feat(scheduling): pluggable captcha (Turnstile) on public booking

apps/booking/pages/[tenantSlug]/[hostSlug]/[eventTypeSlug].vue

@@ -30,6 +30,71 @@ const submitting = ref(false)
 const submitError = ref<string | null>(null)
 const booking = ref<PublicBooking | null>(null)
 
+// Cloudflare Turnstile (optional). Only when a public site-key is configured do
+// we load the script + render a widget on the details step; otherwise the form
+// behaves exactly as before. We never solve the captcha — the widget produces a
+// token that we forward to platform-api, which verifies it server-side.
+const turnstileSiteKey = useRuntimeConfig().public.turnstileSiteKey as string
+const captchaToken = ref<string | null>(null)
+const captchaEl = ref<HTMLElement | null>(null)
+let captchaWidgetId: string | null = null
+const TURNSTILE_SRC = 'https://challenges.cloudflare.com/turnstile/v0/api.js'
+
+function loadTurnstileScript(): Promise<void> {
+  return new Promise((resolve, reject) => {
+    if ((window as any).turnstile) return resolve()
+    const existing = document.querySelector(`script[src^="${TURNSTILE_SRC}"]`) as HTMLScriptElement | null
+    if (existing) {
+      existing.addEventListener('load', () => resolve())
+      existing.addEventListener('error', () => reject(new Error('turnstile load failed')))
+      return
+    }
+    const s = document.createElement('script')
+    s.src = TURNSTILE_SRC
+    s.async = true
+    s.defer = true
+    s.addEventListener('load', () => resolve())
+    s.addEventListener('error', () => reject(new Error('turnstile load failed')))
+    document.head.appendChild(s)
+  })
+}
+
+async function renderCaptcha() {
+  if (!turnstileSiteKey || !import.meta.client || !captchaEl.value || captchaWidgetId) return
+  try {
+    await loadTurnstileScript()
+    const turnstile = (window as any).turnstile
+    if (!turnstile || !captchaEl.value) return
+    captchaWidgetId = turnstile.render(captchaEl.value, {
+      sitekey: turnstileSiteKey,
+      callback: (token: string) => {
+        captchaToken.value = token
+      },
+      'expired-callback': () => {
+        captchaToken.value = null
+      },
+      'error-callback': () => {
+        captchaToken.value = null
+      },
+    })
+  } catch {
+    // If the widget can't load we leave captchaToken null; the server decides
+    // whether that's fatal (it is only when TURNSTILE_SECRET is set).
+  }
+}
+
+function resetCaptcha() {
+  captchaToken.value = null
+  if (import.meta.client && captchaWidgetId && (window as any).turnstile) {
+    ;(window as any).turnstile.reset(captchaWidgetId)
+  }
+}
+
+// Render the widget whenever the details step becomes visible.
+watch(step, (s) => {
+  if (s === 'details' && turnstileSiteKey) void nextTick(renderCaptcha)
+})
+
 // Whitelabel theming — drive the accent from the tenant's brandColor.
 watchEffect(() => {
   if (!import.meta.client || !info.value) return
@@ -90,6 +155,7 @@ async function confirm() {
           attendeeEmail: form.email,
           attendeeTimezone: visitorTz.value,
           attendeeNotes: form.notes || undefined,
+          captchaToken: captchaToken.value || undefined,
         },
       })
     }
@@ -101,6 +167,9 @@ async function confirm() {
       await loadSlots()
     } else if (e?.statusCode === 503) {
       submitError.value = 'The calendar is temporarily unavailable. Please try again in a moment.'
+    } else if (e?.statusCode === 403) {
+      submitError.value = 'Captcha verification failed. Please complete the challenge and try again.'
+      resetCaptcha()
     } else {
       submitError.value = e?.statusMessage || 'Something went wrong. Please try again.'
     }
@@ -222,8 +291,13 @@ useHead(() => ({ title: info.value ? `${info.value.eventType.title} · ${info.va
             <label class="bk-label" for="notes">Notes (optional)</label>
             <textarea id="notes" v-model="form.notes" class="bk-input" maxlength="2000" />
           </div>
+          <div v-if="turnstileSiteKey" ref="captchaEl" class="captcha" />
           <p v-if="submitError" class="err">{{ submitError }}</p>
-          <button type="submit" class="bk-btn bk-btn--primary" :disabled="submitting">
+          <button
+            type="submit"
+            class="bk-btn bk-btn--primary"
+            :disabled="submitting || (!!turnstileSiteKey && !captchaToken)"
+          >
             {{ submitting ? 'Confirming…' : 'Confirm booking' }}
           </button>
         </form>
@@ -271,6 +345,7 @@ useHead(() => ({ title: info.value ? `${info.value.eventType.title} · ${info.va
 .slot { height: 44px; border: 1px solid var(--border); border-radius: 10px; background: var(--surface); font-size: 15px; font-weight: 600; cursor: pointer; }
 .slot:hover { border-color: var(--accent); }
 .form { display: flex; flex-direction: column; gap: 16px; margin-top: 14px; }
+.captcha { min-height: 65px; }
 .chosen { font-weight: 600; margin: 0 0 6px; }
 .back { background: none; border: none; color: var(--text-mute); cursor: pointer; padding: 0 0 12px; font-size: 14px; }
 .done { text-align: center; }