test(ensemble): upload path guard and view-group index regression coverage

modules/ensemble/test/safe_view_group_payload_index_test.dart

@@ -15,5 +15,10 @@ void main() {
       expect(safeViewGroupPayloadIndex(0, 0), 0);
       expect(safeViewGroupPayloadIndex(5, 0), 0);
     });
+
+    test('returns 0 when payload length is invalid', () {
+      expect(safeViewGroupPayloadIndex(0, -1), 0);
+      expect(safeViewGroupPayloadIndex(10, -3), 0);
+    });
   });
 }

modules/ensemble/test/upload_path_security_test.dart

@@ -1,3 +1,4 @@
+import 'package:ensemble/framework/data_context.dart' show File;
 import 'package:ensemble/util/upload_utils.dart';
 import 'package:flutter_test/flutter_test.dart';
 
@@ -17,5 +18,42 @@ void main() {
       expect(uploadPathContainsParentSegment('..'), true);
       expect(uploadPathContainsParentSegment('../etc/passwd'), true);
     });
+
+    test('treats only a full path segment ".." as traversal', () {
+      expect(uploadPathContainsParentSegment('photo..jpg'), false);
+      expect(uploadPathContainsParentSegment('.../x'), false);
+      expect(uploadPathContainsParentSegment(r'a\..\b'), true);
+    });
+
+    test('normalises backslashes before splitting', () {
+      expect(uploadPathContainsParentSegment(r'var\..\evil'), true);
+    });
+  });
+
+  group('UploadUtils.uploadFiles path guard', () {
+    test('throws before any network I/O when path contains ".."', () async {
+      final files = <File>[
+        File(null, null, null, '/tmp/../outside.jpg', null),
+      ];
+
+      await expectLater(
+        UploadUtils.uploadFiles(
+          taskId: 't1',
+          method: 'POST',
+          url: 'http://127.0.0.1:9/should-not-connect',
+          headers: const {},
+          fields: const {},
+          files: files,
+          fieldName: 'file',
+        ),
+        throwsA(
+          isA<FormatException>().having(
+            (e) => e.message,
+            'message',
+            contains('..'),
+          ),
+        ),
+      );
+    });
   });
 }