diff --git a/app/Http/Controllers/Admin/BasicSettings/MachineSettingController.php b/app/Http/Controllers/Admin/BasicSettings/MachineSettingController.php
index b007952..a4fb477 100644
--- a/app/Http/Controllers/Admin/BasicSettings/MachineSettingController.php
+++ b/app/Http/Controllers/Admin/BasicSettings/MachineSettingController.php
@@ -75,8 +75,10 @@ class MachineSettingController extends AdminController
                     break;
 
                 case 'permissions':
+                    // 套用層級可見範圍：系統管理員看全部；租戶僅看可見範圍內帳號（避免跨租戶洩漏）。
                     $userQuery = \App\Models\System\User::query()
                         ->where('is_admin', true)
+                        ->visibleTo($currentUser)
                         ->with(['company', 'machines']);
                     if ($search) {
                         $userQuery->where(function($q) use ($search) {
@@ -121,6 +123,7 @@ class MachineSettingController extends AdminController
 
         $userQuery = \App\Models\System\User::query()
             ->where('is_admin', true)
+            ->visibleTo($currentUser)
             ->with(['company', 'machines']);
         $users_list = $userQuery->latest()->paginate($per_page)->withQueryString();
 
diff --git a/app/Http/Controllers/Admin/Machine/MachinePermissionController.php b/app/Http/Controllers/Admin/Machine/MachinePermissionController.php
index bdc80b3..fbe9d33 100644
--- a/app/Http/Controllers/Admin/Machine/MachinePermissionController.php
+++ b/app/Http/Controllers/Admin/Machine/MachinePermissionController.php
@@ -32,10 +32,9 @@ class MachinePermissionController extends AdminController
             }])
             ->whereNotNull('company_id');
 
-        // 非系統管理員僅能看到同公司的帳號 (因 User Model 排除 TenantScoped 全域過濾，需手動注入)
-        if (!$currentUser->isSystemAdmin()) {
-            $userQuery->where('company_id', $currentUser->company_id);
-        } elseif ($company_id) {
+        // 可見範圍：系統管理員看全部；主帳號看同公司全部；子帳號僅看自己直接建立的下層（避免洩漏旁線帳號）。
+        $userQuery->visibleTo($currentUser);
+        if ($currentUser->isSystemAdmin() && $company_id) {
             // 系統管理員的篩選邏輯
             $userQuery->where('company_id', $company_id);
         }
@@ -54,6 +53,31 @@ class MachinePermissionController extends AdminController
         return view('admin.machines.permissions', compact('users_list', 'companies'));
     }
 
+    /**
+     * 操作者「可授權」的機台 ID 集合（授權子集約束）：
+     * - 系統管理員：指定公司（或全部）的所有機台
+     * - 主帳號：同公司全部機台
+     * - 子帳號：僅自己被授權的機台（machine_user）
+     */
+    private function assignableMachineIds(User $operator, ?int $companyId): \Illuminate\Support\Collection
+    {
+        // 目標帳號無所屬公司（如系統管理員帳號）時，沒有可授權的公司機台。
+        if (is_null($companyId)) {
+            return collect();
+        }
+
+        if ($operator->isSystemAdmin() || $operator->is_admin) {
+            return Machine::withoutGlobalScope('machine_access')
+                ->where('company_id', $companyId)
+                ->pluck('id');
+        }
+
+        return $operator->machines()
+            ->withoutGlobalScope('machine_access')
+            ->where('machines.company_id', $companyId)
+            ->pluck('machines.id');
+    }
+
     /**
      * AJAX: 取得特定帳號的機台分配狀態
      */
@@ -61,17 +85,18 @@ class MachinePermissionController extends AdminController
     {
         $currentUser = auth()->user();
 
-        // 安全檢查：只能操作自己公司的帳號（除非是系統管理員）
-        if (!$currentUser->isSystemAdmin() && $user->company_id !== $currentUser->company_id) {
+        // 層級越權防護：只能操作可管轄範圍內的帳號。
+        if (!$currentUser->canManageAccount($user)) {
             return response()->json(['error' => 'Unauthorized'], 403);
         }
 
-        // 取得該使用者所屬公司之所有機台 (忽略個別帳號的 machine_access 限制，以公司為單位顯示)
+        // 可授權機台清單限縮為「操作者本身可授權」的機台子集，避免把自己沒有的機台授權出去。
+        $assignableIds = $this->assignableMachineIds($currentUser, $user->company_id);
         $machines = Machine::withoutGlobalScope('machine_access')
-            ->where('company_id', $user->company_id)
+            ->whereIn('id', $assignableIds)
             ->get(['id', 'name', 'serial_no']);
-            
-        $assignedIds = $user->machines()->pluck('machines.id')->toArray();
+
+        $assignedIds = $user->machines()->withoutGlobalScope('machine_access')->pluck('machines.id')->toArray();
 
         return response()->json([
             'user' => $user,
@@ -87,8 +112,8 @@ class MachinePermissionController extends AdminController
     {
         $currentUser = auth()->user();
 
-        // 安全檢查
-        if (!$currentUser->isSystemAdmin() && $user->company_id !== $currentUser->company_id) {
+        // 層級越權防護：只能操作可管轄範圍內的帳號。
+        if (!$currentUser->canManageAccount($user)) {
             return response()->json(['error' => 'Unauthorized'], 403);
         }
 
@@ -97,20 +122,27 @@ class MachinePermissionController extends AdminController
             'machine_ids.*' => 'exists:machines,id'
         ]);
 
-        // 加固驗證：確保所有機台 ID 都屬於該使用者的公司 (使用 withoutGlobalScope 避免管理員自身權限影響驗證邏輯)
-        if ($request->has('machine_ids')) {
-            $machineIds = array_unique($request->machine_ids);
-            $validCount = Machine::withoutGlobalScope('machine_access')
-                ->where('company_id', $user->company_id)
-                ->whereIn('id', $machineIds)
-                ->count();
-            
-            if ($validCount !== count($machineIds)) {
-                return response()->json(['error' => 'Invalid machine IDs provided.'], 422);
-            }
+        // 授權子集約束：被指派的機台必須是「操作者本身可授權機台」的子集，
+        // 既確保同公司，也避免子帳號把自己沒被授權的機台授權給他人。
+        $assignableIds = $this->assignableMachineIds($currentUser, $user->company_id);
+        $submittedIds = collect($request->machine_ids ?? [])->map(fn ($id) => (int) $id)->unique();
+        if ($submittedIds->diff($assignableIds)->isNotEmpty()) {
+            return response()->json(['error' => 'Invalid machine IDs provided.'], 422);
         }
 
-        $user->machines()->sync($request->machine_ids ?? []);
+        // 只在「操作者可授權子集」範圍內做增刪；範圍外的既有授權一律保留，避免覆蓋式 sync 誤刪
+        // 操作者看不到（不在其可授權子集內）的機台。明確 detach/attach 以避開 machine_access
+        // 全域 scope 對 sync 取「現有附加」造成的干擾（該 scope 依登入者過濾 Machine 查詢）。
+        $existingIds = $user->machines()->withoutGlobalScope('machine_access')->pluck('machines.id');
+        $currentInScope = $existingIds->intersect($assignableIds);
+        $toAttach = $submittedIds->diff($currentInScope);
+        $toDetach = $currentInScope->diff($submittedIds);
+        if ($toDetach->isNotEmpty()) {
+            $user->machines()->detach($toDetach->all());
+        }
+        if ($toAttach->isNotEmpty()) {
+            $user->machines()->attach($toAttach->all());
+        }
         
         $message = __('Machine permissions updated successfully.');
         session()->flash('success', $message);
diff --git a/app/Http/Controllers/Admin/PermissionController.php b/app/Http/Controllers/Admin/PermissionController.php
index a590113..1fe5d3a 100644
--- a/app/Http/Controllers/Admin/PermissionController.php
+++ b/app/Http/Controllers/Admin/PermissionController.php
@@ -14,10 +14,8 @@ class PermissionController extends Controller
         $user = auth()->user();
         $query = \App\Models\System\Role::query()->with(['permissions', 'users', 'company']);
 
