docs: fix stale zero claim, list what decoded approval amount lines read (closes #369)

The README said a genuine zero always renders `0.0000`, beside a
`Min. received` example, though a zero minimum there now reads
`None (no minimum guaranteed)`. It now says the amount rule renders a
zero as `0.0000` and that two swap lines say a zero in words instead:
`Min. received` for a zero minimum, and `Amount` when it shows a V4
exact-in `amountIn` of zero.

A new list says what the decoded ERC-20 and swap amount lines on the
transaction approval screen can read, including that a zero
`BALANCE_CHECK_ERC20` `minBalance` now reads the no-minimum wording.
The token permission warning on the signature screen is left to the
SignApproval section.

Model: opus-5-5

README.md

@@ -883,18 +883,11 @@ and the value does, the amount is extended to its first significant digit
 instead: `0.000000000000000001 DAI`, not `0.0000 DAI`. The test is on the whole
 truncated string, integer part included, so `1.00005` still shows as `1.0000` —
 the exception only fires where the entire displayed figure would read as zero.
-Truncation stays truncation: `0.99999` shows as `0.9999`, never rounded up. A
-genuine zero reaching this rule renders `0.0000`. The swap screen states a zero
-in words before it gets here in only two places. Its `Min. received` line reads
-`None (no minimum guaranteed)` for any zero minimum. Its `Amount` line reads
-`All available (V4 open delta)` when the amount it shows is a V4 exact-in
-`amountIn` of zero, which V4 treats as the whole open credit rather than a
-quantity. That line shows the amount of one step: the last `PERMIT2_PERMIT` step
-if there is any (a `Permit2 Permit Batch` step does not count), otherwise the
-first V2 or V3 exact-in, `WRAP_ETH` or V4 swap step, where a V4 swap step gives
-the `amountIn` of its first exact-in action. Every other zero amount with a
-known scale renders `0.0000`, the swap's `Amount` line included; the list of
-amount-slot strings below says where.
+Truncation stays truncation: `0.99999` shows as `0.9999`, never rounded up. The
+rule still renders a genuine zero as `0.0000`. Two lines of a swap say a zero in
+words instead: `Min. received` reads `None (no minimum guaranteed)` for a zero
+minimum, and `Amount` reads `All available (V4 open delta)` when the amount it
+shows is a V4 exact-in `amountIn` of zero.
 
 The rule and its exception live in `src/shared/amountDisplay.js` as
 `truncateAmount()` and `truncateAmountNeverZero()`. Everything the approval and
@@ -947,48 +940,40 @@ and compare against. Reading the stored field directly instead answers `null`
 for a bundled or tracked token the explorer merely omitted, which is not a
 refusal the wallet has any reason to make.
 
-**Every string an amount slot can show:** taken together, the exceptions above
-mean an amount line on the dApp approval screen (and the wait/success/error
-screens that carry a figure forward) shows one of a fixed set of strings, not
-always a number:
+**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:
 
