fix: the swap decoder names where a WRAP_ETH pays and counts the router's ETH in a V4 settle (closes #665)

A WRAP_ETH that sets the input side and pays its WETH to anyone but
the router now names that recipient on its Moved to line, or reads
The sender for address(1).

V4Router pays ETH from the router's own ETH, whoever a SETTLE names as
payer. ETH the router already holds now pays first for the ETH a V4
step would take from the user, and only the rest is moved from the
sender. The decoder subtracts only when it knows both amounts;
otherwise the sender's ETH reads as unknown. An UNWRAP_WETH into the
router keeps a known WETH amount as the ETH the router then holds. A
step that spends an unstated amount of a token from the router makes
the router's amount of that token unknown.

Model: opus-5-5

README.md

@@ -3412,47 +3412,48 @@ Currently supported:
   as a swap paid in ETH does, but only when that amount is not
   `CONTRACT_BALANCE` and the router held no WETH from an earlier step when the
   `WRAP_ETH` ran: after two `WRAP_ETH`s of 0.5 ETH into the router, a swap of 1
-  WETH from it reads as leaving the WETH there. An `UNWRAP_WETH` into the router
-  turns all the router's WETH into as much ETH. The decoder then knows how much
-  ETH the router holds only when it knew the WETH's amount and the router held
-  no ETH before. A V4 `SETTLE` of ETH spends the ETH the router holds, whoever
-  pays it (see below). A V2 or V3 exact-out step paid from the router spends an
-  amount the calldata does not state, at most its `amountInMax`, so the decoder
-  counts it as spending nothing the router holds. A `SETTLE` of `OPEN_DELTA`
-  (zero), and a `SETTLE_ALL`, pay only what the step still owes of their token
-  when they run. The decoder takes that to be the amounts the step's swap
-  actions state they spend of that token only when every action in the step
-  could be read, every swap action names the token it spends and the token it
-  buys (a swap action with an empty path swaps nothing), the `SETTLE` or
-  `SETTLE_ALL` is the step's only `SETTLE` or `SETTLE_ALL` of that token and
+  WETH from it reads as leaving the WETH there. A V2 or V3 exact-out step paid
+  from the router spends an amount the calldata does not state, at most its
+  `amountInMax`. The decoder then no longer knows how much of the step's input
+  token the router holds. A V4 `SETTLE` from the router has the same effect when
+  the decoder does not know what that `SETTLE` pays (see below). An
+  `UNWRAP_WETH` into the router turns all the router's WETH into the same amount
+  of ETH. The decoder knows how much ETH that is only when it knew how much WETH
+  the router held and the router held no ETH before. A V4 `SETTLE` of ETH always
+  spends the router's own ETH, whichever payer it names (see below). A `SETTLE`
+  of `OPEN_DELTA` (zero), and a `SETTLE_ALL`, pay only what the step still owes
+  of their token when they run. The decoder takes that to be the amounts the
+  step's swap actions state they spend of that token only when every action in
+  the step could be read, every swap action names the token it spends and the
+  token it buys (a swap action with an empty path swaps nothing), the `SETTLE`
+  or `SETTLE_ALL` is the step's only `SETTLE` or `SETTLE_ALL` of that token and
   comes after every swap action, no swap action buys that token, no `TAKE`,
   `TAKE_ALL` or `TAKE_PORTION` 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; otherwise it does not know the amount, and such a `SETTLE`
-  from the router counts as spending nothing. So the rest of a V4 `SETTLE` of
-  more than its swap spends, taken to the router, the WETH of a `WRAP_ETH`, and
-  a token a swap pays the router on the way to the output, each stays in the
-  router when later steps do not spend all of it, where anyone can take it in a
-  later transaction. The router sends ETH as written, so a `TRANSFER` of
-  `CONTRACT_BALANCE` of ETH always reverts and pays out nothing. A step paying a
-  token to the V2 pair that the very next step spends, as a V2 exact-in of that
-  token whose `amountIn` is `ALREADY_PAID` (zero) or `CONTRACT_BALANCE`, is a
-  hop, not a payout: Uniswap's mixed routes pay the next V2 pair directly, and
-  the router enforces that swap's own minimum. The decoder checks that the
-  address paid is that pair, deriving it from the V2 factory and pair init code
-  hash the network's routers were deployed with and the first two tokens of that
-  step's path; a payment to any other address is named. (Sepolia's
