feat(tier2): editable RSVPs — Block A

Guests can revisit their invitation link and change their response
or plus-ones up to 5 times. Each prior state is snapshotted into
`rsvp_revisions` and surfaced to the host via a per-guest history
modal on the event detail page.

- Migration 0007 adds rsvp_revisions + rsvps.edit_count (with down)
- RSVPRepo.Update wraps snapshot+update+counter in one transaction,
  FOR UPDATE-locking the row so concurrent edits can't bypass the cap
- PATCH /rsvp/{token} re-runs the fraud check on every edit attempt
  (different device on an edit is itself a signal)
- POST /rsvp no longer marks the token used — the link stays valid
  so the guest can come back to edit
- GET /access/{token} now embeds the existing RSVP so the frontend
  renders an edit form instead of a blank submit form on revisit
- New host endpoint GET /events/{id}/guests/{guest_id}/rsvp/history
- Frontend: rsvp/[token].vue toggles between summary + edit form,
  surfaces edits-remaining; dashboard adds a "History" action on
  responded guests opening a revision-trail modal

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/pages/rsvp/[token].vue

@@ -1,17 +1,30 @@
 <script setup lang="ts">
+interface ExistingRSVP {
+  id: string
+  response: 'attending' | 'declined' | 'maybe'
+  plus_ones: number
+  dietary_notes?: string | null
+  submitted_at: string
+  edit_count: number
+}
+
 interface AccessResponse {
   guest: { id: string; name: string; email?: string | null; plus_ones: number }
   event: { id: string; name: string; venue: string; event_date: string }
   token: { id: string; status: string; expires_at: string }
   access_log_id: string
+  rsvp?: ExistingRSVP | null
 }
 
 interface RSVPSubmitResponse {
-  rsvp?: { id: string; response: string; plus_ones: number; risk_score: number }
+  rsvp?: ExistingRSVP & { risk_score?: number }
   fraud: { score: number; risk: string; reasons: string[]; used: boolean }
   blocked: boolean
+  edited?: boolean
 }
 
+const MAX_EDITS = 5
+
 const route = useRoute()
 const token = route.params.token as string
 
@@ -27,10 +40,32 @@ const submitting = ref(false)
 const result = ref<RSVPSubmitResponse | null>(null)
 const submitError = ref<string | null>(null)
 
+// existing tracks the RSVP that was on file when the page loaded.
+// editing toggles the form open over the "already responded" summary.
+const existing = ref<ExistingRSVP | null>(null)
+const editing = ref(false)
+
+const editsRemaining = computed(() => {
+  const used = existing.value?.edit_count ?? 0
+  return Math.max(0, MAX_EDITS - used)
+})
+const editLimitReached = computed(() => editsRemaining.value <= 0)
+
+function prefillFromRSVP(rsvp: ExistingRSVP) {
+  response.value = rsvp.response
+  plusOnes.value = rsvp.plus_ones
+  dietary.value = rsvp.dietary_notes ?? ''
+}
+
 onMounted(async () => {
   try {
     access.value = await useApi<AccessResponse>(`/access/${token}`)
-    if (access.value) plusOnes.value = access.value.guest.plus_ones || 0
+    if (!access.value) return
+    plusOnes.value = access.value.guest.plus_ones || 0
+    if (access.value.rsvp) {
+      existing.value = access.value.rsvp
+      prefillFromRSVP(access.value.rsvp)
+    }
   } catch (e: any) {
     loadError.value = e?.data?.error || e?.message || 'Invitation not found'
   } finally {
@@ -41,10 +76,11 @@ onMounted(async () => {
 async function submit() {
   submitting.value = true
   submitError.value = null
+  const isEdit = !!existing.value
   try {
     const fp = useFingerprint()
     result.value = await useApi<RSVPSubmitResponse>(`/rsvp/${token}`, {
-      method: 'POST',
+      method: isEdit ? 'PATCH' : 'POST',
       body: {
         response: response.value,
         plus_ones: plusOnes.value,
@@ -52,8 +88,22 @@ async function submit() {
         fingerprint: fp,
       },
     })
+    // Refresh the cached "existing" view so a back-to-summary toggle shows
+    // the new state and the edit counter without a page reload.
+    if (result.value?.rsvp) {
+      existing.value = {
+        id: result.value.rsvp.id,
+        response: result.value.rsvp.response,
+        plus_ones: result.value.rsvp.plus_ones,
+        dietary_notes: result.value.rsvp.dietary_notes ?? null,
+        submitted_at: result.value.rsvp.submitted_at,
+        edit_count: result.value.rsvp.edit_count,
+      }
+    }
+    editing.value = false
   } catch (e: any) {
-    // 403 from BLOCK band returns a JSON body; surface its decision too.
+    // BLOCK band returns 403 with the fraud decision; surface it the same
+    // way the first-submit path does.
     if (e?.data?.fraud) {
       result.value = e.data
     } else {
@@ -64,10 +114,28 @@ async function submit() {
   }
 }
 
