feat: show red warning when sending to address with zero tx history

On the confirm-tx screen, asynchronously check the recipient address
via Blockscout API. If the address has never sent or received any
transactions (normal or ERC-20), display a prominent red warning.

Fails open: network errors silently skip the warning to avoid
blocking legitimate sends.

Closes #82

src/popup/views/confirmTx.js

@@ -25,6 +25,7 @@ const { decryptWithPassword } = require("../../shared/vault");
 const { formatUsd, getPrice } = require("../../shared/prices");
 const { getProvider } = require("../../shared/balances");
 const { isScamAddress } = require("../../shared/scamlist");
+const { hasZeroTransactionHistory } = require("../../shared/transactions");
 const { ERC20_ABI } = require("../../shared/constants");
 const { log } = require("../../shared/log");
 const makeBlockie = require("ethereum-blockies-base64");
@@ -244,6 +245,7 @@ function show(txInfo) {
     showView("confirm-tx");
 
     estimateGas(txInfo);
+    checkRecipientHistory(txInfo);
 }
 
 async function estimateGas(txInfo) {
@@ -286,6 +288,23 @@ async function estimateGas(txInfo) {
     }
 }
 
+async function checkRecipientHistory(txInfo) {
+    const isNew = await hasZeroTransactionHistory(
+        txInfo.to,
+        state.blockscoutUrl,
+    );
+    if (!isNew) return;
+
+    const warningsEl = $("confirm-warnings");
+    const warningHtml =
+        `<div class="border border-red-500 border-dashed p-2 mb-1 text-xs font-bold text-red-500">` +
+        `WARNING: This address has ZERO transaction history. ` +
+        `It has never sent or received any funds. ` +
+        `Double-check the address before sending.</div>`;
+    warningsEl.innerHTML = warningHtml + warningsEl.innerHTML;
+    warningsEl.classList.remove("hidden");
+}
+
 function init(ctx) {
     $("btn-confirm-send").addEventListener("click", async () => {
         const password = $("confirm-tx-password").value;

src/shared/transactions.js

@@ -251,4 +251,40 @@ function filterTransactions(txs, filters = {}) {
     return { transactions: filtered, newFraudContracts: newFraud };
 }
 
-module.exports = { fetchRecentTransactions, filterTransactions };
+/**
+ * Check whether an address has any on-chain transaction history.
+ * Returns true if the address has zero normal transactions AND zero
+ * token transfers on the configured Blockscout instance.
+ * Returns false on network errors (fail-open: don't block sends).
+ */
+async function hasZeroTransactionHistory(address, blockscoutUrl) {
+    try {
+        const resp = await debugFetch(
+            blockscoutUrl + "/addresses/" + address + "/transactions?limit=1",
+        );
+        if (!resp.ok) return false;
+        const json = await resp.json();
+        if ((json.items || []).length > 0) return false;
+
+        // Also check token transfers — an address may have only received
+        // ERC-20 tokens without any native ETH transactions.
+        const ttResp = await debugFetch(
+            blockscoutUrl +
+                "/addresses/" +
+                address +
+                "/token-transfers?type=ERC-20&limit=1",
+        );
+        if (!ttResp.ok) return false;
+        const ttJson = await ttResp.json();
+        return (ttJson.items || []).length === 0;
+    } catch (e) {
+        log.errorf("hasZeroTransactionHistory check failed:", e.message);
+        return false;
+    }
+}
+
+module.exports = {
+    fetchRecentTransactions,
+    filterTransactions,
+    hasZeroTransactionHistory,
+};