fix(restaurant): cart displays in menu currency; checkout previews live sat

Cart was storing the menu item's price under a misnamed field
`unit_msat` and labeling it 'sat' in the UI — so Big Jay's
25-GTQ Coffee showed as '25 sat' in the cart with no fiat
conversion. The numbers were purely cosmetic (real money math
goes through POST /orders/quote server-side) but misleading.

stores/cart.ts:
  - rename CartLine.unit_msat → unit_price (since it isn't msat)
  - add CartLine.currency (snapshot from the menu item)
  - rename getter restaurantTotalsMsat → restaurantTotals;
    returns { amount, currency } per restaurant
  - rename grandTotalMsat → grandTotal; returns single
    { amount, currency } when the cart is one-currency, null
    when it spans multiple currencies (future festival
    aggregator with mixed-fiat restaurants — UI then falls
    back to per-restaurant subtotals)

components/CartLineItem.vue: uses line.currency directly instead
of a currencyHint prop and a hard-coded 'sat'.

views/CartPage.vue: per-bucket and grand totals use the cart's
currency. When the cart spans multiple currencies, hide the
grand total and show a small explanatory caption.

views/CheckoutPage.vue:
  - same display rename throughout
  - **new**: live ≈sat preview. On mount and whenever the cart
    changes, fires one POST /orders/quote per restaurant and
    surfaces `required_msat / 1000` as 'Pay in sats: ≈ X sat'
    so the customer sees the actual Lightning amount BEFORE
    clicking 'Pay & place order'.

views/ItemPage.vue + RestaurantPage.vue: pass currency through
to cart.addLine.

Verified live against Big Jay's (GTQ-priced):
  - Coffee menu card: '25 GTQ' (unchanged)
  - Add to cart, /cart shows '25 GTQ'  (was '25 sat')
  - /checkout subtotal: '25 GTQ', preview: '≈ 3,966 sat'
  - Quesadillas with 3 modifier groups: subtotal '80 GTQ',
    preview '≈ 12,691 sat'
  - 2x Tacos (Maíz + Brisket + Chicken): '170 GTQ',
    '≈ 26,968 sat'
  All sat amounts come from the extension's fiat-rate-aware
  /orders/quote endpoint (the companion fix on
  aiolabs/restaurant feat/restaurant-by-slug branch).

Vue-tsc clean; vite build clean.

src/modules/restaurant/components/CartLineItem.vue

@@ -10,7 +10,6 @@ import type { CartLine } from '../stores/cart'
 
 const props = defineProps<{
   line: CartLine
-  currencyHint?: string
 }>()
 
 const emit = defineEmits<{
@@ -24,14 +23,12 @@ const modifierSummary = computed(() =>
 )
 
 const lineTotal = computed(() => {
-  // unit_msat is base + modifier delta snapshot; the cart store
+  // Displayed in the menu item's currency (e.g. GTQ). Authoritative
-  // currently stores it as a sat-major number (price * 1000-less
+  // sat conversion happens server-side at /orders/quote — the
-  // because the extension's `price` is already in the declared
+  // checkout page surfaces that as a "≈ X sat" badge.
-  // currency, not msat — see useCheckout's buildCreateOrder for the
-  // canonical conversion at order-place time).
   const fmt = new Intl.NumberFormat(undefined, { maximumFractionDigits: 2 })
-  const total = props.line.unit_msat * props.line.quantity
+  const total = props.line.unit_price * props.line.quantity
-  return `${fmt.format(total)} ${props.currencyHint || 'sat'}`
+  return `${fmt.format(total)} ${props.line.currency}`
 })
 </script>
 

src/modules/restaurant/stores/cart.ts

@@ -30,8 +30,16 @@ export interface CartLine {
   /** Snapshot at add-time so the cart still renders if the menu
    *  item is later edited / deleted. */
   name: string
-  /** Base price + selected modifier deltas, in msat. */
+  /**
-  unit_msat: number
+   * Base price + selected modifier deltas, **in the menu item's
+   * declared currency** (e.g. 25 for "25 GTQ" or 100 for "100 sat").
+   * Authoritative sat conversion happens server-side via
+   * `POST /orders/quote`; the cart's value is for display only.
+   */
+  unit_price: number
+  /** ISO-ish currency code from the menu item, e.g. "GTQ", "USD",
+   *  "sat". Used for cart-side display labels. */
+  currency: string
   quantity: number
   selected_modifiers: SelectedModifier[]
   note?: string | null
@@ -91,19 +99,42 @@ export const useCartStore = defineStore('restaurant-cart', () => {
     return n
   })
 
