fix: consolidate chain-switching into onChainSwitch()

Introduces src/shared/chainSwitch.js with a single onChainSwitch()
function that handles every state change required when switching
networks:

- Updates networkId, rpcUrl, blockscoutUrl from network config
- Clears price caches (testnet tokens are worthless)
- Resets lastBalanceRefresh to force immediate refresh
- Clears per-address balances and token balances
- Clears tokenHolderCache and fraudContracts (chain-specific)
- Persists state

Both callers (settings UI dropdown, background
wallet_switchEthereumChain) now go through this single code path.
Adding a new chain (e.g. ETC) requires only a new entry in
networks.js with no per-caller wiring.

Also adds defense-in-depth testnet checks in prices.js (getPrice,
getAddressValueUsd, etc.) and fixes a hardcoded etherscan.io link
in addressToken.js to use the network-aware explorer URL.

Closes #139

src/background/index.js

@@ -4,6 +4,7 @@
 
 const { DEFAULT_RPC_URL } = require("../shared/constants");
 const { SUPPORTED_CHAIN_IDS, networkByChainId } = require("../shared/networks");
+const { onChainSwitch } = require("../shared/chainSwitch");
 const { getBytes } = require("ethers");
 const {
     state,
@@ -345,12 +346,8 @@ async function handleRpc(method, params, origin) {
             return { result: null };
         }
         if (SUPPORTED_CHAIN_IDS.has(chainId)) {
-            // Switch to the requested network
             const target = networkByChainId(chainId);
-            state.networkId = target.id;
-            state.rpcUrl = target.defaultRpcUrl;
-            state.blockscoutUrl = target.defaultBlockscoutUrl;
-            await saveState();
+            await onChainSwitch(target.id);
             broadcastChainChanged(target.chainId);
             return { result: null };
         }

src/popup/views/addressToken.js

@@ -50,6 +50,10 @@ function etherscanAddressLink(address) {
     return `${currentNetwork().explorerUrl}/address/${address}`;
 }
 
+function etherscanTokenLink(tokenContract, holderAddress) {
+    return `${currentNetwork().explorerUrl}/token/${tokenContract}?a=${holderAddress}`;
+}
+
 function isoDate(timestamp) {
     const d = new Date(timestamp * 1000);
     const pad = (n) => String(n).padStart(2, "0");
@@ -156,7 +160,10 @@ function show() {
     $("address-token-dot").innerHTML = addressDotHtml(addr.address);
     $("address-token-full").dataset.full = addr.address;
     $("address-token-full").textContent = addr.address;
-    const addrLink = etherscanAddressLink(addr.address);
+    const addrLink =
+        tokenId !== "ETH"
+            ? etherscanTokenLink(tokenId, addr.address)
+            : etherscanAddressLink(addr.address);
     $("address-token-etherscan-link").innerHTML =
         `<a href="${addrLink}" target="_blank" rel="noopener" class="inline-flex items-center">${EXT_ICON}</a>`;
 

src/popup/views/approval.js

@@ -9,6 +9,7 @@ const {
 } = require("./helpers");
 const { state, saveState, currentNetwork } = require("../../shared/state");
 const { formatEther, formatUnits, Interface, toUtf8String } = require("ethers");
+const { getPrice, formatUsd } = require("../../shared/prices");
 const { ERC20_ABI } = require("../../shared/constants");
 const { TOKEN_BY_ADDRESS } = require("../../shared/tokenList");
 const txStatus = require("./txStatus");
@@ -243,8 +244,14 @@ function showTxApproval(details) {
         $("approve-tx-to").innerHTML = escapeHtml("(contract creation)");
     }
 
