fix: every balance is cut to four decimals (closes #757)

The balance lists and Home's ETH line rounded with toFixed(4), so 0.99996
ETH read 1.0000 there and 0.9999 on Send. Send's current balance and
ConfirmTx's balance line kept the nonzero floor, so 0.00004 USDC read
0.0000 in the lists and 0.00004 on Send. All four now cut the stored
decimal string with truncateAmount(), as the history rows do.
balanceLine() takes the stored balance string instead of a parsed number,
and escapes the quantity cell. The amounts, fees and allowances a screen
asks the user to approve keep the floor of truncateAmountNeverZero().

Model: opus-5-5

tests/approvalDisplayFloor.test.js

@@ -25,10 +25,6 @@ const { ERC20_ABI } = require("../src/shared/constants");
 const { state } = require("../src/shared/state");
 const { decodeCalldata } = require("../src/shared/calldataDecoder");
 const uniswap = require("../src/shared/uniswap");
-const {
-    truncateAmount,
-    truncateAmountNeverZero,
-} = require("../src/shared/amountDisplay");
 
 const iface = new Interface(ERC20_ABI);
 
@@ -183,15 +179,4 @@ describe("the four-decimal rule is otherwise unchanged", () => {
     test("a genuine zero still renders as zero", () => {
         expect(amount(transferData(0n), DAI).rawValue).toBe("0.0000");
     });
-
-    // The three truncators now share one module. The floor is a policy of the
-    // approval and confirmation screens only: the history and balance lists
-    // keep plain truncation, because the transaction detail view is the
-    // authoritative record and already shows exact precision.
-    test("the list rule stays unfloored", () => {
-        expect(truncateAmount("0.000000000000000001")).toBe("0.0000");
-        expect(truncateAmountNeverZero("0.000000000000000001")).toBe(
-            "0.000000000000000001",
-        );
-    });
 });

tests/balanceLineEscaping.test.js

@@ -41,13 +41,13 @@ describe("balanceLine", () => {
         // this payload before its id attribute, so an assertion about the
         // rest of the payload would pass on the cap and say nothing about
         // the escape.
-        const html = balanceLine(HOSTILE_SYMBOL, 1, null, null);
+        const html = balanceLine(HOSTILE_SYMBOL, "1", null, null);
         expect(html).not.toContain("<iframe");
         expect(html).toContain("&lt;iframe");
     });
 
     test("caps the symbol before rendering it", () => {
-        const html = balanceLine("A".repeat(4096), 1, null, null);
+        const html = balanceLine("A".repeat(4096), "1", null, null);
         expect(html).toContain("A".repeat(MAX_SYMBOL_LENGTH - 1) + "…");
         expect(html).not.toContain("A".repeat(MAX_SYMBOL_LENGTH + 1));
     });
@@ -55,13 +55,13 @@ describe("balanceLine", () => {
     // The token id lands inside data-token="...", so a quote in it is a
     // way out of the attribute and into a new one.
     test("keeps a quote-bearing token id inside its attribute", () => {
-        const html = balanceLine("TKN", 1, null, '" onclick="alert(1)');
+        const html = balanceLine("TKN", "1", null, '" onclick="alert(1)');
         expect(html).not.toContain('onclick="');
         expect(html).toContain('data-token="&quot; onclick=&quot;alert(1)"');
     });
 
     test("renders an ordinary holding unchanged", () => {
-        const html = balanceLine("USDC", 1.5, null, "0xabc");
+        const html = balanceLine("USDC", "1.5", null, "0xabc");
         expect(html).toContain("<span>USDC</span>");
         expect(html).toContain("<span>1.5000</span>");
         expect(html).toContain('data-token="0xabc"');
@@ -69,7 +69,7 @@ describe("balanceLine", () => {
 
     // formatUsd() writes a value under a cent as "< $0.01".
     test("escapes the USD value along with the symbol", () => {
-        const html = balanceLine("USDC", 0.001, 1, null);
+        const html = balanceLine("USDC", "0.001", 1, null);
         expect(html).toContain("&lt; $0.01");
         expect(html).not.toContain("< $0.01");
     });