-  const restaurantTotalsMsat = computed<Record<string, number>>(() => {
+  /** Per-restaurant subtotal in that restaurant's declared currency. */
-    const out: Record<string, number> = {}
+  const restaurantTotals = computed<
+    Record<string, { amount: number; currency: string }>
+  >(() => {
+    const out: Record<string, { amount: number; currency: string }> = {}
     for (const rid of Object.keys(lines.value)) {
-      out[rid] = lines.value[rid].reduce(
+      const bucket = lines.value[rid]
-        (s, l) => s + l.unit_msat * l.quantity,
+      if (!bucket.length) continue
-        0
+      out[rid] = {
-      )
+        amount: bucket.reduce(
+          (s, l) => s + l.unit_price * l.quantity,
+          0
+        ),
+        currency: bucket[0].currency,
+      }
     }
     return out
   })
 
-  const grandTotalMsat = computed<number>(() =>
+  /**
-    Object.values(restaurantTotalsMsat.value).reduce((s, v) => s + v, 0)
+   * Single-currency cart subtotal. Returns null if the cart spans
+   * multiple currencies (e.g. one restaurant priced in GTQ + another
+   * in USD via the future festival aggregator) — the UI then falls
+   * back to per-restaurant subtotals only.
+   */
+  const grandTotal = computed<{ amount: number; currency: string } | null>(
+    () => {
+      const totals = Object.values(restaurantTotals.value)
+      if (!totals.length) return null
+      const currencies = new Set(totals.map((t) => t.currency))
+      if (currencies.size !== 1) return null
+      return {
+        amount: totals.reduce((s, t) => s + t.amount, 0),
+        currency: totals[0].currency,
+      }
+    }
   )
 
   function linesFor(restaurantId: string): CartLine[] {
@@ -214,8 +245,8 @@ export const useCartStore = defineStore('restaurant-cart', () => {
     // getters
     restaurantsInCart,
     itemCount,
-    restaurantTotalsMsat,
+    restaurantTotals,
-    grandTotalMsat,
+    grandTotal,
     linesFor,
     // actions
     setActiveRestaurant,

src/modules/restaurant/views/CartPage.vue

@@ -25,12 +25,12 @@ const buckets = computed(() =>
     // a separate fetch for the cart page header.
     restaurantSlug: cart.linesFor(rid)[0]?.restaurant_slug ?? '',
     lines: cart.linesFor(rid),
-    totalMsat: cart.restaurantTotalsMsat[rid] ?? 0,
+    total: cart.restaurantTotals[rid] ?? null,
   }))
 )
 
-function fmtSat(value: number): string {
+function fmt(value: number, currency: string): string {
-  return `${new Intl.NumberFormat(undefined, { maximumFractionDigits: 2 }).format(value)} sat`
+  return `${new Intl.NumberFormat(undefined, { maximumFractionDigits: 2 }).format(value)} ${currency}`
 }
 </script>
 
@@ -70,7 +70,7 @@ function fmtSat(value: number): string {
               </button>
             </CardTitle>
             <span class="font-mono text-sm text-primary">
-              {{ fmtSat(b.totalMsat) }}
+              {{ b.total ? fmt(b.total.amount, b.total.currency) : '—' }}
             </span>
           </CardHeader>
           <CardContent>
@@ -91,12 +91,16 @@ function fmtSat(value: number): string {
       <Separator class="my-6" />
 
