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

@@ -243,6 +243,12 @@ 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);
 }
@@ -288,24 +294,30 @@ 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) {
-            const warningsEl = $("confirm-warnings");
-            const warning =
-                `<div class="border border-red-500 border-dashed p-2 mb-1 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>`;
-            if (warningsEl.classList.contains("hidden")) {
-                warningsEl.innerHTML = warning;
-                warningsEl.classList.remove("hidden");
-            } else {
-                warningsEl.innerHTML += warning;
-            }
+            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";
     }
 }