Swap(input) {
             const paysWhatSwapsSpend =
                 !actionUnread &&
                 swaps.every((w) => present(w.tokenIn) && present(w.tokenOut)) &&
-                settledCurrencies.filter((c) => c === s.currency).length ===
-                    1 &&
+                settles.filter((c) => c.currency === s.currency).length === 1 &&
                 s.index > lastSwapAction &&
                 !swaps.some((w) => w.tokenOut === s.currency) &&
+                !takes.some((t) => t.currency === s.currency) &&
                 typeof stated === "bigint";
-            return {
-                currency: s.currency,
-                amount: paysWhatSwapsSpend ? stated : null,
-            };
-        });
+            return paysWhatSwapsSpend ? stated : null;
+        };
+        const settledFromRouter = settles
+            .filter((s) => !s.payerIsUser)
+            .map((s) => ({ currency: s.currency, amount: pays(s) }));
+        const paidByUser = [];
+        for (const s of settles.filter((c) => c.payerIsUser)) {
+            const amount = pays(s);
+            const paid = paidByUser.find((p) => p.currency === s.currency);
+            if (!paid) {
+                paidByUser.push({ currency: s.currency, amount });
+            } else {
+                paid.amount =
+                    typeof paid.amount === "bigint" &&
+                    typeof amount === "bigint"
+                        ? paid.amount + amount
+                        : null;
+            }
+        }
 
         // Rule 3.
         if (swapUndecoded) {
@@ -1052,7 +1089,9 @@ function decodeV4Swap(input) {
                 amountOutMin: null,
                 takes,
                 settledFromRouter,
+                paidByUser,
                 recipientUnread,
+                settleUnread,
                 swapUndecoded,
                 hasSwapAction: true,
             };
@@ -1094,7 +1133,9 @@ function decodeV4Swap(input) {
             amountOutMin,
             takes,
             settledFromRouter,
+            paidByUser,
             recipientUnread,
+            settleUnread,
             swapUndecoded,
             hasSwapAction: swaps.length > 0,
         };
@@ -1125,6 +1166,13 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
         let inputToken = null;
         let inputAmount = null;
         let inputEstablished = false;
+        // The last PERMIT2_PERMIT this decoder read, or null (see
+        // permitStands after the loop).
+        let permit = null;
+        // The index of each step this decoder did not read in full: a
+        // command it does not read, a step whose input it cannot read, in
+        // whole or in part, and one it fails on (see permitStands).
+        const stepsUnread = [];
         let outputToken = null;
         let minOutput = null;
         let outputEstablished = false;
@@ -1135,8 +1183,8 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
         const commandNames = [];
 
         // THE INVARIANT: an amount and the token it is counted in always come
-        // from the same hop. A figure is never rendered against a token that
-        // did not supply it.
+        // from the same hop, or from hops that all spend that token. A figure
+        // is never rendered against a token that did not supply it.
         //
         // Both sides are therefore set as a PAIR — never field by field, and
         // never on truthiness. An address is never falsy once set but an
@@ -1152,7 +1200,9 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
         // states neither half: the output side always, and the input side
         // when no earlier hop set it. A half the establishing hop did not
         // state stays null and the line says so, rather than being filled in
-        // from a different hop.
+        // from a different hop. A PERMIT2_PERMIT sets no side here: after the
+        // loop, the last one read names Token In, and the Amount line is
+        // formed there, in one place (see permitStands).
         const setInput = (token, amount) => {
             inputToken = present(token) ? token : null;
             inputAmount = present(amount) ? amount : null;
@@ -1170,6 +1220,29 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
             outputEstablished = true;
         };
 
+        // What each step but the one that sets the input side takes from the
+        // sender, as { token, amount }, in step order. After the loop each
+        // joins the Amount line or gets lines of its own (see permitStands).
+        const userPaid = [];
+        // A swap step the user pays for (`payerIsUser` true) takes `amount`
+        // of `token` from the sender. A V2 exact-in of ALREADY_PAID takes
+        // nothing.
+        const addUserPaid = (token, amount) => {
+            if (amount !== ALREADY_PAID) userPaid.push({ token, amount });
+        };
+        // A step may take from the sender what this decoder did not read: a
+        // V4 step, other than the one that sets the input side, whose input
+        // or one of whose SETTLEs or SETTLE_ALLs it cannot read; a V2 or V3
+        // exact-in or V2 exact-out step or PERMIT2_TRANSFER_FROM whose input
+        // it cannot read; a PERMIT2_TRANSFER_FROM_BATCH; a V3_SWAP_EXACT_OUT;
+        // an EXECUTE_SUB_PLAN; and a step it fails on. It is recorded with a
+        // null token and amount: one line says so, there is no Amount line,
+        // whose figure may then be too low, and the amount of a permit after
+        // it does not stand (see permitStands).
