fix: fire part_selected after hydration to get real part name

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/(app)/(builder)/builder/page.tsx

@@ -356,6 +356,8 @@ function GunbuilderPageContent() {
   // Parts data state
   // -----------------------------
   const [parts, setParts] = useState<Part[]>([]);
+  const previousPartIdsRef = useRef<Set<string>>(new Set());
+  const isFirstPartsHydrationRef = useRef(true);
   const [loading, setLoading] = useState(false);
   const [error, setError] = useState<string | null>(null);
 
@@ -668,6 +670,20 @@ function GunbuilderPageContent() {
 
         setParts(hydrated);
 
+        // Track newly selected parts (fires after API returns with real names).
+        // Skip the first hydration — that's restoring a saved build, not a new selection.
+        if (isFirstPartsHydrationRef.current) {
+          isFirstPartsHydrationRef.current = false;
+        } else {
+          const prevIds = previousPartIdsRef.current;
+          for (const p of hydrated) {
+            if (!prevIds.has(String(p.id))) {
+              trackPartSelected(p.categoryId as BuilderSlotKey, p.name, String(p.id));
+            }
+          }
+        }
+        previousPartIdsRef.current = new Set(hydrated.map((p) => String(p.id)));
+
         // ✅ Mark key as hydrated ONLY after success
         lastHydrateKeyRef.current = key;
       } catch (err: any) {
@@ -904,10 +920,8 @@ function GunbuilderPageContent() {
         }
         return next;
       });
-      const partName = parts.find((p) => String(p.id) === String(partId))?.name ?? String(partId);
-      trackPartSelected(categoryId, partName, String(partId));
     },
-    [build, parts]
+    [build]
   );
   // Handle URL query parameters (?select, ?remove) and keep platform synced + canonical
   useEffect(() => {