feat: add Sepolia testnet support (#137)

## Summary

Adds Sepolia testnet support to AutistMask.

### Changes

- **New `src/shared/networks.js`** — centralized network definitions (mainnet + Sepolia) with chain IDs, default RPC/Blockscout endpoints, and block explorer URLs
- **State management** — `networkId` added to persisted state; defaults to mainnet for backward compatibility
- **Settings UI** — network selector dropdown lets users switch between Ethereum Mainnet and Sepolia Testnet
- **Dynamic explorer links** — all hardcoded `etherscan.io` URLs replaced with dynamic links from the current network config (`sepolia.etherscan.io` for Sepolia)
- **Background service** — `wallet_switchEthereumChain` now accepts both mainnet (0x1) and Sepolia (0xaa36a7); broadcasts `chainChanged` to connected dApps
- **Inpage provider** — fetches chain ID on init and updates dynamically via `chainChanged` events (no more hardcoded `0x1`)
- **Blockscout API** — uses `eth-sepolia.blockscout.com/api/v2` for Sepolia
- **Etherscan labels** — phishing/scam checks use the correct explorer per network
- **Price fetching** — skipped on testnets (testnet tokens have no real market value)
- **RPC validation** — checks against the selected network's chain ID, not hardcoded mainnet
- **ethers provider** — `getProvider()` uses the correct ethers `Network` for Sepolia

### API Endpoints Verified

| Service | Mainnet | Sepolia |
|---------|---------|--------|
| Etherscan | etherscan.io | sepolia.etherscan.io |
| Blockscout | eth.blockscout.com/api/v2 | eth-sepolia.blockscout.com/api/v2 |
| RPC | ethereum-rpc.publicnode.com | ethereum-sepolia-rpc.publicnode.com |
| CoinDesk (prices) | ✅ | N/A (skipped on testnet) |

closes #110

Reviewed-on: #137

THIS WAS ONESHOTTED USING OPUS 4.  WTAF
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>

src/popup/views/addressDetail.js

@@ -9,7 +9,12 @@ const {
     escapeHtml,
     truncateMiddle,
 } = require("./helpers");
-const { state, currentAddress, saveState } = require("../../shared/state");
+const {
+    state,
+    currentAddress,
+    saveState,
+    currentNetwork,
+} = require("../../shared/state");
 const { formatUsd, getAddressValueUsd } = require("../../shared/prices");
 const {
     fetchRecentTransactions,
@@ -36,7 +41,7 @@ const EXT_ICON =
     `</svg></span>`;
 
 function etherscanAddressLink(address) {
-    return `https://etherscan.io/address/${address}`;
+    return `${currentNetwork().explorerUrl}/address/${address}`;
 }
 
 function show() {

src/popup/views/addressToken.js

@@ -12,7 +12,12 @@ const {
     truncateMiddle,
     balanceLine,
 } = require("./helpers");
-const { state, currentAddress, saveState } = require("../../shared/state");
+const {
+    state,
+    currentAddress,
+    saveState,
+    currentNetwork,
+} = require("../../shared/state");
 const { TOKEN_BY_ADDRESS, resolveSymbol } = require("../../shared/tokenList");
 const {
     formatUsd,
@@ -42,7 +47,7 @@ const EXT_ICON =
     `</svg></span>`;
 
 function etherscanAddressLink(address) {
-    return `https://etherscan.io/address/${address}`;
+    return `${currentNetwork().explorerUrl}/address/${address}`;
 }
 
 function isoDate(timestamp) {
@@ -194,7 +199,7 @@ function show() {
                     : null;
         const tokenHolders = tb && tb.holders != null ? tb.holders : null;
         const dot = addressDotHtml(tokenId);
-        const tokenLink = `https://etherscan.io/token/${escapeHtml(tokenId)}`;
+        const tokenLink = `${currentNetwork().explorerUrl}/token/${escapeHtml(tokenId)}`;
         const projectUrl = knownToken && knownToken.url ? knownToken.url : null;
         let infoHtml = `<div class="font-bold mb-2">Contract Address</div>`;
         infoHtml +=
@@ -381,7 +386,7 @@ function init(_ctx) {
         let staticHtml = `<div class="font-bold">${escapeHtml(currentSymbol)}</div>`;
         if (tokenId !== "ETH") {
             const dot = addressDotHtml(tokenId);
-            const link = `https://etherscan.io/token/${tokenId}`;
+            const link = `${currentNetwork().explorerUrl}/token/${tokenId}`;
             const extLink = `<a href="${link}" target="_blank" rel="noopener" class="inline-flex items-center">${EXT_ICON}</a>`;
             staticHtml +=
                 `<div class="flex items-center text-xs">${dot}` +

