fix: a token symbol read off a contract is never stored cut mid-emoji (closes #458)

lookupTokenInfo() cut the symbol at 12 and the name at 64 UTF-16 units,
so an emoji outside the Basic Multilingual Plane could be cut between its
two halves and the half left over stored and shown as U+FFFD. Both are
now cut on code points, as displaySymbol() does. A symbol already stored
broken is not repaired.

Model: opus-5-5

tests/tokenLookupTruncation.test.js

@@ -0,0 +1,48 @@
+// lookupTokenInfo() cuts the symbol and name it reads off a contract on
+// code-point boundaries, as displaySymbol() counts them, so an emoji outside
+// the Basic Multilingual Plane is never stored cut in half
+// (https://git.eeqj.de/sneak/AutistMask/issues/458).
+
+// An emoji outside the Basic Multilingual Plane: two UTF-16 units.
+const FOX = "\u{1F98A}";
+
+// The leading "A" puts every emoji at an odd UTF-16 offset, so a cut that
+// counts UTF-16 units lands between the two halves of one.
+const SYMBOL = "A" + FOX.repeat(12);
+const NAME = "A" + FOX.repeat(64);
+
+// The contract answers symbol(), decimals() and name() with the values above.
+jest.doMock("ethers", () => ({
+    ...jest.requireActual("ethers"),
+    Contract: function () {
+        return {
+            symbol: async () => SYMBOL,
+            decimals: async () => 18n,
+            name: async () => NAME,
+        };
+    },
+}));
+
+const { lookupTokenInfo } = require("../src/shared/balances");
+
+const ADDRESS = "0x1111111111111111111111111111111111111111";
+const RPC_URL = "https://rpc.example.invalid";
+
+beforeEach(() => {
+    // A token found is logged at info level, which is not under test.
+    jest.spyOn(console, "log").mockImplementation(() => {});
+});
+
+afterEach(() => {
+    jest.restoreAllMocks();
+});
+
+test("the symbol is cut to 12 code points, never inside an emoji", async () => {
+    const { symbol } = await lookupTokenInfo(ADDRESS, RPC_URL, "mainnet");
+    expect(symbol).toBe("A" + FOX.repeat(11));
+});
+
+test("the name is cut to 64 code points, never inside an emoji", async () => {
+    const { name } = await lookupTokenInfo(ADDRESS, RPC_URL, "mainnet");
+    expect(name).toBe("A" + FOX.repeat(63));
+});