fix: the approval screen names the address a swap's output is paid to (closes #594)

The swap decoder read no recipient, so a swap paying its output to another
address still showed Min. received. It now reads the address each swap step,
SWEEP, WRAP_ETH, UNWRAP_WETH, V4 TAKE and TAKE_ALL pays. Min. received shows
only when some step pays the sender, none pays another address, none that may
pay one went unread, and the output does not stay in the router with no later
SWEEP or UNWRAP_WETH paying it out. A payment to the V2 pair the next V2 swap
spends as already paid is a hop, not a payout. Otherwise it reads Min. paid
out, with Paid to lines.

Model: opus-5-5

README.md

@@ -1144,8 +1144,9 @@ fetched, without that cross-address check, and shows the row's figure.
 
 **Decoded amount lines on the transaction approval screen:** the `Amount` line
 of a decoded ERC-20 call, and the `Amount` and `Min. received` lines of a
-decoded swap (see TxApproval below), do not always read as a number. They can
-read:
+decoded swap (see TxApproval below; `Min. received` reads `Min. paid out` unless
+only the user is paid, see Transaction Decoding), do not always read as a
+number. They can read:
 
 - A formatted quantity, e.g. `17.1900 USDT`, when the token's scale is known:
   truncated to four decimals, with the floor and the zero cases described above.
@@ -2288,7 +2289,9 @@ view would leave a wallet one click from deletion.
     - Site origin (bold, scheme and port included) + "wants to send a
       transaction"
     - Decoded action (if calldata is recognized): action name, token details,
-      amounts, steps, deadline (see Transaction Decoding)
+      amounts, steps, deadline, and unless a swap pays only the From address, a
+      `Paid to` line for each other address it pays, or saying that its output
+      stays in the router or who it pays is unknown (see Transaction Decoding)
     - From: color dot + full address + etherscan link
     - Contract: color dot + full address + etherscan link, token symbol label if
       known; for a contract creation, the same sentence as on WaitTx
@@ -2923,7 +2926,39 @@ Currently supported:
   listed as `Execute Sub-Plan (its steps are not shown)`, and whatever the other
   steps state, the summary names no swap direction, `Token In` and `Token Out`
   read `Unknown (could not be decoded)`, and there is no `Amount` or
-  `Min. received` line.
+  `Min. received` line. Each swap step, `SWEEP`, `WRAP_ETH`, `UNWRAP_WETH` and
+  V4 `TAKE` names the address it pays, and `TAKE_ALL` pays the transaction's
+  sender. The router reads `address(1)` as the transaction's sender, and
+  `address(2)` as the router itself, which holds what it is paid until a later
+  step pays it out; a payment to the router, as `address(2)` or by its own
+  address, is not counted as paid out. When a swap step or `TAKE` pays the
+  router the swap's output token, the output stays in the router unless a later
+  `SWEEP` of that token, or a later `UNWRAP_WETH` when it is WETH, pays it out.
+  A swap step or `TAKE` 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. 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 step pays any other address, no step that
+  may pay an address went unread, and the output does not stay in the router.
+  Otherwise it reads `Min. paid out`, a `Paid to` line after `Token Out` names
+  each other address paid, one reads
+  `The router, where it stays (no later step pays it out)` when the output stays
+  in the router, and one more reads `Unknown (could not be decoded)` when such a
+  step went unread, or `Unknown (not named in the calldata)` when no step pays
+  anyone. A step goes unread when its recipient does not decode as an address,
+  or when it is a command or V4 action the decoder does not read: every command
+  other than `PERMIT2_PERMIT`, `V2_SWAP_EXACT_IN`, `V2_SWAP_EXACT_OUT`,
+  `V3_SWAP_EXACT_IN`, `V4_SWAP`, `SWEEP`, `WRAP_ETH`, `UNWRAP_WETH` and
+  `BALANCE_CHECK_ERC20` (`V3_SWAP_EXACT_OUT`, `TRANSFER`, `PAY_PORTION` and
+  `EXECUTE_SUB_PLAN` among them), and V4 `TAKE_PORTION`.
 
 ### Non-Goals Forever