fix: the swap decoder names where a WRAP_ETH pays and counts the router's ETH in a V4 settle (closes #665)

A WRAP_ETH that sets the input side and pays its WETH to anyone but
the router now names that recipient on its Moved to line, or reads
The sender for address(1).

V4Router pays ETH from the router's own ETH, whoever a SETTLE names as
payer. ETH the router already holds now pays first for the ETH a V4
step would take from the user, and only the rest is moved from the
sender. The decoder subtracts only when it knows both amounts;
otherwise the sender's ETH reads as unknown. An UNWRAP_WETH into the
router keeps a known WETH amount as the ETH the router then holds. A
step that spends an unstated amount of a token from the router makes
the router's amount of that token unknown.

Model: opus-5-5

README.md

@@ -3414,18 +3414,23 @@ Currently supported:
   `WRAP_ETH` ran: after two `WRAP_ETH`s of 0.5 ETH into the router, a swap of 1
   WETH from it reads as leaving the WETH there. A V2 or V3 exact-out step paid
   from the router spends an amount the calldata does not state, at most its
-  `amountInMax`, so the decoder counts it as spending nothing the router holds.
-  A `SETTLE` of `OPEN_DELTA` (zero), and a `SETTLE_ALL`, pay only what the step
-  still owes of their token when they run. The decoder takes that to be the
-  amounts the step's swap actions state they spend of that token only when every
-  action in the step could be read, every swap action names the token it spends
-  and the token it buys (a swap action with an empty path swaps nothing), the
-  `SETTLE` or `SETTLE_ALL` is the step's only `SETTLE` or `SETTLE_ALL` of that
-  token and comes after every swap action, no swap action buys that token, no
-  `TAKE`, `TAKE_ALL` or `TAKE_PORTION` in the step takes it (a `TAKE` of a
-  stated amount adds to what the step owes), and the swap actions that spend it
-  state a quantity together; otherwise it does not know the amount, and such a
-  `SETTLE` from the router counts as spending nothing. So the rest of a V4
+  `amountInMax`. The decoder then no longer knows how much of the step's input
+  token the router holds. A V4 `SETTLE` from the router has the same effect when
+  the decoder does not know what that `SETTLE` pays (see below). An
+  `UNWRAP_WETH` into the router turns all the router's WETH into the same amount
+  of ETH. The decoder knows how much ETH that is only when it knew how much WETH
+  the router held and the router held no ETH before. A V4 `SETTLE` of ETH always
+  spends the router's own ETH, whichever payer it names (see below). A `SETTLE`
+  of `OPEN_DELTA` (zero), and a `SETTLE_ALL`, pay only what the step still owes
+  of their token when they run. The decoder takes that to be the amounts the
+  step's swap actions state they spend of that token only when every action in
+  the step could be read, every swap action names the token it spends and the
+  token it buys (a swap action with an empty path swaps nothing), the `SETTLE`
+  or `SETTLE_ALL` is the step's only `SETTLE` or `SETTLE_ALL` of that token and
+  comes after every swap action, no swap action buys that token, no `TAKE`,
+  `TAKE_ALL` or `TAKE_PORTION` in the step takes it (a `TAKE` of a stated amount
+  adds to what the step owes), and the swap actions that spend it state a
+  quantity together; otherwise it does not know the amount. So the rest of a V4
   `SETTLE` of more than its swap spends, taken to the router, the WETH of a
   `WRAP_ETH`, and a token a swap pays the router on the way to the output, each
   stays in the router when later steps do not spend all of it, where anyone can
@@ -3477,70 +3482,79 @@ Currently supported:
   of any amount but `OPEN_DELTA` pays that amount, and a `SETTLE` of
   `OPEN_DELTA` or a `SETTLE_ALL` pays what the step owes, as above. So a V4 step
   that swaps 400 USDT, with a `SETTLE` of 5,000 USDT paid by the user and the
-  rest taken to another address, reads `5000.0000 USDT`. A later step paid from
-  the router spends what the router holds and takes nothing, and so does a V2
-  exact-in whose `amountIn` is `ALREADY_PAID`. A later take of `Token In` is
-  added to the total while both are quantities: a V3 exact-in of 600 USDT and a
-  V2 exact-in of 400 USDT, both paid by the user, read `1000.0000 USDT`. When
-  the decoder does not know a take's amount, the total is not known and there is
-  no `Amount` line. A `PERMIT2_PERMIT` names `Token In` only when its amount,
-  `Unlimited` included, stands as the `Amount` figure in place of the total,
-  which it does only in the plain shape of Uniswap's own routes: it comes before
-  the step that sets the input side, it is the only `PERMIT2_PERMIT` in the
-  transaction and there is no `PERMIT2_PERMIT_BATCH`, its spender is the router,
-  the router may not let it fail, no step before it takes its token, a
-  `PERMIT2_TRANSFER_FROM` of it included, or a token the decoder does not know,
