diff --git a/app/Modules/Integration/Actions/SyncOrderAction.php b/app/Modules/Integration/Actions/SyncOrderAction.php
index 107e5fc..ae2fe7d 100644
--- a/app/Modules/Integration/Actions/SyncOrderAction.php
+++ b/app/Modules/Integration/Actions/SyncOrderAction.php
@@ -58,29 +58,35 @@ class SyncOrderAction
                 ];
             }
 
-            // --- 預檢 (Pre-flight check) N+1 優化 ---
+            // --- 預檢 (Pre-flight check) 僅使用 product_id ---
             $items = $data['items'];
-            $posProductIds = array_column($items, 'pos_product_id');
+            $targetErpIds = array_column($items, 'product_id');
             
             // 一次性查出所有相關的 Product
-            $products = $this->productService->findByExternalPosIds($posProductIds)->keyBy('external_pos_id');
+            $productsById = $this->productService->findByIds($targetErpIds)->keyBy('id');
             
+            $resolvedProducts = [];
             $missingIds = [];
-            foreach ($posProductIds as $id) {
-                if (!$products->has($id)) {
-                    $missingIds[] = $id;
+            
+            foreach ($items as $index => $item) {
+                $productId = $item['product_id'];
+                $product = $productsById->get($productId);
+
+                if ($product) {
+                    $resolvedProducts[$index] = $product;
+                } else {
+                    $missingIds[] = $productId;
                 }
             }
 
             if (!empty($missingIds)) {
-                // 回報所有缺漏的 ID
                 throw ValidationException::withMessages([
-                    'items' => ["The following products are not found: " . implode(', ', $missingIds) . ". Please sync products first."]
+                    'items' => ["The following product IDs are not found: " . implode(', ', array_unique($missingIds)) . ". Please ensure these products exist in the system."]
                 ]);
             }
 
             // --- 執行寫入交易 ---
-            $result = DB::transaction(function () use ($data, $items, $products) {
+            $result = DB::transaction(function () use ($data, $items, $resolvedProducts) {
                 // 1. 建立訂單
                 $order = SalesOrder::create([
                     'external_order_id' => $data['external_order_id'],
@@ -108,11 +114,12 @@ class SyncOrderAction
 
                 // 3. 處理訂單明細
                 $orderItemsData = [];
-                foreach ($items as $itemData) {
-                    $product = $products->get($itemData['pos_product_id']);
+                foreach ($items as $index => $itemData) {
+                    $product = $resolvedProducts[$index];
                     
                     $qty = $itemData['qty'];
                     $price = $itemData['price'];
+                    $batchNumber = $itemData['batch_number'] ?? null;
                     $lineTotal = $qty * $price;
                     $totalAmount += $lineTotal;
 
@@ -134,9 +141,10 @@ class SyncOrderAction
                         $qty,
                         "POS Order: " . $order->external_order_id,
                         true,
-                        null,
+                        null, // Slot (location)
                         \App\Modules\Integration\Models\SalesOrder::class,
-                        $order->id
+                        $order->id,
+                        $batchNumber
                     );
                 }
 
diff --git a/app/Modules/Integration/Controllers/InventorySyncController.php b/app/Modules/Integration/Controllers/InventorySyncController.php
index a1f44fa..6b78329 100644
--- a/app/Modules/Integration/Controllers/InventorySyncController.php
+++ b/app/Modules/Integration/Controllers/InventorySyncController.php
@@ -21,10 +21,13 @@ class InventorySyncController extends Controller
      * @param string $warehouseCode
      * @return JsonResponse
      */
-    public function show(string $warehouseCode): JsonResponse
+    public function show(\Illuminate\Http\Request $request, string $warehouseCode): JsonResponse
     {
-        // 透過 Service 調用跨模組庫存查詢功能
-        $inventoryData = $this->inventoryService->getPosInventoryByWarehouseCode($warehouseCode);
+        // 透過 Service 調用跨模組庫存查詢功能，傳入篩選條件
+        $inventoryData = $this->inventoryService->getPosInventoryByWarehouseCode(
+            $warehouseCode, 
+            $request->only(['product_id', 'barcode', 'code', 'external_pos_id'])
+        );
 
         // 若回傳 null，表示尋無此倉庫代碼
         if (is_null($inventoryData)) {
@@ -40,9 +43,18 @@ class InventorySyncController extends Controller
             'warehouse_code' => $warehouseCode,
             'data' => $inventoryData->map(function ($item) {
                 return [
+                    'product_id' => $item->product_id,
                     'external_pos_id' => $item->external_pos_id,
                     'product_code' => $item->product_code,
                     'product_name' => $item->product_name,
+                    'barcode' => $item->barcode,
+                    'category_name' => $item->category_name ?? '未分類',
+                    'unit_name' => $item->unit_name ?? '個',
+                    'price' => (float) $item->price,
+                    'brand' => $item->brand,
+                    'specification' => $item->specification,
+                    'batch_number' => $item->batch_number,
+                    'expiry_date' => $item->expiry_date,
                     'quantity' => (float) $item->total_quantity,
                 ];
             })
diff --git a/app/Modules/Integration/Controllers/ProductSyncController.php b/app/Modules/Integration/Controllers/ProductSyncController.php
index 4947ea2..e4ff0fe 100644
--- a/app/Modules/Integration/Controllers/ProductSyncController.php
+++ b/app/Modules/Integration/Controllers/ProductSyncController.php
@@ -23,8 +23,8 @@ class ProductSyncController extends Controller
             'name' => 'required|string|max:255',
             'price' => 'nullable|numeric|min:0|max:99999999.99',
             'barcode' => 'nullable|string|max:100',
-            'category' => 'nullable|string|max:100',
-            'unit' => 'nullable|string|max:100',
+            'category' => 'required|string|max:100',
+            'unit' => 'required|string|max:100',
             'brand' => 'nullable|string|max:100',
             'specification' => 'nullable|string|max:255',
             'cost_price' => 'nullable|numeric|min:0|max:99999999.99',
@@ -41,6 +41,8 @@ class ProductSyncController extends Controller
                 'data' => [
                     'id' => $product->id,
                     'external_pos_id' => $product->external_pos_id,
+                    'code' => $product->code,
+                    'barcode' => $product->barcode,
                 ]
             ]);
         } catch (\Exception $e) {
@@ -50,4 +52,63 @@ class ProductSyncController extends Controller
             ], 500);
         }
     }
+
+    /**
+     * 搜尋商品（供外部 API 使用）。
+     *
+     * @param Request $request
+     * @return \Illuminate\Http\JsonResponse
+     */
+    public function index(Request $request)
+    {
+        $request->validate([
+            'product_id' => 'nullable|integer',
+            'external_pos_id' => 'nullable|string|max:255',
+            'barcode' => 'nullable|string|max:100',
+            'code' => 'nullable|string|max:100',
+            'category' => 'nullable|string|max:100',
+            'updated_after' => 'nullable|date',
+            'per_page' => 'nullable|integer|min:1|max:100',
+        ]);
+
+        try {
+            $perPage = $request->input('per_page', 50);
+            $products = $this->productService->searchProducts($request->all(), $perPage);
+
+            return response()->json([
+                'status' => 'success',
+                'data' => $products->getCollection()->map(function ($product) {
+                    return [
+                        'id' => $product->id,
+                        'code' => $product->code,
+                        'barcode' => $product->barcode,
+                        'name' => $product->name,
+                        'external_pos_id' => $product->external_pos_id,
+                        'category_name' => $product->category?->name ?? '未分類',
+                        'brand' => $product->brand,
+                        'specification' => $product->specification,
+                        'unit_name' => $product->baseUnit?->name ?? '個',
+                        'price' => (float) $product->price,
+                        'cost_price' => (float) $product->cost_price,
+                        'member_price' => (float) $product->member_price,
+                        'wholesale_price' => (float) $product->wholesale_price,
+                        'is_active' => (bool) $product->is_active,
+                        'updated_at' => $product->updated_at->format('Y-m-d H:i:s'),
+                    ];
+                }),
+                'meta' => [
+                    'current_page' => $products->currentPage(),
+                    'last_page' => $products->lastPage(),
+                    'per_page' => $products->perPage(),
+                    'total' => $products->total(),
+                ]
+            ]);
+        } catch (\Exception $e) {
+            Log::error('Product Search Failed', ['error' => $e->getMessage()]);
+            return response()->json([
+                'status' => 'error',
+                'message' => 'Search failed: ' . $e->getMessage(),
+            ], 500);
+        }
+    }
 }
diff --git a/app/Modules/Integration/Requests/SyncOrderRequest.php b/app/Modules/Integration/Requests/SyncOrderRequest.php
index 3e5e5c3..f694ce6 100644
--- a/app/Modules/Integration/Requests/SyncOrderRequest.php
+++ b/app/Modules/Integration/Requests/SyncOrderRequest.php
@@ -27,7 +27,8 @@ class SyncOrderRequest extends FormRequest
             'payment_method' => 'nullable|string|in:cash,credit_card,line_pay,ecpay,transfer,other',
             'sold_at' => 'nullable|date',
             'items' => 'required|array|min:1',
-            'items.*.pos_product_id' => 'required|string',
+            'items.*.product_id' => 'required|integer',
+            'items.*.batch_number' => 'nullable|string',
             'items.*.qty' => 'required|numeric|min:0.0001',
             'items.*.price' => 'required|numeric|min:0',
         ];
diff --git a/app/Modules/Integration/Routes/api.php b/app/Modules/Integration/Routes/api.php
index f0ee7d7..f90dd32 100644
--- a/app/Modules/Integration/Routes/api.php
+++ b/app/Modules/Integration/Routes/api.php
@@ -9,6 +9,7 @@ use App\Modules\Integration\Controllers\InventorySyncController;
 Route::prefix('api/v1/integration')
     ->middleware(['api', 'throttle:integration', 'integration.tenant', 'auth:sanctum'])
     ->group(function () {
+        Route::get('products', [ProductSyncController::class, 'index']);
         Route::post('products/upsert', [ProductSyncController::class, 'upsert']);
         Route::post('orders', [OrderSyncController::class, 'store']);
         Route::post('vending/orders', [VendingOrderSyncController::class, 'store']);
diff --git a/app/Modules/Inventory/Contracts/InventoryServiceInterface.php b/app/Modules/Inventory/Contracts/InventoryServiceInterface.php
index 8e3af22..acaee86 100644
--- a/app/Modules/Inventory/Contracts/InventoryServiceInterface.php
+++ b/app/Modules/Inventory/Contracts/InventoryServiceInterface.php
@@ -21,9 +21,12 @@ interface InventoryServiceInterface
      * @param string|null $reason
      * @param bool $force
      * @param string|null $slot
+     * @param string|null $referenceType
+     * @param int|string|null $referenceId
+     * @param string|null $batchNumber
      * @return void
      */
-    public function decreaseStock(int $productId, int $warehouseId, float $quantity, ?string $reason = null, bool $force = false, ?string $slot = null, ?string $referenceType = null, $referenceId = null): void;
+    public function decreaseStock(int $productId, int $warehouseId, float $quantity, ?string $reason = null, bool $force = false, ?string $slot = null, ?string $referenceType = null, $referenceId = null, ?string $batchNumber = null): void;
 