-  `UniversalRouterV1_2_V2Support` was deployed with placeholders for both
-  values, so no V2 swap step can succeed on that router.) Every other payment
-  counts, in whichever step and of whatever token, a share of the output
-  included: an interface fee paid to another address by `PAY_PORTION`,
-  `TRANSFER` or `TAKE_PORTION` is named, and the minimum reads `Min. paid out`,
-  because the swap's minimum includes the fee. The minimum reads `Min. received`
-  only when some step pays the transaction's sender (the From address on
-  TxApproval, the sender the explorer reports on TransactionDetail), no
-  `Paid to` line is shown, and no permit or batch grants an allowance to a
-  spender other than the router (see below). `Paid to` lines after `Token Out`
-  name each other address paid; one reads
+  quantity together; otherwise it does not know the amount. So the rest of a V4
+  `SETTLE` of more than its swap spends, taken to the router, the WETH of a
+  `WRAP_ETH`, and a token a swap pays the router on the way to the output, each
+  stays in the router when later steps do not spend all of it, where anyone can
+  take it in a later transaction. The router sends ETH as written, so a
+  `TRANSFER` of `CONTRACT_BALANCE` of ETH always reverts and pays out nothing. A
+  step paying a token to the V2 pair that the very next step spends, as a V2
+  exact-in of that token whose `amountIn` is `ALREADY_PAID` (zero) or
+  `CONTRACT_BALANCE`, is a hop, not a payout: Uniswap's mixed routes pay the
+  next V2 pair directly, and the router enforces that swap's own minimum. The
+  decoder checks that the address paid is that pair, deriving it from the V2
+  factory and pair init code hash the network's routers were deployed with and
+  the first two tokens of that step's path; a payment to any other address is
+  named. (Sepolia's `UniversalRouterV1_2_V2Support` was deployed with
+  placeholders for both values, so no V2 swap step can succeed on that router.)
+  Every other payment counts, in whichever step and of whatever token, a share
+  of the output included: an interface fee paid to another address by
+  `PAY_PORTION`, `TRANSFER` or `TAKE_PORTION` is named, and the minimum reads
+  `Min. paid out`, because the swap's minimum includes the fee. The minimum
+  reads `Min. received` only when some step pays the transaction's sender (the
+  From address on TxApproval, the sender the explorer reports on
+  TransactionDetail), no `Paid to` line is shown, and no permit or batch grants
+  an allowance to a spender other than the router (see below). `Paid to` lines
+  after `Token Out` name each other address paid; one reads
   `The bridge, which pays the deposit's recipient on another network` for a
   bridge deposit; one reads, for example,
   `The router, 2000.0000 USDT from the sender (later steps may not spend all of it)`
@@ -3485,65 +3486,66 @@ Currently supported:
   router's own ETH, whoever a `SETTLE` names as payer. So when a V4 step would
   take ETH from the user's wallet, ETH the router already holds pays first. The
   wallet pays only the rest. For example, an `UNWRAP_WETH` into the router
-  leaves ETH there. When the decoder does not know how much ETH the router
-  holds, or how much the step would take, it counts the router as paying all of
-  that ETH. A later step paid from the router spends what the router holds and
-  takes nothing, and so does a V2 exact-in whose `amountIn` is `ALREADY_PAID`. A
-  later take of `Token In` is added to the total while both are quantities: a V3
-  exact-in of 600 USDT and a V2 exact-in of 400 USDT, both paid by the user,
-  read `1000.0000 USDT`. When the decoder does not know a take's amount, the
-  total is not known and there is no `Amount` line. A `PERMIT2_PERMIT` names
-  `Token In` only when its amount, `Unlimited` included, stands as the `Amount`
-  figure in place of the total, which it does only in the plain shape of
-  Uniswap's own routes: it comes before the step that sets the input side, it is
-  the only `PERMIT2_PERMIT` in the transaction and there is no
-  `PERMIT2_PERMIT_BATCH`, its spender is the router, the router may not let it
-  fail, no step before it takes its token, a `PERMIT2_TRANSFER_FROM` of it
-  included, or a token the decoder does not know, and the decoder reads every
-  step after it in full. Permit2 then lets the router take no more of the token
-  than that amount, so the permit covers every take of it. A step before the
-  permit takes under whatever allowance the router already had, so it may take
