docs: name every approval-screen amount string, fix stale zero claim (closes #369)

The README's amount-display section claimed a genuine zero always renders
`0.0000`. That is corrected and scoped: it holds for the ERC-20 amount and for
the swap's `Amount` line on a literal-zero `amountIn` in a V2/V3 exact-in swap
or a zero `WRAP_ETH`. Only two zeros are stated in words before the floor — the
swap's `Min. received` (any zero minimum) and its V4 exact-in `Amount` (an
`amountIn` of zero, V4's open delta).

A new list names every string an amount slot can show: a formatted quantity,
`Unlimited`, `All available (V4 open delta)`, `None (no minimum guaranteed)`,
base units with decimals unknown, and `Unknown (not named in the calldata)`. It
also records that a zero `minBalance` on a `BALANCE_CHECK_ERC20` step now reads
the no-minimum wording where it once read `0.0000`. Each claim checked against
the tree. Docs only.

Model: opus-4-8

README.md

@@ -882,9 +882,18 @@ On those screens, when the truncated string would contain no digit from 1 to 9
 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. A
+the exception only fires where the entire displayed figure would read as zero.
-genuine zero still renders `0.0000`, and truncation stays truncation: `0.99999`
+Truncation stays truncation: `0.99999` shows as `0.9999`, never rounded up. A
-shows as `0.9999`, never rounded up.
+genuine zero reaching this rule renders `0.0000`. The ERC-20
+`approve`/`transfer` amount does exactly that, and so does the swap's `Amount`
+line for a literal-zero `amountIn` on a V2 or V3 exact-in swap, or a zero
+`WRAP_ETH` (`0.0000 ETH`). Only two zeros are stated in words before the floor:
+the swap's `Min. received` line reads `None (no minimum guaranteed)` for any
+zero minimum, and its `Amount` line reads `All available (V4 open delta)` for a
+V4 exact-in `amountIn` of zero, which V4 treats as the whole open credit rather
+than a quantity. So the guarantee that a zero is never shown as `0.0000` covers
+the `Min. received` line and the V4 exact-in `Amount`; a V2/V3 or `WRAP_ETH`
+`Amount` still renders it (see the list of amount-slot strings below).
 
 The rule and its exception live in `src/shared/amountDisplay.js` as
 `truncateAmount()` and `truncateAmountNeverZero()`. Everything the approval and
@@ -936,6 +945,38 @@ 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:
+
+- A formatted quantity, e.g. `17.1900 USDT`: the token's scale is known and the
+  figure is at or above the floor, or below it and extended to its first
+  significant digit. This is `truncateAmountNeverZero()`
+  (`src/shared/amountDisplay.js`).
+- `Unlimited`: an unbounded allowance or permit, which needs no scale to
+  describe — a `uint256`-max ERC-20 `approve` (`src/popup/views/approval.js`) or
+  a Permit2 amount at the `uint160` max on a swap's `Amount`
+  (`src/shared/uniswap.js`).
+- `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
+  (`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`).
+
 #### Partial USD totals
 
 Prices are fetched for the top 25 tokens only, so an address can hold assets the

TODO.md

@@ -143,6 +143,21 @@ but the review is broader than any of them.
   both routes take, so they behave the same and the button is live for the next
   delete.
 
+- 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 still renders `0.0000` is corrected: it holds for the
+  ERC-20 amount, and also for the swap's `Amount` line on a literal-zero
+  `amountIn` in a V2/V3 exact-in swap or a zero `WRAP_ETH`. Only two zeros are
+  stated in words upstream — the swap's `Min. received` (any zero minimum) and
+  its V4 exact-in `Amount` (an `amountIn` of zero, V4's open delta). The
+  amount-display section now names every string a slot can show — a formatted
+  quantity, `Unlimited`, `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; each claim checked against the tree.
+
 - 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
   wallet list was the reported case: the address shared one row with the