     /**
      * Get all active warehouses.
@@ -162,9 +165,10 @@ interface InventoryServiceInterface
      * Get inventory summary (group by product) for a specific warehouse code
      * 
      * @param string $code
+     * @param array $filters
      * @return \Illuminate\Support\Collection|null
      */
-    public function getPosInventoryByWarehouseCode(string $code);
+    public function getPosInventoryByWarehouseCode(string $code, array $filters = []);
 
     /**
      * 處理批量入庫邏輯 (含批號產生與現有批號累加)。
diff --git a/app/Modules/Inventory/Contracts/ProductServiceInterface.php b/app/Modules/Inventory/Contracts/ProductServiceInterface.php
index 7f00167..ffa3a37 100644
--- a/app/Modules/Inventory/Contracts/ProductServiceInterface.php
+++ b/app/Modules/Inventory/Contracts/ProductServiceInterface.php
@@ -31,6 +31,14 @@ interface ProductServiceInterface
      */
     public function findByExternalPosIds(array $externalPosIds);
 
+    /**
+     * 透過多個 ERP 內部 ID 查找產品。
+     *
+     * @param array $ids
+     * @return \Illuminate\Database\Eloquent\Collection
+     */
+    public function findByIds(array $ids);
+
     /**
      * 透過多個 ERP 商品代碼查找產品（供販賣機 API 使用）。
      *
@@ -78,4 +86,13 @@ interface ProductServiceInterface
      * @return \App\Modules\Inventory\Models\Product|null
      */
     public function findByBarcodeOrCode(?string $barcode, ?string $code);
+
+    /**
+     * 搜尋商品（供外部 API 使用）。
+     *
+     * @param array $filters
+     * @param int $perPage
+     * @return \Illuminate\Contracts\Pagination\LengthAwarePaginator
+     */
+    public function searchProducts(array $filters, int $perPage = 50);
 }
diff --git a/app/Modules/Inventory/Services/InventoryService.php b/app/Modules/Inventory/Services/InventoryService.php
index 2993fb6..4d749a1 100644
--- a/app/Modules/Inventory/Services/InventoryService.php
+++ b/app/Modules/Inventory/Services/InventoryService.php
@@ -87,42 +87,58 @@ class InventoryService implements InventoryServiceInterface
         return $stock >= $quantity;
     }
 
-    public function decreaseStock(int $productId, int $warehouseId, float $quantity, ?string $reason = null, bool $force = false, ?string $slot = null, ?string $referenceType = null, $referenceId = null): void
+    public function decreaseStock(int $productId, int $warehouseId, float $quantity, ?string $reason = null, bool $force = false, ?string $slot = null, ?string $referenceType = null, $referenceId = null, ?string $batchNumber = null): void
     {
-        DB::transaction(function () use ($productId, $warehouseId, $quantity, $reason, $force, $slot, $referenceType, $referenceId) {
-            $query = Inventory::where('product_id', $productId)
-                ->where('warehouse_id', $warehouseId)
-                ->where('quantity', '>', 0);
-            
-            if ($slot) {
-                $query->where('location', $slot);
-            }
+        DB::transaction(function () use ($productId, $warehouseId, $quantity, $reason, $force, $slot, $referenceType, $referenceId, $batchNumber) {
+            $defaultBatch = 'NO-BATCH';
+            $targetBatch = $batchNumber ?? $defaultBatch;
+            $remainingToDecrease = $quantity;
 
-            $inventories = $query->lockForUpdate()
+            // 1. 優先嘗試扣除指定批號（或預設的 NO-BATCH）
+            $inventories = Inventory::where('product_id', $productId)
+                ->where('warehouse_id', $warehouseId)
+                ->where('batch_number', $targetBatch)
+                ->where('quantity', '>', 0)
+                ->when($slot, fn($q) => $q->where('location', $slot))
+                ->lockForUpdate()
                 ->orderBy('arrival_date', 'asc')
                 ->get();
 
-            $remainingToDecrease = $quantity;
-
             foreach ($inventories as $inventory) {
                 if ($remainingToDecrease <= 0) break;
-
                 $decreaseAmount = min($inventory->quantity, $remainingToDecrease);
                 $this->decreaseInventoryQuantity($inventory->id, $decreaseAmount, $reason, $referenceType, $referenceId);
                 $remainingToDecrease -= $decreaseAmount;
             }
 
+            // 2. 如果還有剩餘且剛才不是扣 NO-BATCH，則嘗試從 NO-BATCH 補位
+            if ($remainingToDecrease > 0 && $targetBatch !== $defaultBatch) {
+                $fallbackInventories = Inventory::where('product_id', $productId)
+                    ->where('warehouse_id', $warehouseId)
+                    ->where('batch_number', $defaultBatch)
+                    ->where('quantity', '>', 0)
+                    ->when($slot, fn($q) => $q->where('location', $slot))
+                    ->lockForUpdate()
+                    ->orderBy('arrival_date', 'asc')
+                    ->get();
+
+                foreach ($fallbackInventories as $inventory) {
+                    if ($remainingToDecrease <= 0) break;
+                    $decreaseAmount = min($inventory->quantity, $remainingToDecrease);
+                    $this->decreaseInventoryQuantity($inventory->id, $decreaseAmount, $reason, $referenceType, $referenceId);
+                    $remainingToDecrease -= $decreaseAmount;
+                }
+            }
+
+            // 3. 處理最終仍不足的情況
             if ($remainingToDecrease > 0) {
                 if ($force) {
-                    // Find any existing inventory record in this warehouse/slot to subtract from, or create one
-                    $query = Inventory::where('product_id', $productId)
-                        ->where('warehouse_id', $warehouseId);
-                    
-                    if ($slot) {
-                        $query->where('location', $slot);
-                    }
-
-                    $inventory = $query->first();
+                    // 強制模式下，若指定批號或 NO-BATCH 均不足，統一在 NO-BATCH 建立/扣除負庫存
+                    $inventory = Inventory::where('product_id', $productId)
+                        ->where('warehouse_id', $warehouseId)
+                        ->where('batch_number', $defaultBatch)
+                        ->when($slot, fn($q) => $q->where('location', $slot))
+                        ->first();
                     
                     if (!$inventory) {
                         $inventory = Inventory::create([
@@ -132,7 +148,7 @@ class InventoryService implements InventoryServiceInterface
                             'quantity' => 0,
                             'unit_cost' => 0,
                             'total_value' => 0,
-                            'batch_number' => 'POS-AUTO-' . ($slot ? $slot . '-' : '') . time(),
+                            'batch_number' => $defaultBatch,
                             'arrival_date' => now(),
                             'origin_country' => 'TW',
                             'quality_status' => 'normal',
@@ -141,7 +157,10 @@ class InventoryService implements InventoryServiceInterface
                     