-        // 租戶隔離：租戶只能看到自己公司的角色
-        if (!$user->isSystemAdmin()) {
-            $query->where('company_id', $user->company_id);
-        }
+        // 層級隔離：系統管理員看全部；主帳號看同公司全部；子帳號僅看自己建立的角色。
+        $query->visibleTo($user);
 
         // 搜尋：角色名稱（支援 roles_search 命名空間 與舊版 search）
         $search = request()->input('roles_search', request()->input('search'));
@@ -88,6 +86,11 @@ class PermissionController extends Controller
         $role = \App\Models\System\Role::findOrFail($id);
         $user = auth()->user();
 
+        // 層級隔離：子帳號只能編輯自己建立的角色，不可開啟上層/旁線建立的角色。
+        if (!$role->canBeManagedBy($user)) {
+            return redirect()->back()->with('error', __('You do not have permission to manage this role.'));
+        }
+
         // 權限遞迴約束與分組邏輯由 getFilteredPermissions 處理
 
         $all_permissions = $this->getFilteredPermissions($user);
@@ -126,6 +129,7 @@ class PermissionController extends Controller
             'name' => $validated['name'],
             'guard_name' => 'web',
             'company_id' => $is_system ? null : auth()->user()->company_id,
+            'created_by' => auth()->id(),
             'is_system' => $is_system,
         ]);
 
@@ -182,6 +186,11 @@ class PermissionController extends Controller
              return redirect()->back()->with('error', __('System roles cannot be modified by tenant administrators.'));
         }
 
+        // 層級隔離：子帳號只能修改自己建立的角色。
+        if (!$role->canBeManagedBy(auth()->user())) {
+            return redirect()->back()->with('error', __('You do not have permission to manage this role.'));
+        }
+
         $is_system = auth()->user()->isSystemAdmin() ? $request->boolean('is_system') : $role->is_system;
 
         $updateData = [
@@ -223,10 +232,20 @@ class PermissionController extends Controller
             return redirect()->back()->with('error', __('The Super Admin role cannot be deleted.'));
         }
 
+        // 公司主帳號角色保護：比照 super-admin，公司層級的「管理員」角色為該公司最高權限角色，不可刪除。
+        if ($role->is_company_admin) {
+            return redirect()->back()->with('error', __('The company admin role cannot be deleted.'));
+        }
+
         if (!auth()->user()->isSystemAdmin() && $role->is_system) {
             return redirect()->back()->with('error', __('System roles cannot be deleted by tenant administrators.'));
         }
 
+        // 層級隔離：子帳號只能刪除自己建立的角色。
+        if (!$role->canBeManagedBy(auth()->user())) {
+            return redirect()->back()->with('error', __('You do not have permission to manage this role.'));
+        }
+
         if ($role->users()->count() > 0) {
             return redirect()->back()->with('error', __('Cannot delete role with active users.'));
         }
@@ -251,10 +270,8 @@ class PermissionController extends Controller
         $currentUserRoleIds = $user->roles->pluck('id')->toArray();
 
         // ── 帳號列表 ──────────────────────────────────────────────────
-        $usersQuery = \App\Models\System\User::query()->with(['company', 'roles', 'machines']);
-        if (!$user->isSystemAdmin()) {
-            $usersQuery->where('company_id', $user->company_id);
-        }
+        // 可見範圍：系統管理員看全部；主帳號看同公司全部；子帳號僅看自己直接建立的下層。
+        $usersQuery = \App\Models\System\User::query()->with(['company', 'roles', 'machines'])->visibleTo($user);
         if ($search = $request->input('accounts_search', $request->input('search'))) {
             $usersQuery->where(function ($q) use ($search) {
                 $q->where('name', 'like', "%{$search}%")
@@ -269,22 +286,24 @@ class PermissionController extends Controller
         $accounts_per_page = $request->input('accounts_per_page', 10);
         $users = $usersQuery->latest()->paginate($accounts_per_page, ['*'], 'accounts_page')->withQueryString();
 
-        // Modal 用的角色選單（不分頁）
-        $rolesForSelect = \App\Models\System\Role::query();
-        if (!$user->isSystemAdmin()) {
-            $rolesForSelect->forCompany($user->company_id);
-        }
+        // Modal 用的角色選單（不分頁）。層級隔離：子帳號僅見自己建立的角色（與角色清單一致）。
+        // 預先載入 permissions 以避免下方子集過濾造成 N+1。
+        $rolesForSelect = \App\Models\System\Role::query()->with('permissions')->visibleTo($user);
         $roles = $rolesForSelect->get();
+        // 子集過濾：租戶只能指派「權限為自身子集」的角色（與 store/update 的後端 guard 一致，避免下拉出現越權選項）。
+        if (!$user->isSystemAdmin()) {
+            $operatorPerms = $user->getAllPermissions()->pluck('name');
+            $roles = $roles->filter(
+                fn($r) => collect($r->getPermissionNames())->diff($operatorPerms)->isEmpty()
+            )->values();
+        }
 
         // ── 角色列表 (僅 data-config Tab 版需要) ─────────────────────
         $paginated_roles = collect();
         $all_permissions = collect();
 
         if ($isSubAccountRoute) {
-            $rolesQuery = \App\Models\System\Role::query()->with(['permissions', 'users', 'company']);
-            if (!$user->isSystemAdmin()) {
-                $rolesQuery->where('company_id', $user->company_id);
-            }
+            $rolesQuery = \App\Models\System\Role::query()->with(['permissions', 'users', 'company'])->visibleTo($user);
             if ($search = $request->input('roles_search')) {
                 $rolesQuery->where('name', 'like', "%{$search}%");
             }
@@ -328,6 +347,12 @@ class PermissionController extends Controller
             'phone' => 'nullable|string|max:20',
         ]);
 
+        // 深度上限：level >= MAX_LEVEL 的子帳號不可再建立下層（系統管理員不受限）。
+        // 此為後端硬擋，獨立於權限判斷（即使持有子帳號管理權限也不得突破層級）。
+        if (!auth()->user()->canCreateSubAccount()) {
+            return redirect()->back()->with('error', __('Sub-accounts at this level cannot create further sub-accounts.'));
+        }
+
         $company_id = auth()->user()->isSystemAdmin() ? ($validated['company_id'] ?? null) : auth()->user()->company_id;
 
         // 查找角色：優先尋找該公司的角色，若無則尋找全域範本
@@ -374,6 +399,7 @@ class PermissionController extends Controller
                     'guard_name' => 'web',
                     'company_id' => $company_id,
                     'is_system' => false,
+                    'is_company_admin' => true,
                 ]);
                 $newRole->syncPermissions($role->getPermissionNames());
                 $role = $newRole;
@@ -383,6 +409,39 @@ class PermissionController extends Controller
             }
         }
 
+        // 角色指派子集驗證：租戶只能指派「權限為自身子集」的角色，避免透過指派高權限角色造成權限提升。
+        if (!auth()->user()->isSystemAdmin()) {
+            $operatorPerms = auth()->user()->getAllPermissions()->pluck('name');
+            if (collect($role->getPermissionNames())->diff($operatorPerms)->isNotEmpty()) {
+                return redirect()->back()->with('error', __('You cannot assign a role with permissions you do not possess.'));
+            }
+        }
+
+        // 主帳號唯一性：一家公司只在「尚無主帳號」時，由系統管理員建立的第一個帳號自動成為主帳號 (is_admin)。
+        // 之後建立的帳號（含子帳號自建）一律 is_admin=false，確保每家公司恰有一個主帳號。
+        $creator = auth()->user();
+        $companyHasAdmin = $company_id
+            ? \App\Models\System\User::where('company_id', $company_id)->where('is_admin', true)->exists()
+            : false;
+        $isMainAccount = $creator->isSystemAdmin() && !empty($company_id) && !$companyHasAdmin;
+
+        // 樹狀層級歸屬：
+        // - 主帳號：level 0、parent_id null。
+        // - 系統管理員建立的非主帳號：掛在該公司主帳號下、level 1。
+        // - 租戶自建：掛在建立者下、level = 建立者 level + 1。
+        if ($isMainAccount) {
+            $parentId = null;
+            $level = 0;
+        } elseif ($creator->isSystemAdmin()) {
+            $parentId = $company_id
+                ? \App\Models\System\User::where('company_id', $company_id)->where('is_admin', true)->value('id')
+                : null;
+            $level = $parentId ? 1 : 0;
+        } else {
+            $parentId = $creator->id;
+            $level = $creator->level + 1;
+        }
+
         $user = \App\Models\System\User::create([
             'name' => $validated['name'],
             'username' => $validated['username'],
@@ -390,8 +449,10 @@ class PermissionController extends Controller
             'password' => \Illuminate\Support\Facades\Hash::make($validated['password']),
             'status' => $validated['status'],
             'company_id' => $company_id,
+            'parent_id' => $parentId,
+            'level' => $level,
             'phone' => $validated['phone'] ?? null,
-            'is_admin' => (auth()->user()->isSystemAdmin() && !empty($validated['company_id'])),
+            'is_admin' => $isMainAccount,
         ]);
 