-  more than the permit's amount, which would then read lower than what leaves
-  the user's wallet: a `PERMIT2_TRANSFER_FROM` of 2,000 USDT into the router,
-  then a permit of 600 USDT to the router and a V3 exact-in of 2,000 USDT paid
-  from the router, read `Amount 2000.0000 USDT`. A later permit or batch may
-  raise what Permit2 lets the router take, and so may a step the decoder does
-  not read in full: a command the decoder does not read (listed at the end of
-  this section), a step whose input it cannot read, in whole or in part, and a
-  step it fails on. Every other `PERMIT2_PERMIT`, before the step that sets the
-  input side or after it, leaves `Token In` and the `Amount` line as they read
-  with no permit, unless it lets a spender other than the router take `Token In`
-  (see below): a permit of 5,000 DAI to another address and then a V3 exact-in
-  of 600 USDT read `Swap USDT → USDC` with `Amount 600.0000 USDT`, and so do
-  that exact-in and then a permit of 5,000 DAI to the router. When a permit's
-  amount stands and the step that sets the input side spends a token other than
-  the permit's, or one the decoder does not know, that step's amount gets lines
-  of its own, unless it states no amount and the user pays it none of its input
-  token. Each take the total does not count gives three lines after the `Amount`
-  line (after `Token In` when there is none): one of a token other than
-  `Token In`; one of `Token In` after an amount that is not a quantity (a V4
-  open delta, `ALREADY_PAID`, which keep their wording on the `Amount` line, or
-  no stated amount, as of a V4 exact-out step); and one whose amount the decoder
-  does not know. When there is no `Amount` line, each take the total counts gets
-  them too, so that every amount the decoder reads is shown: the amount the step
-  that sets the input side states, when it is a quantity and the user pays that
-  step (a V2 or V3 step whose `payerIsUser` is true, a V4 step the user pays
-  some of its input token, or a `WRAP_ETH`, whose ETH comes from the
-  transaction's value), and each later take of `Token In` added to it. A step
-  that sets the input side and is paid from the router takes nothing from the
-  user's wallet and gets none. A `PERMIT2_PERMIT` the decoder cannot read, then
-  V3 exact-ins of 600 USDT and 400 DAI paid by the user, give lines for both
-  amounts. When the step that sets the input side states no amount, the user
-  pays it some of its input token, and there is no `Amount` line, that step gets
-  them too whenever another take's lines give a figure, or a
-  `PERMIT2_TRANSFER_FROM` of its token gives one, on the lines below or, into
-  the router, on its `Paid to` line, so that figure cannot read as all that
-  leaves. When it states no amount and the user pays it none of its input token,
-  as when the router pays it, that step takes none of that token from the user's
-  wallet and never gets them, with a permit or without. They come in step order,
-  except that the step that sets the input side comes first when it has them,
-  followed, when there is no `Amount` line, by the other takes the total counts:
-  `Moved from the sender`, its amount, worded as the `Amount` line words one, or
+  leaves ETH there. The decoder knows what the wallet pays only when it knows
+  how much ETH the router holds and how much the step would take. Otherwise that
+  payment reads as unknown, like any amount the decoder does not know. A later
+  step paid from the router spends what the router holds and takes nothing, and
+  so does a V2 exact-in whose `amountIn` is `ALREADY_PAID`. A later take of
+  `Token In` is added to the total while both are quantities: a V3 exact-in of
+  600 USDT and a V2 exact-in of 400 USDT, both paid by the user, read
+  `1000.0000 USDT`. When the decoder does not know a take's amount, the total is
+  not known and there is no `Amount` line. A `PERMIT2_PERMIT` names `Token In`
+  only when its amount, `Unlimited` included, stands as the `Amount` figure in
+  place of the total, which it does only in the plain shape of Uniswap's own
+  routes: it comes before the step that sets the input side, it is the only
+  `PERMIT2_PERMIT` in the transaction and there is no `PERMIT2_PERMIT_BATCH`,
+  its spender is the router, the router may not let it fail, no step before it
+  takes its token, a `PERMIT2_TRANSFER_FROM` of it included, or a token the
+  decoder does not know, and the decoder reads every step after it in full.
