fix(repair): 修复 InventoryService.deduct 的并发竞态条件

target-service/files/welcome.txt

@@ -0,0 +1 @@
+hello from storage

target-service/src/main/java/com/example/targetservice/repository/InventoryRepository.java

@@ -32,4 +32,26 @@ public InventoryItem save(InventoryItem item) {
     public int stock(String sku) {
         return findBySku(sku).stock();
     }
+
+    /**
+     * Atomically deducts stock for a given SKU.
+     * Uses ConcurrentHashMap.compute to ensure read-check-write atomicity.
+     * @throws IllegalArgumentException if SKU not found or insufficient stock
+     */
+    public InventoryItem deductStock(String sku, int quantity) {
+        if (quantity <= 0) {
+            throw new IllegalArgumentException("quantity must be positive, but got: " + quantity);
+        }
+        return store.compute(sku, (key, item) -> {
+            if (item == null) {
+                throw new IllegalArgumentException("SKU not found: " + sku);
+            }
+            if (item.stock() < quantity) {
+                throw new IllegalArgumentException(
+                        "insufficient stock for " + sku + ": have " + item.stock() + ", need " + quantity);
+            }
+            return new InventoryItem(item.sku(), item.name(),
+                    item.stock() - quantity, item.reserved() + quantity);
+        });
+    }
 }

target-service/src/main/java/com/example/targetservice/service/InventoryService.java

@@ -14,21 +14,10 @@ public InventoryService(InventoryRepository repository) {
     }
 
     /**
-     * Deducts stock for a given SKU.
-     * BUG: No synchronization — concurrent calls can over-sell inventory.
+     * Deducts stock for a given SKU using atomic operation.
      */
     public InventoryItem deduct(String sku, int quantity) {
-        if (quantity <= 0) {
-            throw new IllegalArgumentException("quantity must be positive, but got: " + quantity);
-        }
-        InventoryItem item = repository.findBySku(sku);
-        if (item.stock() < quantity) {
-            throw new IllegalArgumentException(
-                    "insufficient stock for " + sku + ": have " + item.stock() + ", need " + quantity);
-        }
-        InventoryItem updated = new InventoryItem(item.sku(), item.name(),
-                item.stock() - quantity, item.reserved() + quantity);
-        return repository.save(updated);
+        return repository.deductStock(sku, quantity);
     }
 
     public InventoryItem getStock(String sku) {