+        const spentUnread = () => {
+            userPaid.push({ token: null, amount: null });
+        };
+
         // Who the steps pay, in whichever step and of whatever token.
         // MSG_SENDER is the sender. The router itself, as ADDRESS_THIS or by
         // its own address, holds what it is paid until a later step pays it
@@ -1300,20 +1373,40 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
                     // EXECUTE_SUB_PLAN runs a further list of commands held in
                     // its input, which this decoder does not read. The step
                     // says so, and after this loop neither side is named.
-                    // Those commands may pay any address.
+                    // Those commands may pay any address and take from the
+                    // sender.
                     hasSubPlan = true;
                     commandNames[i] += " (its steps are not shown)";
                     payeeUnread = true;
+                    stepsUnread.push(i);
+                    spentUnread();
                 } else if (command === "PERMIT2_PERMIT") {
                     const p = decodePermit2(inputs[i]);
-                    // A permit states both halves itself, so it may replace an
-                    // input side an earlier hop established without breaking
-                    // the invariant.
-                    if (p) setInput(p.token, p.amount);
+                    if (p) {
+                        // Whether a step before it took its token, or may
+                        // have: the step that set the input side or one in
+                        // `userPaid`, when its token is the permit's or not
+                        // known.
+                        const mayBeItsToken = (token) =>
+                            !present(token) || sameAddress(token, p.token);
+                        const tookBefore =
+                            (inputEstablished && mayBeItsToken(inputToken)) ||
+                            userPaid.some((t) => mayBeItsToken(t.token));
+                        permit = {
+                            ...p,
+                            step: i,
+                            allowedToFail,
+                            beforeEveryTake: !tookBefore,
+                        };
+                    } else {
+                        stepsUnread.push(i);
+                    }
                 } else if (command === "PERMIT2_TRANSFER_FROM") {
                     const p = decodePermit2TransferFrom(inputs[i]);
                     if (!p) {
                         payeeUnread = true;
+                        stepsUnread.push(i);
+                        spentUnread();
                     } else if (
                         commandTypeMask === 0x1f &&
                         [MSG_SENDER, ADDRESS_THIS].includes(
@@ -1351,6 +1444,7 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
                         // owner may be any address. It sets no side, and the
                         // step says so.
                         commandNames[i] += " (could not be decoded)";
+                        stepsUnread.push(i);
                     } else if (b.owner.toLowerCase() !== sender) {
                         // The router reads the owner as written (see
                         // decodeBalanceCheck()), so address(1) and address(2)
@@ -1375,7 +1469,11 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
                 } else if (command === "V3_SWAP_EXACT_IN") {
                     const s = decodeV3SwapExactIn(inputs[i]);
                     if (s) {
-                        setInputOnce(s.tokenIn, s.amountIn);
+                        if (!inputEstablished) {
+                            setInputOnce(s.tokenIn, s.amountIn);
+                        } else if (s.payerIsUser) {
+                            addUserPaid(s.tokenIn, s.amountIn);
+                        }
                         // Always update output: in multi-step swaps (V3 → V4),
                         // the last swap step determines the final output token
                         // and minimum received amount.
@@ -1388,11 +1486,25 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
                         }
                     } else {
                         payeeUnread = true;
+                        stepsUnread.push(i);
+                        spentUnread();
                     }
+                } else if (command === "V3_SWAP_EXACT_OUT") {
+                    // This decoder does not read it
+                    // (https://git.eeqj.de/sneak/AutistMask/issues/601). It
+                    // may pay any address and take from the sender, so
+                    // wherever it stands it leaves no Amount figure.