         $user->assignRole($role);
@@ -410,6 +471,11 @@ class PermissionController extends Controller
             return redirect()->back()->with('error', __('System super admin accounts can only be modified by other super admins.'));
         }
 
+        // 層級越權防護：租戶只能管理可管轄範圍內的帳號（主帳號=同公司全部；子帳號=自己直接建立的下層）。
+        if (!auth()->user()->canManageAccount($user)) {
+            return redirect()->back()->with('error', __('You do not have permission to manage this account.'));
+        }
+
         $validated = $request->validate([
             'name' => 'required|string|max:255',
             'username' => 'required|string|max:255|unique:users,username,' . $id,
@@ -500,7 +566,7 @@ class PermissionController extends Controller
                     'guard_name' => 'web',
                     'company_id' => $target_company_id,
                     'is_system' => false,
-                    'is_admin' => true,
+                    'is_company_admin' => true,
                 ]);
                 $newRole->syncPermissions($roleObj->getPermissionNames());
                 $roleObj = $newRole;
@@ -509,6 +575,14 @@ class PermissionController extends Controller
             }
         }
 
+        // 角色指派子集驗證：租戶只能指派「權限為自身子集」的角色，避免權限提升。
+        if (!auth()->user()->isSystemAdmin()) {
+            $operatorPerms = auth()->user()->getAllPermissions()->pluck('name');
+            if (collect($roleObj->getPermissionNames())->diff($operatorPerms)->isNotEmpty()) {
+                return redirect()->back()->with('error', __('You cannot assign a role with permissions you do not possess.'));
+            }
+        }
+
         $user->update($updateData);
 
         // 如果是編輯自己且原本是超級管理員，強制保留 super-admin 角色
@@ -527,15 +601,31 @@ class PermissionController extends Controller
     public function destroyAccount($id)
     {
         $user = \App\Models\System\User::findOrFail($id);
-        
+
         if ($user->hasRole('super-admin') && !auth()->user()->hasRole('super-admin')) {
             return redirect()->back()->with('error', __('System super admin accounts can only be deleted by other super admins.'));
         }
 
+        // 層級越權防護：租戶只能刪除可管轄範圍內的帳號。
+        if (!auth()->user()->canManageAccount($user)) {
+            return redirect()->back()->with('error', __('You do not have permission to manage this account.'));
+        }
+
         if ($user->id === auth()->id()) {
             return redirect()->back()->with('error', __('You cannot delete your own account.'));
         }
 
+        // 主帳號保護：若該帳號是公司唯一主帳號，且公司仍有其他帳號，禁止刪除（須先轉移主帳號身分），
+        // 以維持「有帳號的公司恰有一個主帳號」的不變量。公司僅剩此主帳號時允許刪除（公司歸零）。
+        if ($user->is_admin && $user->company_id) {
+            $hasOtherAccounts = \App\Models\System\User::where('company_id', $user->company_id)
+                ->where('id', '!=', $user->id)
+                ->exists();
+            if ($hasOtherAccounts) {
+                return redirect()->back()->with('error', __('Cannot delete the company main account while other accounts exist. Please transfer the main account role first.'));
+            }
+        }
+
         // 為了解決軟刪除導致的唯一索引佔用問題，刪除前先重命名唯一欄位
         $timestamp = now()->getTimestamp();
         $user->username = $user->username . '.deleted.' . $timestamp;
@@ -556,6 +646,11 @@ class PermissionController extends Controller
             return back()->with('error', __('Only Super Admins can change other Super Admin status.'));
         }
 
+        // 層級越權防護：租戶只能切換可管轄範圍內的帳號狀態。
+        if (!auth()->user()->canManageAccount($user)) {
+            return back()->with('error', __('You do not have permission to manage this account.'));
+        }
+
         $user->status = $user->status ? 0 : 1;
         $user->save();
 
diff --git a/app/Http/Controllers/Admin/WarehouseController.php b/app/Http/Controllers/Admin/WarehouseController.php
index 5c6411e..d467530 100644
--- a/app/Http/Controllers/Admin/WarehouseController.php
+++ b/app/Http/Controllers/Admin/WarehouseController.php
@@ -840,10 +840,9 @@ class WarehouseController extends Controller
         $machines = $applyCompanyFilter(Machine::query())->orderBy('name')->get(['id', 'name', 'serial_no']);
         $products = $applyCompanyFilter(Product::with('translations'))->orderBy('name')->get(['id', 'name', 'image_url', 'name_dictionary_key']);
 
-        $userQuery = \App\Models\System\User::where('status', 1)->orderBy('name');
-        if (!$isSystemAdmin) {
-            $userQuery->where('company_id', $currentUser->company_id);
-        } elseif ($companyId !== '') {
+        // 可見範圍：系統管理員看全部；主帳號看同公司全部；子帳號僅看自己直接建立的下層（避免洩漏旁線帳號）。
+        $userQuery = \App\Models\System\User::where('status', 1)->orderBy('name')->visibleTo($currentUser);
+        if ($isSystemAdmin && $companyId !== '') {
             $userQuery->where('company_id', $companyId);
         }
         $users = $userQuery->get(['id', 'name']);
diff --git a/app/Models/System/Role.php b/app/Models/System/Role.php
index 4c539c0..b1362d1 100644
--- a/app/Models/System/Role.php
+++ b/app/Models/System/Role.php
@@ -10,11 +10,14 @@ class Role extends SpatieRole
         'name',
         'guard_name',
         'company_id',
+        'created_by',
         'is_system',
+        'is_company_admin',
     ];
 
     protected $casts = [
         'is_system' => 'boolean',
+        'is_company_admin' => 'boolean',
     ];
 
     /**
@@ -25,6 +28,14 @@ class Role extends SpatieRole
         return $this->belongsTo(Company::class);
     }
 
+    /**
+     * 建立者帳號。
+     */
+    public function creator()
+    {
+        return $this->belongsTo(User::class, 'created_by');
+    }
+
     /**
      * Scope a query to only include roles for a specific company or system roles.
      */
@@ -35,4 +46,43 @@ class Role extends SpatieRole
               ->orWhereNull('company_id');
         });
     }
+
+    /**
+     * 查詢範圍：限制為指定使用者「可見」的角色（鏡像 User::scopeVisibleTo）。
+     * - 系統管理員：全部
+     * - 主帳號：同公司全部
+     * - 子帳號：僅自己建立的角色
+     */
+    public function scopeVisibleTo($query, User $viewer)
+    {
+        if ($viewer->isSystemAdmin()) {
+            return $query;
+        }
+        $query->where($this->getTable() . '.company_id', $viewer->company_id);
+        if (!$viewer->is_admin) {
+            $query->where($this->getTable() . '.created_by', $viewer->id);
+        }
+        return $query;
+    }
+
+    /**
+     * 操作者是否有權管理（編輯/刪除）此角色。
+     * - 系統管理員：全部
+     * - 跨公司：禁止
+     * - 主帳號：同公司全部
+     * - 子帳號：僅自己建立的角色
+     */
+    public function canBeManagedBy(User $user): bool
+    {
+        if ($user->isSystemAdmin()) {
+            return true;
+        }
+        if ($this->company_id !== $user->company_id) {
+            return false;
+        }
+        if ($user->is_admin) {
+            return true;
+        }
+        return $this->created_by === $user->id;
+    }
 }
diff --git a/app/Models/System/User.php b/app/Models/System/User.php
index 7c0fac3..56a1e17 100644
--- a/app/Models/System/User.php
+++ b/app/Models/System/User.php
@@ -23,6 +23,8 @@ class User extends Authenticatable
      */
     protected $fillable = [
         'company_id',
+        'parent_id',
+        'level',
         'username',
         'name',
         'email',
@@ -53,8 +55,14 @@ class User extends Authenticatable
         'email_verified_at' => 'datetime',
         'password' => 'hashed',
         'is_admin' => 'boolean',
+        'level' => 'integer',
     ];
 
