fix(web): correct timeline yesterday label across month boundaries (#28183)

web/src/lib/utils/timeline-util.spec.ts

@@ -7,6 +7,9 @@ describe('formatGroupTitle', () => {
   beforeAll(() => {
     vi.useFakeTimers();
     process.env.TZ = 'UTC';
+  });
+
+  beforeEach(() => {
     vi.setSystemTime(new Date('2024-07-27T12:00:00Z'));
   });
 
@@ -31,6 +34,13 @@ describe('formatGroupTitle', () => {
     expect(formatGroupTitle(date)).toBe('hier');
   });
 
+  it('formats yesterday across month boundaries', () => {
+    vi.setSystemTime(new Date('2024-05-01T12:00:00Z'));
+    const date = parseUtcDate('2024-04-30T23:59:59Z');
+    locale.set('en');
+    expect(formatGroupTitle(date)).toBe('yesterday');
+  });
+
   it('formats last week', () => {
     const date = parseUtcDate('2024-07-21T00:00:00Z');
     locale.set('en');

web/src/lib/utils/timeline-util.ts

@@ -128,7 +128,7 @@ export function formatGroupTitle(_date: DateTime): string {
 
   // Yesterday
   if (today.minus({ days: 1 }).hasSame(date, 'day')) {
-    return date.toRelativeCalendar({ locale: get(locale) });
+    return date.toRelativeCalendar({ locale: get(locale), unit: 'days' });
   }
 
   // Last week