+                    payeeUnread = true;
+                    stepsUnread.push(i);
+                    spentUnread();
                 } else if (command === "V2_SWAP_EXACT_IN") {
                     const s = decodeV2SwapExactIn(inputs[i]);
                     if (s) {
-                        setInputOnce(s.tokenIn, s.amountIn);
+                        if (!inputEstablished) {
+                            setInputOnce(s.tokenIn, s.amountIn);
+                        } else if (s.payerIsUser) {
+                            addUserPaid(s.tokenIn, s.amountIn);
+                        }
                         setOutput(s.tokenOut, s.amountOutMin);
                         if (!s.payerIsUser) {
                             spendFromRouter(s.tokenIn, s.amountIn);
@@ -1402,20 +1514,34 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
                         }
                     } else {
                         payeeUnread = true;
+                        stepsUnread.push(i);
+                        spentUnread();
                     }
                 } else if (command === "V2_SWAP_EXACT_OUT") {
                     // Buys exactly amountOut and spends at most amountInMax.
                     hasV2ExactOut = true;
                     const s = decodeV2SwapExactOut(inputs[i]);
                     if (s) {
-                        setInputOnce(s.tokenIn, s.amountInMax);
+                        if (!inputEstablished) {
+                            setInputOnce(s.tokenIn, s.amountInMax);
+                        } else if (s.payerIsUser) {
+                            addUserPaid(s.tokenIn, s.amountInMax);
+                        }
                         setOutput(s.tokenOut, s.amountOut);
                         if (!isHop(i, s.tokenOut, s.recipient)) {
                             addPayee(s.recipient, s.tokenOut);
                         }
                     } else {
                         payeeUnread = true;
+                        stepsUnread.push(i);
+                        spentUnread();
                     }
+                } else if (command === "PERMIT2_TRANSFER_FROM_BATCH") {
+                    // It moves the sender's tokens to any addresses, and this
+                    // decoder does not read it.
+                    payeeUnread = true;
+                    stepsUnread.push(i);
+                    spentUnread();
                 } else if (command === "SWEEP") {
                     const s = decodeSweep(inputs[i]);
                     if (s) {
@@ -1425,6 +1551,7 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
                         }
                     } else {
                         payeeUnread = true;
+                        stepsUnread.push(i);
                     }
                 } else if (
                     command === "TRANSFER" ||
@@ -1461,6 +1588,7 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
                         }
                     } else {
                         payeeUnread = true;
+                        stepsUnread.push(i);
                     }
                 } else if (command === "ACROSS_V4_DEPOSIT_V3") {
                     const a = decodeAcrossV4DepositV3(inputs[i]);
@@ -1484,6 +1612,7 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
                         }
                     } else {
                         payeeUnread = true;
+                        stepsUnread.push(i);
                     }
                 } else if (command === "WRAP_ETH") {
                     const w = decodeWrapEth(inputs[i]);
@@ -1514,9 +1643,11 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
                         }
                     } else {
                         payeeUnread = true;
+                        stepsUnread.push(i);
                     }
                 } else if (command === "V4_SWAP") {
                     const v4 = decodeV4Swap(inputs[i]);
+                    const inputSetBefore = inputEstablished;
                     if (v4) {
                         // Each SETTLE paid from the router spends the amount
                         // decodeV4Swap() says it pays.
@@ -1532,6 +1663,14 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
                     if (!v4 || v4.recipientUnread) {
                         payeeUnread = true;
                     }
+                    if (
+                        !v4 ||
+                        v4.recipientUnread ||
+                        v4.settleUnread ||
+                        v4.swapUndecoded
+                    ) {
+                        stepsUnread.push(i);
+                    }
                     if (v4 && v4.swapUndecoded) {
                         // A swap action of this step went unread, so the step
                         // is marked.
@@ -1562,6 +1701,23 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
                         setInputOnce(v4.tokenIn, v4.amountIn);
                         setOutput(v4.tokenOut, v4.amountOutMin);
                     }
+                    // Every V4 step but the one that sets the input side,
+                    // with a swap action or without, takes from the sender
+                    // what the user pays it (an amount an unread action may
+                    // change is null). One whose input, or one of whose
+                    // SETTLEs or SETTLE_ALLs, this decoder could not read may
+                    // take anything: the router still runs it.
+                    const setInputHere = inputEstablished && !inputSetBefore;
+                    if (!setInputHere) {
+                        if (v4) {
+                            for (const p of v4.paidByUser) {
+                                addUserPaid(p.currency, p.amount);
+                            }
+                        }
+                        if (!v4 || v4.settleUnread) {
+                            spentUnread();
+                        }
+                    }
                 } else if (command === "UNWRAP_WETH") {
                     hasUnwrapWeth = true;
                     const u = decodeUnwrapWeth(inputs[i]);
@@ -1582,26 +1738,109 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
                         }
                     } else {
                         payeeUnread = true;
+                        stepsUnread.push(i);
                     }
                 } else {
                     // Any other step may pay an address this decoder does not
-                    // read: V3_SWAP_EXACT_OUT, PERMIT2_TRANSFER_FROM_BATCH and
-                    // the NFT commands among them, and a type the release
-                    // names no command for.
