fix: a swap's unknown first take shows beside a PERMIT2_TRANSFER_FROM, only when the user pays it (closes #634)

decode() now records whether the user pays the V4 step that sets the
input side any of its input token, and decides once, after the loop,
whether that step counts as a take from the sender. A stated amount
counts whoever pays it; with none stated, the step counts only when the
user pays it. Paid from the router, it gets no Moved from the sender
lines, with a PERMIT2_PERMIT of another token or without. When it counts
and states no amount, its Unknown (could not be decoded) line also shows
beside a PERMIT2_TRANSFER_FROM of its token, whose figure is on that
move's own lines or, into the router, on its Paid to line. README
Transaction Decoding says the same.

Model: opus-5-5

src/shared/uniswap.js

@@ -1204,6 +1204,10 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
         let inputToken = null;
         let inputAmount = null;
         let inputEstablished = false;
+        // Whether the user pays the V4 step that set the input side any of
+        // its input currency (see decodeV4Swap()). Only a V4 step can set the
+        // input side with no amount, the one case in which this is read.
+        let inputPaidByUser = false;
         // The last PERMIT2_PERMIT this decoder read, or null (see
         // permitStands after the loop).
         let permit = null;
@@ -1756,6 +1760,7 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
                     // this decoder could not read may take anything: the
                     // router still runs it.
                     const setInputHere = inputEstablished && !inputSetBefore;
+                    if (setInputHere) inputPaidByUser = paidIn !== undefined;
                     if (v4) {
                         for (const p of v4.paidByUser) {
                             if (setInputHere && p === paidIn) continue;
@@ -1844,15 +1849,22 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
         // (see spentUnread()), or a token it does not know.
         const spentFromSender = [];
         let total = null;
+        // Whether the step that set the input side counts as a take from the
+        // sender, which may get lines of its own. The amount it stated counts
+        // whoever pays it. Stating none, it counts only when the user pays it
+        // some of its input token: paid from the router, it takes nothing
+        // from the sender.
+        const hasFirstTake =
+            inputEstablished && (present(inputAmount) || inputPaidByUser);
         // 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)) {
+            if (hasFirstTake && !present(inputAmount)) {
                 firstTakeUnstated = { token: inputToken, amount: null };
             }
-        } else if (inputEstablished) {
+        } else if (hasFirstTake) {
             // 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 });
@@ -1873,14 +1885,18 @@ function decode(data, toAddress, chainId, sources, fromAddress) {
             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.
+        // With no Amount figure, a later take's own figure, or that of a
+        // PERMIT2_TRANSFER_FROM of the same token, into the router or not,
+        // could read as all that leaves, so the step that set the input side,
+        // when the user pays it and 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.some((s) => present(s.amount)) ||
+                [...movedFromSender, ...movedIntoRouter].some((m) =>
+                    sameAddress(m.token, firstTakeUnstated.token),
+                ))
         ) {
             spentFromSender.unshift(firstTakeUnstated);
         }