+  Permit2 then lets the router take no more of the token than that amount, so
+  the permit covers every take of it. A step before the permit takes under
+  whatever allowance the router already had, so it may take more than the
+  permit's amount, which would then read lower than what leaves the user's
+  wallet: a `PERMIT2_TRANSFER_FROM` of 2,000 USDT into the router, then a permit
+  of 600 USDT to the router and a V3 exact-in of 2,000 USDT paid from the
+  router, read `Amount 2000.0000 USDT`. A later permit or batch may raise what
+  Permit2 lets the router take, and so may a step the decoder does not read in
+  full: a command the decoder does not read (listed at the end of this section),
+  a step whose input it cannot read, in whole or in part, and a step it fails
+  on. Every other `PERMIT2_PERMIT`, before the step that sets the input side or
+  after it, leaves `Token In` and the `Amount` line as they read with no permit,
+  unless it lets a spender other than the router take `Token In` (see below): a
+  permit of 5,000 DAI to another address and then a V3 exact-in of 600 USDT read
+  `Swap USDT → USDC` with `Amount 600.0000 USDT`, and so do that exact-in and
+  then a permit of 5,000 DAI to the router. When a permit's amount stands and
+  the step that sets the input side spends a token other than the permit's, or
+  one the decoder does not know, that step's amount gets lines of its own,
+  unless it states no amount and the user pays it none of its input token. Each
+  take the total does not count gives three lines after the `Amount` line (after
+  `Token In` when there is none): one of a token other than `Token In`; one of
+  `Token In` after an amount that is not a quantity (a V4 open delta,
+  `ALREADY_PAID`, which keep their wording on the `Amount` line, or no stated
+  amount, as of a V4 exact-out step); and one whose amount the decoder does not
+  know. When there is no `Amount` line, each take the total counts gets them
+  too, so that every amount the decoder reads is shown: the amount the step that
+  sets the input side states, when it is a quantity and the user pays that step
+  (a V2 or V3 step whose `payerIsUser` is true, a V4 step the user pays some of
+  its input token, or a `WRAP_ETH`, whose ETH comes from the transaction's
+  value), and each later take of `Token In` added to it. A step that sets the
+  input side and is paid from the router takes nothing from the user's wallet
+  and gets none. A `PERMIT2_PERMIT` the decoder cannot read, then V3 exact-ins
+  of 600 USDT and 400 DAI paid by the user, give lines for both amounts. When
+  the step that sets the input side states no amount, the user pays it some of
+  its input token, and there is no `Amount` line, that step gets them too
+  whenever another take's lines give a figure, or a `PERMIT2_TRANSFER_FROM` of
+  its token gives one, on the lines below or, into the router, on its `Paid to`
+  line, so that figure cannot read as all that leaves. When it states no amount
+  and the user pays it none of its input token, as when the router pays it, that
+  step takes none of that token from the user's wallet and never gets them, with
+  a permit or without. They come in step order, except that the step that sets
+  the input side comes first when it has them, followed, when there is no
+  `Amount` line, by the other takes the total counts: `Moved from the sender`,
+  its amount, worded as the `Amount` line words one, or
   `Unknown (could not be decoded)` when the decoder does not know it;
   `Token moved`, giving the token's address as the `Token In` line does; and
   `Moved to`, which reads `The swap step that spends it`. For a `WRAP_ETH` that

src/shared/uniswap.js

@@ -1406,8 +1406,10 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
         // from the router (see spendFromRouter()). A V4 SETTLE of ETH paid by
         // the user spends the router's ETH too (see the V4_SWAP branch). The
         // value is the amount the router holds, in base units, when a
-        // WRAP_ETH stated it, otherwise null. An UNWRAP_WETH into the router
-        // turns that amount of WETH into the same amount of ETH.