src/popup/views/approval.js

@@ -7,7 +7,7 @@ const {
     showError,
     hideError,
 } = require("./helpers");
-const { state, saveState } = require("../../shared/state");
+const { state, saveState, currentNetwork } = require("../../shared/state");
 const { formatEther, formatUnits, Interface, toUtf8String } = require("ethers");
 const { ERC20_ABI } = require("../../shared/constants");
 const { TOKEN_BY_ADDRESS } = require("../../shared/tokenList");
@@ -27,7 +27,7 @@ const erc20Iface = new Interface(ERC20_ABI);
 
 function approvalAddressHtml(address) {
     const dot = addressDotHtml(address);
-    const link = `https://etherscan.io/address/${address}`;
+    const link = `${currentNetwork().explorerUrl}/address/${address}`;
     const extLink = `<a href="${link}" target="_blank" rel="noopener" class="inline-flex items-center">${EXT_ICON}</a>`;
     const title = addressTitle(address, state.wallets);
     let html = "";
@@ -53,7 +53,7 @@ function tokenLabel(address) {
 }
 
 function etherscanTokenLink(address) {
-    return `https://etherscan.io/token/${address}`;
+    return `${currentNetwork().explorerUrl}/token/${address}`;
 }
 
 // Try to decode calldata using known ABIs.

src/popup/views/confirmTx.js

@@ -20,7 +20,7 @@ const {
     addressDotHtml,
     escapeHtml,
 } = require("./helpers");
-const { state } = require("../../shared/state");
+const { state, currentNetwork } = require("../../shared/state");
 const { getSignerForAddress } = require("../../shared/wallet");
 const { decryptWithPassword } = require("../../shared/vault");
 const { formatUsd, getPrice } = require("../../shared/prices");
@@ -51,11 +51,11 @@ function restore() {
 }
 
 function etherscanTokenLink(address) {
-    return `https://etherscan.io/token/${address}`;
+    return `${currentNetwork().explorerUrl}/token/${address}`;
 }
 
 function etherscanAddressLink(address) {
-    return `https://etherscan.io/address/${address}`;
+    return `${currentNetwork().explorerUrl}/address/${address}`;
 }
 
 function blockieHtml(address) {

src/popup/views/home.js

@@ -11,7 +11,12 @@ const {
     escapeHtml,
     truncateMiddle,
 } = require("./helpers");
-const { state, saveState, currentAddress } = require("../../shared/state");
+const {
+    state,
+    saveState,
+    currentAddress,
+    currentNetwork,
+} = require("../../shared/state");
 const {
     updateSendBalance,
     renderSendTokenSelect,
@@ -82,7 +87,7 @@ function renderActiveAddress() {
     if (state.activeAddress) {
         const addr = state.activeAddress;
         const dot = addressDotHtml(addr);
-        const link = `https://etherscan.io/address/${addr}`;
+        const link = `${currentNetwork().explorerUrl}/address/${addr}`;
         el.innerHTML =
             `<span class="underline decoration-dashed cursor-pointer" id="active-addr-copy">${dot}${escapeHtml(addr)}</span>` +
             `<a href="${link}" target="_blank" rel="noopener" class="inline-flex items-center">${EXT_ICON}</a>`;

src/popup/views/receive.js

@@ -6,7 +6,7 @@ const {
     formatAddressHtml,
     addressTitle,
 } = require("./helpers");
-const { state, currentAddress } = require("../../shared/state");
+const { state, currentAddress, currentNetwork } = require("../../shared/state");
 const QRCode = require("qrcode");
 
 const EXT_ICON =
@@ -25,7 +25,8 @@ function show() {
         ? formatAddressHtml(address, ensName, null, title)
         : "";
     $("receive-address-block").dataset.full = address;
-    const link = address ? `https://etherscan.io/address/${address}` : "";
+    const net = currentNetwork();
+    const link = address ? `${net.explorerUrl}/address/${address}` : "";
     $("receive-etherscan-link").innerHTML = link
         ? `<a href="${link}" target="_blank" rel="noopener" class="inline-flex items-center">${EXT_ICON}</a>`
         : "";
@@ -52,7 +53,9 @@ function show() {
         warningEl.textContent =
             "This is an ERC-20 token. Only send " +
             symbol +
-            " on the Ethereum network to this address. Sending tokens on other networks will result in permanent loss.";
+            " on " +
+            currentNetwork().name +
+            " to this address. Sending tokens on other networks will result in permanent loss.";
         warningEl.style.visibility = "visible";
     } else {
         warningEl.textContent = "";