       <div class="space-y-3">
-        <div class="flex items-center justify-between">
+        <div v-if="cart.grandTotal" class="flex items-center justify-between">
           <span class="text-sm text-muted-foreground">Subtotal</span>
           <span class="font-mono text-lg font-semibold text-foreground">
-            {{ fmtSat(cart.grandTotalMsat) }}
+            {{ fmt(cart.grandTotal.amount, cart.grandTotal.currency) }}
           </span>
         </div>
+        <p v-else class="text-xs text-muted-foreground text-center">
+          Cart spans multiple currencies — per-restaurant subtotals above.
+          Lightning sat amount shown at checkout.
+        </p>
         <Button
           class="w-full"
           size="lg"

src/modules/restaurant/views/CheckoutPage.vue

@@ -6,9 +6,9 @@
  * v1 typically has a single bucket. On success: clear cart, route
  * to /orders/<firstOrderId>. On failure: surface the error inline.
  */
-import { computed, onMounted, ref } from 'vue'
+import { computed, onMounted, ref, watch } from 'vue'
 import { useRouter } from 'vue-router'
-import { ArrowLeft, Loader2, CheckCircle2 } from 'lucide-vue-next'
+import { ArrowLeft, Loader2, CheckCircle2, Zap } from 'lucide-vue-next'
 import { Alert, AlertDescription, AlertTitle } from '@/components/ui/alert'
 import { Button } from '@/components/ui/button'
 import {
@@ -21,22 +21,25 @@ import { Separator } from '@/components/ui/separator'
 import { useCartStore } from '../stores/cart'
 import { useCheckout } from '../composables/useCheckout'
 import {
+  injectService,
   tryInjectService,
   SERVICE_TOKENS,
 } from '@/core/di-container'
 import type { StorageService } from '@/core/services/StorageService'
+import type { RestaurantAPI } from '../services/RestaurantAPI'
 
 const router = useRouter()
 const cart = useCartStore()
 const { state, checkout } = useCheckout()
 const storage = tryInjectService<StorageService>(SERVICE_TOKENS.STORAGE_SERVICE)
+const api = injectService<RestaurantAPI>(SERVICE_TOKENS.RESTAURANT_API)
 
 const isSubmitting = computed(
   () => state.value.step !== 'idle' && state.value.step !== 'done' && state.value.step !== 'error'
 )
 
-function fmtSat(value: number) {
+function fmt(value: number, currency: string) {
-  return `${new Intl.NumberFormat(undefined, { maximumFractionDigits: 2 }).format(value)} sat`
+  return `${new Intl.NumberFormat(undefined, { maximumFractionDigits: 2 }).format(value)} ${currency}`
 }
 
 const buckets = computed(() =>
@@ -44,10 +47,53 @@ const buckets = computed(() =>
     restaurantId: rid,
     restaurantSlug: cart.linesFor(rid)[0]?.restaurant_slug ?? '',
     lines: cart.linesFor(rid),
-    totalMsat: cart.restaurantTotalsMsat[rid] ?? 0,
+    total: cart.restaurantTotals[rid] ?? null,
   }))
 )
 
