fix: suppress USD display on testnet networks

When connected to a testnet (e.g. Sepolia), stale mainnet prices from
the in-memory cache caused USD values to display even though
refreshPrices() correctly skipped fetching. Three fixes applied:

- refreshPrices() now clears the price cache when on a testnet instead
  of silently returning, removing any stale mainnet prices
- getPrice(), getAddressValueUsd(), getWalletValueUsd(), and
  getTotalValueUsd() all return null when the current network is a
  testnet, as defense-in-depth
- The settings network switcher immediately clears prices when
  switching to a testnet, so the UI updates without waiting for the
  next refresh cycle

closes #139

src/popup/views/settings.js

@@ -2,6 +2,7 @@ const { $, showView, showFlash, escapeHtml } = require("./helpers");
 const { applyTheme } = require("../theme");
 const { state, saveState, currentNetwork } = require("../../shared/state");
 const { NETWORKS, SUPPORTED_CHAIN_IDS } = require("../../shared/networks");
+const { clearPrices } = require("../../shared/prices");
 const { log, debugFetch } = require("../../shared/log");
 const deleteWallet = require("./deleteWallet");
 
@@ -227,6 +228,7 @@ function init(ctx) {
             state.blockscoutUrl = net.defaultBlockscoutUrl;
             $("settings-rpc").value = state.rpcUrl;
             $("settings-blockscout").value = state.blockscoutUrl;
+            if (net.isTestnet) clearPrices();
             await saveState();
             showFlash("Switched to " + net.name + ".");
         });

src/shared/prices.js

@@ -8,9 +8,13 @@ const prices = {};
 let lastFetchedAt = 0;
 
 async function refreshPrices() {
-    // Testnet tokens have no real market value — skip price fetching.
+    // Testnet tokens have no real market value — skip price fetching
+    // and clear any stale mainnet prices so the UI shows no USD values.
     const { currentNetwork } = require("./state");
-    if (currentNetwork().isTestnet) return;
+    if (currentNetwork().isTestnet) {
+        clearPrices();
+        return;
+    }
     const now = Date.now();
     if (now - lastFetchedAt < PRICE_CACHE_TTL) return;
     try {
@@ -22,7 +26,16 @@ async function refreshPrices() {
     }
 }
 
+function clearPrices() {
+    for (const key of Object.keys(prices)) {
+        delete prices[key];
+    }
+    lastFetchedAt = 0;
+}
+
 function getPrice(symbol) {
+    const { currentNetwork } = require("./state");
+    if (currentNetwork().isTestnet) return null;
     return prices[symbol] || null;
 }
 
@@ -40,6 +53,8 @@ function formatUsd(amount) {
 }
 
 function getAddressValueUsd(addr) {
+    const { currentNetwork } = require("./state");
+    if (currentNetwork().isTestnet) return null;
     if (!prices.ETH) return null;
     let total = 0;
     const ethBal = parseFloat(addr.balance || "0");
@@ -54,6 +69,8 @@ function getAddressValueUsd(addr) {
 }
 
 function getWalletValueUsd(wallet) {
+    const { currentNetwork } = require("./state");
+    if (currentNetwork().isTestnet) return null;
     if (!prices.ETH) return null;
     let total = 0;
     for (const addr of wallet.addresses) {
@@ -63,6 +80,8 @@ function getWalletValueUsd(wallet) {
 }
 
 function getTotalValueUsd(wallets) {
+    const { currentNetwork } = require("./state");
+    if (currentNetwork().isTestnet) return null;
     if (!prices.ETH) return null;
     let total = 0;
     for (const wallet of wallets) {
@@ -74,6 +93,7 @@ function getTotalValueUsd(wallets) {
 module.exports = {
     prices,
     refreshPrices,
+    clearPrices,
     getPrice,
     formatUsd,
     getAddressValueUsd,