fix(explore): allow chart owners to overwrite when owners are objects

The Save chart modal gates "Save (Overwrite)" on canOverwriteSlice(),
which checked slice.owners.includes(user.userId). The Slice type declares
owners as { id: number }[], and the Explore bootstrap can hydrate owners in
object form, so includes() against a numeric userId never matched. A chart
owner who wasn't also an admin was therefore forced into "Save as...",
which is the path that produces the duplicate/stale-chart behavior reported
in the issue.

Normalize owner identity to the numeric id before comparing so owners are
recognized whether they arrive as plain ids or as objects.

Fixes #38911

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

superset-frontend/src/explore/components/SaveModal.test.tsx

@@ -334,6 +334,27 @@ test('enables overwrite option for admin non-owner', () => {
   expect(getByRole('radio', { name: 'Save (Overwrite)' })).toBeEnabled();
 });
 
+test('enables overwrite option for owner when owners are objects', () => {
+  // The Slice type declares `owners: { id: number }[]`, and the explore
+  // bootstrap can deliver owners in object form. A chart owner must still be
+  // able to overwrite their own chart in that case.
+  const { getByRole } = setup(
+    {},
+    mockStore({
+      ...initialState,
+      explore: {
+        ...initialState.explore,
+        slice: {
+          ...initialState.explore.slice,
+          owners: [{ id: 1 }],
+        },
+      },
+      user: { userId: 1 },
+    }),
+  );
+  expect(getByRole('radio', { name: 'Save (Overwrite)' })).toBeEnabled();
+});
+
 test('updates slice name and selected dashboard', async () => {
   const dashboardId = mockEvent.value;
   const saveDataset = jest.fn().mockResolvedValue(undefined);

superset-frontend/src/explore/components/SaveModal.tsx

@@ -227,13 +227,26 @@ const SaveModal = ({
   const history = useHistory();
   const theme = useTheme();
 
+  const isCurrentUserOwner = useCallback((): boolean => {
+    const userId = user?.userId;
+    if (userId === undefined) {
+      return false;
+    }
+    // Owners can arrive either as plain ids (number) or as objects depending on
+    // where the slice was hydrated from (bootstrap vs. SLICE_UPDATED reducer),
+    // so normalize to the numeric id before comparing.
+    return Boolean(
+      slice?.owners?.some((owner: number | { id?: number }) =>
+        typeof owner === 'number' ? owner === userId : owner?.id === userId,
+      ),
+    );
+  }, [slice, user]);
+
   const canOverwriteSlice = useCallback(
     (): boolean =>
-      (can_overwrite ||
-        isUserAdmin(user) ||
-        slice?.owners?.includes(user.userId)) &&
+      (can_overwrite || isUserAdmin(user) || isCurrentUserOwner()) &&
       !slice?.is_managed_externally,
-    [can_overwrite, slice, user],
+    [can_overwrite, slice, user, isCurrentUserOwner],
   );
 
   const [newSliceName, setNewSliceName] = useState<string | undefined>(