src/popup/views/send.js

@@ -7,7 +7,7 @@ const {
     addressTitle,
     escapeHtml,
 } = require("./helpers");
-const { state, currentAddress } = require("../../shared/state");
+const { state, currentAddress, currentNetwork } = require("../../shared/state");
 let ctx;
 const { getProvider } = require("../../shared/balances");
 const { KNOWN_SYMBOLS, resolveSymbol } = require("../../shared/tokenList");
@@ -149,7 +149,7 @@ function updateSendBalance() {
     const addr = currentAddress();
     if (!addr) return;
     const dot = addressDotHtml(addr.address);
-    const link = `https://etherscan.io/address/${addr.address}`;
+    const link = `${currentNetwork().explorerUrl}/address/${addr.address}`;
     const extLink = `<a href="${link}" target="_blank" rel="noopener" class="inline-flex items-center">${EXT_ICON}</a>`;
     const title = addressTitle(addr.address, state.wallets);
     let fromHtml = "";

src/popup/views/settings.js

@@ -1,7 +1,7 @@
 const { $, showView, showFlash, escapeHtml } = require("./helpers");
 const { applyTheme } = require("../theme");
-const { state, saveState } = require("../../shared/state");
-const { ETHEREUM_MAINNET_CHAIN_ID } = require("../../shared/constants");
+const { state, saveState, currentNetwork } = require("../../shared/state");
+const { NETWORKS, SUPPORTED_CHAIN_IDS } = require("../../shared/networks");
 const { log, debugFetch } = require("../../shared/log");
 const deleteWallet = require("./deleteWallet");
 
@@ -125,6 +125,10 @@ function renderWalletListSettings() {
 function show() {
     $("settings-rpc").value = state.rpcUrl;
     $("settings-blockscout").value = state.blockscoutUrl;
+    const networkSelect = $("settings-network");
+    if (networkSelect) {
+        networkSelect.value = state.networkId;
+    }
     renderTrackedTokens();
     renderSiteLists();
     renderWalletListSettings();
@@ -168,9 +172,12 @@ function init(ctx) {
                 showFlash("Endpoint returned error: " + json.error.message);
                 return;
             }
-            if (json.result !== ETHEREUM_MAINNET_CHAIN_ID) {
+            const net = currentNetwork();
+            if (json.result !== net.chainId) {
                 showFlash(
-                    "Wrong network (expected mainnet, got chain " +
+                    "Wrong network (expected " +
+                        net.name +
+                        ", got chain " +
                         json.result +
                         ").",
                 );
@@ -209,6 +216,22 @@ function init(ctx) {
         showFlash("Saved.");
     });
 
+    const networkSelect = $("settings-network");
+    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;
+            $("settings-rpc").value = state.rpcUrl;
+            $("settings-blockscout").value = state.blockscoutUrl;
+            await saveState();
+            showFlash("Switched to " + net.name + ".");
+        });
+    }
+
     $("settings-show-zero-balances").checked = state.showZeroBalanceTokens;
     $("settings-show-zero-balances").addEventListener("change", async () => {
         state.showZeroBalanceTokens = $("settings-show-zero-balances").checked;

src/popup/views/transactionDetail.js

@@ -12,7 +12,7 @@ const {
     isoDate,
     timeAgo,
 } = require("./helpers");
-const { state } = require("../../shared/state");
+const { state, currentNetwork } = require("../../shared/state");
 const { formatEther, formatUnits } = require("ethers");
 const makeBlockie = require("ethereum-blockies-base64");
 const { log, debugFetch } = require("../../shared/log");
@@ -69,7 +69,7 @@ function etherscanLinkHtml(url) {
 function txAddressHtml(address, ensName, title) {
     const blockie = blockieHtml(address);
     const dot = addressDotHtml(address);
-    const link = `https://etherscan.io/address/${address}`;
+    const link = `${currentNetwork().explorerUrl}/address/${address}`;
     const extLink = etherscanLinkHtml(link);
     let html = `<div class="mb-1">${blockie}</div>`;
     if (title) {
@@ -95,7 +95,7 @@ function txAddressHtml(address, ensName, title) {
 }
 
