fix: a network switch in Settings leaves no balance from the previous network stored (closes #653)

The switch's save now applies the switch to the stored record it has just read, as well as to the page's state. A save writes only the fields that the page changed since its last save. When the page had last saved "0" for an address, the cleared "0" was no change. A balance that the background's refresh stored in between then stayed under the new network. The background's own switch already applies the switch to the record it writes whole, so it cannot keep such a balance. A test lands the background's save while the switch waits for the lock.

Model: opus-5-5

src/shared/chainSwitch.js

@@ -47,12 +47,20 @@ function clearPopupCaches() {
 // lock, so it is never switched while a follow of a switch saved elsewhere
 // waits for the lock (followStoredSettings() in src/popup/index.js): that
 // follow runs first, and this switch is made after it.
+//
+// The switch is also applied to the stored record that the save has just read,
+// as the background applies its own switch. A save writes only the fields that
+// this page changed since its last save. A cleared balance of "0" is no change
+// when this page last saved "0" too. The balance that the background stored
+// since then would otherwise stay under the new network
+// (https://git.eeqj.de/sneak/AutistMask/issues/653).
 async function onChainSwitch(newNetworkId) {
     const { state, saveState } = require("./state");
     let net = null;
-    await saveState(() => {
+    await saveState((stored) => {
         if (state.networkId === newNetworkId) return false;
         net = applyChainSwitchFields(state, newNetworkId);
+        applyChainSwitchFields(stored, newNetworkId);
         clearPopupCaches();
     });
     return net;

src/shared/chainSwitchFields.js

@@ -4,8 +4,9 @@
 // Split out of chainSwitch.js so the background can perform a chain switch
 // without the singleton being reachable from its bundle at all. The popup
 // still goes through onChainSwitch() (chainSwitch.js), which applies this to
-// the singleton and saves; the background applies it to the detached record of
-// its own read-modify-write (src/background/state.js).
+// the singleton and to the stored record that its save reads; the background
+// applies it to the detached record of its own read-modify-write
+// (src/background/state.js).
 //
 // Everything here is synchronous and touches nothing but the objects it is
 // given: no storage, no caches, no imports beyond the network table. That is

src/shared/state.js

@@ -591,8 +591,10 @@ function reportSaveFailure(err) {
 //
 // `beforeWrite`, when given, is called inside the lock with the stored record
 // as just read, before this page's state is compared against it. It may change
-// `state`, and this save writes that change. When it returns false, nothing is
-// written; any other return lets the save go ahead.
+// `state`, and this save writes that change. It may also change the stored
+// record: a field that this page did not change is written as `beforeWrite`
+// left it. When it returns false, nothing is written; any other return lets the
+// save go ahead.
 function saveState(beforeWrite) {
     const turn = withLock("autistmask", () => saveStateOnce(beforeWrite));
     // Every failed save is reported, whether or not the caller awaited this

tests/balanceRefreshNetworkSwitch.test.js

@@ -6,6 +6,9 @@
 // approved a site's request, which changes only the stored record. Driven
 // through the real popup over a stored profile on Ethereum Mainnet. The same
 // refresh in the background is in tests/backgroundStateIsolation.test.js.
+//
+// The last test covers a refresh by the background that is saved just before
+// the switch in Settings (https://git.eeqj.de/sneak/AutistMask/issues/653).
 
 const {
     bootPopup,
@@ -159,3 +162,49 @@ test("a refresh that returns after the background switched the network writes no
 
     expectNothingStored(page);
 });
+
+// The background's refresh saves Ethereum Mainnet's balances while the switch
+// in Settings waits for the lock. This page last saved a balance of "0" and no
+// tokens, the same values the switch sets.
+test("a background refresh saved while a switch in Settings waits for the lock leaves none of its balances stored", async () => {
+    const profile = unversionedValidProfile();
+    profile.wallets[0].addresses[0].balance = "0";
+    const page = await bootPopup(profile);
+    expect(page.pageErrors).toEqual([]);
+    const background = require("../src/background/state");
+    await page.click("btn-settings");
+
+    // The background takes the lock first. Once let go, the background saves
+    // balances as backgroundRefresh() in src/background/index.js does.
+    let letGo;
+    const refreshSave = background.updateState(async (fresh) => {
+        await new Promise((resolve) => {
+            letGo = resolve;
+        });
+        fresh.wallets[0].addresses[0].balance = "7.0";
+        fresh.wallets[0].addresses[0].tokenBalances = [
+            {
+                address: TOKEN_ADDRESS,
+                name: "Test Token",
+                symbol: "TST",
+                decimals: 18,
+                balance: "5.0",
+                holders: null,
+            },
+        ];
+        fresh.lastBalanceRefresh = Date.now();
+    });
+    await page.settle();
+
+    const select = page.node("settings-network");
+    select.value = "sepolia";
+    const switching = Promise.all(select.listeners.change.map((fn) => fn()));
+    await page.settle();
+
+    letGo();
+    await refreshSave;
+    await switching;
+    await page.settle();
+
+    expectNothingStored(page);
+});