finish new demo

frontend/src/hooks/useFilters.test.ts

@@ -228,6 +228,43 @@ describe('useFilters', () => {
     expect(Object.keys(result.current.filters)).toHaveLength(2);
   });
 
+  it('blocks adding new filters when lockAdds is set (shared link), but allows replacing existing ones', () => {
+    const sixFeatures: FeatureMeta[] = ['a', 'b', 'c', 'd', 'e', 'f'].map((name) => ({
+      name,
+      type: 'numeric',
+      min: 0,
+      max: 100,
+    }));
+    const onFilterLimitReached = vi.fn();
+
+    // A non-paying user on a shared link: still under the cap (5), but adds are
+    // locked. They can adjust the shared filter ('a') but not add a new one.
+    const { result } = renderHook(() =>
+      useFilters({
+        initialFilters: { a: [0, 100] },
+        features: sixFeatures,
+        filterLimit: 5,
+        lockAdds: true,
+        onFilterLimitReached,
+      })
+    );
+
+    // Adding a brand-new filter is blocked and reported, even though count < cap.
+    act(() => {
+      result.current.handleAddFilter('b');
+    });
+    expect(Object.keys(result.current.filters)).toHaveLength(1);
+    expect(result.current.filters.b).toBeUndefined();
+    expect(onFilterLimitReached).toHaveBeenCalledTimes(1);
+
+    // Re-applying the existing filter replaces it (no new key) and is allowed.
+    act(() => {
+      result.current.handleAddFilter('a');
+    });
+    expect(Object.keys(result.current.filters)).toHaveLength(1);
+    expect(onFilterLimitReached).toHaveBeenCalledTimes(1);
+  });
+
   it('does not cap filters when filterLimit is null (licensed users)', () => {
     const sixFeatures: FeatureMeta[] = ['a', 'b', 'c', 'd', 'e', 'f'].map((name) => ({
       name,