+    const ethValueFormatted = formatTxValue(
+        formatEther(details.txParams.value || "0"),
+    );
+    const ethPrice = getPrice("ETH");
+    const ethUsd = ethPrice ? parseFloat(ethValueFormatted) * ethPrice : null;
+    const usdStr = formatUsd(ethUsd);
     $("approve-tx-value").textContent =
-        formatTxValue(formatEther(details.txParams.value || "0")) + " ETH";
+        ethValueFormatted + " ETH" + (usdStr ? " (" + usdStr + ")" : "");
 
     // Decode calldata (reuse decoded from above)
     const decodedEl = $("approve-tx-decoded");

src/popup/views/settings.js

@@ -2,7 +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 { onChainSwitch } = require("../../shared/chainSwitch");
 const { log, debugFetch } = require("../../shared/log");
 const deleteWallet = require("./deleteWallet");
 
@@ -221,15 +221,9 @@ function init(ctx) {
     if (networkSelect) {
         networkSelect.addEventListener("change", async () => {
             const newId = networkSelect.value;
-            const net = NETWORKS[newId];
-            if (!net) return;
-            state.networkId = newId;
-            state.rpcUrl = net.defaultRpcUrl;
-            state.blockscoutUrl = net.defaultBlockscoutUrl;
+            const net = await onChainSwitch(newId);
             $("settings-rpc").value = state.rpcUrl;
             $("settings-blockscout").value = state.blockscoutUrl;
-            if (net.isTestnet) clearPrices();
-            await saveState();
             showFlash("Switched to " + net.name + ".");
         });
     }

src/shared/chainSwitch.js

@@ -0,0 +1,57 @@
+// Consolidated chain-switch handler.
+//
+// Every state change required when the active network changes is
+// performed here so that callers (settings UI, background
+// wallet_switchEthereumChain, future chain additions) all go
+// through a single code path.
+//
+// Adding a new chain (e.g. ETC) requires only a new entry in
+// networks.js — no per-caller wiring is needed.
+
+const { networkById } = require("./networks");
+const { clearPrices } = require("./prices");
+
+// Switch the active chain and reset all chain-specific cached state.
+// Returns the network configuration object for the new chain.
+async function onChainSwitch(newNetworkId) {
+    const { state, saveState } = require("./state");
+
+    const net = networkById(newNetworkId);
+
+    // --- core identity ---
+    state.networkId = net.id;
+    state.rpcUrl = net.defaultRpcUrl;
+    state.blockscoutUrl = net.defaultBlockscoutUrl;
+
+    // --- price cache ---
+    // Prices are chain-specific (testnet tokens are worthless,
+    // ETC has different pricing, etc.).
+    clearPrices();
+
+    // --- balance / refresh state ---
+    // Reset last-refresh timestamp so the next polling cycle
+    // triggers an immediate balance refresh on the new chain.
+    state.lastBalanceRefresh = 0;
+
+    // Clear per-address balances and token balances so stale data
+    // from the previous chain is never displayed while the first
+    // refresh on the new chain is in flight.
+    for (const wallet of state.wallets) {
+        for (const addr of wallet.addresses) {
+            addr.balance = "0";
+            addr.tokenBalances = [];
+        }
+    }
+
+    // --- chain-specific caches ---
+    // Token holder counts and fraud contract lists are
+    // chain-specific and must not carry over.
+    state.tokenHolderCache = {};
+    state.fraudContracts = [];
+
+    await saveState();
+
+    return net;
+}
+
+module.exports = { onChainSwitch };

src/shared/prices.js

@@ -26,6 +26,8 @@ async function refreshPrices() {
     }
 }
 
+// Clear all cached prices and reset the fetch timestamp so the
+// next refreshPrices() call will fetch fresh data.
 function clearPrices() {
     for (const key of Object.keys(prices)) {
         delete prices[key];
@@ -33,6 +35,7 @@ function clearPrices() {
     lastFetchedAt = 0;
 }
 
+// Return the USD price for a symbol, or null on testnet / unknown.
 function getPrice(symbol) {
     const { currentNetwork } = require("./state");
     if (currentNetwork().isTestnet) return null;