feat: expand warning types for send confirmation

- Combine MEW darklist (652) and CryptoScamDB (2043) into 2314 scam addresses
- Add null/burn address detection with permanent loss warning
- Add contract address detection warning (sending directly to contracts)
- Unify all warnings into single warnings element (sync + async)
- Zero-history warning now uses unified warning system

Closes #114

src/popup/views/confirmTx.js

@@ -24,7 +24,7 @@ const { getSignerForAddress } = require("../../shared/wallet");
 const { decryptWithPassword } = require("../../shared/vault");
 const { formatUsd, getPrice } = require("../../shared/prices");
 const { getProvider } = require("../../shared/balances");
-const { isScamAddress } = require("../../shared/scamlist");
+const { isScamAddress, isNullOrBurnAddress } = require("../../shared/scamlist");
 const { ERC20_ABI } = require("../../shared/constants");
 const { log } = require("../../shared/log");
 const makeBlockie = require("ethereum-blockies-base64");
@@ -38,6 +38,28 @@ const EXT_ICON =
     `</svg></span>`;
 
 let pendingTx = null;
+// Track active warnings so async checks can append without overwriting.
+let activeWarnings = [];
+
+function renderWarnings(el, warnings) {
+    activeWarnings = warnings.slice();
+    if (warnings.length > 0) {
+        el.innerHTML = warnings
+            .map(
+                (w) =>
+                    `<div class="border border-border border-dashed p-2 mb-1 text-xs font-bold">WARNING: ${w}</div>`,
+            )
+            .join("");
+        el.classList.remove("hidden");
+    } else {
+        el.classList.add("hidden");
+    }
+}
+
+function appendWarning(el, message) {
+    activeWarnings.push(message);
+    renderWarnings(el, activeWarnings);
+}
 
 function restore() {
     const d = state.viewData;
@@ -165,29 +187,24 @@ function show(txInfo) {
         $("confirm-balance").textContent = valueWithUsd(bal + " ETH", balUsd);
     }
 
-    // Check for warnings
+    // Check for warnings (synchronous checks first, async checks added later)
     const warnings = [];
     if (isScamAddress(txInfo.to)) {
         warnings.push(
             "This address is on a known scam/fraud list. Do not send funds to this address.",
         );
     }
+    if (isNullOrBurnAddress(txInfo.to)) {
+        warnings.push(
+            "This is a null or burn address. Funds sent here will be permanently lost.",
+        );
+    }
     if (txInfo.to.toLowerCase() === txInfo.from.toLowerCase()) {
         warnings.push("You are sending to your own address.");
     }
 
     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");
-    }
+    renderWarnings(warningsEl, warnings);
 
     // Check for errors
     const errors = [];
@@ -243,8 +260,11 @@ function show(txInfo) {
     state.viewData = { pendingTx: txInfo };
     showView("confirm-tx");
 
-    // Reset recipient warning to hidden (space always reserved, no layout shift)
-    $("confirm-recipient-warning").style.visibility = "hidden";
+    // Hide the legacy recipient warning element (warnings now unified)
+    const legacyWarningEl = $("confirm-recipient-warning");
+    if (legacyWarningEl) {
+        legacyWarningEl.style.display = "none";
+    }
 
     estimateGas(txInfo);
     checkRecipientHistory(txInfo);
@@ -291,19 +311,24 @@ async function estimateGas(txInfo) {
 }
 
 async function checkRecipientHistory(txInfo) {
-    const el = $("confirm-recipient-warning");
+    const warningsEl = $("confirm-warnings");
     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") {
+            // Recipient is a contract address — warn the user
+            appendWarning(
+                warningsEl,
+                "The recipient is a contract address. Sending tokens directly to a contract may result in permanent loss of funds.",
+            );
             return;
         }
         const txCount = await provider.getTransactionCount(txInfo.to);
         if (txCount === 0) {
-            el.style.visibility = "visible";
+            appendWarning(
+                warningsEl,
+                "The recipient address has ZERO transaction history. This may indicate a fresh or unused address. Double-check the address before sending.",
+            );
         }
     } catch (e) {
         log.errorf("recipient history check failed:", e.message);