 function txHashHtml(hash) {
-    const link = `https://etherscan.io/tx/${hash}`;
+    const link = `${currentNetwork().explorerUrl}/tx/${hash}`;
     const extLink = etherscanLinkHtml(link);
     return copyableHtml(hash, "break-all") + extLink;
 }
@@ -172,7 +172,7 @@ function render() {
     if (tokenContractSection && tokenContractEl) {
         if (tx.contractAddress) {
             const dot = addressDotHtml(tx.contractAddress);
-            const link = `https://etherscan.io/token/${tx.contractAddress}`;
+            const link = `${currentNetwork().explorerUrl}/token/${tx.contractAddress}`;
             tokenContractEl.innerHTML =
                 `<div class="flex items-center">${dot}` +
                 copyableHtml(tx.contractAddress, "break-all") +
@@ -234,7 +234,7 @@ function showDetailField(sectionId, contentId, value) {
 function populateOnChainDetails(txData) {
     // Block number
     if (txData.block_number != null) {
-        const blockLink = `https://etherscan.io/block/${txData.block_number}`;
+        const blockLink = `${currentNetwork().explorerUrl}/block/${txData.block_number}`;
         const blockSection = $("tx-detail-block-section");
         const blockEl = $("tx-detail-block");
         if (blockSection && blockEl) {
@@ -361,12 +361,12 @@ async function loadFullTxDetails(txHash, toAddress, isContractCall) {
                     if (tokenSymbol) {
                         detailsHtml += `<div class="font-bold">${escapeHtml(tokenSymbol)}</div>`;
                     }
-                    const etherscanUrl = `https://etherscan.io/token/${d.address}`;
+                    const etherscanUrl = `${currentNetwork().explorerUrl}/token/${d.address}`;
                     detailsHtml += `<div class="flex items-center">${dot}${copyableHtml(d.address, "break-all")}${etherscanLinkHtml(etherscanUrl)}</div>`;
                 } else if (d.address) {
                     // Protocol/contract entry: show name + Etherscan link
                     const dot = addressDotHtml(d.address);
-                    const etherscanUrl = `https://etherscan.io/address/${d.address}`;
+                    const etherscanUrl = `${currentNetwork().explorerUrl}/address/${d.address}`;
                     detailsHtml += `<div class="flex items-center">${dot}${copyableHtml(d.value, "break-all")}${etherscanLinkHtml(etherscanUrl)}</div>`;
                 } else {
                     detailsHtml += `<div class="font-bold">${escapeHtml(d.value)}</div>`;

src/popup/views/txStatus.js

@@ -10,7 +10,7 @@ const {
     escapeHtml,
 } = require("./helpers");
 const { TOKEN_BY_ADDRESS } = require("../../shared/tokenList");
-const { state, saveState } = require("../../shared/state");
+const { state, saveState, currentNetwork } = require("../../shared/state");
 const { getProvider } = require("../../shared/balances");
 const { log } = require("../../shared/log");
 
@@ -38,7 +38,7 @@ function clearTimers() {
 
 function toAddressHtml(address) {
     const dot = addressDotHtml(address);
-    const link = `https://etherscan.io/address/${address}`;
+    const link = `${currentNetwork().explorerUrl}/address/${address}`;
     const extLink = `<a href="${link}" target="_blank" rel="noopener" class="inline-flex items-center">${EXT_ICON}</a>`;
     const title = addressTitle(address, state.wallets);
     if (title) {
@@ -52,7 +52,7 @@ function toAddressHtml(address) {
 }
 
 function txHashHtml(hash) {
-    const link = `https://etherscan.io/tx/${hash}`;
+    const link = `${currentNetwork().explorerUrl}/tx/${hash}`;
     const extLink = `<a href="${link}" target="_blank" rel="noopener" class="inline-flex items-center">${EXT_ICON}</a>`;
     return (
         `<span class="underline decoration-dashed cursor-pointer break-all" data-copy="${escapeHtml(hash)}">${escapeHtml(hash)}</span>` +
@@ -62,7 +62,7 @@ function txHashHtml(hash) {
 
 function blockNumberHtml(blockNumber) {
     const num = String(blockNumber);
-    const link = `https://etherscan.io/block/${num}`;
+    const link = `${currentNetwork().explorerUrl}/block/${num}`;
     const extLink = `<a href="${link}" target="_blank" rel="noopener" class="inline-flex items-center">${EXT_ICON}</a>`;
     return (
         `<span class="underline decoration-dashed cursor-pointer" data-copy="${escapeHtml(num)}">${escapeHtml(num)}</span>` +
@@ -147,7 +147,7 @@ function tokenLabel(address) {
 }
 
 function etherscanTokenLink(address) {
-    return `https://etherscan.io/token/${address}`;
+    return `${currentNetwork().explorerUrl}/token/${address}`;
 }
 
 function decodedDetailsHtml(decoded) {