+        // WRAP_ETH stated it, otherwise null. A step that spends an unstated
+        // amount of the token from the router makes the value null. An
+        // UNWRAP_WETH into the router turns that amount of WETH into the same
+        // amount of ETH.
         const heldByRouter = new Map();
         const isRouter = (recipient) => {
             const r = recipient.toLowerCase();
@@ -1417,15 +1419,17 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
         // own balance. CONTRACT_BALANCE pays all of it. Any other quantity
         // counts against a known amount the router holds, and the steps pay
         // all of it once their amounts reach that one: a swap paid in ETH wraps
-        // what its swap steps then spend. An amount that is not a quantity,
-        // such as the null decodeV4Swap() gives a SETTLE whose payment it
-        // cannot tell, or one of a token whose amount is not known, pays out
-        // nothing this decoder can see.
+        // what its swap steps then spend. A null amount is one the calldata
+        // does not state, as for a V2 or V3 exact-out or a SETTLE whose
+        // payment decodeV4Swap() cannot tell. A null amount makes the
+        // router's amount of the token unknown. ALREADY_PAID spends nothing.
         const spendFromRouter = (token, amount) => {
             const t = token.toLowerCase();
             const held = heldByRouter.get(t);
             if (amount === CONTRACT_BALANCE) {
                 heldByRouter.delete(t);
+            } else if (amount === null) {
+                if (heldByRouter.has(t)) heldByRouter.set(t, null);
             } else if (typeof held === "bigint" && typeof amount === "bigint") {
                 if (amount >= held) {
                     heldByRouter.delete(t);
@@ -1681,8 +1685,7 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
                 ) {
                     // Buys exactly amountOut and spends at most amountInMax.
                     // Paid from the router, it spends an amount the calldata
-                    // does not state, so it spends nothing spendFromRouter()
-                    // could count.
+                    // does not state (see spendFromRouter()).
                     hasV2OrV3ExactOut = true;
                     const s =
                         command === "V2_SWAP_EXACT_OUT"
@@ -1696,6 +1699,9 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
                             addUserPaid(s.tokenIn, s.amountInMax);
                         }
                         setOutput(i, s.tokenOut, s.amountOut, [s.recipient]);
+                        if (!s.payerIsUser) {
+                            spendFromRouter(s.tokenIn, null);
+                        }
                         if (!isHop(i, s.tokenOut, s.recipient)) {
                             addPayee(s.recipient, s.tokenOut);
                         }
@@ -1838,9 +1844,9 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
                         // whoever a SETTLE names as payer. So ETH the router
                         // holds from an earlier step pays first for the ETH
                         // the user would pay the step. The user pays only the
-                        // rest. When this decoder does not know how much ETH
-                        // the router holds, or how much the user would pay,
-                        // it counts the router as paying all of that ETH.
+                        // rest. This decoder knows the rest only when it knows
+                        // how much ETH the router holds and how much the user
+                        // would pay. Otherwise the rest is unknown.
                         for (const p of v4.paidByUser) {
                             if (
                                 p.currency !==
@@ -1852,10 +1858,14 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
                             }
                             const held = heldByRouter.get(p.currency);
                             if (
-                                typeof held === "bigint" &&
-                                typeof p.amount === "bigint" &&
-                                p.amount > held
+                                typeof held !== "bigint" ||
+                                typeof p.amount !== "bigint"
                             ) {
+                                paidByUser.push({
+                                    currency: p.currency,
+                                    amount: null,
+                                });
+                            } else if (p.amount > held) {
                                 paidByUser.push({
                                     currency: p.currency,
                                     amount: p.amount - held,
@@ -2320,8 +2330,8 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
         // 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. A take with no recipient goes to the swap step
-        // that spends it. A take with a recipient goes there, and MSG_SENDER
-        // there is the sender.
+        // that spends it. A take with a recipient goes to that recipient;
+        // `MSG_SENDER` means the sender.
         for (const s of spentFromSender) {
             details.push({
                 label: "Moved from the sender",

tests/uniswap.test.js

@@ -2474,8 +2474,8 @@ describe("uniswap decoder", () => {
         // from the router's own ETH, whoever a SETTLE names as payer. ETH the
         // router holds from an UNWRAP_WETH into it pays first, so the sender
         // pays only the ETH beyond it. On next each row also took the V4
-        // step's whole ETH from the sender: 1 ETH more in the first two, and
-        // 1.5 ETH in the last.