-- A formatted quantity, e.g. `17.1900 USDT`: the token's scale is known. A
-  figure at or above the floor is truncated to four decimals, one below it is
-  extended to its first significant digit, and a genuine zero renders `0.0000`,
-  e.g. `0.0000 USDT`. That zero reaches the ERC-20 `approve`/`transfer` line for
-  an amount of zero, and the swap's `Amount` line when the step that sets it
-  states zero: a `PERMIT2_PERMIT` step, a V2 or V3 exact-in `amountIn`, or a
-  `WRAP_ETH` (`0.0000 ETH`). This is `truncateAmountNeverZero()`
-  (`src/shared/amountDisplay.js`).
-- `Unlimited`: named rather than formatted, since it needs no scale to describe.
-  On the ERC-20 line it is an `approve` of the `uint256` maximum, an unbounded
-  allowance (`src/popup/views/approval.js`); `transfer` has no such case. On a
-  swap's `Amount` line it is any input amount at or above the `uint160` maximum,
-  whichever step set the line (`src/shared/uniswap.js`): a `PERMIT2_PERMIT`
+- 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.
+- `<amount> base units (decimals unknown)` when the scale is unknown: the
+  base-unit integer, rather than a figure at a guessed scale (see Unknown token
+  scale above).
+- `Unlimited`: on the ERC-20 `Amount` line, an `approve` of the `uint256`
+  maximum, an unbounded allowance. On the swap's `Amount` line, any amount at or
+  above the `uint160` maximum, whichever step set the line: a `PERMIT2_PERMIT`
   amount at that maximum, which is an unbounded permit, or a V2 or V3 exact-in
-  `amountIn` or `WRAP_ETH` amount that large. That includes the router's
-  whole-balance value (`2^255`), which tells the router to use all it holds of
-  the token — a quantity decided at execution, not an allowance.
-- `All available (V4 open delta)`: a V4 exact-in swap whose `amountIn` is zero.
-  V4 reads that zero as "use the whole open delta", not as a literal zero, so
-  the calldata states no quantity at all. Swap `Amount` line only, and only when
-  the swap has no `PERMIT2_PERMIT` step and its first V2 or V3 exact-in,
-  `WRAP_ETH` or V4 swap step is a V4 swap step whose first exact-in action has
-  an `amountIn` of zero (`src/shared/uniswap.js`).
-- `None (no minimum guaranteed)`: a zero minimum — the swap guarantees nothing
-  back. It is a literal zero slippage floor on a V2/V3/V4 swap, and it also
-  reaches a `BALANCE_CHECK_ERC20` step: a zero `minBalance`, which once rendered
-  `0.0000` beside the token symbol, now reads this. Swap `Min. received` line
-  (`src/shared/uniswap.js`).
-- `<amount> base units (decimals unknown)`: the token's scale could not be
-  resolved, so the base-unit integer is shown with that caveat rather than
-  formatted (see Unknown token scale above). Reaches both the ERC-20 amount line
-  and the swap's `Amount` and `Min. received` (`unknownDecimalsAmount()` in
-  `src/shared/approvalAmount.js`).
-- `Unknown (not named in the calldata)`: not an amount but the currency itself —
-  the `Token In` or `Token Out` line when nothing in the calldata established
-  which token, shown beside the amount and, like the strings above, a sentence
-  rather than a value (`src/shared/uniswap.js`).
+  or `WRAP_ETH` amount that large, which is not an allowance. The router's
+  whole-balance value, `CONTRACT_BALANCE` (`2^255`), is one such amount.
+- `All available (V4 open delta)`: the swap's `Amount` line, when the amount it
+  shows is a V4 exact-in `amountIn` of zero. V4 reads that zero as "use the
+  whole open delta", so the calldata states no quantity. The line shows the
+  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,
+  `WRAP_ETH` or V4 swap step, a V4 swap step giving the `amountIn` of its first
+  readable exact-in action.
+- `None (no minimum guaranteed)`: the swap's `Min. received` line, when the
+  minimum it shows is zero, whether a V2, V3 or V4 swap's minimum or a
+  `BALANCE_CHECK_ERC20` step's `minBalance`. Before
+  [#359](https://git.eeqj.de/sneak/AutistMask/issues/359), a zero `minBalance`
+  read `0.0000` when the token's scale was known.
+
+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. The token permission warning on the signature screen has its own
+amount wording, including `Unknown`; the SignApproval section below describes
+it.
 
 #### Partial USD totals
 

TODO.md

@@ -173,23 +173,19 @@ but the review is broader than any of them.
   standalone storage entry, never part of the versioned `autistmask` profile, so
   the state schema is untouched and no existing profile is affected.
 
-- 2026-09-21: `README.md` now documents the approval screen's amount-slot
-  vocabulary and no longer contradicts itself
-  ([#369](https://git.eeqj.de/sneak/AutistMask/issues/369)). The stale claim
-  that a genuine zero always renders `0.0000` is corrected: a zero with a known
-  scale does, except where the swap screen states it in words first —
-  `Min. received` always, and the `Amount` line when the amount it shows is a V4
-  exact-in `amountIn` of zero. That line shows the amount of the last
-  `PERMIT2_PERMIT` step if there is any, otherwise of the first V2/V3 exact-in,
-  `WRAP_ETH` or V4 swap step, where a V4 swap step uses its first exact-in
-  action; any other known-scale zero there reads `0.0000`. The amount-display
-  section now names every string a slot can show and when — a formatted quantity
-  (a known-scale zero included), `Unlimited` (on a swap also the router's
-  whole-balance value), `All available (V4 open delta)`,
-  `None (no minimum guaranteed)`, base units with decimals unknown, and
-  `Unknown (not named in the calldata)` — and records that a zero `minBalance`
-  on a `BALANCE_CHECK_ERC20` step now reads `None (no minimum guaranteed)` where
-  it once read `0.0000`. Docs only.
+- 2026-09-21: `README.md` no longer says a genuine zero always renders `0.0000`
+  ([#369](https://git.eeqj.de/sneak/AutistMask/issues/369)). The amount rule
+  still renders one as `0.0000`, but two swap lines say a zero in words instead:
+  `Min. received` reads `None (no minimum guaranteed)` for a zero minimum, and
+  `Amount` reads `All available (V4 open delta)` when the amount it shows is a
+  V4 exact-in `amountIn` of zero. A new list says what the decoded ERC-20 and
+  swap amount lines on the transaction approval screen can read: a formatted
+  quantity, base units with decimals unknown, `Unlimited`,
+  `All available (V4 open delta)` and `None (no minimum guaranteed)`, which a
+  zero `minBalance` on a `BALANCE_CHECK_ERC20` step now reads instead of
+  `0.0000` at a known scale. The README also names
+  `Unknown (not named in the calldata)` on the swap's token lines, and points to
+  SignApproval for the token permission warning's own wording. Docs only.
 
 - 2026-08-30: An address no longer wraps, or is shortened to fit, in any of the
   common views ([#380](https://git.eeqj.de/sneak/AutistMask/issues/380)). The