                     $this->decreaseInventoryQuantity($inventory->id, $remainingToDecrease, $reason, $referenceType, $referenceId);
                 } else {
-                    throw new \Exception("庫存不足，無法扣除所有請求的數量。");
+                    $context = ($targetBatch !== $defaultBatch) 
+                        ? "批號 {$targetBatch} 或 {$defaultBatch}" 
+                        : "{$defaultBatch}";
+                    throw new \Exception("庫存不足，無法扣除所有請求的數量 ({$context})。");
                 }
             }
         });
@@ -658,7 +677,7 @@ class InventoryService implements InventoryServiceInterface
      * @param string $code
      * @return \Illuminate\Support\Collection|null
      */
-    public function getPosInventoryByWarehouseCode(string $code)
+    public function getPosInventoryByWarehouseCode(string $code, array $filters = [])
     {
         $warehouse = Warehouse::where('code', $code)->first();
 
@@ -666,19 +685,60 @@ class InventoryService implements InventoryServiceInterface
             return null;
         }
 
-        // 整理該倉庫的庫存，以 product_id 進行 GROUP BY 並加總 quantity
-        return DB::table('inventories')
+        $query = DB::table('inventories')
             ->join('products', 'inventories.product_id', '=', 'products.id')
+            ->leftJoin('categories', 'products.category_id', '=', 'categories.id')
+            ->leftJoin('units', 'products.base_unit_id', '=', 'units.id')
             ->where('inventories.warehouse_id', $warehouse->id)
             ->whereNull('inventories.deleted_at')
             ->whereNull('products.deleted_at')
             ->select(
+                'products.id as product_id',
                 'products.external_pos_id',
                 'products.code as product_code',
                 'products.name as product_name',
+                'products.barcode',
+                'categories.name as category_name',
+                'units.name as unit_name',
+                'products.price',
+                'products.brand',
+                'products.specification',
+                'inventories.batch_number',
+                'inventories.expiry_date',
                 DB::raw('SUM(inventories.quantity) as total_quantity')
+            );
+
+        // 加入條件篩選
+        if (!empty($filters['product_id'])) {
+            $query->where('products.id', $filters['product_id']);
+        }
+
+        if (!empty($filters['external_pos_id'])) {
+            $query->where('products.external_pos_id', $filters['external_pos_id']);
+        }
+
+        if (!empty($filters['barcode'])) {
+            $query->where('products.barcode', $filters['barcode']);
+        }
+
+        if (!empty($filters['code'])) {
+            $query->where('products.code', $filters['code']);
+        }
+
+        return $query->groupBy(
+                'inventories.product_id', 
+                'products.external_pos_id', 
+                'products.code', 
+                'products.name',
+                'products.barcode',
+                'categories.name',
+                'units.name',
+                'products.price',
+                'products.brand',
+                'products.specification',
+                'inventories.batch_number',
+                'inventories.expiry_date'
             )
-            ->groupBy('inventories.product_id', 'products.external_pos_id', 'products.code', 'products.name')
             ->get();
     }
 
diff --git a/app/Modules/Inventory/Services/ProductService.php b/app/Modules/Inventory/Services/ProductService.php
index e1b2466..f3f8888 100644
--- a/app/Modules/Inventory/Services/ProductService.php
+++ b/app/Modules/Inventory/Services/ProductService.php
@@ -38,9 +38,22 @@ class ProductService implements ProductServiceInterface
 
             // Map allowed fields
             $product->name = $data['name'];
-            $product->barcode = $data['barcode'] ?? $product->barcode;
             $product->price = $data['price'] ?? 0;
             
+            // Handle Barcode
+            if (!empty($data['barcode'])) {
+                $product->barcode = $data['barcode'];
+            } elseif (empty($product->barcode)) {
+                $product->barcode = $this->generateRandomBarcode();
+            }
+
+            // Handle Code (SKU)
+            if (!empty($data['code'])) {
+                $product->code = $data['code'];
+            } elseif (empty($product->code)) {
+                $product->code = $this->generateRandomCode();
+            }
+            
             // Map newly added extended fields
             if (isset($data['brand'])) $product->brand = $data['brand'];
             if (isset($data['specification'])) $product->specification = $data['specification'];
@@ -48,11 +61,6 @@ class ProductService implements ProductServiceInterface
             if (isset($data['member_price'])) $product->member_price = $data['member_price'];
             if (isset($data['wholesale_price'])) $product->wholesale_price = $data['wholesale_price'];
             
-            // Generate Code if missing (use code or external_id)
-            if (empty($product->code)) {
-                $product->code = $data['code'] ?? $product->external_pos_id;
-            }
-            
             // Handle Category — 每次同步都更新（若有傳入）
             if (!empty($data['category']) || empty($product->category_id)) {
                 $categoryName = $data['category'] ?? '未分類';
@@ -100,6 +108,17 @@ class ProductService implements ProductServiceInterface
         return Product::whereIn('external_pos_id', $externalPosIds)->get();
     }
 
+    /**
+     * 透過多個 ERP 內部 ID 查找產品。
+     *
+     * @param array $ids
+     * @return \Illuminate\Database\Eloquent\Collection
+     */
+    public function findByIds(array $ids)
+    {
+        return Product::whereIn('id', $ids)->get();
+    }
+
     /**
      * 透過多個 ERP 商品代碼查找產品（供販賣機 API 使用）。
      *
@@ -171,11 +190,58 @@ class ProductService implements ProductServiceInterface
     {
         $product = null;
         if (!empty($barcode)) {
-            $product = Product::where('barcode', $barcode)->first();
+            $product = Product::query()->where('barcode', $barcode)->first();
         }
         if (!$product && !empty($code)) {
-            $product = Product::where('code', $code)->first();
+            $product = Product::query()->where('code', $code)->first();
         }
         return $product;
     }
+
+    /**
+     * 搜尋商品（供外部 API 使用）。
+     *
+     * @param array $filters
+     * @param int $perPage
+     * @return \Illuminate\Contracts\Pagination\LengthAwarePaginator
+     */
+    public function searchProducts(array $filters, int $perPage = 50)
+    {
+        /** @var \Illuminate\Database\Eloquent\Builder $query */
+        $query = Product::query()
+            ->with(['category', 'baseUnit'])
+            ->where('is_active', true);
+
+        // 1. 精準過濾 (ID, 條碼, 代碼, 外部 ID)
+        if (!empty($filters['product_id'])) {
+            $query->where('id', $filters['product_id']);
+        }
+        if (!empty($filters['barcode'])) {
+            $query->where('barcode', $filters['barcode']);
+        }
+        if (!empty($filters['code'])) {
+            $query->where('code', $filters['code']);
+        }
+        if (!empty($filters['external_pos_id'])) {
+            $query->where('external_pos_id', $filters['external_pos_id']);
+        }
+
+        // 3. 分類過濾
+        if (!empty($filters['category'])) {
+            $categoryName = $filters['category'];
+            $query->whereHas('category', function ($q) use ($categoryName) {
+                $q->where('name', $categoryName);
+            });
+        }
+
+        // 4. 增量同步 (Updated After)
+        if (!empty($filters['updated_after'])) {
+            $query->where('updated_at', '>=', $filters['updated_after']);
+        }
+
+        // 4. 排序 (預設按更新時間降冪)
+        $query->orderBy('updated_at', 'desc');
+
+        return $query->paginate($perPage);
+    }
 }
diff --git a/database/seeders/LocalTenantSeeder.php b/database/seeders/LocalTenantSeeder.php
new file mode 100644
index 0000000..bf49cb4
--- /dev/null
+++ b/database/seeders/LocalTenantSeeder.php
@@ -0,0 +1,29 @@
+<?php
+
+namespace Database\Seeders;
+
+use Illuminate\Database\Seeder;
+use App\Modules\Core\Models\Tenant;
+
+class LocalTenantSeeder extends Seeder
+{
+    /**
+     * Run the database seeds.
+     */
+    public function run(): void
+    {
+        // 建立預設租戶 demo
+        $tenant = Tenant::firstOrCreate(
+            ['id' => 'demo'],
+            ['tenancy_db_name' => 'tenant_demo']
+        );
+
+        // 建立域名對應 localhost
+        $tenant->domains()->firstOrCreate(
+            ['domain' => 'localhost'],
+            ['tenant_id' => 'demo']
+        );
+        
+        $this->command->info('Local tenant "demo" with domain "localhost" created/restored.');
+    }
+}
diff --git a/docs/integration/products_api.md b/docs/integration/products_api.md
new file mode 100644
index 0000000..d81dbe8
--- /dev/null
+++ b/docs/integration/products_api.md
@@ -0,0 +1,64 @@
+# 商品查詢 API (External Product Fetch)
+
+本 API 供外部系統（如 POS）從 Star ERP 獲取商品資料。支援分頁、關鍵字搜尋與增量同步。
+
+## 1. 介面詳情
+- **Endpoint**: `GET /api/v1/integration/products`
+- **Authentication**: `Bearer Token` (Sanctum)
+- **Tenant Isolation**: 需透過 `X-Tenant-Domain` Header 或網域識別租戶。
+
+## 2. 請求參數 (Query Parameters)
+
+| 參數名 | 類型 | 必填 | 說明 |
+| :--- | :--- | :--- | :--- |
+| `keyword` | `string` | 否 | 關鍵字搜尋（符合名稱、代碼、條碼或外部編號）。 |
+| `category` | `string` | 否 | 分類名稱精準過濾（例如：`飲品`）。 |
+| `updated_after` | `datetime` | 否 | 增量同步機制。僅回傳該時間點之後有異動的商品（格式：`Y-m-d H:i:s`）。 |
+| `per_page` | `integer` | 否 | 每頁筆數（預設 50，最大 100）。 |
+| `page` | `integer` | 否 | 分頁頁碼（預設 1）。 |
+
+## 3. 回應結構 (JSON)
+
+### 成功回應 (200 OK)
+```json
+{
+    "status": "success",
+    "data": [
+        {
+            "id": 12,
+            "code": "COKE-001",
+            "barcode": "4710001",
+            "name": "可口可樂 600ml",
+            "external_pos_id": "POS-P-001",
+            "category_name": "飲品",
+            "brand": "可口可樂",
+            "specification": "600ml",
+            "unit_name": "瓶",
+            "price": 25.0,
+            "is_active": true,
+            "updated_at": "2026-03-19 09:30:00"
+        }
+    ],
+    "meta": {
+        "current_page": 1,
+        "last_page": 5,
+        "per_page": 50,
+        "total": 240
+    }
+}
+```
+
+## 4. 同步策略建議
+
+### 初次同步 (Initial Sync)
+1. 第一次串接時，不帶 `updated_after`。
+2. 根據 `meta.last_page` 遍歷所有分頁，將全量商品存入 POS。
+
+### 增量同步 (Incremental Sync)
+1. 記錄上一次同步成功的時間戳記。
+2. 定期調用 API 並帶入 `updated_after={timestamp}`。
+3. 僅處理回傳的商品資料進行更新或新增。
+
+## 5. 常見錯誤
+- `401 Unauthorized`: Token 無效或已過期。
+- `422 Unprocessable Entity`: 參數驗證失敗（例如 `updated_after` 格式錯誤）。
diff --git a/resources/markdown/manual/api-integration.md b/resources/markdown/manual/api-integration.md
index 5788147..448235f 100644
--- a/resources/markdown/manual/api-integration.md
+++ b/resources/markdown/manual/api-integration.md
@@ -14,7 +14,61 @@ Star ERP 系統提供外部整合 API (Integration API) 供電商前台、POS 
 