+function startEditing() {
+  if (existing.value) prefillFromRSVP(existing.value)
+  result.value = null
+  editing.value = true
+}
+
+function cancelEditing() {
+  if (existing.value) prefillFromRSVP(existing.value)
+  editing.value = false
+}
+
 function fmtDate(iso?: string) {
   if (!iso) return ''
   try { return new Date(iso).toLocaleString() } catch { return iso }
 }
+
+// showForm = no prior submission, or the guest has clicked "Change my response"
+const showForm = computed(() => editing.value || !existing.value)
+const submitLabel = computed(() => {
+  if (submitting.value) return existing.value ? 'Updating…' : 'Submitting…'
+  return existing.value ? 'Update RSVP' : 'Submit RSVP'
+})
 </script>
 
 <template>
@@ -89,8 +157,10 @@ function fmtDate(iso?: string) {
       </p>
     </div>
 
-    <div v-else-if="result?.rsvp" class="card border-brand-900/60 bg-brand-950/20">
-      <h1 class="mb-2 text-xl font-semibold text-brand-200">You're confirmed</h1>
+    <div v-else-if="result?.rsvp && !editing" class="card border-brand-900/60 bg-brand-950/20">
+      <h1 class="mb-2 text-xl font-semibold text-brand-200">
+        {{ result.edited ? 'Your response has been updated' : "You're confirmed" }}
+      </h1>
       <p class="text-sm text-brand-300">
         Response recorded as <strong>{{ result.rsvp.response }}</strong> with
         +{{ result.rsvp.plus_ones }} plus-ones.
@@ -99,10 +169,45 @@ function fmtDate(iso?: string) {
         Risk score {{ result.fraud.score }} · {{ result.fraud.risk }}
         <span v-if="!result.fraud.used"> · fallback</span>
       </p>
+      <div v-if="!editLimitReached" class="mt-5 flex items-center justify-between gap-3 border-t border-zinc-800 pt-4">
+        <p class="text-xs text-zinc-500">
+          Need to change something? You have {{ editsRemaining }}
+          {{ editsRemaining === 1 ? 'edit' : 'edits' }} left.
+        </p>
+        <button type="button" class="btn-ghost text-sm" @click="startEditing">Change my response</button>
+      </div>
+      <p v-else class="mt-5 border-t border-zinc-800 pt-4 text-xs text-zinc-500">
+        You've used all {{ MAX_EDITS }} edits on this invitation — contact your host if you need
+        to change anything else.
+      </p>
     </div>
 
-    <div v-else-if="access" class="card">
-      <p class="text-xs uppercase tracking-widest text-brand-500">Invitation</p>
+    <div v-else-if="existing && !editing" class="card border-brand-900/60 bg-brand-950/20">
+      <p class="text-xs uppercase tracking-widest text-brand-500">RSVP on file</p>
+      <h1 class="mb-1 text-2xl font-semibold">{{ access?.event.name }}</h1>
+      <p class="mb-5 text-sm text-zinc-400">
+        {{ access?.event.venue }} · {{ fmtDate(access?.event.event_date) }}
+      </p>
+      <p class="mb-4 text-sm">
+        You responded <strong class="capitalize">{{ existing.response }}</strong>
+        <span v-if="existing.plus_ones > 0"> with +{{ existing.plus_ones }} plus-ones</span>
+        on {{ fmtDate(existing.submitted_at) }}.
+      </p>
+      <div v-if="!editLimitReached" class="flex items-center justify-between gap-3 border-t border-zinc-800 pt-4">
+        <p class="text-xs text-zinc-500">
+          {{ editsRemaining }} {{ editsRemaining === 1 ? 'edit' : 'edits' }} remaining.
+        </p>
+        <button type="button" class="btn-ghost text-sm" @click="startEditing">Change my response</button>
+      </div>
+      <p v-else class="border-t border-zinc-800 pt-4 text-xs text-zinc-500">
+        You've used all {{ MAX_EDITS }} edits on this invitation.
+      </p>
+    </div>
+
+    <div v-else-if="access && showForm" class="card">
+      <p class="text-xs uppercase tracking-widest text-brand-500">
+        {{ existing ? 'Update your response' : 'Invitation' }}
+      </p>
       <h1 class="mb-1 text-2xl font-semibold">{{ access.event.name }}</h1>
       <p class="mb-6 text-sm text-zinc-400">
         {{ access.event.venue }} · {{ fmtDate(access.event.event_date) }}
@@ -110,7 +215,9 @@ function fmtDate(iso?: string) {
 
       <p class="mb-6 text-sm">
         Hi <span class="font-medium text-zinc-100">{{ access.guest.name }}</span> —
-        please confirm your response below.
+        <template v-if="existing">change your response below — {{ editsRemaining }}
+          {{ editsRemaining === 1 ? 'edit' : 'edits' }} remaining.</template>
+        <template v-else>please confirm your response below.</template>
       </p>
 
       <div class="mb-4">
@@ -159,9 +266,14 @@ function fmtDate(iso?: string) {
         <input v-model="dietary" class="input" placeholder="e.g. vegetarian" />
       </div>
 
-      <button class="btn-primary w-full" :disabled="submitting" @click="submit">
-        {{ submitting ? 'Submitting…' : 'Submit RSVP' }}
-      </button>
+      <div class="flex items-center gap-3">
+        <button class="btn-primary flex-1" :disabled="submitting" @click="submit">
+          {{ submitLabel }}
+        </button>
+        <button v-if="existing" type="button" class="btn-ghost" :disabled="submitting" @click="cancelEditing">
+          Cancel
+        </button>
+      </div>
 
       <p v-if="submitError" class="mt-3 text-sm text-red-400">{{ submitError }}</p>
     </div>