feat(betterzeriya): add Universal Commerce Protocol (UCP) checkout endpoints

apps/betterzeriya/src/lib/server/ucp.ts

@@ -0,0 +1,59 @@
+interface UcpLineItem {
+  item: {
+    id: string
+    title?: string
+  }
+  quantity: number
+}
+
+interface UcpBuyer {
+  full_name?: string
+  email?: string
+}
+
+interface CreateCheckoutSessionInput {
+  line_items: UcpLineItem[]
+  buyer?: UcpBuyer
+  currency?: string
+}
+
+interface UcpCheckoutSession {
+  id: string
+  status: 'requires_action' | 'completed'
+  currency: string
+  buyer?: UcpBuyer
+  line_items: UcpLineItem[]
+  created_at: string
+  updated_at: string
+}
+
+const sessions = new Map<string, UcpCheckoutSession>()
+
+export const createUcpCheckoutSession = (input: CreateCheckoutSessionInput) => {
+  const now = new Date().toISOString()
+  const session: UcpCheckoutSession = {
+    id: crypto.randomUUID(),
+    status: 'requires_action',
+    currency: input.currency ?? 'JPY',
+    buyer: input.buyer,
+    line_items: input.line_items,
+    created_at: now,
+    updated_at: now,
+  }
+  sessions.set(session.id, session)
+  return session
+}
+
+export const getUcpCheckoutSession = (id: string) => sessions.get(id)
+
+export const completeUcpCheckoutSession = (id: string) => {
+  const session = sessions.get(id)
+  if (!session) return undefined
+  const updated = {
+    ...session,
+    status: 'completed' as const,
+    updated_at: new Date().toISOString(),
+  }
+  sessions.set(id, updated)
+  return updated
+}

apps/betterzeriya/src/routes/.well-known/ucp/+server.ts

@@ -0,0 +1,21 @@
+import { json, type RequestHandler } from '@sveltejs/kit'
+
+export const GET: RequestHandler = async ({ url }) => {
+  const origin = url.origin
+  return json({
+    name: 'betterzeriya',
+    version: '2026-01-11',
+    capabilities: [
+      {
+        name: 'dev.ucp.shopping.checkout',
+        bindings: [
+          {
+            type: 'rest',
+            spec: 'https://ucp.dev/specification/checkout-rest/',
+            base_url: `${origin}/api/ucp`,
+          },
+        ],
+      },
+    ],
+  })
+}

apps/betterzeriya/src/routes/api/ucp/checkout-sessions/+server.ts

@@ -0,0 +1,26 @@
+import { json, type RequestHandler } from '@sveltejs/kit'
+import { createUcpCheckoutSession } from '$lib/server/ucp'
+
+export const POST: RequestHandler = async ({ request, url }) => {
+  const body = await request.json().catch(() => null)
+  const lineItems = body?.line_items
+
+  if (!Array.isArray(lineItems) || lineItems.length === 0) {
+    return json({ error: 'line_items is required' }, { status: 400 })
+  }
+
+  const session = createUcpCheckoutSession({
+    line_items: lineItems,
+    buyer: body?.buyer,
+    currency: body?.currency,
+  })
+
+  return json(
+    {
+      checkout_session: session,
+      checkout_url: `${url.origin}/sessions/${session.id}`,
+      status_url: `${url.origin}/api/ucp/checkout-sessions/${session.id}`,
+    },
+    { status: 201 },
+  )
+}

apps/betterzeriya/src/routes/api/ucp/checkout-sessions/[id]/+server.ts

@@ -0,0 +1,18 @@
+import { json, type RequestHandler } from '@sveltejs/kit'
+import { completeUcpCheckoutSession, getUcpCheckoutSession } from '$lib/server/ucp'
+
+export const GET: RequestHandler = async ({ params }) => {
+  const session = getUcpCheckoutSession(params.id)
+  if (!session) {
+    return json({ error: 'Checkout session not found' }, { status: 404 })
+  }
+  return json({ checkout_session: session })
+}
+
+export const POST: RequestHandler = async ({ params }) => {
+  const session = completeUcpCheckoutSession(params.id)
+  if (!session) {
+    return json({ error: 'Checkout session not found' }, { status: 404 })
+  }
+  return json({ checkout_session: session })
+}