fix: the ETH line reads unknown at an address no refresh has read (closes #736)

An address's ETH balance is now null until a refresh has read it. That covers
a new address, a new wallet, addresses a wallet scan finds, and every address
after a network switch.

Its line reads `quantity unknown`, Home's balance `unknown (ETH)`, and Send
`Current balance: unknown (ETH)`. Max says the balance is unknown. Send is no
longer refused as zero. The address has no total, and DeleteAddress warns that
it may hold a balance.

A refresh also deletes `balanceNotFetched` only when it read every address in
the stored record.

Model: opus-5-5

src/popup/views/helpers.js

@@ -283,9 +283,10 @@ function showFlash(msg, duration = 2000) {
     flashTimer = setTimeout(clearFlash, duration);
 }
 
-// A stored token balance as a number, or null when there is no number in it.
-// balances.js writes null for a holding whose scale nothing knows, and this
-// keeps that null from becoming a zero one dereference later.
+// A stored balance as a number, or null when there is no number in it.
+// balances.js writes null for a holding whose scale nothing knows, and an
+// address's ETH balance is null until a refresh has read it. This keeps that
+// null from becoming a zero one dereference later.
 function unknownableAmount(balance) {
     if (balance == null) return null;
     const n = parseFloat(balance);
@@ -394,10 +395,10 @@ function formatFee(wei, symbol, chainId) {
 // holding renders through here.
 //
 // `amount` is null for a holding whose scale nothing knows
-// (https://git.eeqj.de/sneak/AutistMask/issues/349). There is no quantity to
-// print for it and no fiat value to derive from one, and printing 0.0000 for
-// a real holding is the failure this whole rule exists to prevent, so the row
-// says so instead.
+// (https://git.eeqj.de/sneak/AutistMask/issues/349), and for a balance no
+// refresh has read. There is no quantity to print for it and no fiat value to
+// derive from one, and printing 0.0000 for a real holding is the failure this
+// whole rule exists to prevent, so the row says so instead.
 function balanceLine(symbol, amount, price, tokenId) {
     const qty = amount === null ? "quantity unknown" : amount.toFixed(4);
     const usd =
@@ -440,7 +441,7 @@ function markTrackedTokensNotFetched() {
 function balanceLinesForAddress(addr, trackedTokens, showZero) {
     let html = balanceLine(
         nativeCurrency(),
-        parseFloat(addr.balance || "0"),
+        unknownableAmount(addr.balance),
         getPrice("ETH"),
         "ETH",
     );
@@ -493,7 +494,10 @@ function balanceLinesForAddress(addr, trackedTokens, showZero) {
 // about holdings must ask this, not the rendered figure.
 function addressHoldsFunds(addr) {
     if (!addr) return false;
-    if (parseFloat(addr.balance || "0") > 0) return true;
+    // A null or absent ETH balance reads as unknown, so the address may hold
+    // funds. Warning about funds must err towards warning.
+    if (addr.balance == null) return true;
+    if (parseFloat(addr.balance) > 0) return true;
     for (const t of addr.tokenBalances || []) {
         if (isBelowOneMillionth(t.balance)) continue;
         // A null balance is a holding whose amount could not be stated —