+    /**
+     * 帳號層級上限：子帳號最多兩層（主帳號 level 0 → 子 level 1 → 孫 level 2，level 2 不可再建）。
+     */
+    public const MAX_LEVEL = 2;
+
     /**
      * Get the login logs for the user.
      */
@@ -95,6 +103,85 @@ class User extends Authenticatable
         return !is_null($this->company_id);
     }
 
+    /**
+     * 上層（建立者）帳號。
+     */
+    public function parent()
+    {
+        return $this->belongsTo(self::class, 'parent_id');
+    }
+
+    /**
+     * 直接建立的下層帳號。
+     */
+    public function children()
+    {
+        return $this->hasMany(self::class, 'parent_id');
+    }
+
+    /**
+     * 是否為該公司主帳號（租戶層級且 is_admin）。
+     */
+    public function isMainAccount(): bool
+    {
+        return $this->isTenant() && $this->is_admin;
+    }
+
+    /**
+     * 是否為子帳號（租戶層級且非主帳號）。
+     */
+    public function isSubAccount(): bool
+    {
+        return $this->isTenant() && !$this->is_admin;
+    }
+
+    /**
+     * 是否還能再建立下層子帳號（深度上限約束，系統管理員不受限）。
+     */
+    public function canCreateSubAccount(): bool
+    {
+        return $this->isSystemAdmin() || $this->level < self::MAX_LEVEL;
+    }
+
+    /**
+     * 查詢範圍：限制為指定使用者「可見」的帳號。
+     * - 系統管理員：全部
+     * - 主帳號：同公司全部（安全網）
+     * - 子帳號：僅自己直接建立的下層帳號
+     */
+    public function scopeVisibleTo($query, self $viewer)
+    {
+        if ($viewer->isSystemAdmin()) {
+            return $query;
+        }
+        $query->where($this->getTable() . '.company_id', $viewer->company_id);
+        if (!$viewer->is_admin) {
+            $query->where($this->getTable() . '.parent_id', $viewer->id);
+        }
+        return $query;
+    }
+
+    /**
+     * 操作者是否有權管理（編輯/刪除/停用）指定帳號。
+     * - 系統管理員：全部
+     * - 跨公司：禁止
+     * - 主帳號：同公司全部
+     * - 子帳號：僅自己直接建立的下層帳號
+     */
+    public function canManageAccount(self $target): bool
+    {
+        if ($this->isSystemAdmin()) {
+            return true;
+        }
+        if ($target->company_id !== $this->company_id) {
+            return false;
+        }
+        if ($this->is_admin) {
+            return true;
+        }
+        return $target->parent_id === $this->id;
+    }
+
     /**
      * Get the URL for the user's avatar.
      */
diff --git a/database/migrations/2026_06_25_100000_add_is_company_admin_to_roles_table.php b/database/migrations/2026_06_25_100000_add_is_company_admin_to_roles_table.php
new file mode 100644
index 0000000..fd27bd1
--- /dev/null
+++ b/database/migrations/2026_06_25_100000_add_is_company_admin_to_roles_table.php
@@ -0,0 +1,42 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+use Illuminate\Support\Facades\DB;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     *
+     * 為公司層級的「管理員」角色加入明確的權威旗標 is_company_admin，
+     * 取代過去靠中文 name='管理員' 來辨識主帳號角色的脆弱作法。
+     */
+    public function up(): void
+    {
+        if (!Schema::hasColumn('roles', 'is_company_admin')) {
+            Schema::table('roles', function (Blueprint $table) {
+                $table->boolean('is_company_admin')->default(false)->after('is_system');
+            });
+        }
+
+        // Backfill：既有的公司層級「管理員」角色標記為 is_company_admin = true
+        DB::table('roles')
+            ->whereNotNull('company_id')
+            ->where('name', '管理員')
+            ->update(['is_company_admin' => true]);
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        if (Schema::hasColumn('roles', 'is_company_admin')) {
+            Schema::table('roles', function (Blueprint $table) {
+                $table->dropColumn('is_company_admin');
+            });
+        }
+    }
+};
diff --git a/database/migrations/2026_06_25_100100_add_parent_id_and_level_to_users_table.php b/database/migrations/2026_06_25_100100_add_parent_id_and_level_to_users_table.php
new file mode 100644
index 0000000..e83fea2
--- /dev/null
+++ b/database/migrations/2026_06_25_100100_add_parent_id_and_level_to_users_table.php
@@ -0,0 +1,113 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+use Illuminate\Support\Facades\DB;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     *
+     * 帳號樹狀層級化：加入 parent_id（建立者）與 level（主帳號=0）。
+     * 並對既有資料做兩步 backfill：
+     *   1. is_admin 正規化：每家「有帳號但無主帳號」的公司，將最早建立的帳號設為主帳號；多主帳號則只保留最早一個。
+     *   2. 回填 parent_id / level：主帳號 level=0、parent_id=null；其餘帳號掛在該公司主帳號下、level=1。
+     */
+    public function up(): void
+    {
+        Schema::table('users', function (Blueprint $table) {
+            $table->unsignedBigInteger('parent_id')->nullable()->after('company_id');
+            $table->unsignedTinyInteger('level')->default(0)->after('parent_id');
+            $table->foreign('parent_id')->references('id')->on('users')->nullOnDelete();
+            $table->index('parent_id');
+        });
+
+        $companyIds = DB::table('companies')->pluck('id');
+
+        // 1. is_admin 正規化
+        foreach ($companyIds as $cid) {
+            // a. 軟刪除帳號一律不得為主帳號
+            DB::table('users')
+                ->where('company_id', $cid)
+                ->whereNotNull('deleted_at')
+                ->where('is_admin', true)
+                ->update(['is_admin' => false]);
+
+            // b. 在「未軟刪除」帳號中確保恰有一個主帳號
+            $admins = DB::table('users')
+                ->where('company_id', $cid)
+                ->whereNull('deleted_at')
+                ->where('is_admin', true)
+                ->orderBy('id')
+                ->pluck('id');
+
+            if ($admins->isEmpty()) {
+                // 無主帳號 → 將最早建立的帳號補為主帳號
+                $firstId = DB::table('users')
+                    ->where('company_id', $cid)
+                    ->whereNull('deleted_at')
+                    ->orderBy('id')
+                    ->value('id');
+                if ($firstId) {
+                    DB::table('users')->where('id', $firstId)->update(['is_admin' => true]);
+                }
+            } elseif ($admins->count() > 1) {
+                // 多主帳號 → 只保留最早一個，其餘降為一般帳號
+                DB::table('users')
+                    ->whereIn('id', $admins->slice(1)->values())
+                    ->update(['is_admin' => false]);
+            }
+        }
+
+        // 2. 回填 parent_id / level
+        foreach ($companyIds as $cid) {
+            // 主帳號必須取自「未軟刪除」帳號
+            $mainId = DB::table('users')
+                ->where('company_id', $cid)
+                ->whereNull('deleted_at')
+                ->where('is_admin', true)
+                ->value('id');
+
+            if (!$mainId) {
+                continue; // 空公司，略過
+            }
+
+            // 主帳號
+            DB::table('users')->where('id', $mainId)->update(['parent_id' => null, 'level' => 0]);
+            // 其餘帳號（含軟刪除）掛在主帳號下，level=1
+            DB::table('users')
+                ->where('company_id', $cid)
+                ->where('id', '!=', $mainId)
+                ->update(['parent_id' => $mainId, 'level' => 1]);
+        }
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        // 防禦式：外鍵 / 索引 / 欄位可能因 DDL 半途失敗而部分不存在，逐項忽略不存在的情況。
+        try {
+            Schema::table('users', fn (Blueprint $t) => $t->dropForeign(['parent_id']));
+        } catch (\Throwable $e) {
+            // 外鍵已不存在，略過
+        }
+        try {
+            Schema::table('users', fn (Blueprint $t) => $t->dropIndex('users_parent_id_index'));
+        } catch (\Throwable $e) {
+            // 索引已不存在，略過
+        }
+        Schema::table('users', function (Blueprint $table) {
+            $cols = array_values(array_filter(
+                ['parent_id', 'level'],