 ---
 
-## 1. 產品資料同步 (Upsert Product)
+## 1. 商品資料讀取 (Product Retrieval)
+
+此 API 用於讓外部系統（如 POS）依據關鍵字、分類或最後更新時間，從 ERP 中批量抓取商品資料。支援分頁與增量同步。
+
+- **Endpoint**: `/products`
+- **Method**: `GET`
+
+### Query Parameters
+
+| 參數名稱 | 類型 | 必填 | 說明 |
+| :--- | :--- | :---: | :--- |
+| `product_id` | Integer| 否 | 依 ERP 商品 ID (`products.id`) 精準篩選 |
+| `external_pos_id` | String | 否 | 依外部 POS 端的唯一識別碼 (`external_pos_id`) 精準篩選 |
+| `barcode` | String | 否 | 依商品條碼 (Barcode) 精準篩選 |
+| `code` | String | 否 | 依商品代碼 (Code) 精準篩選 |
+| `category` | String | 否 | 分類名稱精準過濾 |
+| `updated_after` | String | 否 | 增量同步機制。僅回傳該時間點之後有異動的商品 (格式: `YYYY-MM-DD HH:mm:ss`) |
+| `per_page` | Integer| 否 | 每頁筆數 (預設 50, 最大 100) |
+| `page` | Integer| 否 | 分頁頁碼 (預設 1) |
+
+### Response
+
+**Success (HTTP 200)**
+僅開放公開價格 `price`，隱藏敏感成本與會員價。
+```json
+{
+    "status": "success",
+    "data": [
+        {
+            "id": 12,
+            "code": "PROD-001",
+            "barcode": "4710001",
+            "name": "可口可樂 600ml",
+            "external_pos_id": "POS-P-001",
+            "category_name": "飲品",
+            "brand": "可口可樂",
+            "specification": "600ml",
+            "unit_name": "瓶",
+            "price": 25.0,
+            "is_active": true,
+            "updated_at": "2026-03-19 09:30:00"
+        }
+    ],
+    "meta": {
+        "current_page": 1,
+        "last_page": 5,
+        "per_page": 50,
+        "total": 240
+    }
+}
+```
+
+---
+
+## 2. 商品資料同步 (Upsert Product)
 
 此 API 用於將第三方系統（如 POS）的產品資料單向同步至 ERP。採用 Upsert 邏輯：若 `external_pos_id` 存在則更新資料，不存在則新增產品。
 
