fix: event details dialog crashed on a string timestamp

frontend/e2e/admin-events.spec.ts

@@ -40,6 +40,14 @@ test.describe('Admin Events', () => {
       await adminPage.goto(PATH);
       await expectTableColumn(adminPage, 'Time', EMPTY_PATTERN);
     });
+
+    test('opens the details of an event with its timestamp', async ({ adminPage }) => {
+      await adminPage.goto(PATH);
+      await adminPage.getByRole('button', { name: /View details for event/ }).first().click();
+      const dialog = adminPage.getByRole('dialog', { name: 'Event Details' });
+      await expect(dialog).toBeVisible();
+      await expect(dialog.getByRole('row', { name: /Timestamp/ })).toContainText(/\d{4}/);
+    });
   });
 
   test.describe('Refresh', () => {

frontend/src/lib/admin/stores/__tests__/eventsStore.test.ts

@@ -156,6 +156,16 @@ describe('EventsStore', () => {
             );
         });
 
+        it('turns the event timestamp the generated transformer skips into a Date', async () => {
+            const event = { ...createMockEvent(), timestamp: '2026-10-11T08:00:00Z' };
+            mockApi(getEventDetailApiV1AdminEventsEventIdGet).ok({ event, related_events: [], timeline: [] });
+
+            createStore();
+            await store.openEventDetail('evt-1');
+
+            expect(store.selectedEvent?.event.timestamp).toEqual(new Date('2026-10-11T08:00:00Z'));
+        });
+
         it('leaves selectedEvent empty when the load fails', async () => {
             mockApi(getEventDetailApiV1AdminEventsEventIdGet).err({ detail: 'Event not found' });
 

frontend/src/lib/admin/stores/eventsStore.svelte.ts

@@ -86,7 +86,14 @@ class EventsStore {
     async openEventDetail(eventId: string): Promise<void> {
         // A failed load already showed the interceptor's toast, so the modal just stays closed
         this.selectedEvent = await this.#queryClient
-            .query(getEventDetailApiV1AdminEventsEventIdGetOptions({ path: { event_id: eventId } }))
+            .query({
+                ...getEventDetailApiV1AdminEventsEventIdGetOptions({ path: { event_id: eventId } }),
+                // hey-api's transformer skips a union-typed field, so `event.timestamp` arrives as a string
+                select: (detail) => ({
+                    ...detail,
+                    event: { ...detail.event, timestamp: new Date(detail.event.timestamp) },
+                }),
+            })
             .catch(() => null);
     }