+                fn ($c) => Schema::hasColumn('users', $c)
+            ));
+            if ($cols) {
+                $table->dropColumn($cols);
+            }
+        });
+    }
+};
diff --git a/database/migrations/2026_06_25_100200_add_created_by_to_roles_table.php b/database/migrations/2026_06_25_100200_add_created_by_to_roles_table.php
new file mode 100644
index 0000000..acaee16
--- /dev/null
+++ b/database/migrations/2026_06_25_100200_add_created_by_to_roles_table.php
@@ -0,0 +1,60 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+use Illuminate\Support\Facades\DB;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     *
+     * 角色樹狀層級化：加入 created_by（建立者帳號）。
+     * Backfill：既有公司層級角色 created_by 指向該公司主帳號；全域系統角色維持 null。
+     */
+    public function up(): void
+    {
+        Schema::table('roles', function (Blueprint $table) {
+            $table->unsignedBigInteger('created_by')->nullable()->after('company_id');
+            $table->foreign('created_by')->references('id')->on('users')->nullOnDelete();
+            $table->index('created_by');
+        });
+
+        // 既有公司角色歸屬該公司主帳號（未軟刪除的 is_admin）
+        $companyIds = DB::table('roles')->whereNotNull('company_id')->distinct()->pluck('company_id');
+        foreach ($companyIds as $cid) {
+            $mainId = DB::table('users')
+                ->where('company_id', $cid)
+                ->whereNull('deleted_at')
+                ->where('is_admin', true)
+                ->value('id');
+            if ($mainId) {
+                DB::table('roles')
+                    ->where('company_id', $cid)
+                    ->whereNull('created_by')
+                    ->update(['created_by' => $mainId]);
+            }
+        }
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        try {
+            Schema::table('roles', fn (Blueprint $t) => $t->dropForeign(['created_by']));
+        } catch (\Throwable $e) {
+            // 外鍵已不存在，略過
+        }
+        try {
+            Schema::table('roles', fn (Blueprint $t) => $t->dropIndex('roles_created_by_index'));
+        } catch (\Throwable $e) {
+            // 索引已不存在，略過
+        }
+        if (Schema::hasColumn('roles', 'created_by')) {
+            Schema::table('roles', fn (Blueprint $t) => $t->dropColumn('created_by'));
+        }
+    }
+};
diff --git a/lang/en.json b/lang/en.json
index 755cff3..108b4ee 100644
--- a/lang/en.json
+++ b/lang/en.json
@@ -275,6 +275,7 @@
     "Cannot delete company with active accounts.": "Cannot delete company with active accounts.",
     "Cannot delete model that is currently in use by machines.": "Cannot delete model that is currently in use by machines.",
     "Cannot delete role with active users.": "Cannot delete role with active users.",
+    "Cannot delete the company main account while other accounts exist. Please transfer the main account role first.": "Cannot delete the company main account while other accounts exist. Please transfer the main account role first.",
     "Cannot delete warehouse with existing stock": "Cannot delete warehouse with existing stock",
     "Cannot match original stored-value transaction": "Cannot match original stored-value transaction",
     "Card Machine System": "Card Machine System",
@@ -2065,6 +2066,7 @@
     "Sub Account Management": "Sub Account Management",
     "Sub Account Roles": "Sub Account Roles",
     "Sub Accounts": "Sub Accounts",
+    "Sub-accounts at this level cannot create further sub-accounts.": "Sub-accounts at this level cannot create further sub-accounts.",
     "Sub-actions": "Sub-actions",
     "Sub-machine": "Sub-machine",
     "Sub-machine Status": "Sub-machine Status",
@@ -2151,6 +2153,7 @@
     "The Super Admin role cannot be deleted.": "The Super Admin role cannot be deleted.",
     "The Super Admin role is immutable.": "The Super Admin role is immutable.",
     "The Super Admin role name cannot be modified.": "The Super Admin role name cannot be modified.",
+    "The company admin role cannot be deleted.": "The company admin role cannot be deleted.",
     "The image archive contains too many files": "The image archive contains too many files",
     "The image archive is too large when extracted": "The image archive is too large when extracted",
     "The image is too large. Please upload an image smaller than 1MB.": "The image is too large. Please upload an image smaller than 1MB.",
@@ -2414,9 +2417,12 @@
     "Yesterday": "Yesterday",
     "You can assign or change the personnel handling this order": "You can assign or change the personnel handling this order",
     "You can select at most :max languages.": "You can select at most :max languages.",
+    "You cannot assign a role with permissions you do not possess.": "You cannot assign a role with permissions you do not possess.",
     "You cannot assign permissions you do not possess.": "You cannot assign permissions you do not possess.",
     "You cannot delete your own account.": "You cannot delete your own account.",
     "You do not have permission to access replenishment orders": "You do not have permission to access replenishment orders",
+    "You do not have permission to manage this account.": "You do not have permission to manage this account.",
+    "You do not have permission to manage this role.": "You do not have permission to manage this role.",
     "Your account is disabled.": "Your account is disabled.",
     "Your recent account activity": "Your recent account activity",
     "[PickupCode] Verification failed: :code": "[PickupCode] Verification failed: :code",
diff --git a/lang/ja.json b/lang/ja.json
index ca815fd..64003b0 100644
--- a/lang/ja.json
+++ b/lang/ja.json
@@ -275,6 +275,7 @@
     "Cannot delete company with active accounts.": "有効なアカウントを持つ顧客は削除できません。",
     "Cannot delete model that is currently in use by machines.": "機器で使用中のモデルは削除できません。",
     "Cannot delete role with active users.": "ユーザーが紐付けられているロールは削除できません。",
+    "Cannot delete the company main account while other accounts exist. Please transfer the main account role first.": "他のアカウントが存在する間は、会社のメインアカウントを削除できません。先にメインアカウントの権限を移譲してください。",
     "Cannot delete warehouse with existing stock": "在庫がある倉庫は削除できません",
     "Cannot match original stored-value transaction": "元の電子マネー取引と照合できません",
     "Card Machine System": "カードリーダーシステム",
@@ -2065,6 +2066,7 @@
     "Sub Account Management": "サブアカウント管理",
     "Sub Account Roles": "サブアカウントロール",
     "Sub Accounts": "サブアカウント",
+    "Sub-accounts at this level cannot create further sub-accounts.": "このレベルのサブアカウントは、これ以上下位のサブアカウントを作成できません。",
     "Sub-actions": "サブアクション",
     "Sub-machine": "サブマシン",
     "Sub-machine Status": "Sub-machine Status",
@@ -2151,6 +2153,7 @@
     "The Super Admin role cannot be deleted.": "特権管理者ロールは削除できません。",
     "The Super Admin role is immutable.": "特権管理者ロールは変更できません。",
     "The Super Admin role name cannot be modified.": "特権管理者ロールの名前は変更できません。",
+    "The company admin role cannot be deleted.": "会社管理者ロールは削除できません。",
     "The image archive contains too many files": "画像アーカイブのファイル数が多すぎます",
     "The image archive is too large when extracted": "画像アーカイブの展開後のサイズが大きすぎます",
     "The image is too large. Please upload an image smaller than 1MB.": "画像サイズが大きすぎます。1MB未満の画像をアップロードしてください。",
@@ -2414,9 +2417,12 @@
     "Yesterday": "昨日",
     "You can assign or change the personnel handling this order": "この注文を処理する担当者を割り当て、または変更できます",
     "You can select at most :max languages.": "最大 :max 言語まで選択できます。",
