fix: zero-tx warning layout shift and contract address false positive

- Reserve space for the warning upfront using visibility:hidden instead
  of display:none, preventing layout shift per README policy
- Move warning HTML to index.html as a static element rather than
  injecting dynamically
- Skip warning for contract addresses (check getCode first) since
  getTransactionCount only returns outgoing tx nonce
- Collapse reserved space when warning is not needed (address has
  history, is a contract, or on RPC error)

src/popup/index.html

@@ -577,6 +577,19 @@
                     <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

@@ -86,42 +86,6 @@ 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;
 
@@ -212,10 +176,18 @@ function show(txInfo) {
         warnings.push("You are sending to your own address.");
     }
 
-    renderWarnings(warnings);
-
-    // Async check: warn if destination address has zero transaction history
-    checkAddressHistory(txInfo.to, 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">WARNING: ${w}</div>`,
+            )
+            .join("");
+        warningsEl.classList.remove("hidden");
+    } else {
+        warningsEl.classList.add("hidden");
+    }
 
     // Check for errors
     const errors = [];
@@ -271,7 +243,14 @@ 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) {
@@ -314,6 +293,34 @@ 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;