diff --git a/components/calendar/__tests__/calendar-app-event-sheet-ux-pim.test.tsx b/components/calendar/__tests__/calendar-app-event-sheet-ux-pim.test.tsx
new file mode 100644
index 000000000..efb806734
--- /dev/null
+++ b/components/calendar/__tests__/calendar-app-event-sheet-ux-pim.test.tsx
@@ -0,0 +1,82 @@
+import { render, screen, fireEvent } from '@testing-library/react';
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import type { Calendar, CalendarEvent } from '@/lib/jmap/types';
+import { useCalendarStore } from '@/stores/calendar-store';
+import { useAuthStore } from '@/stores/auth-store';
+import { useSettingsStore } from '@/stores/settings-store';
+import { useTaskStore } from '@/stores/task-store';
+
+// pim-25: the event editor sat beside the week grid and squeezed its seven
+// columns to ~85 px at 1366x768. It now opens as a sheet over the grid from
+// the right, and the grid keeps its width.
+
+vi.mock('@/hooks/use-media-query', () => ({
+  useIsMobile: () => false,
+  useIsDesktop: () => true,
+  useIsTablet: () => false,
+  useMediaQuery: () => false,
+}));
+vi.mock('@/components/layout/navigation-rail', () => ({ NavigationRail: () => null }));
+vi.mock('@/components/layout/sidebar-apps-modal', () => ({ SidebarAppsModal: () => null }));
+vi.mock('@/components/layout/inline-app-view', () => ({ InlineAppView: () => null }));
+vi.mock('@/components/layout/mv-top-bar', () => ({ MvTopBar: () => null }));
+vi.mock('@/components/plugins/app-top-banner-slot', () => ({ AppTopBannerSlot: () => null }));
+vi.mock('@/hooks/use-refresh-gesture', () => ({ useRefreshGesture: () => ({ indicator: null }) }));
+vi.mock('@/hooks/use-calendar-push-refresh', () => ({ useCalendarPushRefresh: () => {} }));
+vi.mock('@/hooks/use-account-principal-emails', () => ({ useAccountPrincipalEmails: () => [] }));
+vi.mock('../participant-availability', () => ({ ParticipantAvailability: () => null }));
+vi.mock('@/hooks/use-config', () => ({ useConfig: () => ({ demoMode: false }) }));
+
+import { CalendarApp } from '../calendar-app';
+
+vi.setConfig({ testTimeout: 30000 });
+
+const RIGHTS = {
+  mayReadFreeBusy: true, mayReadItems: true, mayWriteAll: true, mayWriteOwn: true,
+  mayUpdatePrivate: true, mayRSVP: true, mayShare: true, mayDelete: true,
+};
+const calendars = [{
+  id: 'cal', name: 'Personal', color: '#123456', isDefault: true, sortOrder: 0, description: null,
+  isSubscribed: true, isVisible: true, includeInAvailability: 'all', defaultAlertsWithTime: null,
+  defaultAlertsWithoutTime: null, timeZone: null, shareWith: null, myRights: RIGHTS,
+}] as unknown as Calendar[];
+const event = {
+  id: 'e1', uid: 'u1', '@type': 'Event', title: 'Standup', description: '', start: '2026-10-12T10:00:00',
+  duration: 'PT1H', timeZone: null, showWithoutTime: false, calendarIds: { cal: true },
+  participants: null, alerts: null, recurrenceRules: null, isOrigin: true, status: 'confirmed',
+} as unknown as CalendarEvent;
+const client = {
+  getAccountId: () => 'acc',
+  getMaxParticipantsPerEvent: () => null,
+  supportsCalendars: () => true,
+  queryCalendarEvents: vi.fn().mockResolvedValue([]),
+  getCalendarEvent: vi.fn().mockResolvedValue(null),
+  getCalendarTasks: vi.fn().mockResolvedValue([]),
+};
+
+beforeEach(() => {
+  useAuthStore.setState({ isAuthenticated: true, client: client as never, isLoading: false, activeAccountId: 'acc' });
+  useCalendarStore.setState({
+    calendars, events: [event], supportsCalendar: true, selectedCalendarIds: ['cal'], viewMode: 'week',
+    selectedDate: new Date(2026, 9, 12), isLoading: false, isLoadingEvents: false, error: null,
+    fetchCalendars: vi.fn(), fetchEvents: vi.fn(), refreshAllSubscriptions: vi.fn(),
+    createEvent: vi.fn(), updateEvent: vi.fn(), deleteEvent: vi.fn(), rsvpEvent: vi.fn(),
+  } as never);
+  useSettingsStore.setState({ calendarHoverPreview: 'instant', enableCalendarTasks: true, proInterface: false } as never);
+  useTaskStore.setState({ tasks: [] } as never);
+});
+
+describe('CalendarApp event editor (pim-25)', () => {
+  it('opens over the grid instead of beside it', async () => {
+    render(<CalendarApp />);
+    fireEvent.keyDown(document.body, { key: 'n', code: 'KeyN' });
+    const editor = await screen.findByRole('dialog', { name: 'events.create' });
+    const sheet = editor.parentElement!;
+    // Out of the row's flow, pinned to its end edge, above the grid.
+    expect(sheet.className).toMatch(/\babsolute\b/);
+    expect(sheet.className).toMatch(/\binset-y-0\b/);
+    expect(sheet.className).toMatch(/\bend-0\b/);
+    expect(sheet.className).not.toMatch(/\bflex-shrink-0\b/);
+    expect(sheet.parentElement!.className).toMatch(/\brelative\b/);
+  });
+});
diff --git a/components/calendar/calendar-app.tsx b/components/calendar/calendar-app.tsx
index 0714adb1c..8a2840c69 100644
--- a/components/calendar/calendar-app.tsx
+++ b/components/calendar/calendar-app.tsx
@@ -2362,9 +2362,11 @@ export function CalendarApp({ linkSegments: routeSegments }: CalendarAppProps =
             {renderView()}
           </div>
 
-          {/* Desktop event panel */}
+          {/* Desktop event panel: a sheet over the grid from the right, as
+              on small screens, so the week keeps its width (pim-25). Above
+              the views' sticky headers (z-50) inside this isolated row. */}
           {!isMobile && showEventModal && (
-            <div className="w-[400px] border-s border-border flex-shrink-0 overflow-hidden">
+            <div data-testid="event-panel" className="absolute inset-y-0 end-0 z-[55] w-[400px] max-w-full border-s border-border bg-background shadow-xl overflow-hidden">
               <EventModal
                 key={`${editEvent?.id ?? 'new'}${modalStartsInEdit ? ':edit' : ''}`}
                 event={editEvent}