scope batch rename conflicts by parent directory

lib/models/batch_rename.dart

@@ -123,7 +123,7 @@ List<BatchRenamePreview> buildRenamePreviews(
   }
   final existing = <String, Set<String>>{};
   for (final file in files) {
-    final key = _destinationKey(file.cloudPath, file.name);
+    final key = _destinationKey(file, file.name);
     (existing[key] ??= <String>{}).add(file.id);
   }
   final reserved = <String, Set<String>>{
@@ -131,7 +131,7 @@ List<BatchRenamePreview> buildRenamePreviews(
   };
   final proposedCounts = <String, int>{};
   for (final item in values.where((item) => item.applicable)) {
-    final key = _destinationKey(item.file.cloudPath, item.newName);
+    final key = _destinationKey(item.file, item.newName);
     proposedCounts[key] = (proposedCounts[key] ?? 0) + 1;
   }
   final result = <BatchRenamePreview>[];
@@ -141,7 +141,7 @@ List<BatchRenamePreview> buildRenamePreviews(
       continue;
     }
     var targetName = item.newName;
-    var targetKey = _destinationKey(item.file.cloudPath, targetName);
+    var targetKey = _destinationKey(item.file, targetName);
     if (conflictStrategy == BatchRenameConflictStrategy.reject &&
         proposedCounts[targetKey]! > 1) {
       result.add(
@@ -160,7 +160,7 @@ List<BatchRenamePreview> buildRenamePreviews(
       var index = 2;
       do {
         targetName = _appendIndex(item.newName, index++);
-        targetKey = _destinationKey(item.file.cloudPath, targetName);
+        targetKey = _destinationKey(item.file, targetName);
       } while (conflicts());
     }
     if (conflicts()) {
@@ -188,7 +188,12 @@ String _appendIndex(String name, int index) {
 }
 
 /// Collision scope is a single cloud directory, never the whole drive.
-String _destinationKey(String path, String name) {
+String _destinationKey(CloudFile file, String name) {
+  final parentID = file.parentID?.trim();
+  if (parentID != null && parentID.isNotEmpty) {
+    return 'id:$parentID/${name.toLowerCase()}';
+  }
+  final path = file.cloudPath;
   final separator = path.lastIndexOf('/');
   final parent = separator < 0 ? '' : path.substring(0, separator);
   return '${parent.toLowerCase()}/${name.toLowerCase()}';

lib/models/cloud_file.dart

@@ -35,6 +35,11 @@ class CloudFile {
   final int? subFileCount;
   final String modifiedAt;
   final String cloudPath;
+
+  /// Stable parent directory ID from the cloud API, used for directory-scoped
+  /// operations even when the API omits a full display path.
+  final String? parentID;
+  final String? fullParentIDs;
   final int fileType;
 
   const CloudFile({
@@ -47,6 +52,8 @@ class CloudFile {
     this.subFileCount,
     this.modifiedAt = '',
     this.cloudPath = '',
+    this.parentID,
+    this.fullParentIDs,
     this.fileType = 0,
   });
 
@@ -104,6 +111,8 @@ class CloudFile {
     int? subFileCount,
     String? modifiedAt,
     String? cloudPath,
+    String? parentID,
+    String? fullParentIDs,
     int? fileType,
   }) {
     return CloudFile(
@@ -116,6 +125,8 @@ class CloudFile {
       subFileCount: subFileCount ?? this.subFileCount,
       modifiedAt: modifiedAt ?? this.modifiedAt,
       cloudPath: cloudPath ?? this.cloudPath,
+      parentID: parentID ?? this.parentID,
+      fullParentIDs: fullParentIDs ?? this.fullParentIDs,
       fileType: fileType ?? this.fileType,
     );
   }
@@ -191,6 +202,12 @@ class CloudFile {
       cloudPath:
           _extractString(json, ['location', 'path', 'fullPath']) ??
           name.toString(),
+      parentID: _extractString(json, ['parentId', 'parent_id', 'parentID']),
+      fullParentIDs: _extractString(json, [
+        'fullParentIds',
+        'fullParentIDs',
+        'full_parent_ids',
+      ]),
       fileType: type,
     );
   }
@@ -205,6 +222,8 @@ class CloudFile {
     'subFileCount': subFileCount,
     'updateTime': modifiedAt,
     'path': cloudPath,
+    'parentId': parentID,
+    'fullParentIds': fullParentIDs,
     'fileType': fileType,
   };