fix: stop re-rendering every row when a search starts

components/email/__tests__/thread-list-item-source-folder.test.tsx

@@ -1,4 +1,5 @@
-import { render, screen } from '@testing-library/react';
+import { Profiler } from 'react';
+import { act, render, screen } from '@testing-library/react';
 import { describe, it, expect, vi, beforeEach } from 'vitest';
 import { ThreadListItem } from '../thread-list-item';
 import { useSettingsStore, DEFAULT_KEYWORDS } from '@/stores/settings-store';
@@ -56,6 +57,7 @@ function renderThread(emails: Email[]) {
   );
 }
 
+const noop = () => {};
 const single = () => [makeEmail()];
 const conversation = () => [
   makeEmail({ id: 'email-1', receivedAt: '2024-01-15T10:00:00Z' }),
@@ -123,5 +125,20 @@ describe('ThreadListItem folder chip in search results (#1172)', () => {
       renderThread(emails());
       expect(screen.getByTitle('Archive')).toBeTruthy();
     });
+
+    it('does not re-render a row without a folder when a search starts', () => {
+      // The folder's own list stays on screen until the results arrive; its
+      // rows carry no sourceFolder and have no chip to show.
+      const [thread] = groupEmailsByThread(emails().map((e) => ({ ...e, sourceFolder: undefined })));
+      const onRender = vi.fn();
+      render(
+        <Profiler id="row" onRender={onRender}>
+          <ThreadListItem thread={thread} isExpanded={false} onToggleExpand={noop} onEmailSelect={noop} />
+        </Profiler>,
+      );
+      onRender.mockClear();
+      act(() => useEmailStore.setState({ searchQuery: 'invoice', searchMailboxId: '' }));
+      expect(onRender).not.toHaveBeenCalled();
+    });
   });
 });

components/email/thread-list-item.tsx

@@ -253,9 +253,13 @@ function SourceFolderTag({ name }: { name: string }) {
  * Whether rows show their folder chip: in the aggregate "All …" views, and in
  * search results that span every folder rather than the one picked in the
  * search panel (#1172). Rows of a single-folder list carry no sourceFolder.
+ *
+ * Such a row never subscribes to the view state: starting a search flips it
+ * while the old list is still on screen, and every row re-rendered for a chip
+ * it has nothing to put in.
  */
-function useShowSourceFolder(): boolean {
-  return useEmailStore((state) => state.isUnifiedView || isUnscopedSearchActive(state));
+function useShowSourceFolder(sourceFolder: string | undefined): boolean {
+  return useEmailStore((state) => !!sourceFolder && (state.isUnifiedView || isUnscopedSearchActive(state)));
 }
 
 /**
@@ -377,7 +381,7 @@ const SingleEmailItem = React.forwardRef<HTMLDivElement, SingleEmailItemProps>(
     const interfaceLayout = useSettingsStore((state) => state.interfaceLayout);
     const hideJunkAvatarImages = currentMailboxRole === 'junk' && !showAvatarsInJunk;
     // Show the originating folder in the aggregate "All …" views.
-    const showSourceFolder = useShowSourceFolder() && !!email.sourceFolder;
+    const showSourceFolder = useShowSourceFolder(email.sourceFolder);
     const getAccountById = useAccountStore((state) => state.getAccountById);
     const account = email.accountId ? getAccountById(email.accountId) : undefined;
     const accountColor = account?.avatarColor;
@@ -932,7 +936,7 @@ export const ThreadListItem = React.forwardRef<HTMLDivElement, ThreadListItemPro
       selectRangeEmails: state.selectRangeEmails,
       isUnifiedView: state.isUnifiedView,
     })));
-    const showSourceFolder = useShowSourceFolder() && !!latestEmail.sourceFolder;
+    const showSourceFolder = useShowSourceFolder(latestEmail.sourceFolder);
     const getAccountById = useAccountStore((state) => state.getAccountById);
     const threadAccount = latestEmail.accountId ? getAccountById(latestEmail.accountId) : undefined;
     const threadAccountColor = threadAccount?.avatarColor;