fix: a V4 swap action not in the deployed shape is shown as not decoded (closes #358)

The four V4 swap actions are read only as the parameter structs deployed
on mainnet and Sepolia. ethers decoded the newer v4-periphery structs,
which add minHopPriceX36, as the deployed ones without an error, and the
newer multi-hop exact-in struct showed the offset of its hop-price array
as the swap amount. A decode now counts only when encoding it again gives
back the same bytes. When a swap action fails that, the Steps line lists
its step as "V4 Swap (could not be decoded)", so the screen no longer
looks complete without it. The README records the pinned shape.

Model: opus-5-5

src/shared/uniswap.js

@@ -295,6 +295,24 @@ function v4ExactInAmount(raw) {
     return raw === 0n ? OPEN_DELTA : raw;
 }
 
+// The V4 swap actions are read only in the parameter structs V4Router has
+// deployed on mainnet and Sepolia. v4-periphery `main` has since added a
+// `minHopPriceX36` field to all four (`src/interfaces/IV4Router.sol`), and
+// reading a shape nobody has deployed would be guessing. ethers alone would
+// read the newer structs anyway: it takes whatever word sits where a
+// deployed field would be, ignores bytes left over, and holds back an error
+// in a field until that field is used. The newer multi-hop exact-in struct
+// then yields the offset of its hop-price array as `amountIn`. So a decode
+// counts only when encoding the result again gives back the same bytes;
+// otherwise this throws, and decodeV4Swap() marks the step as not decoded.
+function decodeExactly(types, data) {
+    const decoded = coder.decode(types, data);
+    if (coder.encode(types, decoded) !== data) {
+        throw new Error("Not in the deployed V4 parameter shape.");
+    }
+    return decoded;
+}
+
 // Decode V4_SWAP (command 0x10) input bytes.
 // The input is ABI-encoded as (bytes actions, bytes[] params).
 // We extract token addresses from SETTLE (input) and TAKE (output) sub-actions,
@@ -309,6 +327,10 @@ function decodeV4Swap(input) {
         let takeToken = null;
         let amountIn = null;
         let amountOutMin = null;
+        // Set when a swap action's parameters are not in the deployed shape
+        // (see decodeExactly()), so nothing was read from that action. SETTLE
+        // and TAKE may still name both currencies.
+        let swapUndecoded = false;
 
         for (let i = 0; i < actions.length; i++) {
             const actionId = actions[i];
@@ -337,7 +359,7 @@ function decodeV4Swap(input) {
                         //   tuple(address,uint24,int24,address,bytes)[] path,
                         //   uint128 amountIn, uint128 amountOutMin)
                         try {
-                            const s = coder.decode(
+                            const s = decodeExactly(
                                 [
                                     "tuple(address,tuple(address,uint24,int24,address,bytes)[],uint128,uint128)",
                                 ],
@@ -355,13 +377,13 @@ function decodeV4Swap(input) {
                                 amountOutMin = s[0][3];
                             }
                         } catch {
-                            // Fall through — SETTLE/TAKE will provide tokens
+                            swapUndecoded = true;
                         }
                     } else {
                         // ExactInputSingleParams: (tuple(address,address,uint24,int24,address) poolKey,
                         //   bool zeroForOne, uint128 amountIn, uint128 amountOutMin, bytes hookData)
                         try {
-                            const s = coder.decode(
+                            const s = decodeExactly(
                                 [
                                     "tuple(tuple(address,address,uint24,int24,address),bool,uint128,uint128,bytes)",
                                 ],
@@ -384,7 +406,7 @@ function decodeV4Swap(input) {
                                 amountOutMin = s[0][3];
                             }
                         } catch {
-                            // Fall through
+                            swapUndecoded = true;
                         }
                     }
                 } else if (
@@ -393,7 +415,7 @@ function decodeV4Swap(input) {
                 ) {
                     if (actionId === V4_SWAP_EXACT_OUT) {
                         try {
-                            const s = coder.decode(
+                            const s = decodeExactly(
                                 [
                                     "tuple(address,tuple(address,uint24,int24,address,bytes)[],uint128,uint128)",
                                 ],
@@ -405,11 +427,11 @@ function decodeV4Swap(input) {
                                 settleToken = path[path.length - 1][0];
                             }
                         } catch {
-                            // Fall through
+                            swapUndecoded = true;
                         }
                     } else {
                         try {
-                            const s = coder.decode(
+                            const s = decodeExactly(
                                 [
                                     "tuple(tuple(address,address,uint24,int24,address),bool,uint128,uint128,bytes)",
                                 ],
@@ -426,7 +448,7 @@ function decodeV4Swap(input) {
                                     ? poolKey[1]
                                     : poolKey[0];
                         } catch {
-                            // Fall through
+                            swapUndecoded = true;
                         }
                     }
                 }
@@ -440,6 +462,7 @@ function decodeV4Swap(input) {
             tokenOut: takeToken,
             amountIn,
             amountOutMin,
+            swapUndecoded,
         };
     } catch {
         return null;
@@ -568,6 +591,11 @@ function decode(data, toAddress, sources) {
                 if (cmdId === 0x10) {
                     const v4 = decodeV4Swap(inputs[i]);
                     if (v4) {
+                        // Without this, a swap action that went unread would
+                        // look like one that had nothing to show.
+                        if (v4.swapUndecoded) {
+                            commandNames[i] += " (could not be decoded)";
+                        }
                         setInputOnce(v4.tokenIn, v4.amountIn);
                         // Always update output: last swap step wins. A step
                         // that carries the Min. received figure but decoded no