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

The README's amount-display section carried a claim that contradicted the
tree: it said a genuine zero renders `0.0000`, but a swap's `Min. received`
worked example now shows `None (no minimum guaranteed)` for a zero minimum.
The claim is corrected — it holds for the ERC-20 amount, while the swap's
`Amount` and `Min. received` state their two misleading zeros (a V4 open
delta and a zero minimum) in words before the floor is reached.

A new list names every string an amount slot can show and what each means:
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 was checked against the
tree. Docs only; no code or tests change.

Model: opus-4-8

README.md

@@ -882,9 +882,14 @@ 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
-genuine zero still renders `0.0000`, and truncation stays truncation: `0.99999`
-shows as `0.9999`, never rounded up.
+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`, and the ERC-20
+`approve`/`transfer` amount does exactly that. The swap's `Amount` and
+`Min. received` lines never hand it one: the two zeros that would mislead there
+— a V4 open-delta amount and a zero minimum — are stated in words before the
+floor is reached, so on those lines a zero is never shown as `0.0000` (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 +941,38 @@ 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

@@ -132,6 +132,18 @@ but the review is broader than any of them.
   constant rather than `isDebug()`, so it survives only in a debug build; a
   testnet or the runtime debug toggle still raises the banner but without the
   view id.
+- 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, but the swap's `Amount` and `Min. received` state their two
+  misleading zeros in words upstream. 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