fix: the wallet's own send shows its amount to four decimal places (closes #522)

ConfirmTx and the wait, success and error screens printed the text from
Send's amount field as typed or as Max filled it in: `0.5 ETH`, `.5 ETH`, or
`1.234147890123456789 ETH` after Max, where TxApproval shows a site's send
as `0.5000 ETH`. ConfirmTx now writes the amount as TxApproval does: parsed
at the scale it is encoded with, written back as plain decimal text, and cut
by truncateAmountNeverZero(). It hands the status screens a copy carrying
that text. The transaction is still signed for the exact amount, which stays
on the pending transaction, and the USD value is priced from it. A saved
confirmation screen whose amount is not text is no longer redrawn.

Model: opus-5-5

README.md

@@ -1082,19 +1082,21 @@ The rule and its exception live in `src/shared/amountDisplay.js` as
 confirmation screens display goes through the floored one — the ERC-20 amount,
 the ETH value and max fee (`src/popup/views/approval.js`), the swap's `Amount`
 and `Min. received` lines (`src/shared/uniswap.js`), the Send screen's
-`Current balance` (`src/popup/views/send.js`), and the balance and network fee
-on the confirmation screen for the wallet's own send
-(`src/popup/views/confirmTx.js`). Both screens render a network fee through
-`formatFee()` in `src/popup/views/helpers.js`, which prices the exact fee in USD
-rather than its truncated figure, so the same fee reads the same on both, USD
-value included. Balances are stored exactly (`src/shared/balances.js`), whatever
-decimals a token declares, so a balance below the floor reaches these screens as
-it is. The history list (`src/shared/transactions.js`) uses the unfloored one:
-the transaction detail view is the authoritative record and already shows exact
-precision. The balance lists use neither: they round to four places with
-`toFixed(4)` (`balanceLine()` in `src/popup/views/helpers.js`). The 4-decimal
-rule is unchanged everywhere else, including for amounts at or above the floor
-on the approval screens.
+`Current balance` (`src/popup/views/send.js`), and the amount, balance and
+network fee on the confirmation screen for the wallet's own send
+(`src/popup/views/confirmTx.js`), which hands the wait, success and error
+screens the amount as it showed it. The transaction is still signed for the
+exact amount, and its USD value is priced from it. Both screens render a network
+fee through `formatFee()` in `src/popup/views/helpers.js`, which prices the
+exact fee in USD rather than its truncated figure, so the same fee reads the
+same on both, USD value included. Balances are stored exactly
+(`src/shared/balances.js`), whatever decimals a token declares, so a balance
+below the floor reaches these screens as it is. The history list
+(`src/shared/transactions.js`) uses the unfloored one: the transaction detail
+view is the authoritative record and already shows exact precision. The balance
+lists use neither: they round to four places with `toFixed(4)` (`balanceLine()`
+in `src/popup/views/helpers.js`). The 4-decimal rule is unchanged everywhere
+else, including for amounts at or above the floor on the approval screens.
 
 The floor applies only where the token's scale is known. Where it is not, the
 approval screen states base units instead of a quantity — see Unknown token
@@ -1761,14 +1763,17 @@ view would leave a wallet one click from deletion.
     - Token contract: full address + etherscan link (ERC-20 only)
     - From: blockie + color dot + full address + etherscan link + wallet title
     - To: blockie + color dot + full address + etherscan link + ENS name
-    - Amount: value + symbol (USD in parentheses). An ETH amount Send's "Max"
-      filled in is worked out again from this screen's own fee estimate when it
-      arrives, as the balance minus the reserve, and the transaction is signed
-      with that estimate's fee fields, so a fee fetched again at signing cannot
-      exceed what the amount leaves behind. The address keeps whatever part of
-      the reserve the transaction does not use. If the balance could not be read
-      or no longer covers the fee, the amount is left as it was and one of the
-      errors below blocks the send
+    - Amount: value + symbol (USD in parentheses), the value to four decimal
+      places with the nonzero floor, as on TxApproval (see Display Consistency),
+      however Send's amount field wrote it (`.5` and `0.5` both read `0.5000`).
+      An ETH amount Send's "Max" filled in is worked out again from this
+      screen's own fee estimate when it arrives, as the balance minus the
+      reserve, and the transaction is signed with that estimate's fee fields, so
+      a fee fetched again at signing cannot exceed what the amount leaves
+      behind. The address keeps whatever part of the reserve the transaction
+      does not use. If the balance could not be read or no longer covers the
+      fee, the amount is left as it was and one of the errors below blocks the
+      send
     - Your balance: the From address's balance on the network its transaction
       was reviewed on, read from that network's RPC endpoint each time the
       screen is shown, so a screen the popup reopens onto states and checks that