+    "You cannot assign a role with permissions you do not possess.": "自分が保有していない権限を含むロールは割り当てできません。",
     "You cannot assign permissions you do not possess.": "自身が持っていない権限を割り当てることはできません。",
     "You cannot delete your own account.": "自分自身のアカウントは削除できません。",
     "You do not have permission to access replenishment orders": "補充伝票のアクセス権限がありません",
+    "You do not have permission to manage this account.": "このアカウントを管理する権限がありません。",
+    "You do not have permission to manage this role.": "このロールを管理する権限がありません。",
     "Your account is disabled.": "アカウントが無効化されています。",
     "Your recent account activity": "最近のアカウントアクティビティ",
     "[PickupCode] Verification failed: :code": "[受取コード] 検証失敗: :code",
diff --git a/lang/zh_TW.json b/lang/zh_TW.json
index 8bfb550..6ad0935 100644
--- a/lang/zh_TW.json
+++ b/lang/zh_TW.json
@@ -275,6 +275,7 @@
     "Cannot delete company with active accounts.": "無法刪除仍有客用帳號的客戶。",
     "Cannot delete model that is currently in use by machines.": "無法刪除目前正在被機台使用的型號。",
     "Cannot delete role with active users.": "無法刪除已有綁定帳號的角色。",
+    "Cannot delete the company main account while other accounts exist. Please transfer the main account role first.": "公司主帳號為唯一主帳號，仍有其他帳號時不可刪除，請先轉移主帳號身分。",
     "Cannot delete warehouse with existing stock": "無法刪除仍有庫存的倉庫",
     "Cannot match original stored-value transaction": "無法比對原始電票交易",
     "Card Machine System": "刷卡機系統",
@@ -2065,6 +2066,7 @@
     "Sub Account Management": "子帳號管理",
     "Sub Account Roles": "子帳號角色",
     "Sub Accounts": "子帳號",
+    "Sub-accounts at this level cannot create further sub-accounts.": "此層級的子帳號無法再建立下層子帳號。",
     "Sub-actions": "子項目",
     "Sub-machine": "下位機",
     "Sub-machine Status": "下位機狀態",
@@ -2151,6 +2153,7 @@
     "The Super Admin role cannot be deleted.": "超級管理員角色不可刪除。",
     "The Super Admin role is immutable.": "超級管理員角色不可修改。",
     "The Super Admin role name cannot be modified.": "超級管理員角色的名稱無法修改。",
+    "The company admin role cannot be deleted.": "公司管理員角色不可刪除。",
     "The image archive contains too many files": "圖片壓縮檔內的檔案數量過多",
     "The image archive is too large when extracted": "圖片壓縮檔解壓後的體積過大",
     "The image is too large. Please upload an image smaller than 1MB.": "圖片檔案太大，請上傳小於 1MB 的圖片。",
@@ -2414,9 +2417,12 @@
     "Yesterday": "昨日",
     "You can assign or change the personnel handling this order": "您可以指派或變更處理此訂單的人員",
     "You can select at most :max languages.": "最多只能選擇 :max 種語系。",
+    "You cannot assign a role with permissions you do not possess.": "您無法指派含有您本身未持有權限的角色。",
     "You cannot assign permissions you do not possess.": "您無法指派您自身不具備的權限。",
     "You cannot delete your own account.": "您無法刪除自己的帳號。",
     "You do not have permission to access replenishment orders": "您沒有機台補貨單的權限",
+    "You do not have permission to manage this account.": "您沒有權限管理此帳號。",
+    "You do not have permission to manage this role.": "您沒有權限管理此角色。",
     "Your account is disabled.": "您的帳號已被停用。",
     "Your recent account activity": "最近的帳號活動",
     "[PickupCode] Verification failed: :code": "[取貨碼] 驗證失敗: :code",
diff --git a/tests/Feature/Admin/AccountHierarchyTest.php b/tests/Feature/Admin/AccountHierarchyTest.php
new file mode 100644
index 0000000..37e4d8a
--- /dev/null
+++ b/tests/Feature/Admin/AccountHierarchyTest.php
@@ -0,0 +1,157 @@
+<?php
+
+namespace Tests\Feature\Admin;
+
+use App\Models\System\Company;
+use App\Models\System\Role;
+use App\Models\System\User;
+use Spatie\Permission\Models\Permission;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Tests\TestCase;
+
+/**
+ * 帳號樹狀層級隔離（第二+三批）行為測試：
+ * - 主帳號唯一性（第一個帳號自動成為主帳號）
+ * - parent_id / level 歸屬
+ * - 子帳號深度上限（level 2 不可再建）
+ * - visibleTo 可見範圍隔離（只看自己直建的）
+ * - canManageAccount 越權防護（不能管旁線）
+ */
+class AccountHierarchyTest extends TestCase
+{
+    use RefreshDatabase;
+
+    protected User $sysAdmin;
+    protected Company $company;
+    protected Role $tenantRole;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        foreach (['menu.permissions.accounts', 'menu.data-config.sub-accounts'] as $p) {
+            Permission::create(['name' => $p, 'guard_name' => 'web']);
+        }
+
+        $superAdmin = Role::create(['name' => 'super-admin', 'company_id' => null, 'is_system' => true, 'guard_name' => 'web']);
+        $superAdmin->syncPermissions(['menu.permissions.accounts', 'menu.data-config.sub-accounts']);
+
+        Role::create(['name' => '客戶管理員角色模板', 'company_id' => null, 'is_system' => true, 'guard_name' => 'web'])
+            ->syncPermissions(['menu.permissions.accounts', 'menu.data-config.sub-accounts']);
+
+        $this->company = Company::create(['name' => 'Test Co', 'code' => 'TEST']);
+
+        $this->sysAdmin = User::factory()->create(['company_id' => null]);
+        $this->sysAdmin->assignRole($superAdmin);
+
+        // 供租戶帳號使用、帶有子帳號管理權限的公司層級角色
+        $this->tenantRole = Role::create(['name' => 'tenant-mgr', 'company_id' => $this->company->id, 'is_system' => false, 'guard_name' => 'web']);
+        $this->tenantRole->syncPermissions(['menu.permissions.accounts', 'menu.data-config.sub-accounts']);
+    }
+
+    /** 建立一個租戶帳號（直接寫入層級欄位）並賦予可建子帳號的角色 */
+    private function makeTenantUser(array $attrs): User
+    {
+        $user = User::factory()->create(array_merge(['company_id' => $this->company->id], $attrs));
+        $user->assignRole($this->tenantRole);
+        return $user;
+    }
+
+    public function test_first_company_account_becomes_main(): void
+    {
+        $this->actingAs($this->sysAdmin)->post(route('admin.permission.accounts.store'), [
+            'name' => 'First', 'username' => 'first', 'email' => 'first@test.co', 'password' => 'password123',
+            'role' => '客戶管理員角色模板', 'status' => 1, 'company_id' => $this->company->id,
+        ])->assertSessionHas('success');
+
+        $u = User::where('username', 'first')->first();
+        $this->assertTrue($u->is_admin);
+        $this->assertSame(0, $u->level);
+        $this->assertNull($u->parent_id);
+    }
+
+    public function test_second_company_account_is_not_main_and_is_child(): void
+    {
+        $main = $this->makeTenantUser(['is_admin' => true, 'level' => 0, 'parent_id' => null]);
+
+        $this->actingAs($this->sysAdmin)->post(route('admin.permission.accounts.store'), [
+            'name' => 'Second', 'username' => 'second', 'email' => 'second@test.co', 'password' => 'password123',
+            'role' => 'tenant-mgr', 'status' => 1, 'company_id' => $this->company->id,
+        ])->assertSessionHas('success');
+
+        $u = User::where('username', 'second')->first();
+        $this->assertFalse($u->is_admin);
+        $this->assertSame(1, $u->level);
+        $this->assertSame($main->id, $u->parent_id);
+    }
+
+    public function test_tenant_admin_creates_sub_account_sets_parent_and_level(): void
+    {
+        $main = $this->makeTenantUser(['is_admin' => true, 'level' => 0, 'parent_id' => null]);
+
+        $this->actingAs($main)->post(route('admin.data-config.sub-accounts.store'), [
+            'name' => 'Sub', 'username' => 'sub', 'email' => 'sub@test.co', 'password' => 'password123',
+            'role' => 'tenant-mgr', 'status' => 1,
+        ])->assertSessionHas('success');
+
+        $u = User::where('username', 'sub')->first();
+        $this->assertFalse($u->is_admin);
+        $this->assertSame(1, $u->level);
+        $this->assertSame($main->id, $u->parent_id);
+        $this->assertSame($this->company->id, $u->company_id);