-  and the decoder reads every step after it in full. Permit2 then lets the
-  router take no more of the token than that amount, so the permit covers every
-  take of it. A step before the permit takes under whatever allowance the router
-  already had, so it may take more than the permit's amount, which would then
-  read lower than what leaves the user's wallet: a `PERMIT2_TRANSFER_FROM` of
-  2,000 USDT into the router, then a permit of 600 USDT to the router and a V3
-  exact-in of 2,000 USDT paid from the router, read `Amount 2000.0000 USDT`. A
-  later permit or batch may raise what Permit2 lets the router take, and so may
-  a step the decoder does not read in full: a command the decoder does not read
-  (listed at the end of this section), a step whose input it cannot read, in
-  whole or in part, and a step it fails on. Every other `PERMIT2_PERMIT`, before
-  the step that sets the input side or after it, leaves `Token In` and the
-  `Amount` line as they read with no permit, unless it lets a spender other than
-  the router take `Token In` (see below): a permit of 5,000 DAI to another
-  address and then a V3 exact-in of 600 USDT read `Swap USDT → USDC` with
-  `Amount 600.0000 USDT`, and so do that exact-in and then a permit of 5,000 DAI
-  to the router. When a permit's amount stands and the step that sets the input
-  side spends a token other than the permit's, or one the decoder does not know,
-  that step's amount gets lines of its own, unless it states no amount and the
-  user pays it none of its input token. Each take the total does not count gives
-  three lines after the `Amount` line (after `Token In` when there is none): one
-  of a token other than `Token In`; one of `Token In` after an amount that is
-  not a quantity (a V4 open delta, `ALREADY_PAID`, which keep their wording on
-  the `Amount` line, or no stated amount, as of a V4 exact-out step); and one
-  whose amount the decoder does not know. When there is no `Amount` line, each
-  take the total counts gets them too, so that every amount the decoder reads is
-  shown: the amount the step that sets the input side states, when it is a
-  quantity and the user pays that step (a V2 or V3 step whose `payerIsUser` is
-  true, a V4 step the user pays some of its input token, or a `WRAP_ETH`, whose
-  ETH comes from the transaction's value), and each later take of `Token In`
-  added to it. A step that sets the input side and is paid from the router takes
-  nothing from the user's wallet and gets none. A `PERMIT2_PERMIT` the decoder
-  cannot read, then V3 exact-ins of 600 USDT and 400 DAI paid by the user, give
-  lines for both amounts. When the step that sets the input side states no
-  amount, the user pays it some of its input token, and there is no `Amount`
-  line, that step gets them too whenever another take's lines give a figure, or
-  a `PERMIT2_TRANSFER_FROM` of its token gives one, on the lines below or, into
-  the router, on its `Paid to` line, so that figure cannot read as all that
-  leaves. When it states no amount and the user pays it none of its input token,
-  as when the router pays it, that step takes none of that token from the user's
-  wallet and never gets them, with a permit or without. They come in step order,
-  except that the step that sets the input side comes first when it has them,
-  followed, when there is no `Amount` line, by the other takes the total counts:
-  `Moved from the sender`, its amount, worded as the `Amount` line words one, or
+  rest taken to another address, reads `5000.0000 USDT`. V4 pays ETH from the
+  router's own ETH, whoever a `SETTLE` names as payer. So when a V4 step would
+  take ETH from the user's wallet, ETH the router already holds pays first. The
+  wallet pays only the rest. For example, an `UNWRAP_WETH` into the router
+  leaves ETH there. The decoder knows what the wallet pays only when it knows
+  how much ETH the router holds and how much the step would take. Otherwise that
+  payment reads as unknown, like any amount the decoder does not know. A later
+  step paid from the router spends what the router holds and takes nothing, and
+  so does a V2 exact-in whose `amountIn` is `ALREADY_PAID`. A later take of
+  `Token In` is added to the total while both are quantities: a V3 exact-in of
+  600 USDT and a V2 exact-in of 400 USDT, both paid by the user, read
+  `1000.0000 USDT`. When the decoder does not know a take's amount, the total is
+  not known and there is no `Amount` line. A `PERMIT2_PERMIT` names `Token In`
+  only when its amount, `Unlimited` included, stands as the `Amount` figure in
+  place of the total, which it does only in the plain shape of Uniswap's own
+  routes: it comes before the step that sets the input side, it is the only
+  `PERMIT2_PERMIT` in the transaction and there is no `PERMIT2_PERMIT_BATCH`,
+  its spender is the router, the router may not let it fail, no step before it