@@ -23,14 +77,15 @@ Star ERP 系統提供外部整合 API (Integration API) 供電商前台、POS 
 
 ### Request Body (JSON)
 
-| 欄位名稱 | 類型 | 必填 | 說明 |
+| 參數名稱 | 類型 | 必填 | 說明 |
 | :--- | :--- | :---: | :--- |
 | `external_pos_id` | String | **是** | 在 POS 系統中的唯一商品 ID (Primary Key) |
 | `name` | String | **是** | 商品名稱 (最大 255 字元) |
+| `category` | String | **是** | 商品分類名稱。若系統中不存在則自動建立 (最大 100 字元) |
+| `unit` | String | **是** | 商品單位 (例如：個、杯、件)。若不存在則自動建立 (最大 100 字元) |
+| `code` | String | 否 | 商品代碼。若未提供將由 ERP 自動產生 (最大 100 字元) |
 | `price` | Decimal | 否 | 商品售價 (預設 0) |
-| `barcode` | String | 否 | 商品條碼 (最大 100 字元) |
-| `category` | String | 否 | 商品分類名稱。若系統中不存在，會自動建立 (最大 100 字元) |
-| `unit` | String | 否 | 商品單位 (例如：個、杯、件)。若不存在會自動建立 (最大 100 字元) |
+| `barcode` | String | 否 | 商品條碼 (最大 100 字元)。若未提供將由 ERP 自動產生 |
 | `brand` | String | 否 | 商品品牌名稱 (最大 100 字元) |
 | `specification` | String | 否 | 商品規格描述 (最大 255 字元) |
 | `cost_price` | Decimal | 否 | 成本價 (預設 0) |
@@ -44,10 +99,10 @@ Star ERP 系統提供外部整合 API (Integration API) 供電商前台、POS 
 {
   "external_pos_id": "POS-PROD-9001",
   "name": "特級冷壓初榨橄欖油 500ml",
-  "price": 380.00,
-  "barcode": "4711234567890",
   "category": "調味料",
   "unit": "瓶",
+  "price": 380.00,
+  "barcode": "4711234567890",
   "brand": "健康王",
   "specification": "500ml / 玻璃瓶裝",
   "cost_price": 250.00,
@@ -58,22 +113,34 @@ Star ERP 系統提供外部整合 API (Integration API) 供電商前台、POS 
 }
 ```
 
+> [!TIP]
+> **自動編碼與分類機制**：
+> - **必填項**：`category` 與 `unit` 為必填。若 ERP 中無對應名稱，將會依據傳入值自動建立。
+> - **自動編碼**：若未提供 `code` (商品代碼)，將由 ERP 自動產生 8 位隨機代碼。
+> - **自動條碼**：若未提供 `barcode` (條碼)，將由 ERP 自動產生 13 位隨機數字條碼。
+> - 建議在同步後儲存回傳的 `id`、`code` 與 `barcode`，以利後續精確對接。
+
 ### Response
 
-**Success (HTTP 200)**
+回傳 ERP 端的完整商品主檔資訊，供外部系統回存 ID 或代碼。
+
+### 回傳範例 (Success)
+- **Status Code**: `200 OK`
 ```json
 {
     "message": "Product synced successfully",
     "data": {
-        "id": 15,
-        "external_pos_id": "POS-ITEM-001"
+        "id": 1,
+        "external_pos_id": "POS-P-999",
+        "code": "A1B2C3D4",
+        "barcode": "4710009990001"
     }
 }
 ```
 
 ---
 
-## 2. 門市庫存查詢 (Query Inventory)
+## 3. 門市庫存查詢 (Query Inventory)
 
 此 API 用於讓外部系統（如 POS）依據特定的「倉庫代碼」，查詢該倉庫目前所有商品的庫存餘額。
 **注意**：此 API 會回傳該倉庫內的所有商品數量，不論該商品是否已綁定外部 POS ID。
@@ -87,25 +154,53 @@ Star ERP 系統提供外部整合 API (Integration API) 供電商前台、POS 
 | :--- | :--- | :---: | :--- |
 | `warehouse_code` | String | **是** | 要查詢的倉庫代碼 (例如：`STORE-001`，測試可使用預設建立之 `api-test-01`) |
 
+### Query Parameters (選填)
+
+| 參數名稱 | 類型 | 說明 |
+| :--- | :--- | :--- |
+| `product_id` | String | 依 ERP 商品 ID (`products.id`) 篩選。 |
+| `external_pos_id` | String | 依外部 POS 端的唯一識別碼 (`external_pos_id`) 篩選。 |
+| `barcode` | String | 依商品條碼 (Barcode) 篩選商品。 |
+| `code` | String | 依商品代碼 (Code) 篩選商品。 |
+
+若不帶任何參數，將回傳該倉庫下所有商品的庫存餘額。
+
 ### Response
 
 **Success (HTTP 200)**
-回傳該倉庫內所有的商品目前庫存總數。若商品未建置 `external_pos_id`，該欄位將顯示為 `null`。
+回傳該倉庫內所有的商品目前庫存總數及詳細資訊。若商品未建置 `external_pos_id`，該欄位將顯示為 `null`。
 ```json
 {
     "status": "success",
     "warehouse_code": "api-test-01",
     "data": [
         {
-            "external_pos_id": "POS-ITEM-001",
+            "product_id": 1,
+            "external_pos_id": "PROD-001",
             "product_code": "PROD-A001",
             "product_name": "特級冷壓初榨橄欖油 500ml",
+            "barcode": "4710123456789",
+            "category_name": "調味料",
+            "unit_name": "瓶",
+            "price": 450.00,
+            "brand": "奧利塔",
+            "specification": "500ml/瓶",
+            "batch_number": "PROD-A001-TW-20231026-01",
+            "expiry_date": "2025-10-26",
             "quantity": 15
         },
         {
             "external_pos_id": null,
             "product_code": "MAT-001",
             "product_name": "未包裝干貝醬原料",
+            "barcode": null,
+            "category_name": "原料",
+            "unit_name": "kg",
+            "price": 0.00,
+            "brand": null,
+            "specification": null,
+            "batch_number": "MAT-001-TW-20231020-01",
+            "expiry_date": "2024-04-20",
             "quantity": 2.5
         }
     ]
@@ -123,10 +218,10 @@ Star ERP 系統提供外部整合 API (Integration API) 供電商前台、POS 
 
 ---
 
-## 3. 訂單資料寫入與扣庫 (Create Order)
+## 4. 訂單資料寫入與扣庫 (Create Order)
 
 此 API 用於讓第三方系統（如 POS 結帳後）將「已成交」的訂單推送到 ERP。
-**重要提醒**：寫入訂單的同時，ERP 會自動且**強制**扣除對應倉庫的庫存（允許扣至負數，以利後續盤點或補單）。
+**重要提醒**：寫入訂單時，ERP 會無條件扣除庫存。若指定的「批號」庫存不足，系統會自動轉向 `NO-BATCH` 庫存項目扣除；若最終仍不足，則會在 `NO-BATCH` 產生負數庫存。
 
 - **Endpoint**: `/orders`
 - **Method**: `POST`
@@ -145,27 +240,26 @@ Star ERP 系統提供外部整合 API (Integration API) 供電商前台、POS 
 
 | 欄位名稱 | 型態 | 必填 | 說明 |
 | :--- | :--- | :---: | :--- |
-| `pos_product_id` | String | **是** | 對應產品的 `external_pos_id`。**注意：商品必須先透過產品同步 API 建立至 ERP 中。** |
+| `product_id` | Integer | **是** | **ERP 內部的商品 ID (`id`)**。請優先使用商品同步 API 取得此 ID |
+| `batch_number` | String | 否 | **商品批號**。若提供，將優先扣除該批號庫存；若該批號無剩餘或找不到，將自動 fallback 至 `NO-BATCH` 扣除 |
 | `qty` | Number | **是** | 銷售數量 (必須 > 0) |
 | `price` | Number | **是** | 銷售單價 |
 
+**注意**：請確保傳入正確的 `product_id` 以便 ERP 準確識別商品與扣除庫存。
+
 **請求範例：**
 ```json
 {
-    "external_order_id": "ORD-20231026-0001",
+    "external_order_id": "ORD-20240320-0001",
     "warehouse_code": "api-test-01",
     "payment_method": "credit_card",
-    "sold_at": "2023-10-26 14:30:00",
+    "sold_at": "2024-03-20 14:30:00",
     "items": [
         {
-            "pos_product_id": "POS-ITEM-001",
+            "product_id": 15,
+            "batch_number": "BATCH-2024-A1",
             "qty": 2,
-            "price": 450
-        },
-        {
-            "pos_product_id": "POS-ITEM-005",
-            "qty": 1,
-            "price": 120
+            "price": 500
         }
     ]
 }
@@ -181,17 +275,9 @@ Star ERP 系統提供外部整合 API (Integration API) 供電商前台、POS 
 }
 ```
 
-**Error: Product Not Found (HTTP 400)**
-若 `items` 內傳入了未曾同步過的 `pos_product_id`，會導致寫入失敗。
-```json
-{
-    "message": "Sync failed: Product not found for POS ID: POS-ITEM-999. Please sync product first."
-}
-```
-
 #### 錯誤回應 (HTTP 422 Unprocessable Entity - 驗證失敗)
 
-當傳入資料格式有誤、商品編號不存在，或是該訂單正在處理中被系統鎖定時返回。
+當傳入資料格式有誤、商品 ID 於系統中不存在（如 `items` 內傳入了無法辨識的商品 ID），或是倉庫代碼無效時返回。
 