+    }
+
+    public function test_level_two_sub_account_cannot_create_further(): void
+    {
+        $deep = $this->makeTenantUser(['is_admin' => false, 'level' => 2, 'parent_id' => null]);
+
+        $this->actingAs($deep)->post(route('admin.data-config.sub-accounts.store'), [
+            'name' => 'TooDeep', 'username' => 'toodeep', 'email' => 'toodeep@test.co', 'password' => 'password123',
+            'role' => 'tenant-mgr', 'status' => 1,
+        ])->assertSessionHas('error');
+
+        $this->assertDatabaseMissing('users', ['username' => 'toodeep']);
+    }
+
+    public function test_visible_to_isolates_siblings_and_self(): void
+    {
+        $main = $this->makeTenantUser(['is_admin' => true, 'level' => 0, 'parent_id' => null]);
+        $a = $this->makeTenantUser(['is_admin' => false, 'level' => 1, 'parent_id' => $main->id]);
+        $b = $this->makeTenantUser(['is_admin' => false, 'level' => 1, 'parent_id' => $main->id]);
+        $c = $this->makeTenantUser(['is_admin' => false, 'level' => 2, 'parent_id' => $a->id]);
+
+        // 子帳號 A 只看得到自己直建的 C，看不到自己、旁線 B、主帳號
+        $visibleToA = User::visibleTo($a)->pluck('id')->all();
+        $this->assertSame([$c->id], $visibleToA);
+
+        // 主帳號看得到同公司全部
+        $visibleToMain = User::visibleTo($main)->pluck('id')->sort()->values()->all();
+        $this->assertEquals(collect([$main->id, $a->id, $b->id, $c->id])->sort()->values()->all(), $visibleToMain);
+    }
+
+    public function test_sub_account_cannot_manage_sibling(): void
+    {
+        $main = $this->makeTenantUser(['is_admin' => true, 'level' => 0, 'parent_id' => null]);
+        $a = $this->makeTenantUser(['is_admin' => false, 'level' => 1, 'parent_id' => $main->id]);
+        $b = $this->makeTenantUser(['is_admin' => false, 'level' => 1, 'parent_id' => $main->id]);
+
+        // A 嘗試刪除旁線 B → 被擋
+        $this->actingAs($a)->delete(route('admin.data-config.sub-accounts.destroy', $b->id))
+            ->assertSessionHas('error');
+        $this->assertDatabaseHas('users', ['id' => $b->id, 'deleted_at' => null]);
+
+        // A 嘗試停用旁線 B → 被擋
+        $this->actingAs($a)->patch(route('admin.data-config.sub-accounts.status.toggle', $b->id))
+            ->assertSessionHas('error');
+    }
+
+    public function test_main_account_can_manage_company_sub_account(): void
+    {
+        $main = $this->makeTenantUser(['is_admin' => true, 'level' => 0, 'parent_id' => null]);
+        $a = $this->makeTenantUser(['is_admin' => false, 'level' => 1, 'parent_id' => $main->id]);
+
+        // 主帳號可停用同公司子帳號
+        $this->actingAs($main)->patch(route('admin.data-config.sub-accounts.status.toggle', $a->id))
+            ->assertSessionHas('success');
+    }
+}
diff --git a/tests/Feature/Admin/AccountSubsetGuardTest.php b/tests/Feature/Admin/AccountSubsetGuardTest.php
new file mode 100644
index 0000000..39955fc
--- /dev/null
+++ b/tests/Feature/Admin/AccountSubsetGuardTest.php
@@ -0,0 +1,160 @@
+<?php
+
+namespace Tests\Feature\Admin;
+
+use App\Models\Machine\Machine;
+use App\Models\System\Company;
+use App\Models\System\Role;
+use App\Models\System\User;
+use Spatie\Permission\Models\Permission;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Tests\TestCase;
+
+/**
+ * 第四批：角色指派子集 與 機台授權子集 把關測試。
+ * - 操作者不可指派「含自身未持有權限」的角色（防權限提升）。
+ * - 操作者不可授權「自己未被授權」的機台給他人（防機台層級提升）。
+ * - 操作者不可對非管轄帳號操作機台授權（越權）。
+ */
+class AccountSubsetGuardTest extends TestCase
+{
+    use RefreshDatabase;
+
+    protected Company $company;
+    protected User $main;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        foreach (['menu.permissions.accounts', 'menu.data-config.sub-accounts', 'extra.high.perm'] as $p) {
+            Permission::create(['name' => $p, 'guard_name' => 'web']);
+        }
+
+        $this->company = Company::create(['name' => 'Test Co', 'code' => 'TEST']);
+
+        // 主帳號角色：僅持有兩個權限（不含 extra.high.perm）
+        $mainRole = Role::create(['name' => 'tenant-mgr', 'company_id' => $this->company->id, 'is_system' => false, 'guard_name' => 'web']);
+        $mainRole->syncPermissions(['menu.permissions.accounts', 'menu.data-config.sub-accounts']);
+
+        $this->main = User::factory()->create([
+            'company_id' => $this->company->id, 'is_admin' => true, 'level' => 0, 'parent_id' => null,
+        ]);
+        $this->main->assignRole($mainRole);
+    }
+
+    // ── 角色指派子集 ─────────────────────────────────────────────
+
+    public function test_operator_cannot_assign_role_exceeding_own_permissions(): void
+    {
+        // 高權限角色：多出操作者沒有的 extra.high.perm
+        $highRole = Role::create(['name' => 'high-role', 'company_id' => $this->company->id, 'is_system' => false, 'guard_name' => 'web']);
+        $highRole->syncPermissions(['menu.permissions.accounts', 'menu.data-config.sub-accounts', 'extra.high.perm']);
+
+        $this->actingAs($this->main)->post(route('admin.data-config.sub-accounts.store'), [
+            'name' => 'X', 'username' => 'escalated', 'email' => 'e@test.co', 'password' => 'password123',
+            'role' => 'high-role', 'status' => 1,
+        ])->assertSessionHas('error');
+
+        $this->assertDatabaseMissing('users', ['username' => 'escalated']);
+    }
+
+    public function test_operator_can_assign_role_within_own_permissions(): void
+    {
+        $this->actingAs($this->main)->post(route('admin.data-config.sub-accounts.store'), [
+            'name' => 'X', 'username' => 'ok_sub', 'email' => 'ok@test.co', 'password' => 'password123',
+            'role' => 'tenant-mgr', 'status' => 1,
+        ])->assertSessionHas('success');
+
+        $this->assertDatabaseHas('users', ['username' => 'ok_sub']);
+    }
+
+    // ── 機台授權子集 ─────────────────────────────────────────────
+
+    public function test_operator_cannot_grant_machine_they_are_not_assigned(): void
+    {
+        $operator = User::factory()->create([
+            'company_id' => $this->company->id, 'is_admin' => false, 'level' => 1, 'parent_id' => $this->main->id,
+        ]);
+        $target = User::factory()->create([
+            'company_id' => $this->company->id, 'is_admin' => false, 'level' => 2, 'parent_id' => $operator->id,
+        ]);
+
+        $m1 = Machine::factory()->create(['company_id' => $this->company->id]);
+        $m2 = Machine::factory()->create(['company_id' => $this->company->id]);
+        $operator->machines()->attach($m1->id); // 操作者只被授權 m1
+
+        // 嘗試把自己沒有的 m2 授權給 target → 422
+        $this->actingAs($operator)->postJson(route('admin.machines.permissions.accounts.sync', $target->id), [
+            'machine_ids' => [$m1->id, $m2->id],
+        ])->assertStatus(422);
+
+        // 只授權自己有的 m1 → 成功
+        $this->actingAs($operator)->postJson(route('admin.machines.permissions.accounts.sync', $target->id), [
+            'machine_ids' => [$m1->id],
+        ])->assertStatus(200);
+
+        $this->assertDatabaseHas('machine_user', ['user_id' => $target->id, 'machine_id' => $m1->id]);
+        $this->assertDatabaseMissing('machine_user', ['user_id' => $target->id, 'machine_id' => $m2->id]);
+    }
+
+    public function test_operator_cannot_assign_machines_to_non_managed_account(): void
+    {
+        $operator = User::factory()->create([
+            'company_id' => $this->company->id, 'is_admin' => false, 'level' => 1, 'parent_id' => $this->main->id,
+        ]);
+        // 旁線帳號（非 operator 的下層）
