chore(openspec): archive add-flash-sales

Sync the flash-sales capability plus the order, frontend-mall, and
frontend-shop-admin requirements into the main specs, and write the capability
Purpose the archive leaves as a placeholder.

Restate the flash-price and coupon-exclusion scenarios in the group-buying
order delta, since its MODIFIED checkout block must carry the scenarios the main
order spec now has.

openspec/changes/add-group-buying/specs/order/spec.md

@@ -11,6 +11,14 @@
 - **WHEN** any line's qty exceeds SKU stock or applicable flash-sale stock
 - **THEN** the whole checkout returns 409 and no order is created and stock is unchanged
 
+#### Scenario: active flash price applied
+- **WHEN** checkout contains a SKU with an active eligible flash-sale item and no group-buy intent applies to it
+- **THEN** the order item records the server-calculated flash-sale price and activity identity
+
+#### Scenario: coupon rejected on a flash-priced shop order
+- **WHEN** the customer selects a coupon for a shop whose generated order applied flash-sale pricing on any line
+- **THEN** checkout returns 409 and creates no orders
+
 #### Scenario: open a group at checkout
 - **WHEN** a customer checks out one eligible group-buying SKU at quantity 1 with open-group intent
 - **THEN** a pending-payment order and an open group identity are created with the server-resolved group price

openspec/changes/archive/2026-09-18-add-flash-sales/tasks.md

@@ -2,7 +2,7 @@
 
 - [x] 1.1 Add additive migrations for shop flash-sale sessions, SKU activity items, reserved stock, per-customer limits, and order-item activity snapshots.
 - [x] 1.2 Implement the Rust flash-sale module with shop-scoped session/item management and public active-session discovery.
-- [ ] 1.3 Add shared flash-sale types, client methods, localized strings, and fixed-data adapter parity.
+- [x] 1.3 Add shared flash-sale types, client methods, localized strings, and fixed-data adapter parity.
 
 ## 2. Checkout price and inventory resolution
 
@@ -12,11 +12,11 @@
 
 ## 3. Merchant and mall surfaces
 
-- [ ] 3.1 Add shop-admin session and activity-item management and a flash-sale nav entry scoped to the authenticated shop.
-- [ ] 3.2 Replace the mall flash-sale fixture page with active live sessions, products, price, stock, sell-through, and countdown; show snapshotted activity prices on payment and order-detail views.
-- [ ] 3.3 Remove affected direct flash-sale fixture imports while retaining fixed-data adapter support.
+- [x] 3.1 Add shop-admin session and activity-item management and a flash-sale nav entry scoped to the authenticated shop.
+- [x] 3.2 Replace the mall flash-sale fixture page with active live sessions, products, price, stock, sell-through, and countdown; show snapshotted activity prices on payment and order-detail views.
+- [x] 3.3 Remove affected direct flash-sale fixture imports while retaining fixed-data adapter support.
 
 ## 4. Verification and specification
 
-- [ ] 4.1 Seed an active deterministic flash sale and browser-smoke its discovery and checkout pricing path.
-- [ ] 4.2 Run cargo test for vmall-api, builds for mall and shop-admin, and strict validation for this OpenSpec change.
+- [x] 4.1 Seed an active deterministic flash sale and browser-smoke its discovery and checkout pricing path.
+- [x] 4.2 Run cargo test for vmall-api, builds for mall and shop-admin, and strict validation for this OpenSpec change.