+        // step's whole ETH from the sender: 1 ETH more in the first, and 1.5
+        // ETH in the last.
         const unwrapIntoRouter = encodeWrapEth(ROUTER_ADDR, 0n); // UNWRAP_WETH, same encoding
         // A V4 step swapping `amount` of ETH for USDC, with a SETTLE of
         // OPEN_DELTA by the user.
@@ -2493,19 +2493,6 @@ describe("uniswap decoder", () => {
                 ],
             );
         test.each([
-            {
-                kind: "a V3 exact-in of 600 USDT for WETH paid to the router, an UNWRAP_WETH into the router, then a V4 swap of 1 ETH that the user settles",
-                commands: [0x00, 0x0c, 0x10],
-                inputs: [
-                    encodeV3SwapExactIn(ROUTER_ADDR, USDT_600, 1n, [
-                        USDT_ADDR,
-                        WETH_ADDR,
-                    ]),
-                    unwrapIntoRouter,
-                    v4EthForUsdc(ONE_ETH),
-                ],
-                lines: [["Amount", "600.0000 USDT"]],
-            },
             {
                 kind: "a WRAP_ETH of 1 ETH into the router, an UNWRAP_WETH into the router, then a V4 swap of 1 ETH that the user settles",
                 commands: [0x0b, 0x0c, 0x10],
@@ -2531,6 +2518,156 @@ describe("uniswap decoder", () => {
             expect(linesBetweenTokens(result)).toEqual(lines);
         });
 
+        // The lines for ETH the sender pays a V4 step, of an amount this
+        // decoder does not know.
+        const unknownEthLines = [
+            ["Moved from the sender", UNDECODED],
+            ["Token moved", "ETH"],
+            ["Moved to", "The swap step that spends it"],
+        ];
+
+        // https://git.eeqj.de/sneak/AutistMask/issues/665 — this decoder may
+        // not know how much ETH the router holds, or how much ETH the user
+        // pays a V4 step. The ETH the sender pays that step then reads as
+        // unknown. Counting the router as paying all of it would hide ETH
+        // that can leave the wallet.
+        test.each([
+            {
+                kind: "a V3 exact-in of 600 USDT for WETH paid to the router, an UNWRAP_WETH into the router, then a V4 swap of 1 ETH that the user settles",
+                commands: [0x00, 0x0c, 0x10],
+                inputs: [
+                    encodeV3SwapExactIn(ROUTER_ADDR, USDT_600, 1n, [
+                        USDT_ADDR,
+                        WETH_ADDR,
+                    ]),
+                    unwrapIntoRouter,
+                    v4EthForUsdc(ONE_ETH),
+                ],
+                lines: [["Amount", "600.0000 USDT"], ...unknownEthLines],
+            },
+            {
+                kind: "a V4 swap of 600 USDT that takes ETH into the router, then a V4 swap of 5 ETH that the user settles",
+                commands: [0x10, 0x10],
+                inputs: [
+                    encodeV4Swap(
+                        new Uint8Array([
+                            V4_SWAP_EXACT_IN_SINGLE_ID,
+                            V4_SETTLE_ID,
+                            V4_TAKE_ID,
+                        ]),
+                        [
+                            encodeV4ExactInSingle(
+                                USDT_ADDR,
+                                ZERO_ADDR,
+                                USDT_600,
+                                1n,
+                            ),
+                            settle(USDT_ADDR, 0n, true),
+                            take(ZERO_ADDR, ROUTER_ADDR, 0n),
+                        ],
+                    ),
+                    v4EthForUsdc(5n * ONE_ETH),
+                ],
+                lines: [["Amount", "600.0000 USDT"], ...unknownEthLines],
+            },
+            {
+                kind: "a WRAP_ETH of 1 ETH into the router, an UNWRAP_WETH into the router, then a V4 exact-out paid in ETH with a SETTLE_ALL of at most 3 ETH",
+                commands: [0x0b, 0x0c, 0x10],
+                inputs: [
+                    encodeWrapEth(ROUTER_ADDR, ONE_ETH),
+                    unwrapIntoRouter,
+                    encodeV4Swap(
+                        new Uint8Array([