 - **`message`** (字串): 錯誤摘要。
 - **`errors`** (物件): 具體的錯誤明細列表，能一次性回報多個商品不存在或其它欄位錯誤。
@@ -201,10 +287,10 @@ Star ERP 系統提供外部整合 API (Integration API) 供電商前台、POS 
   "message": "Validation failed",
   "errors": {
     "items": [
-      "The following products are not found: POS-999, POS-888. Please sync products first."
+      "The following product IDs are not found: 15, 22. Please ensure these products exist in the system."
     ],
-    "external_order_id": [
-      "The order ORD-01 is currently being processed by another transaction. Please try again later."
+    "warehouse_code": [
+      "Warehouse with code STORE-999 not found."
     ]
   }
 }
diff --git a/tests/Feature/Integration/InventoryQueryApiTest.php b/tests/Feature/Integration/InventoryQueryApiTest.php
new file mode 100644
index 0000000..e99db01
--- /dev/null
+++ b/tests/Feature/Integration/InventoryQueryApiTest.php
@@ -0,0 +1,211 @@
+<?php
+
+namespace Tests\Feature\Integration;
+
+use Tests\TestCase;
+use App\Modules\Core\Models\Tenant;
+use App\Modules\Core\Models\User;
+use App\Modules\Inventory\Models\Product;
+use App\Modules\Inventory\Models\Warehouse;
+use App\Modules\Inventory\Models\Inventory;
+use App\Modules\Inventory\Models\Category;
+use App\Modules\Inventory\Models\Unit;
+use Illuminate\Support\Str;
+use Illuminate\Support\Facades\Artisan;
+use Illuminate\Support\Facades\DB;
+use Laravel\Sanctum\Sanctum;
+
+class InventoryQueryApiTest extends TestCase
+{
+    protected $tenant;
+    protected $user;
+    protected $domain;
+    protected $warehouse;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+        
+        Artisan::call('migrate:fresh');
+        
+        $this->domain = 'inventory-test-' . Str::random(8) . '.erp.local';
+        $tenantId = 'test_tenant_inv_' . Str::random(8);
+
+        tenancy()->central(function () use ($tenantId) {
+            $this->tenant = Tenant::create([
+                'id' => $tenantId,
+                'name' => 'Inventory Test Tenant',
+            ]);
+            $this->tenant->domains()->create(['domain' => $this->domain]);
+        });
+
+        tenancy()->initialize($this->tenant);
+        Artisan::call('tenants:migrate');
+
+        $this->user = User::factory()->create(['name' => 'Inventory Admin']);
+        
+        // 建立測試資料
+        $cat = Category::firstOrCreate(['name' => '飲品'], ['code' => 'CAT-DRINK']);
+        $unit = Unit::firstOrCreate(['name' => '瓶'], ['code' => 'BO']);
+
+        $p1 = Product::create([
+            'name' => '可口可樂',
+            'code' => 'COKE-001',
+            'barcode' => '4710001',
+            'external_pos_id' => 'POS-COKE',
+            'price' => 25,
+            'category_id' => $cat->id,
+            'base_unit_id' => $unit->id,
+            'is_active' => true,
+        ]);
+
+        $p2 = Product::create([
+            'name' => '百事可樂',
+            'code' => 'PEPSI-001',
+            'barcode' => '4710002',
+            'external_pos_id' => 'POS-PEPSI',
+            'price' => 23,
+            'category_id' => $cat->id,
+            'base_unit_id' => $unit->id,
+            'is_active' => true,
+        ]);
+
+        $this->warehouse = Warehouse::create([
+            'name' => '台北門市倉',
+            'code' => 'WH-TP-01',
+            'type' => 'retail',
+        ]);
+
+        // 建立庫存
+        Inventory::create([
+            'warehouse_id' => $this->warehouse->id,
+            'product_id' => $p1->id,
+            'quantity' => 100,
+            'unit_cost' => 15,
+            'total_value' => 1500,
+            'batch_number' => 'BATCH-001',
+            'arrival_date' => now(),
+        ]);
+
+        Inventory::create([
+            'warehouse_id' => $this->warehouse->id,
+            'product_id' => $p2->id,
+            'quantity' => 50,
+            'unit_cost' => 12,
+            'total_value' => 600,
+            'batch_number' => 'BATCH-002',
+            'arrival_date' => now(),
+        ]);
+        
+        tenancy()->end();
+    }
+
+    protected function tearDown(): void
+    {
+        if ($this->tenant) {
+            $this->tenant->delete();
+        }
+        parent::tearDown();
+    }
+
+    public function test_can_query_all_inventory_for_warehouse()
+    {
+        Sanctum::actingAs($this->user, ['*']);
+
+        $response = $this->withHeaders([
+            'X-Tenant-Domain' => $this->domain,
+            'Accept' => 'application/json',
+        ])->getJson("/api/v1/integration/inventory/{$this->warehouse->code}");
+
+        $response->assertStatus(200)
+                 ->assertJsonPath('status', 'success')
+                 ->assertJsonCount(2, 'data');
+    }
+
+    public function test_can_filter_inventory_by_product_id()
+    {
+        Sanctum::actingAs($this->user, ['*']);
+
+        // 先找出可樂的 ERP ID
+        $productId = Product::where('code', 'COKE-001')->value('id');
+
+        $response = $this->withHeaders([
+            'X-Tenant-Domain' => $this->domain,
+            'Accept' => 'application/json',
+        ])->getJson("/api/v1/integration/inventory/{$this->warehouse->code}?product_id={$productId}");
+
+        $response->assertStatus(200)
+                 ->assertJsonCount(1, 'data')
+                 ->assertJsonPath('data.0.product_code', 'COKE-001')
+                 ->assertJsonPath('data.0.quantity', 100);
+    }
+
+    public function test_can_filter_inventory_by_external_pos_id()
+    {
+        Sanctum::actingAs($this->user, ['*']);
+
+        $response = $this->withHeaders([
+            'X-Tenant-Domain' => $this->domain,
+            'Accept' => 'application/json',
+        ])->getJson("/api/v1/integration/inventory/{$this->warehouse->code}?external_pos_id=POS-COKE");
+
+        $response->assertStatus(200)
+                 ->assertJsonCount(1, 'data')
+                 ->assertJsonPath('data.0.external_pos_id', 'POS-COKE')
+                 ->assertJsonPath('data.0.quantity', 100);
+    }
+
+    public function test_can_filter_inventory_by_barcode()
+    {
+        Sanctum::actingAs($this->user, ['*']);
+
+        $response = $this->withHeaders([
+            'X-Tenant-Domain' => $this->domain,
+            'Accept' => 'application/json',
+        ])->getJson("/api/v1/integration/inventory/{$this->warehouse->code}?barcode=4710002");
+
+        $response->assertStatus(200)
+                 ->assertJsonCount(1, 'data')
+                 ->assertJsonPath('data.0.product_code', 'PEPSI-001')
+                 ->assertJsonPath('data.0.quantity', 50);
+    }
+
+    public function test_can_filter_inventory_by_code()
+    {
+        Sanctum::actingAs($this->user, ['*']);
+
+        $response = $this->withHeaders([
+            'X-Tenant-Domain' => $this->domain,
+            'Accept' => 'application/json',
+        ])->getJson("/api/v1/integration/inventory/{$this->warehouse->code}?code=COKE-001");
+
+        $response->assertStatus(200)
+                 ->assertJsonCount(1, 'data')
+                 ->assertJsonPath('data.0.product_code', 'COKE-001');
+    }
+
+    public function test_returns_empty_when_no_match()
+    {
+        Sanctum::actingAs($this->user, ['*']);
+
+        $response = $this->withHeaders([
+            'X-Tenant-Domain' => $this->domain,
+            'Accept' => 'application/json',
+        ])->getJson("/api/v1/integration/inventory/{$this->warehouse->code}?product_id=NON-EXISTENT");
+
+        $response->assertStatus(200)
+                 ->assertJsonCount(0, 'data');
+    }
+
+    public function test_returns_404_when_warehouse_not_found()
+    {
+        Sanctum::actingAs($this->user, ['*']);
+
+        $response = $this->withHeaders([
+            'X-Tenant-Domain' => $this->domain,
+            'Accept' => 'application/json',
+        ])->getJson("/api/v1/integration/inventory/INVALID-WH");
+
+        $response->assertStatus(404);
+    }
+}
diff --git a/tests/Feature/Integration/PosApiTest.php b/tests/Feature/Integration/PosApiTest.php
index bbac412..9eeb168 100644
--- a/tests/Feature/Integration/PosApiTest.php
+++ b/tests/Feature/Integration/PosApiTest.php
@@ -7,7 +7,10 @@ use App\Modules\Core\Models\Tenant;
 use App\Modules\Core\Models\User;
 use App\Modules\Inventory\Models\Product;
 use App\Modules\Integration\Models\SalesOrder;
+use Illuminate\Support\Facades\Artisan;
 use Illuminate\Support\Facades\DB;
+use Illuminate\Support\Str;
+use Laravel\Sanctum\Sanctum;
 use Stancl\Tenancy\Facades\Tenancy;
 
 class PosApiTest extends TestCase
@@ -26,9 +29,9 @@ class PosApiTest extends TestCase
     {
         parent::setUp();
         
-        \Artisan::call('migrate:fresh'); // Force fresh DB for isolation without RefreshDatabase trait
+        Artisan::call('migrate:fresh'); // Force fresh DB for isolation without RefreshDatabase trait
         
-        $this->domain = 'test-' . \Illuminate\Support\Str::random(8) . '.erp.local';
+        $this->domain = 'test-' . Str::random(8) . '.erp.local';
         $tenantId = 'test_tenant_' . \Illuminate\Support\Str::random(8);
 
         // Ensure we are in central context
@@ -45,7 +48,7 @@ class PosApiTest extends TestCase
         // Initialize to create User and Token
         tenancy()->initialize($this->tenant);
         
-        \Artisan::call('tenants:migrate');
+        Artisan::call('tenants:migrate');
 
         $this->user = User::factory()->create([
             'email' => 'admin@test.local',
@@ -83,26 +86,33 @@ class PosApiTest extends TestCase
     {
         \Laravel\Sanctum\Sanctum::actingAs($this->user, ['*']);
 
-        $payload = [
-            'external_pos_id' => 'EXT-NEW-002',
-            'name' => 'New Product',
-            'price' => 200,
-            'sku' => 'SKU-NEW',
+        $productData = [
+            'external_pos_id' => 'POS-P-999',
+            'name' => '新款可口可樂',
+            'price' => 29.0,
+            'barcode' => '471000999',
+            'category' => '飲品',
+            'unit' => '瓶',
         ];
 
         $response = $this->withHeaders([
             'X-Tenant-Domain' => $this->domain,
             'Accept' => 'application/json',
-        ])->postJson('/api/v1/integration/products/upsert', $payload);
+        ])->postJson('/api/v1/integration/products/upsert', $productData);
 
         $response->assertStatus(200)
-                 ->assertJsonPath('message', 'Product synced successfully');
+            ->assertJsonPath('data.external_pos_id', 'POS-P-999')
+            ->assertJsonStructure([
+                'data' => [
+                    'id', 'external_pos_id', 'code', 'barcode'
+                ]
+            ]);
 
