docs(openspec): plan shop coupons, accounts, points, flash sales, and group buying

Capture exclusive promotion composition, empty-group cancel, and mall surface scope so the five marketing changes can be implemented without stacking or lifecycle ambiguity. Co-authored-by: Cursor <cursoragent@cursor.com>
2026-09-18 17:32:08 +08:00
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+## ADDED Requirements
+
+### Requirement: Live shop coupon surfaces
+The mall SHALL load a product's currently claimable shop coupons and the signed-in customer's coupon list through the shared API client, replacing direct coupon fixtures. Checkout SHALL present eligible owned coupons separately for each shop order and show the server-returned discount after submission. Payment and order-detail views SHALL show the persisted `discount_minor` and post-discount total from the order payload.
+
+#### Scenario: claim from a product page
+- **WHEN** a signed-in shopper claims an active coupon with remaining stock from a product page
+- **THEN** it appears in the shopper's coupon list without a fixture import
+
+#### Scenario: select coupon by shop
+- **WHEN** a cart spans two shops and the shopper selects a coupon for one shop
+- **THEN** checkout submits the choice only for that shop and the other shop remains undiscounted
+
+#### Scenario: order shows realized discount
+- **WHEN** checkout succeeds with a coupon on one shop order
+- **THEN** that order's payment and detail views show the server discount and reduced total without a client-calculated amount
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+## ADDED Requirements
+
+### Requirement: Merchant coupon management
+Shop users SHALL manage only their shop's coupon templates from shop-admin, including localized title, amount and threshold in minor units, currency, claim stock, active window, and enabled state. Shop-admin SHALL expose a coupons navigation entry beside existing shop operations.
+
+#### Scenario: create an active template
+- **WHEN** a shop owner creates a valid coupon template
+- **THEN** the template is available for eligible customers to claim during its active window
+
+#### Scenario: coupons appear in shop navigation
+- **WHEN** an authenticated shop user opens shop-admin
+- **THEN** a coupons management entry is reachable without leaving the shop-scoped console
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+## MODIFIED Requirements
+
+### Requirement: Checkout splits by shop
+`POST /api/orders/checkout` SHALL create one order per distinct shop in the cart, in a single database transaction: stock decrement, order + item insert with price snapshots, cart clear, and requested coupon redemption. All amounts use the cart's SKU currencies converted into the buyer-chosen display currency at checkout time. The request MAY select at most one owned coupon per generated shop order; the server SHALL validate its ownership, shop, status, validity window, threshold, and converted amount, then persist `coupon_id`, `discount_minor`, and the post-discount `total_minor`. The client SHALL NOT provide a discount amount. This requirement does not define activity prices; a later flash-sale or group-buying change that rewrites checkout SHALL restate these coupon clauses and SHALL reject a coupon on any shop order that applied an activity price.
+
+#### Scenario: two shops → two orders
+- **WHEN** the cart contains SKUs from shops A and B
+- **THEN** two orders are created, each with only its shop's items, and the cart is empty
+
+#### Scenario: insufficient stock
+- **WHEN** any line's qty exceeds SKU stock
+- **THEN** the whole checkout returns 409 and no order is created and stock is unchanged
+
+#### Scenario: coupon applies to one matching shop
+- **WHEN** the customer selects an eligible coupon issued by shop A for a cart containing shops A and B
+- **THEN** only shop A's order records that coupon and its server-calculated discount
+
+### Requirement: Order lifecycle
+Status transitions SHALL be: pending_payment → paid → fulfilling → shipped → completed; cancellable only from pending_payment, which MUST restore stock and restore a redeemed coupon to claimed status when the order has one.
+
+#### Scenario: cancel restores stock
+- **WHEN** a customer cancels a pending_payment order
+- **THEN** stock of each SKU increases by the ordered qty and status is cancelled
+
+#### Scenario: cancel restores coupon
+- **WHEN** a customer cancels a pending_payment order with a redeemed coupon
+- **THEN** the coupon is detached from the order and becomes claimed
+
+#### Scenario: illegal transition rejected
+- **WHEN** cancelling a paid order via the customer endpoint
+- **THEN** the API returns 409
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+## ADDED Requirements
+
+### Requirement: Shop coupon template management
+A shop_owner or shop_staff SHALL create, list, update, disable, and delete only that shop's coupon templates. A template SHALL contain localized title, fixed `amount_minor`, `threshold_minor`, enabled ISO currency, non-negative claim stock, and an inclusive active window; amount MUST be positive and threshold MUST NOT be negative.
+
+#### Scenario: cross-shop template is hidden
+- **WHEN** a shop user requests or mutates another shop's coupon template
+- **THEN** the API returns 404
+
+### Requirement: Customer coupon claim and listing
+An authenticated customer SHALL list owned coupons and claim an active template at most once. Claiming SHALL atomically create a user-held snapshot and decrement claim stock only when stock remains; listing SHALL distinguish claimed, redeemed, and expired coupons.
+
+#### Scenario: concurrent final claim
+- **WHEN** two customers claim the final remaining template instance concurrently
+- **THEN** exactly one claim succeeds and the other receives 409
+
+### Requirement: Coupon redemption lifecycle
+A claimed coupon SHALL be redeemable only by its owner, for its issuing shop, within its snapshot window, and when the shop-order subtotal reaches its snapshot threshold. Redemption SHALL bind the coupon to one order; cancellation of that pending-payment order SHALL restore it to claimed. Later activity-priced shop orders (flash sale or group buy) SHALL NOT redeem a coupon; those changes restated this exclusion on checkout.
+
+#### Scenario: cancelled order restores coupon
+- **WHEN** a customer cancels a pending-payment order redeemed with a coupon
+- **THEN** the coupon again has claimed status and no order binding