fix: a second click on Add while the lookup waits tracks the token once (closes #727)

The "already tracked" check ran only before the contract lookup, so a second click while the first lookup waited tracked the token twice. AddToken and SettingsAddToken now check again when the lookup answers. An answer for a token tracked meanwhile shows the "already tracked" flash message and tracks nothing.

Model: opus-5-5

src/popup/views/addToken.js

@@ -17,6 +17,11 @@ const { log } = require("../../shared/log");
 // AddToken was last opened changes neither the screen nor the status line.
 let addTokenScreenOpenings = 0;
 
+function findTracked(address) {
+    const lower = address.toLowerCase();
+    return state.trackedTokens.find((t) => t.address.toLowerCase() === lower);
+}
+
 function show() {
     addTokenScreenOpenings++;
     $("add-token-address").value = "";
@@ -50,9 +55,7 @@ function init(ctx) {
             showFlash("Enter a valid contract address starting with 0x.");
             return;
         }
-        const already = state.trackedTokens.find(
-            (t) => t.address.toLowerCase() === contractAddr.toLowerCase(),
-        );
+        const already = findTracked(contractAddr);
         if (already) {
             showFlash(already.symbol + " is already being tracked.");
             return;
@@ -85,6 +88,18 @@ function init(ctx) {
                 );
                 return;
             }
+            // Another click on Add may have tracked this token while this
+            // lookup waited.
+            const trackedMeanwhile = findTracked(contractAddr);
+            if (trackedMeanwhile) {
+                showFlash(
+                    trackedMeanwhile.symbol + " is already being tracked.",
+                );
+                if (addTokenScreenOpenings !== opening) return;
+                infoEl.textContent = "";
+                infoEl.style.visibility = "hidden";
+                return;
+            }
             // The balance list never shows a token that the spoof rule
             // refuses, so such a token is not tracked.
             if (isSpoofedSymbol(info.symbol, contractAddr, chainId)) {