feat: show red warning on confirm-tx for addresses with zero transaction history

When sending to an address that has never sent or received funds (zero
nonce and zero balance), display a prominent red warning on the
transaction confirmation screen advising the user to double-check the
address.

Closes #82

src/popup/index.html

@@ -577,19 +577,6 @@
                     <div id="confirm-fee-amount" class="text-xs"></div>
                 </div>
                 <div id="confirm-warnings" class="mb-2 hidden"></div>
-                <div
-                    id="confirm-recipient-warning"
-                    class="mb-2"
-                    style="visibility: hidden"
-                >
-                    <div
-                        class="border border-red-500 border-dashed p-2 text-xs font-bold text-red-500"
-                    >
-                        WARNING: The recipient address has ZERO transaction
-                        history. This may indicate a fresh or unused address.
-                        Double-check the address before sending.
-                    </div>
-                </div>
                 <div
                     id="confirm-errors"
                     class="mb-2 border border-border border-dashed p-2 hidden"

src/popup/views/confirmTx.js

@@ -86,6 +86,42 @@ function valueWithUsd(text, usdAmount) {
     return text;
 }
 
+function renderWarnings(warnings) {
+    const warningsEl = $("confirm-warnings");
+    if (warnings.length > 0) {
+        warningsEl.innerHTML = warnings
+            .map(
+                (w) =>
+                    `<div class="border border-border border-dashed p-2 mb-1 text-xs font-bold" style="color:#c00">WARNING: ${w}</div>`,
+            )
+            .join("");
+        warningsEl.classList.remove("hidden");
+    } else {
+        warningsEl.classList.add("hidden");
+    }
+}
+
+async function checkAddressHistory(address, existingWarnings) {
+    try {
+        const provider = getProvider(state.rpcUrl);
+        const [balance, txCount] = await Promise.all([
+            provider.getBalance(address),
+            provider.getTransactionCount(address),
+        ]);
+        if (balance === 0n && txCount === 0) {
+            const warnings = existingWarnings.slice();
+            warnings.push(
+                "This address has ZERO transaction history. " +
+                    "It has never sent or received funds. " +
+                    "Double-check that the address is correct before sending.",
+            );
+            renderWarnings(warnings);
+        }
+    } catch (e) {
+        log.errorf("address history check failed:", e.message);
+    }
+}
+
 function show(txInfo) {
     pendingTx = txInfo;
 
@@ -176,18 +212,10 @@ function show(txInfo) {
         warnings.push("You are sending to your own address.");
     }
 
-    const warningsEl = $("confirm-warnings");
+    renderWarnings(warnings);
-    if (warnings.length > 0) {
+
-        warningsEl.innerHTML = warnings
+    // Async check: warn if destination address has zero transaction history
-            .map(
+    checkAddressHistory(txInfo.to, warnings);
-                (w) =>
-                    `<div class="border border-border border-dashed p-2 mb-1 text-xs font-bold">WARNING: ${w}</div>`,
-            )
-            .join("");
-        warningsEl.classList.remove("hidden");
-    } else {
-        warningsEl.classList.add("hidden");
-    }
 
     // Check for errors
     const errors = [];
@@ -243,14 +271,7 @@ function show(txInfo) {
     state.viewData = { pendingTx: txInfo };
     showView("confirm-tx");
 
-    // Reset recipient warning: reserve space (visibility:hidden) while
-    // the async check runs, preventing layout shift per README policy.
-    const recipientWarning = $("confirm-recipient-warning");
-    recipientWarning.style.display = "";
-    recipientWarning.style.visibility = "hidden";
-
     estimateGas(txInfo);
-    checkRecipientHistory(txInfo);
 }
 
 async function estimateGas(txInfo) {
@@ -293,34 +314,6 @@ async function estimateGas(txInfo) {
     }
 }
 
-async function checkRecipientHistory(txInfo) {
-    const el = $("confirm-recipient-warning");
-    try {
-        const provider = getProvider(state.rpcUrl);
-        // Skip warning for contract addresses — they may legitimately
-        // have zero outgoing transactions (getTransactionCount returns
-        // the nonce, i.e. sent-tx count only).
-        const code = await provider.getCode(txInfo.to);
-        if (code && code !== "0x") {
-            // Contract address — hide the reserved space entirely
-            el.style.display = "none";
-            return;
-        }
-        const txCount = await provider.getTransactionCount(txInfo.to);
-        if (txCount === 0) {
-            el.style.visibility = "visible";
-        } else {
-            // Address has history — collapse the reserved space
-            el.style.display = "none";
-        }
-    } catch (e) {
-        log.errorf("recipient history check failed:", e.message);
-        // On error, collapse the reserved space rather than showing a
-        // false warning or leaving an empty gap
-        el.style.display = "none";
-    }
-}
-
 function init(ctx) {
     $("btn-confirm-send").addEventListener("click", async () => {
         const password = $("confirm-tx-password").value;