+        $sibling = User::factory()->create([
+            'company_id' => $this->company->id, 'is_admin' => false, 'level' => 1, 'parent_id' => $this->main->id,
+        ]);
+        $m1 = Machine::factory()->create(['company_id' => $this->company->id]);
+        $operator->machines()->attach($m1->id);
+
+        $this->actingAs($operator)->postJson(route('admin.machines.permissions.accounts.sync', $sibling->id), [
+            'machine_ids' => [$m1->id],
+        ])->assertStatus(403);
+    }
+
+    public function test_sync_preserves_authorizations_outside_operator_subset(): void
+    {
+        $operator = User::factory()->create([
+            'company_id' => $this->company->id, 'is_admin' => false, 'level' => 1, 'parent_id' => $this->main->id,
+        ]);
+        $target = User::factory()->create([
+            'company_id' => $this->company->id, 'is_admin' => false, 'level' => 2, 'parent_id' => $operator->id,
+        ]);
+        $m1 = Machine::factory()->create(['company_id' => $this->company->id]);
+        $m2 = Machine::factory()->create(['company_id' => $this->company->id]);
+
+        $operator->machines()->attach($m1->id);       // 操作者只可授權 m1
+        $target->machines()->attach([$m1->id, $m2->id]); // 目標既有 m1、m2（m2 在操作者範圍外）
+
+        // 操作者送出清空（[]）：應只移除自己範圍內的 m1，保留範圍外的 m2
+        $this->actingAs($operator)->postJson(route('admin.machines.permissions.accounts.sync', $target->id), [
+            'machine_ids' => [],
+        ])->assertStatus(200);
+
+        $this->assertDatabaseMissing('machine_user', ['user_id' => $target->id, 'machine_id' => $m1->id]);
+        $this->assertDatabaseHas('machine_user', ['user_id' => $target->id, 'machine_id' => $m2->id]);
+    }
+
+    public function test_get_account_machines_only_lists_operator_subset(): void
+    {
+        $operator = User::factory()->create([
+            'company_id' => $this->company->id, 'is_admin' => false, 'level' => 1, 'parent_id' => $this->main->id,
+        ]);
+        $target = User::factory()->create([
+            'company_id' => $this->company->id, 'is_admin' => false, 'level' => 2, 'parent_id' => $operator->id,
+        ]);
+        $m1 = Machine::factory()->create(['company_id' => $this->company->id]);
+        $m2 = Machine::factory()->create(['company_id' => $this->company->id]);
+        $operator->machines()->attach($m1->id);
+
+        $response = $this->actingAs($operator)->getJson(route('admin.machines.permissions.accounts.get', $target->id));
+        $response->assertStatus(200);
+        $ids = collect($response->json('machines'))->pluck('id')->all();
+
+        $this->assertContains($m1->id, $ids);
+        $this->assertNotContains($m2->id, $ids); // 操作者沒被授權的機台不應出現在可授權清單
+    }
+}
diff --git a/tests/Feature/Admin/RoleHierarchyTest.php b/tests/Feature/Admin/RoleHierarchyTest.php
new file mode 100644
index 0000000..c8f8a57
--- /dev/null
+++ b/tests/Feature/Admin/RoleHierarchyTest.php
@@ -0,0 +1,117 @@
+<?php
+
+namespace Tests\Feature\Admin;
+
+use App\Models\System\Company;
+use App\Models\System\Role;
+use App\Models\System\User;
+use Spatie\Permission\Models\Permission;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Tests\TestCase;
+
+/**
+ * 第五批：角色層級隔離測試。
+ * - 子帳號只看得到 / 只能管理 自己建立的角色（看不到上層/旁線建的）。
+ * - 主帳號看得到同公司全部角色。
+ * - storeRole 寫入 created_by；update/destroy 受 canBeManagedBy 守衛。
+ */
+class RoleHierarchyTest extends TestCase
+{
+    use RefreshDatabase;
+
+    protected Company $company;
+    protected User $main;
+    protected User $subA;
+    protected User $subB;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        Permission::create(['name' => 'menu.data-config.sub-accounts', 'guard_name' => 'web']);
+
+        $this->company = Company::create(['name' => 'Test Co', 'code' => 'TEST']);
+
+        $role = Role::create(['name' => 'tenant-mgr', 'company_id' => $this->company->id, 'is_system' => false, 'guard_name' => 'web']);
+        $role->syncPermissions(['menu.data-config.sub-accounts']);
+
+        $this->main = User::factory()->create(['company_id' => $this->company->id, 'is_admin' => true, 'level' => 0, 'parent_id' => null]);
+        $this->main->assignRole($role);
+
+        $this->subA = User::factory()->create(['company_id' => $this->company->id, 'is_admin' => false, 'level' => 1, 'parent_id' => $this->main->id]);
+        $this->subA->assignRole($role);
+
+        $this->subB = User::factory()->create(['company_id' => $this->company->id, 'is_admin' => false, 'level' => 1, 'parent_id' => $this->main->id]);
+        $this->subB->assignRole($role);
+    }
+
+    private function makeRole(string $name, User $creator): Role
+    {
+        return Role::create([
+            'name' => $name, 'company_id' => $this->company->id, 'is_system' => false,
+            'guard_name' => 'web', 'created_by' => $creator->id,
+        ]);
+    }
+
+    public function test_role_visible_to_isolates_by_creator(): void
+    {
+        $roleMain = $this->makeRole('role-main', $this->main);
+        $roleA = $this->makeRole('role-a', $this->subA);
+        $roleB = $this->makeRole('role-b', $this->subB);
+
+        // 子帳號 A 只看得到自己建立的角色
+        $this->assertSame([$roleA->id], Role::visibleTo($this->subA)->pluck('id')->all());
+
+        // 主帳號看得到同公司全部角色（含 tenant-mgr 與三個新建的）
+        $mainVisible = Role::visibleTo($this->main)->pluck('id')->all();
+        foreach ([$roleMain->id, $roleA->id, $roleB->id] as $id) {
+            $this->assertContains($id, $mainVisible);
+        }
+    }
+
+    public function test_can_be_managed_by_creator_only_for_sub_account(): void
+    {
+        $roleMain = $this->makeRole('role-main', $this->main);
+        $roleA = $this->makeRole('role-a', $this->subA);
+
+        $this->assertTrue($roleA->canBeManagedBy($this->subA));      // 自己建的
+        $this->assertFalse($roleMain->canBeManagedBy($this->subA));  // 上層建的
+        $this->assertTrue($roleMain->canBeManagedBy($this->main));   // 主帳號管全公司
+        $this->assertTrue($roleA->canBeManagedBy($this->main));      // 主帳號管全公司
+    }
+
+    public function test_store_role_sets_created_by(): void
+    {
+        $this->actingAs($this->subA)->post(route('admin.data-config.sub-account-roles.store'), [
+            'name' => 'a-created-role',
+            'permissions' => ['menu.data-config.sub-accounts'],
+        ])->assertSessionHas('success');
+
+        $role = Role::where('name', 'a-created-role')->where('company_id', $this->company->id)->first();
+        $this->assertNotNull($role);
+        $this->assertSame($this->subA->id, $role->created_by);
+    }
+
+    public function test_sub_account_cannot_update_others_role(): void
+    {
+        $roleB = $this->makeRole('role-b', $this->subB);
+
+        // A 嘗試改 B 建的角色 → 被擋
+        $this->actingAs($this->subA)->put(route('admin.data-config.sub-account-roles.update', $roleB->id), [
+            'name' => 'hijacked',
+            'permissions' => [],
+        ])->assertSessionHas('error');
+
+        $this->assertDatabaseHas('roles', ['id' => $roleB->id, 'name' => 'role-b']);
+    }
+
+    public function test_sub_account_cannot_delete_others_role(): void
+    {
+        $roleMain = $this->makeRole('role-main', $this->main);
+
+        $this->actingAs($this->subA)->delete(route('admin.data-config.sub-account-roles.destroy', $roleMain->id))
+            ->assertSessionHas('error');
+
+        $this->assertDatabaseHas('roles', ['id' => $roleMain->id]);
+    }
+}