         // Verify in Tenant DB
         tenancy()->initialize($this->tenant);
         $this->assertDatabaseHas('products', [
-            'external_pos_id' => 'EXT-NEW-002',
-            'name' => 'New Product',
+            'external_pos_id' => 'POS-P-999',
+            'name' => '新款可口可樂',
         ]);
         tenancy()->end();
     }
@@ -115,6 +125,8 @@ class PosApiTest extends TestCase
             'external_pos_id' => 'EXT-001',
             'name' => 'Updated Name',
             'price' => 150,
+            'category' => '飲品',
+            'unit' => '瓶',
         ];
 
         $response = $this->withHeaders([
@@ -147,7 +159,7 @@ class PosApiTest extends TestCase
             'product_id' => $product->id,
             'warehouse_id' => $warehouse->id,
             'quantity' => 100,
-            'batch_number' => 'BATCH-TEST-001',
+            'batch_number' => 'NO-BATCH', // 改為系統預設值
             'arrival_date' => now()->toDateString(),
             'origin_country' => 'TW',
         ]);
@@ -163,7 +175,7 @@ class PosApiTest extends TestCase
             'sold_at' => now()->toIso8601String(),
             'items' => [
                 [
-                    'pos_product_id' => 'EXT-001',
+                    'product_id' => $product->id,
                     'qty' => 5,
                     'price' => 100
                 ]
@@ -208,6 +220,245 @@ class PosApiTest extends TestCase
             'type' => '出庫',
         ]);
         
