## 1. Flash-sale domain and contract

- [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.
- [x] 1.3 Add shared flash-sale types, client methods, localized strings, and fixed-data adapter parity.

## 2. Checkout price and inventory resolution

- [x] 2.1 Resolve active eligible activity items server-side during checkout and snapshot final line pricing and activity identity. Reject coupon selection on any shop order that applied flash pricing; restate coupon persistence for non-flash shop orders.
- [x] 2.2 Conditionally decrement and restore activity inventory with SKU inventory in deterministic lock order; enforce the per-customer limit. Pending-payment cancellation restores both inventories and any redeemed coupon.
- [x] 2.3 Add integration tests for inactive-window fallback, cross-shop configuration rejection, overlapping group-buy SKU rejection, final reserved-stock contention, customer limits, coupon rejection on flash-priced shop orders, coupon restore on cancel, and cancellation restoration.

## 3. Merchant and mall surfaces

- [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

- [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.