Implement cancel-event feature (016)

Add PATCH /events/{eventToken} endpoint for organizers to cancel events,
cancellation banner for visitors, and RSVP rejection on cancelled events.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/e2e/cancel-event.spec.ts

@@ -0,0 +1,162 @@
+import { http, HttpResponse } from 'msw'
+import { test, expect } from './msw-setup'
+import type { StoredEvent } from '../src/composables/useEventStorage'
+
+const STORAGE_KEY = 'fete:events'
+
+const fullEvent = {
+  eventToken: 'a1b2c3d4-e5f6-7890-abcd-ef1234567890',
+  title: 'Summer BBQ',
+  description: 'Bring your own drinks!',
+  dateTime: '2026-03-15T20:00:00+01:00',
+  timezone: 'Europe/Berlin',
+  location: 'Central Park, NYC',
+  attendeeCount: 12,
+  cancelled: false,
+  cancellationReason: null,
+}
+
+const organizerToken = '550e8400-e29b-41d4-a716-446655440001'
+
+function seedEvents(events: StoredEvent[]): string {
+  return `window.localStorage.setItem('${STORAGE_KEY}', ${JSON.stringify(JSON.stringify(events))})`
+}
+
+function organizerSeed(): StoredEvent {
+  return {
+    eventToken: fullEvent.eventToken,
+    organizerToken,
+    title: fullEvent.title,
+    dateTime: fullEvent.dateTime,
+  }
+}
+
+test.describe('US1: Organizer cancels event with reason', () => {
+  test('organizer opens cancel bottom sheet, enters reason, confirms — event shows as cancelled on reload', async ({
+    page,
+    network,
+  }) => {
+    let cancelled = false
+    network.use(
+      http.get('*/api/events/:token', () => {
+        if (cancelled) {
+          return HttpResponse.json({
+            ...fullEvent,
+            cancelled: true,
+            cancellationReason: 'Venue closed',
+          })
+        }
+        return HttpResponse.json(fullEvent)
+      }),
+      http.patch('*/api/events/:token', ({ request }) => {
+        const url = new URL(request.url)
+        const token = url.searchParams.get('organizerToken')
+        if (token === organizerToken) {
+          cancelled = true
+          return new HttpResponse(null, { status: 204 })
+        }
+        return HttpResponse.json(
+          { type: 'urn:problem-type:invalid-organizer-token', title: 'Forbidden', status: 403 },
+          { status: 403 },
+        )
+      }),
+    )
+    await page.addInitScript(seedEvents([organizerSeed()]))
+    await page.goto(`/events/${fullEvent.eventToken}`)
+
+    // Cancel button visible for organizer
+    const cancelBtn = page.getByRole('button', { name: /Cancel event/i })
+    await expect(cancelBtn).toBeVisible()
+
+    // Open cancel bottom sheet
+    await cancelBtn.click()
+
+    // Fill in reason
+    const reasonField = page.getByLabel(/reason/i)
+    await expect(reasonField).toBeVisible()
+    await reasonField.fill('Venue closed')
+
+    // Confirm cancellation
+    await page.getByRole('button', { name: /Confirm cancellation/i }).click()
+
+    // Event should show as cancelled
+    await expect(page.getByText(/This event has been cancelled/i)).toBeVisible()
+    await expect(page.getByText('Venue closed')).toBeVisible()
+
+    // Cancel button should be gone
+    await expect(cancelBtn).not.toBeVisible()
+  })
+})
+
+test.describe('US1: Organizer cancels event without reason', () => {
+  test('organizer cancels without reason — event shows as cancelled', async ({
+    page,
+    network,
+  }) => {
+    let cancelled = false
+    network.use(
+      http.get('*/api/events/:token', () => {
+        if (cancelled) {
+          return HttpResponse.json({
+            ...fullEvent,
+            cancelled: true,
+            cancellationReason: null,
+          })
+        }
+        return HttpResponse.json(fullEvent)
+      }),
+      http.patch('*/api/events/:token', ({ request }) => {
+        const url = new URL(request.url)
+        const token = url.searchParams.get('organizerToken')
+        if (token === organizerToken) {
+          cancelled = true
+          return new HttpResponse(null, { status: 204 })
+        }
+        return HttpResponse.json({}, { status: 403 })
+      }),
+    )
+    await page.addInitScript(seedEvents([organizerSeed()]))
+    await page.goto(`/events/${fullEvent.eventToken}`)
+
+    await page.getByRole('button', { name: /Cancel event/i }).click()
+
+    // Don't fill in reason, just confirm
+    await page.getByRole('button', { name: /Confirm cancellation/i }).click()
+
+    // Event should show as cancelled without reason text
+    await expect(page.getByText(/This event has been cancelled/i)).toBeVisible()
+  })
+})
+
+test.describe('US1: Cancel API failure', () => {
+  test('cancel API fails — error displayed in bottom sheet, button re-enabled for retry', async ({
+    page,
+    network,
+  }) => {
+    network.use(
+      http.get('*/api/events/:token', () => HttpResponse.json(fullEvent)),
+      http.patch('*/api/events/:token', () => {
+        return HttpResponse.json(
+          {
+            type: 'about:blank',
+            title: 'Internal Server Error',
+            status: 500,
+            detail: 'Something went wrong',
+          },
+          { status: 500, headers: { 'Content-Type': 'application/problem+json' } },
+        )
+      }),
+    )
+    await page.addInitScript(seedEvents([organizerSeed()]))
+    await page.goto(`/events/${fullEvent.eventToken}`)
+
+    await page.getByRole('button', { name: /Cancel event/i }).click()
+    await page.getByRole('button', { name: /Confirm cancellation/i }).click()
+
+    // Error message in bottom sheet
+    await expect(page.getByText(/Could not cancel event/i)).toBeVisible()
+
+    // Confirm button should be re-enabled
+    await expect(page.getByRole('button', { name: /Confirm cancellation/i })).toBeEnabled()
+  })
+})