fix: dismiss chat selection bubble on scroll (#672)

The chat add-to-session popover is anchored to viewport coordinates, so it can float over unrelated messages after the transcript scrolls. The shared selection-popover dismissal hook now treats captured scroll as a dismissal signal, matching the existing outside-click behavior and clearing the stale text selection.\n\nConstraint: Desktop selection popovers are owned by message/workspace child components, not by the transcript scroll container.\nRejected: Thread scroll state through every selectable message | would re-render message rows during scroll for a global dismissal concern.\nConfidence: high\nScope-risk: narrow\nDirective: Keep selection popover dismissal centralized unless a future menu needs scroll persistence explicitly.\nTested: bun run test -- src/components/chat/MessageList.test.tsx -t "dismisses the selected-message action when the message list scrolls"\nTested: bun run test -- src/components/chat/MessageList.test.tsx\nTested: bun run check:desktop

desktop/src/components/chat/MessageList.test.tsx

@@ -1715,6 +1715,36 @@ describe('MessageList nested tool calls', () => {
     expect(window.getSelection()?.toString()).toBe('')
   })
 
+  it('dismisses the selected-message action when the message list scrolls', async () => {
+    useChatStore.setState({
+      sessions: {
+        [ACTIVE_TAB]: makeSessionState({
+          messages: [{
+            id: 'assistant-1',
+            type: 'assistant_text',
+            content: 'Scrolling should clear this selected reply.',
+            timestamp: 1,
+          }],
+        }),
+      },
+    })
+
+    const { container } = render(<MessageList />)
+
+    const assistantText = screen.getByText(/Scrolling should clear/)
+    await selectMessageText(assistantText, 'selected reply')
+    expect(screen.getByRole('button', { name: 'Add to chat' })).toBeTruthy()
+
+    const scroller = container.querySelector('.overflow-y-auto') as HTMLDivElement
+    await act(async () => {
+      fireEvent.scroll(scroller)
+      await Promise.resolve()
+    })
+
+    expect(screen.queryByRole('button', { name: 'Add to chat' })).toBeNull()
+    expect(window.getSelection()?.toString()).toBe('')
+  })
+
   it('keeps only the latest selected-message action when selecting across messages', async () => {
     useChatStore.setState({
       sessions: {

desktop/src/hooks/useSelectionPopoverDismiss.ts

@@ -76,6 +76,11 @@ export function useSelectionPopoverDismiss({
   useEffect(() => {
     if (!active) return
 
+    const dismiss = () => {
+      onDismiss()
+      clearWindowSelection()
+    }
+
     const handlePointerDown = (event: PointerEvent) => {
       const popover = popoverRef.current
       const target = event.target
@@ -83,11 +88,18 @@ export function useSelectionPopoverDismiss({
         return
       }
 
-      onDismiss()
-      clearWindowSelection()
+      dismiss()
+    }
+
+    const handleScroll = () => {
+      dismiss()
     }
 
     document.addEventListener('pointerdown', handlePointerDown, true)
-    return () => document.removeEventListener('pointerdown', handlePointerDown, true)
+    document.addEventListener('scroll', handleScroll, true)
+    return () => {
+      document.removeEventListener('pointerdown', handlePointerDown, true)
+      document.removeEventListener('scroll', handleScroll, true)
+    }
   }, [active, onDismiss, popoverRef])
 }