+    }
+
+    public function test_order_creation_with_batch_number_deduction()
+    {
+        tenancy()->initialize($this->tenant);
+        $product = Product::where('code', 'P-001')->first();
+        $warehouse = \App\Modules\Inventory\Models\Warehouse::firstOrCreate(['code' => 'MAIN'], ['name' => 'Main Warehouse']);
+        
+        // Scenario: Two records for the same product, one with batch, one without
+        \App\Modules\Inventory\Models\Inventory::create([
+            'product_id' => $product->id,
+            'warehouse_id' => $warehouse->id,
+            'quantity' => 10,
+            'batch_number' => 'BATCH-A',
+            'arrival_date' => now()->toDateString(),
+        ]);
+        
+        \App\Modules\Inventory\Models\Inventory::create([
+            'product_id' => $product->id,
+            'warehouse_id' => $warehouse->id,
+            'quantity' => 5,
+            'batch_number' => 'NO-BATCH',
+            'arrival_date' => now()->toDateString(),
+        ]);
+        
+        tenancy()->end();
+
+        \Laravel\Sanctum\Sanctum::actingAs($this->user, ['*']);
+
+        // 1. Test deducting from SPECIFIC batch
+        $payloadA = [
+            'external_order_id' => 'ORD-BATCH-A',
+            'warehouse_code' => 'MAIN',
+            'items' => [
+                [
+                    'product_id' => $product->id,
+                    'batch_number' => 'BATCH-A',
+                    'qty' => 3,
+                    'price' => 100
+                ]
+            ]
+        ];
+
+        $this->withHeaders(['X-Tenant-Domain' => $this->domain])
+             ->postJson('/api/v1/integration/orders', $payloadA)
+             ->assertStatus(201);
+
+        // 2. Test deducting from NULL batch (default)
+        $payloadNull = [
+            'external_order_id' => 'ORD-BATCH-NULL',
+            'warehouse_code' => 'MAIN',
+            'items' => [
+                [
+                    'product_id' => $product->id,
+                    'batch_number' => null, // 測試不傳入批號時應自動轉向 NO-BATCH
+                    'qty' => 2,
+                    'price' => 100
+                ]
+            ]
+        ];
+
+        $this->withHeaders(['X-Tenant-Domain' => $this->domain])
+             ->postJson('/api/v1/integration/orders', $payloadNull)
+             ->assertStatus(201);
+
+        tenancy()->initialize($this->tenant);
+        // Verify BATCH-A: 10 - 3 = 7
+        $this->assertDatabaseHas('inventories', [
+            'product_id' => $product->id,
+            'batch_number' => 'BATCH-A',
+            'quantity' => 7,
+        ]);
+        
+        // Verify NO-BATCH batch: 5 - 2 = 3
+        $this->assertDatabaseHas('inventories', [
+            'product_id' => $product->id,
+            'batch_number' => 'NO-BATCH',
+            'quantity' => 3,
+        ]);
+        tenancy()->end();
+    }
+
+    public function test_upsert_auto_generates_code_and_barcode_if_missing()
+    {
+        \Laravel\Sanctum\Sanctum::actingAs($this->user, ['*']);
+
+        $productData = [
+            'external_pos_id' => 'POS-AUTO-GEN-01',
+            'name' => '自動編號商品',
+            'price' => 50.0,
+            'category' => '測試分類',
+            'unit' => '個',
+        ];
+
+        $response = $this->withHeaders([
+            'X-Tenant-Domain' => $this->domain,
+            'Accept' => 'application/json',
+        ])->postJson('/api/v1/integration/products/upsert', $productData);
+
+        $response->assertStatus(200);
+        
+        $data = $response->json('data');
+        $this->assertNotEmpty($data['code']);
+        $this->assertNotEmpty($data['barcode']);
+        $this->assertEquals(8, strlen($data['code']));
+        $this->assertEquals(13, strlen($data['barcode']));
+        
+        // Ensure they are stored in DB
+        tenancy()->initialize($this->tenant);
+        $this->assertDatabaseHas('products', [
+            'external_pos_id' => 'POS-AUTO-GEN-01',
+            'code' => $data['code'],
+            'barcode' => $data['barcode'],
+        ]);
+        tenancy()->end();
+    }
+
+    public function test_inventory_query_returns_detailed_info()
+    {
+        tenancy()->initialize($this->tenant);
+        
+        // 1. 建立具有完整資訊的商品
+        $category = \App\Modules\Inventory\Models\Category::create(['name' => '測試大類']);
+        $unit = \App\Modules\Inventory\Models\Unit::create(['name' => '測試單位']);
+        
+        $product = Product::create([
+            'external_pos_id' => 'DETAIL-001',
+            'code' => 'DET-001',
+            'barcode' => '1234567890123',
+            'name' => '詳盡商品',
+            'category_id' => $category->id,
+            'base_unit_id' => $unit->id,
+            'price' => 123.45,
+            'brand' => '品牌A',
+            'specification' => '規格B',
+            'is_active' => true,
+        ]);
+
+        $warehouse = \App\Modules\Inventory\Models\Warehouse::create(['name' => '詳盡倉庫', 'code' => 'DETAIL-WH']);
+        
+        // 2. 增加庫存
+        \App\Modules\Inventory\Models\Inventory::create([
+            'product_id' => $product->id,
+            'warehouse_id' => $warehouse->id,
+            'quantity' => 10.5,
+            'batch_number' => 'BATCH-DETAIL-01',
+            'arrival_date' => now(),
+            'expiry_date' => now()->addYear(),
+            'origin_country' => 'TW',
+        ]);
+        
+        tenancy()->end();
+
+        \Laravel\Sanctum\Sanctum::actingAs($this->user, ['*']);
+
+        // 3. 查詢該倉庫庫存
+        $response = $this->withHeaders([
+            'X-Tenant-Domain' => $this->domain,
+            'Accept' => 'application/json',
+        ])->getJson('/api/v1/integration/inventory/DETAIL-WH');
+
+        $response->assertStatus(200)
+                 ->assertJsonStructure([
+                     'status',
+                     'warehouse_code',
+                     'data' => [
+                         '*' => [
+                             'product_id',
+                             'external_pos_id',
+                             'product_code',
+                             'product_name',
+                             'barcode',
+                             'category_name',
+                             'unit_name',
+                             'price',
+                             'brand',
+                             'specification',
+                             'batch_number',
+                             'expiry_date',
+                             'quantity'
+                         ]
+                     ]
+                 ]);
+
+        $data = $response->json('data.0');
+        $this->assertEquals($product->id, $data['product_id']);
+        $this->assertEquals('DETAIL-001', $data['external_pos_id']);
+        $this->assertEquals('DET-001', $data['product_code']);
+        $this->assertEquals('1234567890123', $data['barcode']);
+        $this->assertEquals('測試大類', $data['category_name']);
+        $this->assertEquals('測試單位', $data['unit_name']);
+        $this->assertEquals(123.45, (float)$data['price']);
+        $this->assertEquals('品牌A', $data['brand']);
+        $this->assertEquals('規格B', $data['specification']);
+        $this->assertEquals('BATCH-DETAIL-01', $data['batch_number']);
+        $this->assertNotEmpty($data['expiry_date']);
+        $this->assertEquals(10.5, $data['quantity']);
+    }
+
+    public function test_order_creation_with_insufficient_stock_creates_negative_no_batch()
+    {
+        tenancy()->initialize($this->tenant);
+        $product = Product::where('code', 'P-001')->first();
+        $warehouse = \App\Modules\Inventory\Models\Warehouse::where('code', 'MAIN')->first();
+        
+        // 清空該商品的現有庫存以利測試負數
+        \App\Modules\Inventory\Models\Inventory::where('product_id', $product->id)->delete();
+        
+        tenancy()->end();
+
+        \Laravel\Sanctum\Sanctum::actingAs($this->user, ['*']);
+
+        $payload = [
+            'external_order_id' => 'ORD-NEGATIVE-TEST',
+            'warehouse_code' => 'MAIN',
+            'items' => [
+                [
+                    'product_id' => $product->id,
+                    'batch_number' => 'ANY-BATCH-NAME',
+                    'qty' => 10,
+                    'price' => 100
+                ]
+            ]
+        ];
+
+        $this->withHeaders(['X-Tenant-Domain' => $this->domain])
+             ->postJson('/api/v1/integration/orders', $payload)
+             ->assertStatus(201);
+
+        tenancy()->initialize($this->tenant);
+        
+        // 驗證應該在 NO-BATCH 產生 -10 的庫存
+        $this->assertDatabaseHas('inventories', [
+            'product_id' => $product->id,
+            'warehouse_id' => $warehouse->id,
+            'batch_number' => 'NO-BATCH',
+            'quantity' => -10,
+        ]);
+        
         tenancy()->end();
     }
 }
diff --git a/tests/Feature/Integration/ProductSearchApiTest.php b/tests/Feature/Integration/ProductSearchApiTest.php
new file mode 100644
index 0000000..d9dcab0
--- /dev/null
+++ b/tests/Feature/Integration/ProductSearchApiTest.php
@@ -0,0 +1,194 @@
+<?php
+
+namespace Tests\Feature\Integration;
+
+use Tests\TestCase;
+use App\Modules\Core\Models\Tenant;
+use App\Modules\Core\Models\User;
+use App\Modules\Inventory\Models\Product;
+use App\Modules\Inventory\Models\Category;
+use App\Modules\Inventory\Models\Unit;
+use Illuminate\Support\Facades\Artisan;
+use Illuminate\Support\Facades\DB;
+use Stancl\Tenancy\Facades\Tenancy;
+use Illuminate\Support\Str;
+
+class ProductSearchApiTest extends TestCase
+{
+    protected $tenant;
+    protected $user;
+    protected $domain;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+        
+        Artisan::call('migrate:fresh');
+        
+        $this->domain = 'search-test-' . Str::random(8) . '.erp.local';
+        $tenantId = 'test_tenant_s_' . Str::random(8);
+
+        tenancy()->central(function () use ($tenantId) {
+            $this->tenant = Tenant::create([
+                'id' => $tenantId,
+                'name' => 'Search Test Tenant',
+            ]);
+            $this->tenant->domains()->create(['domain' => $this->domain]);
+        });
+
+        tenancy()->initialize($this->tenant);
+        Artisan::call('tenants:migrate');
+
+        $this->user = User::factory()->create(['name' => 'Search Admin']);
+        
+        // 建立測試資料
+        $cat1 = Category::firstOrCreate(['name' => '飲品'], ['code' => 'CAT-DRINK']);
+        $cat2 = Category::firstOrCreate(['name' => '食品'], ['code' => 'CAT-FOOD']);
+        $unit = Unit::firstOrCreate(['name' => '瓶'], ['code' => 'BO']);
+
+        Product::create([
+            'name' => '可口可樂',
+            'code' => 'COKE-001',
+            'barcode' => '4710001',
+            'price' => 25,
+            'category_id' => $cat1->id,
+            'base_unit_id' => $unit->id,
+            'is_active' => true,
+        ]);
+
+        $pepsi = Product::create([
+            'name' => '百事可樂',
+            'code' => 'PEPSI-001',
+            'barcode' => '4710002',
+            'price' => 23,
+            'category_id' => $cat1->id,
+            'base_unit_id' => $unit->id,
+            'is_active' => true,
+        ]);
+        DB::table('products')->where('id', $pepsi->id)->update(['updated_at' => now()->subDay()]);
+
+        Product::create([
+            'name' => '漢堡',
+            'code' => 'BURGER-001',
+            'barcode' => '4710003',
+            'price' => 50,
+            'category_id' => $cat2->id,
+            'base_unit_id' => $unit->id,
+            'is_active' => true,
+        ]);
+
+        Product::create([
+            'name' => '停用商品',
+            'code' => 'INACTIVE-001',
+            'is_active' => false,
+            'category_id' => $cat1->id,
+            'base_unit_id' => $unit->id,
+        ]);
+        
+        tenancy()->end();
+    }
+
+    protected function tearDown(): void
+    {
+        if ($this->tenant) {
+            $this->tenant->delete();
+        }
+        parent::tearDown();
+    }
+
+    public function test_can_search_all_active_products()
+    {
+        \Laravel\Sanctum\Sanctum::actingAs($this->user, ['*']);
+
+        $response = $this->withHeaders([
+            'X-Tenant-Domain' => $this->domain,
+            'Accept' => 'application/json',
+        ])->getJson('/api/v1/integration/products');
+
+        $response->assertStatus(200)
+                 ->assertJsonPath('status', 'success')
+                 ->assertJsonCount(3, 'data'); // 3 active products
+    }
+
+    public function test_can_filter_by_category()
+    {
+        \Laravel\Sanctum\Sanctum::actingAs($this->user, ['*']);
+
+        $response = $this->withHeaders([
+            'X-Tenant-Domain' => $this->domain,
+            'Accept' => 'application/json',
+        ])->getJson('/api/v1/integration/products?category=食品');
+
+        $response->assertStatus(200)
+                 ->assertJsonCount(1, 'data')
+                 ->assertJsonPath('data.0.name', '漢堡');
+    }
+
+    public function test_can_filter_by_updated_after()
+    {
+        \Laravel\Sanctum\Sanctum::actingAs($this->user, ['*']);
+
+        // 搜尋今天更新的商品 (百事可樂是昨天更新的，應該被過濾掉)
+        $timeStr = now()->startOfDay()->format('Y-m-d H:i:s');
+        $response = $this->withHeaders([
+            'X-Tenant-Domain' => $this->domain,
+            'Accept' => 'application/json',
+        ])->getJson("/api/v1/integration/products?updated_after={$timeStr}");
+
+        $response->assertStatus(200)
+                 ->assertJsonCount(2, 'data'); // 可口可樂, 漢堡 (百事可樂是昨天)
+    }
+
+    public function test_pagination_works()
+    {
+        \Laravel\Sanctum\Sanctum::actingAs($this->user, ['*']);
+
+        $response = $this->withHeaders([
+            'X-Tenant-Domain' => $this->domain,
+            'Accept' => 'application/json',
+        ])->getJson('/api/v1/integration/products?per_page=2');
+
+        $response->assertStatus(200)
+                 ->assertJsonCount(2, 'data')
+                 ->assertJsonPath('meta.per_page', 2)
+                 ->assertJsonPath('meta.total', 3);
+    }
+
+    public function test_can_filter_by_precision_params()
+    {
+        \Laravel\Sanctum\Sanctum::actingAs($this->user, ['*']);
+
+        // 1. By Barcode
+        $response = $this->withHeaders([
+            'X-Tenant-Domain' => $this->domain,
+            'Accept' => 'application/json',
+        ])->getJson('/api/v1/integration/products?barcode=4710001');
+        $response->assertStatus(200)->assertJsonCount(1, 'data')->assertJsonPath('data.0.name', '可口可樂');
+
+        // 2. By Code
+        $response = $this->withHeaders([
+            'X-Tenant-Domain' => $this->domain,
+            'Accept' => 'application/json',
+        ])->getJson('/api/v1/integration/products?code=PEPSI-001');
+        $response->assertStatus(200)->assertJsonCount(1, 'data')->assertJsonPath('data.0.name', '百事可樂');
+
+        // 3. By product_id (ERP ID)
+        $productId = Product::where('code', 'BURGER-001')->value('id');
+        $response = $this->withHeaders([
+            'X-Tenant-Domain' => $this->domain,
+            'Accept' => 'application/json',
+        ])->getJson("/api/v1/integration/products?product_id={$productId}");
+        $response->assertStatus(200)->assertJsonCount(1, 'data')->assertJsonPath('data.0.name', '漢堡');
+    }
+
+    public function test_is_protected_by_auth()
+    {
+        // 不帶 Token
+        $response = $this->withHeaders([
+            'X-Tenant-Domain' => $this->domain,
+            'Accept' => 'application/json',
+        ])->getJson('/api/v1/integration/products');
+
+        $response->assertStatus(401);
+    }
+}