+/**
+ * Live ≈sat preview: a single /orders/quote per restaurant the
+ * moment the cart is loaded. Surfaces the actual Lightning amount
+ * the customer will pay, separately from the menu-currency
+ * subtotal. Recomputes whenever the cart changes.
+ */
+const previewSatPerRestaurant = ref<Record<string, number | null>>({})
+const previewSatTotal = computed<number | null>(() => {
+  const vals = Object.values(previewSatPerRestaurant.value)
+  if (!vals.length || vals.some((v) => v === null)) return null
+  return (vals as number[]).reduce((s, v) => s + v, 0)
+})
+
+watch(
+  () => cart.restaurantsInCart.map((rid) => ({
+    rid,
+    lines: cart.linesFor(rid),
+  })),
+  async (groups) => {
+    const next: Record<string, number | null> = {}
+    for (const g of groups) {
+      try {
+        const q = await api.quoteOrder(
+          g.lines.map((l) => ({
+            menu_item_id: l.menu_item_id,
+            quantity: l.quantity,
+            selected_modifiers: l.selected_modifiers,
+            note: l.note ?? undefined,
+          }))
+        )
+        next[g.rid] = Math.ceil(q.required_msat / 1000)
+      } catch {
+        // Best-effort preview only; if the quote endpoint hiccups
+        // we just don't show the sat estimate. The real quote runs
+        // again inside useCheckout when the customer clicks pay.
+        next[g.rid] = null
+      }
+    }
+    previewSatPerRestaurant.value = next
+  },
+  { immediate: true, deep: true }
+)
+
 const placedOrders = ref<
   Array<{ orderId: string; restaurantSlug: string; placedAt: number; totalMsat: number; restaurantId: string }>
 >([])
@@ -112,7 +158,7 @@ async function placeOrder() {
         <CardHeader class="flex flex-row items-baseline justify-between space-y-0">
           <CardTitle class="text-base">{{ b.restaurantSlug }}</CardTitle>
           <span class="font-mono text-sm text-primary">
-            {{ fmtSat(b.totalMsat) }}
+            {{ b.total ? fmt(b.total.amount, b.total.currency) : '—' }}
           </span>
         </CardHeader>
         <CardContent class="space-y-1">
@@ -131,9 +177,16 @@ async function placeOrder() {
               </span>
             </span>
             <span class="font-mono text-xs text-muted-foreground">
-              {{ fmtSat(line.unit_msat * line.quantity) }}
+              {{ fmt(line.unit_price * line.quantity, line.currency) }}
             </span>
           </div>
+          <div
+            v-if="previewSatPerRestaurant[b.restaurantId] != null"
+            class="mt-1 flex items-center justify-end gap-1 text-xs text-muted-foreground"
+          >
+            <Zap class="h-3 w-3" />
+            ≈ {{ new Intl.NumberFormat().format(previewSatPerRestaurant[b.restaurantId]!) }} sat
+          </div>
         </CardContent>
       </Card>
     </div>
@@ -141,10 +194,22 @@ async function placeOrder() {
     <Separator class="my-6" />
 
     <div class="space-y-3">
-      <div class="flex items-baseline justify-between">
+      <div v-if="cart.grandTotal" class="flex items-baseline justify-between">
         <span class="text-sm text-muted-foreground">Total</span>
         <span class="font-mono text-xl font-bold text-foreground">
-          {{ fmtSat(cart.grandTotalMsat) }}
+          {{ fmt(cart.grandTotal.amount, cart.grandTotal.currency) }}
+        </span>
+      </div>
+      <div
+        v-if="previewSatTotal != null"
+        class="flex items-center justify-between rounded-lg border border-border bg-muted/40 px-3 py-2 text-sm"
+      >
+        <span class="inline-flex items-center gap-1 text-muted-foreground">
+          <Zap class="h-3.5 w-3.5" />
+          Pay in sats
+        </span>
+        <span class="font-mono font-semibold text-foreground">
+          ≈ {{ new Intl.NumberFormat().format(previewSatTotal) }} sat
         </span>
       </div>
 

src/modules/restaurant/views/ItemPage.vue

@@ -87,7 +87,8 @@ function addToCart() {
     restaurant_slug: restaurant.value.slug,
     menu_item_id: item.value.id,
     name: item.value.name,
-    unit_msat: unitPrice.value,
+    unit_price: unitPrice.value,
+    currency: item.value.currency || restaurant.value.currency,
     quantity: quantity.value,
     selected_modifiers: selectedModifiers.value,
     note: note.value || null,

src/modules/restaurant/views/RestaurantPage.vue

@@ -84,7 +84,8 @@ function quickAdd(itemId: string) {
     restaurant_slug: restaurant.value.slug,
     menu_item_id: it.id,
     name: it.name,
-    unit_msat: it.price,
+    unit_price: it.price,
+    currency: it.currency || restaurant.value.currency,
     quantity: 1,
     selected_modifiers: [],
     note: null,