fix(results): stop a hidden tab's grid from answering copy and select-all

The grid listens on document for copy and select-all, and answers for a
selection whose endpoints are inside its own container — bypassing the
active-pane check on purpose (#330). A kept-alive tab stays mounted with
its selection intact, so Ctrl+C in the tab the user switched to could
copy rows from the tab they left, unseen.

Both listeners are installed only while the tab is on screen.

Author: deveshk0

src/components/DataGrid.tsx

@@ -34,6 +34,7 @@ import { Badge } from '@/components/ui/badge';
 import { useThemeOptional } from '@/hooks/use-theme';
 import { getScaledRowHeight } from '@/lib/themes/ui-scale';
 import { cn } from '@/lib/utils';
+import { useTabVisible } from '@/workspace/tabVisibility';
 import type { SpacingDensity } from '@/lib/themes/schema';
 
 interface DataGridProps {
@@ -1160,6 +1161,13 @@ export const DataGrid: React.FC<DataGridProps> = ({
   // still mounted, and the copy is rebuilt from the line data rather than from
   // the DOM.
   const jsonViewRef = React.useRef<HTMLDivElement | null>(null);
+  // These grids listen on `document` for copy and select-all, and answer for a
+  // selection whose endpoints are inside their own container — which bypasses
+  // the active-pane check on purpose (#330). A kept-alive tab (#240) stays
+  // mounted with its selection intact, so a hidden grid would go on answering
+  // Ctrl+C in the tab the user switched to, copying data they cannot see. Only
+  // the grid on screen listens.
+  const tabVisible = useTabVisible();
   // The two ends of the selection, each remembered independently at the last
   // row it was seen on. Modelling the ends rather than a min/max span is what
   // lets the range CONTRACT: during a drag the anchor is fixed and only the
@@ -1404,7 +1412,7 @@ export const DataGrid: React.FC<DataGridProps> = ({
   // meaning of the shortcut too: in a results pane, select-all is about the
   // results, not about the whole application around them.
   useEffect(() => {
-    if (viewMode !== 'json') return;
+    if (viewMode !== 'json' || !tabVisible) return;
     const onKeyDown = (e: KeyboardEvent) => {
       if (e.defaultPrevented) return;
       if (e.key !== 'a' && e.key !== 'A') return;
@@ -1432,20 +1440,20 @@ export const DataGrid: React.FC<DataGridProps> = ({
     // any window-level handler that would otherwise claim the key first.
     document.addEventListener('keydown', onKeyDown, true);
     return () => document.removeEventListener('keydown', onKeyDown, true);
-  }, [viewMode]);
+  }, [viewMode, tabVisible]);
 
   const jsonCopyRef = React.useRef(handleJsonCopy);
   useEffect(() => {
     jsonCopyRef.current = handleJsonCopy;
   });
   useEffect(() => {
-    if (viewMode !== 'json') return;
+    if (viewMode !== 'json' || !tabVisible) return;
     const onCopy = (e: ClipboardEvent) => jsonCopyRef.current(e);
     document.addEventListener('copy', onCopy);
     // Nothing to unwind: ownership is the pane registry's, and a pane
     // unregisters itself there when it goes.
     return () => document.removeEventListener('copy', onCopy);
-  }, [viewMode]);
+  }, [viewMode, tabVisible]);
 
   const toggleFold = (id: number) => {
     setCollapsedFolds((prev) => {

src/components/__tests__/DataGrid.test.tsx

@@ -36,6 +36,7 @@ vi.mock('@/hooks/use-theme', () => ({
 }));
 
 import { DataGrid, getExplainTree } from '../DataGrid';
+import { TabVisibleContext } from '../../workspace/tabVisibility';
 import { resetResultsFindShortcutForTests } from '@/lib/resultsFindShortcut';
 
 // Collect every node name in the tree (depth-first) for assertions.
@@ -2186,3 +2187,46 @@ describe('DataGrid — tab guards survive StrictMode replay (#325 review)', () =
     expect(onActiveTabChange).toHaveBeenCalledWith('explain');
   });
 });
+
+describe('DataGrid — a hidden tab does not answer the clipboard (#240)', () => {
+  const view = (visible: boolean) => (
+    <TabVisibleContext.Provider value={visible}>
+      <DataGrid documents={mockDocuments} />
+    </TabVisibleContext.Provider>
+  );
+
+  const pressSelectAll = (target: EventTarget) => {
+    const event = new KeyboardEvent('keydown', { key: 'a', ctrlKey: true, bubbles: true, cancelable: true });
+    target.dispatchEvent(event);
+    return event;
+  };
+
+  it('leaves select-all alone once its tab is hidden', () => {
+    // The grid stays mounted (#240), so without this it would still claim the
+    // key pressed in the tab the user switched to.
+    const { rerender } = render(view(true));
+    const json = screen.getByTestId('json-view');
+    document.getSelection()?.removeAllRanges();
+    expect(pressSelectAll(json).defaultPrevented).toBe(true);
+
+    rerender(view(false));
+    expect(pressSelectAll(json).defaultPrevented).toBe(false);
+  });
+
+  it('leaves a copy alone once its tab is hidden', () => {
+    const { rerender } = render(view(true));
+    const json = screen.getByTestId('json-view');
+    document.getSelection()?.removeAllRanges();
+    pressSelectAll(json);
+    document.dispatchEvent(new Event('selectionchange'));
+
+    const shown = vi.fn();
+    fireEvent.copy(json, { clipboardData: { setData: shown, getData: () => '' } });
+    expect(shown).toHaveBeenCalled();
+
+    rerender(view(false));
+    const hidden = vi.fn();
+    fireEvent.copy(json, { clipboardData: { setData: hidden, getData: () => '' } });
+    expect(hidden).not.toHaveBeenCalled();
+  });
+});