tests/balanceTruncation.test.js

@@ -0,0 +1,91 @@
+// The balance lists, Home's ETH line and Send's current balance show a balance
+// as the history rows do (README.md, Amounts): cut to four decimal places,
+// never rounded up (https://git.eeqj.de/sneak/AutistMask/issues/757).
+//
+// Driven through the real popup over a stored profile on Ethereum Mainnet.
+
+const {
+    ADDRESS,
+    bootPopup,
+    cleanupPopup,
+    unversionedValidProfile,
+} = require("./support/popupBoot");
+const { balanceLine } = require("../src/popup/views/helpers");
+
+const USDC = "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48";
+
+afterEach(() => {
+    cleanupPopup();
+});
+
+// The quantity cell of a balance row.
+function quantity(row) {
+    return row.match(/<span>([^<]*)<\/span><\/span>/)[1];
+}
+
+// The popup on Home over one address holding `eth` ETH and `usdc` USDC.
+function bootHolding(eth, usdc) {
+    const profile = unversionedValidProfile({
+        trackedTokens: [{ address: USDC, symbol: "USDC", decimals: 6 }],
+    });
+    profile.wallets[0].addresses[0] = {
+        address: ADDRESS,
+        balance: eth,
+        tokenBalances: [
+            { address: USDC, symbol: "USDC", decimals: 6, balance: usdc },
+        ],
+    };
+    return bootPopup(profile);
+}
+
+// The balance row for `token` in Home's wallet list.
+function homeRow(page, token) {
+    return page
+        .node("wallet-list")
+        .innerHTML.split("<div ")
+        .find((row) => row.includes('data-token="' + token + '"'));
+}
+
+describe("balanceLine", () => {
+    test("cuts 0.99996 to 0.9999, never rounding it up to 1.0000", () => {
+        expect(quantity(balanceLine("ETH", "0.99996", null, "ETH"))).toBe(
+            "0.9999",
+        );
+    });
+
+    test("cuts 0.00004 to 0.0000", () => {
+        expect(quantity(balanceLine("USDC", "0.00004", null, USDC))).toBe(
+            "0.0000",
+        );
+    });
+});
+
+describe("Home", () => {
+    test("the ETH line and the balance list read 0.99996 ETH as 0.9999", async () => {
+        const page = await bootHolding("0.99996", "0.00004");
+
+        expect(page.visibleViews()).toEqual(["main"]);
+        expect(page.text("total-value")).toBe("0.9999 ETH");
+        expect(quantity(homeRow(page, "ETH"))).toBe("0.9999");
+    });
+
+    test("the balance list reads 0.00004 USDC as 0.0000", async () => {
+        const page = await bootHolding("0.99996", "0.00004");
+
+        expect(quantity(homeRow(page, USDC.toLowerCase()))).toBe("0.0000");
+    });
+});
+
+describe("Send", () => {
+    test("the current balance reads 0.00004 USDC as 0.0000", async () => {
+        const page = await bootHolding("0.99996", "0.00004");
+        await page.click("btn-main-send");
+        // USDC chosen in the dropdown, as the user does.
+        const dropdown = page.node("send-token");
+        dropdown.value = USDC;
+        for (const fn of dropdown.listeners.change) await fn();
+
+        expect(page.visibleViews()).toEqual(["send"]);
+        expect(page.text("send-balance")).toBe("Current balance: 0.0000 USDC");
+    });
+});

tests/deleteAddress.test.js

@@ -4,8 +4,8 @@
 // the copy is the substance and is tested as such. Two things it must not
 // get wrong: what it takes to get the address back — the app refuses both
 // obvious routes — and what counts as holding something, which is any
-// ERC-20 as well as ETH, at any size, including a balance that rounds to
-// zero at the four decimals the balance lines render. The DOM behaviour
+// ERC-20 as well as ETH, at any size, including a balance below the four
+// decimals the balance lines render. The DOM behaviour
 // around them is driven against the real popup by tests/e2e/run.js.
 
 // helpers.js pulls in state.js, which reads chrome.storage.local at load.
@@ -165,9 +165,9 @@ describe("the balance warning on the removal confirmation", () => {
     });
 
     // The sentence must not assert an amount, because any amount it could
-    // assert has been rounded: "This address holds 0.0000 ETH." is what the
-    // rounded form produces for an address that holds real money.
-    test("the warning sentence asserts no rounded amount", () => {
+    // assert has been cut to four decimals: "This address holds 0.0000 ETH." is
+    // what the cut form produces for an address that holds real money.
+    test("the warning sentence asserts no cut amount", () => {
         for (const addr of [DUST, ETH_ONLY, TOKEN_ONLY]) {
             expect(balanceWarningHtml(addr)).not.toMatch(
                 /holds [\d.]+ (ETH|USDC)/,

tests/e2e/run.js

@@ -829,12 +829,11 @@ test("a common-token quick-pick fills in the contract address (#150)", async (en
     await visible(env.page, "#view-address");
 });
 
