fix: useAdminUsers null guard, unmount cleanup, split test

- Guard setUsers against null data with nullish coalescing (data ?? [])
- Add isMounted flag in useEffect to prevent setState after unmount
- Split combined inviteUser+deleteUser test into two independent it blocks

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

src/admin/users/__tests__/useAdminUsers.test.js

@@ -48,14 +48,13 @@ describe('useAdminUsers', () => {
     expect(result.current.users).toEqual([]);
   });
 
-  it('inviteUser appends new user to state; deleteUser removes user from state', async () => {
+  it('inviteUser appends a user to state', async () => {
     const existingUser = { id: '1', email: 'a@example.com', created_at: '2024-01-01', last_sign_in_at: null };
     const newUser = { id: '2', email: 'b@example.com', created_at: '2024-01-03', last_sign_in_at: null };
 
     mockInvoke
       .mockResolvedValueOnce({ data: [existingUser], error: null })
-      .mockResolvedValueOnce({ data: newUser, error: null })
-      .mockResolvedValueOnce({ data: {}, error: null });
+      .mockResolvedValueOnce({ data: newUser, error: null });
 
     const { result } = renderHook(() => useAdminUsers());
     await act(async () => {});
@@ -65,6 +64,19 @@ describe('useAdminUsers', () => {
       await result.current.inviteUser('b@example.com');
     });
     expect(result.current.users).toEqual([existingUser, newUser]);
+  });
+
+  it('deleteUser removes a user from state', async () => {
+    const existingUser = { id: '1', email: 'a@example.com', created_at: '2024-01-01', last_sign_in_at: null };
+    const newUser = { id: '2', email: 'b@example.com', created_at: '2024-01-03', last_sign_in_at: null };
+
+    mockInvoke
+      .mockResolvedValueOnce({ data: [existingUser, newUser], error: null })
+      .mockResolvedValueOnce({ data: {}, error: null });
+
+    const { result } = renderHook(() => useAdminUsers());
+    await act(async () => {});
+    expect(result.current.users).toEqual([existingUser, newUser]);
 
     await act(async () => {
       await result.current.deleteUser('1');

src/admin/users/useAdminUsers.js

@@ -6,19 +6,25 @@ export function useAdminUsers() {
   const [loading, setLoading] = useState(true);
   const [error, setError] = useState(null);
 
-  const fetchUsers = useCallback(async () => {
+  const fetchUsers = useCallback(async (isMounted) => {
     const { data, error } = await supabase.functions.invoke('list-admin-users');
 
+    if (!isMounted) return;
+
     if (error) {
       setError(error.message);
     } else {
-      setUsers(data);
+      setUsers(data ?? []);
     }
     setLoading(false);
   }, []);
 
   useEffect(() => {
-    fetchUsers();
+    let isMounted = true;
+    fetchUsers(isMounted);
+    return () => {
+      isMounted = false;
+    };
   }, [fetchUsers]);
 
   const inviteUser = async (email) => {