🪟 fix: Re-measure sidebar chat list on width change to fix date-group spacing

When the sidebar is expanded from a collapsed reload, virtualized rows first
measure mid-animation at a narrow width, so date-group headers wrap and cache an
inflated height. CellMeasurerCache(fixedWidth) keys heights by row, not width, so
the stale height persists once full width is reached — leaving gaps under headers.

Invalidate the measurement cache and recompute row heights whenever the measured
list width changes. Adds a Playwright mock e2e (seeds backdated convos across date
groups via a new db helper) that fails without the fix and passes with it.

client/src/components/Conversations/Conversations.tsx

@@ -58,7 +58,12 @@ const MeasuredRow: FC<MeasuredRowProps> = memo(
   ({ cache, rowKey, parent, index, style, children }) => (
     <CellMeasurer cache={cache} columnIndex={0} key={rowKey} parent={parent} rowIndex={index}>
       {({ registerChild }) => (
-        <div ref={registerChild as React.LegacyRef<HTMLDivElement>} style={style} className="px-3">
+        <div
+          ref={registerChild as React.LegacyRef<HTMLDivElement>}
+          style={style}
+          className="px-3"
+          data-testid="convo-list-row"
+        >
           {children}
         </div>
       )}
@@ -341,6 +346,24 @@ const Conversations: FC<ConversationsProps> = ({
     return () => cancelAnimationFrame(frameId);
   }, [flattenedItems, containerRef]);
 
+  /** CellMeasurerCache(fixedWidth) keys heights by row, not width. Rows first measured
+   *  at a narrow width (e.g. mid expand-animation from a collapsed sidebar) would
+   *  otherwise persist their wrapped heights — re-measure when the width changes. */
+  const measuredWidthRef = useRef(0);
+  useEffect(() => {
+    if (listWidth === 0 || listWidth === measuredWidthRef.current) {
+      return;
+    }
+    measuredWidthRef.current = listWidth;
+    const frameId = requestAnimationFrame(() => {
+      cache.clearAll();
+      if (containerRef.current && 'recomputeRowHeights' in containerRef.current) {
+        containerRef.current.recomputeRowHeights(0);
+      }
+    });
+    return () => cancelAnimationFrame(frameId);
+  }, [listWidth, cache, containerRef]);
+
   const rowRenderer = useCallback(
     ({ index, key, parent, style }) => {
       const item = flattenedItems[index];

e2e/specs/mock/db.ts

@@ -0,0 +1,69 @@
+import fs from 'fs';
+import path from 'path';
+import { MongoClient } from 'mongodb';
+import type { Db } from 'mongodb';
+
+const DEFAULT_MONGO_URI = 'mongodb://127.0.0.1:27017/LibreChat-e2e';
+/** Written by e2e/setup/start-server.js on boot; authoritative even for memory MongoDB. */
+const RUNTIME_ENV_PATH = path.resolve(__dirname, '../.test-results/runtime-env.json');
+
+function getMongoUri(): string {
+  try {
+    const env = JSON.parse(fs.readFileSync(RUNTIME_ENV_PATH, 'utf8')) as { MONGO_URI?: string };
+    if (env.MONGO_URI) {
+      return env.MONGO_URI;
+    }
+  } catch {
+    /* fall through to env/default */
+  }
+  return process.env.MONGO_URI ?? DEFAULT_MONGO_URI;
+}
+
+/** Connect to the e2e MongoDB, run `fn`, and always close the client. */
+export async function withMongo<T>(fn: (db: Db) => Promise<T>): Promise<T> {
+  const client = new MongoClient(getMongoUri());
+  await client.connect();
+  try {
+    return await fn(client.db());
+  } finally {
+    await client.close();
+  }
+}
+
+export interface SeedConvo {
+  conversationId: string;
+  title: string;
+  /** Drives the sidebar date group ("Today", "Previous 7 days", ...). */
+  updatedAt: Date;
+}
+
+/**
+ * Inserts conversation documents directly (bypassing mongoose timestamps) so their
+ * `updatedAt` can be backdated into specific sidebar date groups.
+ */
+export async function seedConversations(userEmail: string, convos: SeedConvo[]): Promise<void> {
+  await withMongo(async (db) => {
+    const user = await db.collection('users').findOne({ email: userEmail });
+    if (!user) {
+      throw new Error(`E2E seed: user "${userEmail}" not found`);
+    }
+    const userId = user._id.toString();
+    const docs = convos.map((convo) => ({
+      conversationId: convo.conversationId,
+      title: convo.title,
+      user: userId,
+      endpoint: 'openAI',
+      isArchived: false,
+      createdAt: convo.updatedAt,
+      updatedAt: convo.updatedAt,
+      __v: 0,
+    }));
+    await db.collection('conversations').insertMany(docs);
+  });
+}
+
+export async function deleteConversations(conversationIds: string[]): Promise<void> {
+  await withMongo(async (db) => {
+    await db.collection('conversations').deleteMany({ conversationId: { $in: conversationIds } });
+  });
+}

e2e/specs/mock/sidebar.spec.ts

@@ -1,5 +1,9 @@
+import { randomUUID } from 'crypto';
 import { expect, test } from '@playwright/test';
 import type { Page } from '@playwright/test';
+import { getE2EUser } from '../../setup/user';
+import { deleteConversations, seedConversations } from './db';
+import type { SeedConvo } from './db';
 
