fix(dashboard): prevent filter dropdown button from disappearing during layout recalculations

superset-frontend/packages/superset-ui-core/src/components/DropdownContainer/DropdownContainer.test.tsx

@@ -158,6 +158,25 @@ test('accepts custom style props', () => {
   expect(container).toHaveStyle('padding: 10px');
 });
 
+test('shows dropdown button when alwaysShowDropdownButton is true even without overflow', () => {
+  render(
+    <DropdownContainer items={generateItems(3)} alwaysShowDropdownButton />,
+  );
+  expect(screen.getByTestId('dropdown-container-btn')).toBeInTheDocument();
+});
+
+test('does not show dropdown button when alwaysShowDropdownButton is false and not overflowing', () => {
+  render(
+    <DropdownContainer
+      items={generateItems(3)}
+      alwaysShowDropdownButton={false}
+    />,
+  );
+  expect(
+    screen.queryByTestId('dropdown-container-btn'),
+  ).not.toBeInTheDocument();
+});
+
 // Integration test that doesn't rely on specific overflow behavior
 test('component renders and functions without throwing errors', () => {
   const onOverflowingStateChange = jest.fn();

superset-frontend/packages/superset-ui-core/src/components/DropdownContainer/DropdownContainer.tsx

@@ -53,6 +53,7 @@ export const DropdownContainer = forwardRef(
       dropdownTriggerTooltip = null,
       forceRender,
       style,
+      alwaysShowDropdownButton,
     }: DropdownContainerProps,
     outerRef: RefObject<DropdownRef>,
   ) => {
@@ -314,7 +315,7 @@ export const DropdownContainer = forwardRef(
         >
           {notOverflowedItems.map(item => item.element)}
         </div>
-        {popoverContent && (
+        {(popoverContent || alwaysShowDropdownButton) && (
           <>
             <Global
               styles={css`

superset-frontend/packages/superset-ui-core/src/components/DropdownContainer/types.ts

@@ -87,6 +87,11 @@ export interface DropdownContainerProps {
    * Force render popover content before it's first opened
    */
   forceRender?: boolean;
+  /**
+   * Always show the dropdown button, even when no items are overflowing.
+   * Useful to prevent button flickering during layout recalculations.
+   */
+  alwaysShowDropdownButton?: boolean;
 }
 
 export type DropdownRef = HTMLDivElement & { open: () => void };

superset-frontend/src/dashboard/components/nativeFilters/FilterBar/FilterControls/FilterControls.tsx

@@ -625,6 +625,7 @@ const FilterControls: FC<FilterControlsProps> = ({
               : undefined
           }
           forceRender={hasRequiredFirst}
+          alwaysShowDropdownButton={items.length > 0}
           ref={popoverRef}
           onOverflowingStateChange={({ overflowed: nextOverflowedIds }) => {
             if (