fix: a V4 step of chained swap actions shows what the user receives (closes #563)

A V4 step's input side is now the currency its SETTLE or SETTLE_ALL
names, and its output side the one its TAKE or TAKE_ALL names. A side
none of them names comes from the swap actions, lined up as the
exact-out ones in reverse order and then the exact-in ones in order,
since the router runs exact-out actions from the output end: the input
from the first, the output from the last. Amount is the first action's
amountIn and Min. received the last one's minimum, each shown only when
that action spends the input currency or buys the output currency.
SETTLE_ALL and TAKE_ALL were not read before, and the first swap action
set both sides.

Model: opus-5-5

README.md

@@ -1164,8 +1164,9 @@ read:
   amount of one step that names an input token or amount: the last
   `PERMIT2_PERMIT` step if there is one, otherwise the first V2 or V3 exact-in,
   V2 exact-out, `WRAP_ETH` or V4 swap step. A V2 exact-out step gives its
-  `amountInMax`, and a V4 swap step the `amountIn` of its first readable
-  exact-in action.
+  `amountInMax`, and a V4 swap step the `amountIn` of the first of its swap
+  actions as they are lined up below, or none when that action is exact-out,
+  could not be read or does not spend the step's input currency.
 - `Whatever an earlier step sent to the pair (V2 already paid)`: the swap's
   `Amount` line, when the amount it shows is a V2 exact-in `amountIn` of zero.
   The router reads that zero as "the pair already holds the input tokens": the
@@ -1186,17 +1187,35 @@ 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, or `Unknown (could not be decoded)` instead when a V4 swap action in
-the transaction could not be read (see Transaction Decoding below). A V4 step
-whose swap action could not be read still sets each side as a swap step does,
-and a side its `SETTLE` or `TAKE` did not name is then unknown: no other step's
-token or figure is shown for it. 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 transaction could not be read (see Transaction Decoding below). A V4 step's
+input side is the currency its `SETTLE` or `SETTLE_ALL` names, and its output
+side the currency its `TAKE` or `TAKE_ALL` names. A side none of them names
+comes from the step's swap actions, lined up as the exact-out actions in reverse
+order, then the exact-in actions in the order they appear: the input side from
+the first action in that line, the output side from the last. The router runs
+exact-in actions from the input end and a chain of exact-out actions from the
+output end, so a step whose swap actions are all of one kind is lined up from
+what the user pays to what the user receives. A step that mixes the two kinds
+need not be: one that buys WETH with USDT exact-in and then USDC with that WETH
+exact-out is lined up with the USDC purchase first. `Amount` is the first
+action's `amountIn`, shown only when that action spends the step's input
+currency, and `Min. received` the last action's `amountOutMin`, shown only when
+that action buys the step's output currency, so no figure is shown against a
+currency it is not counted in. The decoder reads no amount from an exact-out
+action. That mixed step, ending in `SETTLE_ALL` USDT and `TAKE_ALL` USDC, reads
+`Swap USDT → USDC` with neither figure, since its first action in the line is
+exact-out and its last buys WETH. A swap action that could not be read keeps its
+place in the line and states nothing, so a side or figure that would come from
+it is unknown, while one from a readable action is shown. Such a step still sets
+each side as a swap step does, and no other step's token or figure is shown for
+an unknown one. 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