-// The native amount as the transaction list writes it (four decimals) and
-// as the detail screen writes it (full precision). Both are rendered here
-// from the fixture rather than read off the screen, so the assertions
-// compare against the wei the stub served.
-const NATIVE_ROW_TEXT =
-    parseFloat(formatEther(STUB_NATIVE_VALUE_WEI)).toFixed(4) + " ETH";
+// The native amount as the transaction list writes it (cut to four decimals,
+// quantity() below) and as the detail screen writes it (full precision). Both
+// are rendered here from the fixture rather than read off the screen, so the
+// assertions compare against the wei the stub served.
+const NATIVE_ROW_TEXT = quantity(STUB_NATIVE_VALUE_WEI) + " ETH";
 const NATIVE_DETAIL_TEXT = formatEther(STUB_NATIVE_VALUE_WEI) + " ETH";
 
 test("the native ETH transaction detail still renders (#151)", async (env) => {
@@ -2724,10 +2723,11 @@ async function goToConfirm(page, send) {
     await assertAddressesFit(page, "the confirmation screen");
 }
 
-// A balance as the main view renders it: balanceLinesForAddress() writes
-// every quantity with four decimal places.
+// An amount in wei as the main view's balance lines and the transaction list
+// write it: cut to four decimal places, never rounded, as feeEth() does.
 function quantity(wei) {
-    return parseFloat(formatEther(wei)).toFixed(4);
+    const [whole, frac = ""] = formatEther(wei).split(".");
+    return whole + "." + (frac + "0000").slice(0, 4);
 }
 
 // Wait on the main view until a changed balance fixture has been picked up.

tests/sendDisplayFloor.test.js

@@ -6,8 +6,10 @@
 // balances and the fee were each cut to six decimal places, a rule of their
 // own, and a token holding cut to zero was dropped, while the approval screen
 // showed the same fee through src/shared/amountDisplay.js with the nonzero
-// floor. The balances are now stored exactly, every nonzero token holding
-// kept, and the screens show them and the fee through that helper.
+// floor. The balances are now stored exactly, and every nonzero token holding
+// is kept. The fee lines show the fee through that helper with the floor. The
+// balance lines cut a balance to four decimals, as the balance lists do, so a
+// balance below 0.0001 reads 0.0000.
 //
 // Driven through the real refreshBalances(), Send screen, confirmation screen
 // and approval screen, with only the node, the explorer and the DOM stubbed: a
@@ -278,21 +280,22 @@ beforeEach(() => {
     mockNode.feeData = { maxFeePerGas: 1n, gasPrice: 1n };
 });
 
-describe("an ETH balance below 0.000001 never renders as zero", () => {
+describe("an ETH balance below 0.0001 reads 0.0000", () => {
     test("on the Send screen", async () => {
         await refreshWith(HALF_MICRO_ETH);
         state.selectedToken = "ETH";
         send.updateSendBalance();
-        expect(text("send-balance")).toBe("Current balance: 0.0000005 ETH");
+        expect(text("send-balance")).toBe("Current balance: 0.0000 ETH");
+        expect(state.wallets[0].addresses[0].balance).toBe("0.0000005");
     });
 
     test("on the confirmation screen", async () => {
         await refreshWith(HALF_MICRO_ETH);
         await confirmSend("0.0000001");
-        expect(text("confirm-balance")).toBe("0.0000005 ETH");
+        expect(text("confirm-balance")).toBe("0.0000 ETH");
     });
 
-    test("while a balance above the floor keeps four decimals", async () => {
+    test("while a larger balance is cut to four decimals", async () => {
         await refreshWith(1234567890000000000n);
         await confirmSend("0.1");
         expect(text("confirm-balance")).toBe("1.2345 ETH");
@@ -302,7 +305,7 @@ describe("an ETH balance below 0.000001 never renders as zero", () => {
 // A token the user tracks stays on the balance list when the explorer's row is
 // dropped, so a holding of it below 0.000001 reached these screens as zero, and
 // the send was checked against zero.
-describe("a tracked token holding below 0.000001 never renders as zero", () => {
+describe("a tracked token holding below 0.000001 reads 0.0000", () => {
     beforeEach(() => {
         state.trackedTokens = [
             { address: TOKEN, symbol: "TOK", name: "Token", decimals: 18 },
@@ -313,13 +316,17 @@ describe("a tracked token holding below 0.000001 never renders as zero", () => {
         await refreshWith(10n ** 18n, [tokenRow(HALF_MICRO_ETH)]);
         state.selectedToken = TOKEN;
         send.updateSendBalance();
-        expect(text("send-balance")).toBe("Current balance: 0.0000005 TOK");
+        expect(text("send-balance")).toBe("Current balance: 0.0000 TOK");
+        const stored = state.wallets[0].addresses[0].tokenBalances.find(
+            (t) => t.address === TOKEN,
+        );
+        expect(stored.balance).toBe("0.0000005");
     });
 
