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, its step is listed as
"V4 Swap (could not be decoded)", and a token line left without a
currency reads "Unknown (could not be decoded)" rather than "not named in
the calldata". The README records both.

Model: opus-5-5

README.md

@@ -1110,14 +1110,16 @@ read:
 
 The swap's `Token In` and `Token Out` lines name a currency, not an amount; each
 reads `Unknown (not named in the calldata)` when the decoder found no token for
-that side. An `UNWRAP_WETH` step makes `Token Out` ETH only when the output side
-is WETH, on mainnet or Sepolia, or when no step set the output side; a WETH
-`Min. received` figure then reads in ETH. 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.
+that side, or `Unknown (could not be decoded)` instead when a V4 swap action in
+the transaction could not be read (see Transaction Decoding below). An
+`UNWRAP_WETH` step makes `Token Out` ETH only when the output side is WETH, on
+mainnet or Sepolia, or when no step set the output side; a WETH `Min. received`
+figure then reads in ETH. 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
@@ -2690,7 +2692,11 @@ Currently supported:
   or recipient, and amount.
 - **Uniswap Universal Router**: `execute()` calls — shows swap direction (e.g.
   "Swap USDT → ETH"), token addresses, amounts, execution steps, and deadline.
-  Decodes Permit2, V2/V3/V4 swaps, wrap/unwrap, and balance checks.
+  Decodes Permit2, V2/V3/V4 swaps, wrap/unwrap, and balance checks. A V4 swap
+  action is read only in the parameter shape deployed on mainnet and Sepolia,
+  not in the newer one on `v4-periphery` `main`, which adds a `minHopPriceX36`
+  field. An action in any other shape is not read, and its step is listed as
+  `V4 Swap (could not be decoded)`.
 
 ### Non-Goals Forever