fix and update

apps/frontend/lib/selected-family-storage.ts

@@ -0,0 +1,43 @@
+export const SELECTED_FAMILY_STORAGE_KEY = 'id-selected-family-group-id';
+
+export function readStoredFamilyGroupId(): string | null {
+  if (typeof window === 'undefined') {
+    return null;
+  }
+  const stored = window.localStorage.getItem(SELECTED_FAMILY_STORAGE_KEY);
+  return stored?.trim() ? stored : null;
+}
+
+export function writeStoredFamilyGroupId(groupId: string | null) {
+  if (typeof window === 'undefined') {
+    return;
+  }
+  if (groupId) {
+    window.localStorage.setItem(SELECTED_FAMILY_STORAGE_KEY, groupId);
+  } else {
+    window.localStorage.removeItem(SELECTED_FAMILY_STORAGE_KEY);
+  }
+}
+
+export function resolveFamilyGroupId(
+  groups: Array<{ id: string }>,
+  selectedGroupId: string | null,
+  isSelectionHydrated: boolean
+): string | null {
+  if (!groups.length) {
+    return null;
+  }
+
+  const candidates: Array<string | null> = [selectedGroupId];
+  if (!isSelectionHydrated) {
+    candidates.unshift(readStoredFamilyGroupId());
+  }
+
+  for (const candidate of candidates) {
+    if (candidate && groups.some((group) => group.id === candidate)) {
+      return candidate;
+    }
+  }
+
+  return isSelectionHydrated ? groups[0]!.id : null;
+}