     test("on the confirmation screen, which checks the send against it", async () => {
         await refreshWith(10n ** 18n, [tokenRow(HALF_MICRO_ETH)]);
         await confirmSend("0.0000005", TOKEN);
-        expect(text("confirm-balance")).toBe("0.0000005 TOK");
+        expect(text("confirm-balance")).toBe("0.0000 TOK");
         expect(errors()).toBe("");
         expect(balanceError()).toBe("");
         await confirmSend("0.0000006", TOKEN);
@@ -347,11 +354,9 @@ describe("a tracked token holding below 0.000001 never renders as zero", () => {
         await refreshWith(10n ** 18n, [tokenRow(1n, { decimals: "24" })]);
         state.selectedToken = TOKEN;
         send.updateSendBalance();
-        expect(text("send-balance")).toBe(
-            "Current balance: 0.000000000000000000000001 TOK",
-        );
+        expect(text("send-balance")).toBe("Current balance: 0.0000 TOK");
         await confirmSend("0.000000000000000001", TOKEN);
-        expect(text("confirm-balance")).toBe("0.000000000000000000000001 TOK");
+        expect(text("confirm-balance")).toBe("0.0000 TOK");
         expect(balanceError()).toContain(
             "Your TOK balance does not cover this amount.",
         );
@@ -363,20 +368,20 @@ describe("a tracked token holding below 0.000001 never renders as zero", () => {
 // selected while its own screen is open: after sending 2 of a 2.0000003
 // holding, the user is back on that screen, and Send read the missing row as
 // zero.
-describe("an untracked token holding below 0.000001 never renders as zero", () => {
+describe("an untracked token holding below 0.000001 reads 0.0000", () => {
     const row = () => tokenRow(HALF_MICRO_ETH, { holders_count: "50000" });
 
     test("on the Send screen", async () => {
         await refreshWith(10n ** 18n, [row()]);
         state.selectedToken = TOKEN;
         send.updateSendBalance();
-        expect(text("send-balance")).toBe("Current balance: 0.0000005 TOK");
+        expect(text("send-balance")).toBe("Current balance: 0.0000 TOK");
     });
 
     test("on the confirmation screen, which checks the send against it", async () => {
         await refreshWith(10n ** 18n, [row()]);
         await confirmSend("0.0000005", TOKEN);
-        expect(text("confirm-balance")).toBe("0.0000005 TOK");
+        expect(text("confirm-balance")).toBe("0.0000 TOK");
         expect(errors()).toBe("");
         expect(balanceError()).toBe("");
         await confirmSend("0.0000006", TOKEN);

tests/transactions.test.js

@@ -1361,6 +1361,31 @@ describe("fetchRecentTransactions merge and dedup", () => {
         expect(txs[0].holders).toBe(3500000);
     });
 
+    // README.md, Amounts: a history row cuts to four decimals, with no floor.
+    test("a token transfer below 0.0001 reads 0.0000", async () => {
+        respondWith(
+            [],
+            [
+                {
+                    transaction_hash: "0x" + "4".repeat(64),
+                    block_number: 21000040,
+                    timestamp: TS,
+                    from: { hash: ORDINARY_PEER },
+                    to: { hash: VICTIM },
+                    total: { value: "40", decimals: "6" },
+                    token: {
+                        symbol: "USDC",
+                        address_hash: USDC_CONTRACT,
+                        holders_count: "3500000",
+                    },
+                },
+            ],
+        );
+
+        const txs = await fetchRecentTransactions(VICTIM, BLOCKSCOUT, "0x1");
+        expect(txs[0].value).toBe("0.0000");
+    });
+
     test("two transfers of the same token in one transaction collapse to one entry", async () => {
         const hash = "0x" + "3".repeat(64);
         const leg = (value) => ({

tests/unknownScaleDisplay.test.js

@@ -96,7 +96,7 @@ afterEach(() => {
 describe("balanceLine", () => {
     test("an unknown quantity and a zero one render differently", () => {
         const unknown = balanceLine("NOVEL", null, null, NOVEL);
-        const zero = balanceLine("NOVEL", 0, null, NOVEL);
+        const zero = balanceLine("NOVEL", "0", null, NOVEL);
         expect(unknown).not.toBe(zero);
         expect(quantities(unknown)).toEqual(["NOVEL", "quantity unknown"]);
         expect(quantities(zero)).toEqual(["NOVEL", "0.0000"]);
@@ -105,7 +105,7 @@ describe("balanceLine", () => {
     test("an unknown quantity produces no fiat figure, a zero one does", () => {
         prices[NOVEL] = 3;
         const unknown = balanceLine("NOVEL", null, 3, NOVEL);
-        const zero = balanceLine("NOVEL", 0, 3, NOVEL);
+        const zero = balanceLine("NOVEL", "0", 3, NOVEL);
         // A price times an unknown quantity is not $0.00: that is the same
         // claim of "nothing here" the quantity cell just refused to make.
         expect(unknown).toContain(