 /** Size of the virtualized chat list grid vs. its measured container. */
 const sizes = (page: Page) =>
@@ -80,3 +84,95 @@ test.describe('sidebar chat list', () => {
     expect(shrunken.gridH).toBeLessThan(reopened.gridH);
   });
 });
+
+/**
+ * Regression: expanding the sidebar from a collapsed reload first measured the
+ * virtualized conversation rows mid-animation (narrow width), so date-group headers
+ * ("Previous 7 days", ...) wrapped and cached oversized heights. With `fixedWidth`
+ * the cache never re-measured at full width, leaving a gap between each header's
+ * text and the row beneath it.
+ */
+const DAY_MS = 24 * 60 * 60 * 1000;
+const userEmail = getE2EUser().email;
+
+/**
+ * The header `<h2>` is single-line; its row wrapper should hug it (just the small
+ * top margin). A stale wrapped measurement inflates the wrapper well past this.
+ */
+const MAX_HEADER_PADDING = 24;
+
+const GROUPS = [
+  { label: 'Today', offsetDays: 0 },
+  { label: 'Previous 7 days', offsetDays: 3 },
+  { label: 'Previous 30 days', offsetDays: 15 },
+] as const;
+
+function buildSeed(): SeedConvo[] {
+  const now = Date.now();
+  return GROUPS.flatMap((group, groupIndex) =>
+    [0, 1].map((n) => ({
+      conversationId: randomUUID(),
+      title: `E2E ${group.label} #${n}`,
+      // Subtract minutes so "today" entries stay strictly in the past and ordered.
+      updatedAt: new Date(now - group.offsetDays * DAY_MS - (groupIndex + n + 1) * 60_000),
+    })),
+  );
+}
+
+// The DateLabel <h2> exposes an aria-label ("Chats from {date}"), so its accessible
+// name is the full phrase, not the visible group label.
+const heading = (page: Page, label: string) =>
+  page.getByRole('heading', { name: `Chats from ${label}`, exact: true });
+
+const headerRow = (page: Page, label: string) =>
+  page.getByTestId('convo-list-row').filter({ has: heading(page, label) });
+
+test.describe('sidebar conversation grouping', () => {
+  let seeded: SeedConvo[] = [];
+
+  test.afterEach(async () => {
+    if (seeded.length) {
+      await deleteConversations(seeded.map((c) => c.conversationId));
+      seeded = [];
+    }
+  });
+
+  test('keeps date-group spacing tight after expanding from a collapsed reload', async ({
+    page,
+  }) => {
+    test.setTimeout(60000);
+    seeded = buildSeed();
+    await seedConversations(userEmail, seeded);
+
+    // Default load is expanded: confirm the seeded conversations render at all.
+    await page.goto('/c/new', { timeout: 10000 });
+    await expect(page.getByTestId('convo-item').first()).toBeVisible({ timeout: 15000 });
+
+    // Force the collapsed start state, then reload so the list mounts collapsed.
+    await page.evaluate(() =>
+      localStorage.setItem('unifiedSidebarExpanded', JSON.stringify(false)),
+    );
+    await page.reload({ timeout: 10000 });
+    await expect(page.getByTestId('open-sidebar-button')).toBeVisible();
+
+    // Expand: rows first measure during the width animation — the regression window.
+    await page.getByTestId('open-sidebar-button').click();
+    await expect(page.getByTestId('close-sidebar-button')).toBeVisible();
+    await expect(page.getByTestId('convo-item').first()).toBeVisible({ timeout: 15000 });
+
+    // Each header row must hug its single-line text, not retain an inflated height.
+    for (const { label } of GROUPS) {
+      const row = headerRow(page, label);
+      await expect(row).toBeVisible({ timeout: 10000 });
+      const rowBox = await row.boundingBox();
+      const textBox = await heading(page, label).boundingBox();
+      expect(rowBox, `row "${label}" should have a bounding box`).not.toBeNull();
+      expect(textBox, `heading "${label}" should have a bounding box`).not.toBeNull();
+      const padding = rowBox!.height - textBox!.height;
+      expect(
+        padding,
+        `header "${label}" row (${rowBox!.height}px) should hug its text (${textBox!.height}px)`,
+      ).toBeLessThan(MAX_HEADER_PADDING);
+    }
+  });
+});