+                    // read: PERMIT2_PERMIT_BATCH and the NFT commands among
+                    // them, and a type the release names no command for.
                     payeeUnread = true;
+                    stepsUnread.push(i);
                 }
             } catch {
-                // Skip commands we can't decode. One may pay any address.
+                // Skip commands we can't decode. One may pay any address and
+                // take from the sender.
                 payeeUnread = true;
+                stepsUnread.push(i);
+                spentUnread();
             }
             if (allowedToFail) {
                 commandNames[i] += " (allowed to fail)";
             }
         }
 
+        // The Amount line, and the lines for what the steps take beyond it.
+        //
+        // The total is what the steps take of Token In: the amount of the
+        // step that set the input side, with each later take of that token
+        // added to it while both are quantities. A take that cannot be added,
+        // being of another token or coming after an amount that is not a
+        // quantity (a V4 open delta, ALREADY_PAID, or none stated), gets
+        // lines of its own. One whose amount is not known also leaves the
+        // total unknown, with no figure.
+        //
+        // The last PERMIT2_PERMIT read names Token In. Its amount stands as
+        // the Amount figure in place of the total only in the plain shape of
+        // Uniswap's own routes: it is the only PERMIT2_PERMIT, its spender is
+        // the router, the router may not let it fail, no step before it took
+        // its token or one not known, and this decoder read every step after
+        // it in full (see stepsUnread). Permit2 then lets the router take no
+        // more of the token than that amount, so the permit covers every take
+        // of it. A later step this decoder did not read may raise what Permit2
+        // lets the router take, as a PERMIT2_PERMIT_BATCH can. A step that
+        // may take from the sender what this decoder did not read leaves no
+        // figure, permit or not (see spentUnread()), and an EXECUTE_SUB_PLAN
+        // step leaves both sides unknown (below).
+        const stepCommands = Array.from(
+            commandsBytes,
+            (b) => commands[b & commandTypeMask],
+        );
+        const permitStands =
+            permit !== null &&
+            stepCommands.filter((c) => c === "PERMIT2_PERMIT").length === 1 &&
+            sameAddress(permit.spender, toAddress) &&
+            !permit.allowedToFail &&
+            permit.beforeEveryTake &&
+            !stepsUnread.some((step) => step > permit.step);
+        // What the steps take that the Amount line does not give, as
+        // { token, amount }. A null token is a step this decoder did not read
+        // (see spentUnread()), or a token it does not know.
+        const spentFromSender = [];
+        let total = null;
+        // The take of the step that set the input side, when the total
+        // starts from it and it stated no amount (see below), or null.
+        let firstTakeUnstated = null;
+        if (permit === null || sameAddress(inputToken, permit.token)) {
+            total = inputAmount;
+            if (inputEstablished && !present(inputAmount)) {
+                firstTakeUnstated = { token: inputToken, amount: null };
+            }
+        } else if (inputEstablished) {
+            // The step that set the input side spent a token other than the
+            // permit's, or one not known, so the total starts with no figure.
+            spentFromSender.push({ token: inputToken, amount: inputAmount });
+        }
+        if (permit !== null) inputToken = permit.token;
+        for (const t of userPaid) {
+            const ofTokenIn = sameAddress(t.token, inputToken);
+            if (ofTokenIn && permitStands) continue;
+            if (
+                ofTokenIn &&
+                typeof total === "bigint" &&
+                typeof t.amount === "bigint"
+            ) {
+                total += t.amount;
+                continue;
+            }
+            spentFromSender.push(t);
+            if (ofTokenIn && !present(t.amount)) total = null;
+        }
+        inputAmount = permitStands ? permit.amount : total;
+        // With no Amount figure, a later take's own figure could read as all
+        // that leaves, so the step that set the input side, when it stated
+        // no amount, then gets lines of its own too, first, saying its amount
+        // is not known.