+  takes its token, a `PERMIT2_TRANSFER_FROM` of it included, or a token the
+  decoder does not know, and the decoder reads every step after it in full.
+  Permit2 then lets the router take no more of the token than that amount, so
+  the permit covers every take of it. A step before the permit takes under
+  whatever allowance the router already had, so it may take more than the
+  permit's amount, which would then read lower than what leaves the user's
+  wallet: a `PERMIT2_TRANSFER_FROM` of 2,000 USDT into the router, then a permit
+  of 600 USDT to the router and a V3 exact-in of 2,000 USDT paid from the
+  router, read `Amount 2000.0000 USDT`. A later permit or batch may raise what
+  Permit2 lets the router take, and so may a step the decoder does not read in
+  full: a command the decoder does not read (listed at the end of this section),
+  a step whose input it cannot read, in whole or in part, and a step it fails
+  on. Every other `PERMIT2_PERMIT`, before the step that sets the input side or
+  after it, leaves `Token In` and the `Amount` line as they read with no permit,
+  unless it lets a spender other than the router take `Token In` (see below): a
+  permit of 5,000 DAI to another address and then a V3 exact-in of 600 USDT read
+  `Swap USDT → USDC` with `Amount 600.0000 USDT`, and so do that exact-in and
+  then a permit of 5,000 DAI to the router. When a permit's amount stands and
+  the step that sets the input side spends a token other than the permit's, or
+  one the decoder does not know, that step's amount gets lines of its own,
+  unless it states no amount and the user pays it none of its input token. Each
+  take the total does not count gives three lines after the `Amount` line (after
+  `Token In` when there is none): one of a token other than `Token In`; one of
+  `Token In` after an amount that is not a quantity (a V4 open delta,
+  `ALREADY_PAID`, which keep their wording on the `Amount` line, or no stated
+  amount, as of a V4 exact-out step); and one whose amount the decoder does not
+  know. When there is no `Amount` line, each take the total counts gets them
+  too, so that every amount the decoder reads is shown: the amount the step that
+  sets the input side states, when it is a quantity and the user pays that step
+  (a V2 or V3 step whose `payerIsUser` is true, a V4 step the user pays some of
+  its input token, or a `WRAP_ETH`, whose ETH comes from the transaction's
+  value), and each later take of `Token In` added to it. A step that sets the
+  input side and is paid from the router takes nothing from the user's wallet
+  and gets none. A `PERMIT2_PERMIT` the decoder cannot read, then V3 exact-ins
+  of 600 USDT and 400 DAI paid by the user, give lines for both amounts. When
+  the step that sets the input side states no amount, the user pays it some of
+  its input token, and there is no `Amount` line, that step gets them too
+  whenever another take's lines give a figure, or a `PERMIT2_TRANSFER_FROM` of
+  its token gives one, on the lines below or, into the router, on its `Paid to`
+  line, so that figure cannot read as all that leaves. When it states no amount
+  and the user pays it none of its input token, as when the router pays it, that
+  step takes none of that token from the user's wallet and never gets them, with
+  a permit or without. They come in step order, except that the step that sets
+  the input side comes first when it has them, followed, when there is no
+  `Amount` line, by the other takes the total counts: `Moved from the sender`,
+  its amount, worded as the `Amount` line words one, or
   `Unknown (could not be decoded)` when the decoder does not know it;
   `Token moved`, giving the token's address as the `Token In` line does; and
-  `Moved to`, which reads `The swap step that spends it`. A token the decoder
-  does not know gives the `Moved from the sender` line alone. A step may also
-  take from the user's wallet what the decoder did not read: a V4 step whose
-  input or one of whose `SETTLE`s or `SETTLE_ALL`s it cannot read, which the
-  router still runs; a V2 or V3 exact-in or exact-out step or a
+  `Moved to`, which reads `The swap step that spends it`. For a `WRAP_ETH` that
+  pays its WETH to anyone but the router, `Moved to` names that recipient
+  instead: `The sender` for `address(1)`, and otherwise the address. A token the
+  decoder does not know gives the `Moved from the sender` line alone. A step may
+  also take from the user's wallet what the decoder did not read: a V4 step
+  whose input or one of whose `SETTLE`s or `SETTLE_ALL`s it cannot read, which
+  the router still runs; a V2 or V3 exact-in or exact-out step or a
   `PERMIT2_TRANSFER_FROM` whose input it cannot read, such as a V3 step whose
   path is shorter than one token address or has bytes after its last hop; every
   `PERMIT2_TRANSFER_FROM_BATCH`; every `EXECUTE_SUB_PLAN`, wherever it stands;