Cancellation notification sent to customer

A customer who cancels an order — or whose order is admin-cancelled — and receives no email confirmation is left wondering whether the cancellation actually went through. Without notification, they may place a duplicate order, not monitor their bank account for the refund, or contact support unnecessarily. If the admin cancels an order on behalf of a customer (for a fraud flag, inventory issue, or address problem), the customer deserves immediate notification with context. The iso-25010:2011 reliability dimension: the cancellation event occurred in the system but the customer has no evidence of it.

Add a cancellation email call to the cancellation handler at app/api/orders/[id]/cancel/route.ts, fired after the successful transitionOrder call.

// After transitionOrder(orderId, 'cancelled', ...) in app/api/orders/[id]/cancel/route.ts:
await sendCancellationEmail({
  to: order.user.email,
  orderNumber: order.id,
  refundExpected: order.total > 0,
  refundTimelineDays: REFUND_WINDOW_DAYS,
  supportUrl: 'https://yoursite.com/support',
})

Add sendCancellationEmail to lib/email/order-emails.ts and ensure the admin cancellation path also sends the same notification.