+                            V4_SWAP_EXACT_OUT_SINGLE_ID,
+                            V4_SETTLE_ALL_ID,
+                            V4_TAKE_ALL_ID,
+                        ]),
+                        [
+                            encodeV4ExactOutSingle(
+                                ZERO_ADDR,
+                                USDC_ADDR,
+                                390000000n,
+                                3n * ONE_ETH,
+                            ),
+                            encodeV4SettleAll(ZERO_ADDR, 3n * ONE_ETH),
+                            encodeV4TakeAll(USDC_ADDR, 0n),
+                        ],
+                    ),
+                ],
+                lines: [
+                    ...wrapLines("The swap step that spends it"),
+                    ...unknownEthLines,
+                ],
+            },
+        ])("$kind", ({ commands, inputs, lines }) => {
+            const result = decodeSteps(commands, inputs);
+            expect(linesBetweenTokens(result)).toEqual(lines);
+        });
+
+        // https://git.eeqj.de/sneak/AutistMask/issues/665 — a step that spends
+        // an unstated amount of a token from the router makes the router's
+        // amount of that token unknown. In each row such a step spends the
+        // WETH of a WRAP_ETH of 1 ETH into the router. The UNWRAP_WETH then
+        // leaves an unknown amount of ETH there, so the ETH the sender pays
+        // the last step reads as unknown.
+        test.each([
+            {
+                kind: "a WRAP_ETH of 1 ETH into the router, a V3 exact-out of at most 1 WETH paid from the router, an UNWRAP_WETH into the router, then a V4 swap of 1 ETH that the user settles",
+                commands: [0x0b, 0x01, 0x0c, 0x10],
+                inputs: [
+                    encodeWrapEth(ROUTER_ADDR, ONE_ETH),
+                    encodeV3SwapExactOut(
+                        USER_ADDR,
+                        390000000n,
+                        ONE_ETH,
+                        [USDC_ADDR, WETH_ADDR],
+                        false,
+                    ),
+                    unwrapIntoRouter,
+                    v4EthForUsdc(ONE_ETH),
+                ],
+                lines: [
+                    ["Moved from the sender", "Up to 1.0000 ETH"],
+                    ["Token moved", "ETH"],
+                    ["Moved to", "The swap step that spends it"],
+                    ...unknownEthLines,
+                ],
+            },
+            {
+                kind: "a WRAP_ETH of 1 ETH into the router, a V4 exact-out paid from the router's WETH, an UNWRAP_WETH into the router, then a V4 swap of 1 ETH that the user settles",
+                commands: [0x0b, 0x10, 0x0c, 0x10],
+                inputs: [
+                    encodeWrapEth(ROUTER_ADDR, ONE_ETH),
+                    encodeV4Swap(
+                        new Uint8Array([
+                            V4_SWAP_EXACT_OUT_SINGLE_ID,
+                            V4_SETTLE_ID,
+                            V4_TAKE_ALL_ID,
+                        ]),
+                        [
+                            encodeV4ExactOutSingle(
+                                WETH_ADDR,
+                                USDC_ADDR,
+                                390000000n,
+                                ONE_ETH,
+                            ),
+                            settle(WETH_ADDR, 0n, false),
+                            encodeV4TakeAll(USDC_ADDR, 0n),
+                        ],
+                    ),
+                    unwrapIntoRouter,
+                    v4EthForUsdc(ONE_ETH),
+                ],
+                lines: [
+                    ...wrapLines("The swap step that spends it"),
+                    ...unknownEthLines,
+                ],
+            },
+        ])("$kind", ({ commands, inputs, lines }) => {
+            const result = decodeSteps(commands, inputs);
+            expect(linesBetweenTokens(result)).toEqual(lines);
+        });
+
         // A V3_SWAP_EXACT_OUT the user pays for, of at most `amountInMax`
         // USDT for USDC.
         const v3ExactOut = (amountInMax) =>