[codex] Fix preparation step order

lib/data/models/get_preparation_step_response_model.dart

@@ -48,7 +48,38 @@ class GetPreparationStepResponseModel {
 extension PreparationResponseModelListExtension
     on List<GetPreparationStepResponseModel> {
   PreparationEntity toPreparationEntity() {
-    final steps = map((model) => model.toEntity()).toList();
+    if (isEmpty) {
+      return PreparationEntity(preparationStepList: []);
+    }
+
+    final modelsById = {
+      for (final model in this) model.id: model,
+    };
+    final referencedIds = {
+      for (final model in this)
+        if (model.nextPreparationId != null) model.nextPreparationId!,
+    };
+    final firstModel = firstWhere(
+      (model) => !referencedIds.contains(model.id),
+      orElse: () => first,
+    );
+
+    final orderedModels = <GetPreparationStepResponseModel>[];
+    final visitedIds = <String>{};
+    GetPreparationStepResponseModel? currentModel = firstModel;
+    while (currentModel != null && visitedIds.add(currentModel.id)) {
+      orderedModels.add(currentModel);
+      final nextId = currentModel.nextPreparationId;
+      currentModel = nextId == null ? null : modelsById[nextId];
+    }
+
+    for (final model in this) {
+      if (visitedIds.add(model.id)) {
+        orderedModels.add(model);
+      }
+    }
+
+    final steps = orderedModels.map((model) => model.toEntity()).toList();
     return PreparationEntity(preparationStepList: steps);
   }
 }

test/data/models/get_preparation_step_response_model_test.dart

@@ -0,0 +1,66 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:on_time_front/data/models/get_preparation_step_response_model.dart';
+
+void main() {
+  group('PreparationResponseModelListExtension', () {
+    test('orders preparation steps by nextPreparationId chain', () {
+      final models = [
+        GetPreparationStepResponseModel(
+          id: 'third',
+          preparationName: 'Put on shoes',
+          preparationTime: 3,
+          nextPreparationId: null,
+        ),
+        GetPreparationStepResponseModel(
+          id: 'first',
+          preparationName: 'Shower',
+          preparationTime: 10,
+          nextPreparationId: 'second',
+        ),
+        GetPreparationStepResponseModel(
+          id: 'second',
+          preparationName: 'Get dressed',
+          preparationTime: 5,
+          nextPreparationId: 'third',
+        ),
+      ];
+
+      final preparation = models.toPreparationEntity();
+
+      expect(
+        preparation.preparationStepList.map((step) => step.id),
+        ['first', 'second', 'third'],
+      );
+    });
+
+    test('keeps unlinked steps instead of dropping them', () {
+      final models = [
+        GetPreparationStepResponseModel(
+          id: 'first',
+          preparationName: 'Shower',
+          preparationTime: 10,
+          nextPreparationId: 'second',
+        ),
+        GetPreparationStepResponseModel(
+          id: 'second',
+          preparationName: 'Get dressed',
+          preparationTime: 5,
+          nextPreparationId: null,
+        ),
+        GetPreparationStepResponseModel(
+          id: 'unlinked',
+          preparationName: 'Pack bag',
+          preparationTime: 2,
+          nextPreparationId: null,
+        ),
+      ];
+
+      final preparation = models.toPreparationEntity();
+
+      expect(
+        preparation.preparationStepList.map((step) => step.id),
+        ['first', 'second', 'unlinked'],
+      );
+    });
+  });
+}