+        if (
+            !present(inputAmount) &&
+            firstTakeUnstated !== null &&
+            spentFromSender.some((s) => present(s.amount))
+        ) {
+            spentFromSender.unshift(firstTakeUnstated);
+        }
+
         // The commands of an EXECUTE_SUB_PLAN step may spend the user's tokens
         // or pay the user, before or after any other step, and a permit among
-        // them would replace the input side. What the other steps state is
+        // them would name Token In. What the other steps state is
         // then not the whole swap, so both sides are set unknown, with no
         // figure, wherever the step stands.
         if (hasSubPlan) {
@@ -1672,37 +1911,49 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
             });
         }
 
-        if (present(inputAmount)) {
-            // Three amounts need no scale to describe and are named rather
-            // than formatted: V4's open delta and V2's already-paid zero,
-            // neither of which is a quantity at all (see OPEN_DELTA and
-            // ALREADY_PAID), and an unbounded permit. Those two tests come
-            // first — the sentinels are not bigints and cannot be compared
-            // with one.
-            let amount;
-            if (inputAmount === OPEN_DELTA) {
-                amount = { raw: OPEN_DELTA_AMOUNT, display: OPEN_DELTA_AMOUNT };
-            } else if (inputAmount === ALREADY_PAID) {
-                amount = {
+        // The text of an amount the swap steps spend, for the Amount line and
+        // the lines for other tokens below it. Three amounts need no scale to
+        // describe and are named rather than formatted: V4's open delta and
+        // V2's already-paid zero, neither of which is a quantity at all (see
+        // OPEN_DELTA and ALREADY_PAID), and an unbounded permit. Those two
+        // tests come first — the sentinels are not bigints and cannot be
+        // compared with one.
+        const spentText = (amount, info) => {
+            if (amount === OPEN_DELTA) {
+                return { raw: OPEN_DELTA_AMOUNT, display: OPEN_DELTA_AMOUNT };
+            }
+            if (amount === ALREADY_PAID) {
+                return {
                     raw: ALREADY_PAID_AMOUNT,
                     display: ALREADY_PAID_AMOUNT,
                 };
-            } else if (inputAmount >= MAX_UINT160) {
-                amount = { raw: "Unlimited", display: "Unlimited" };
-            } else if (hasV2ExactOut) {
+            }
+            if (amount >= MAX_UINT160) {
+                return { raw: "Unlimited", display: "Unlimited" };
+            }
+            if (hasV2ExactOut) {
                 // A V2 exact-out swap spends at most this figure, whichever
-                // step set the line (its amountInMax, the WRAP_ETH of a swap
-                // paid in ETH, a permit), so it is said to be a maximum, in
-                // `raw` too: the wait, success and error screens show `raw` as
-                // the transaction's amount.
-                const most = amountText(inputAmount, inInfo);
-                amount = {
+                // steps gave it (an amountInMax, the WRAP_ETH of a swap paid
+                // in ETH, a permit, or several steps' total), so it is said to
+                // be a maximum, in `raw` too: the wait, success and error
+                // screens show `raw` as the transaction's amount.
+                const most = amountText(amount, info);
+                return {
                     raw: "Up to " + most.raw,
                     display: "Up to " + most.display,
                 };
-            } else {
-                amount = amountText(inputAmount, inInfo);
             }
+            return amountText(amount, info);
+        };
+
+        // A null token in `spentFromSender`, a step this decoder did not read
+        // or a token it does not know, leaves no Amount figure, which may
+        // then be too low.
+        if (
+            present(inputAmount) &&
+            spentFromSender.every((s) => present(s.token))
+        ) {
+            const amount = spentText(inputAmount, inInfo);
             details.push({
                 label: "Amount",
                 value: amount.display,
@@ -1710,6 +1961,26 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
             });
         }
 
+        // What steps take from the sender beyond the Amount line, in the shape
+        // of the lines below for a PERMIT2_TRANSFER_FROM. An amount this
+        // decoder does not know is said so, and a step it did not read gets
+        // that one line alone.
+        for (const s of spentFromSender) {
+            details.push({
+                label: "Moved from the sender",
+                value: present(s.amount)
+                    ? spentText(s.amount, tokenInfo(s.token, sources)).display
+                    : UNDECODED_CURRENCY,
+            });
+            if (present(s.token)) {
+                details.push(tokenMovedLine("Token moved", s.token, sources));
+                details.push({
+                    label: "Moved to",
+                    value: "The swap step that spends it",
+                });
+            }
+        }
+
         // What each PERMIT2_TRANSFER_FROM moves: its amount, its token and
         // where it goes, an address on a line of its own.
         for (const m of movedFromSender) {