实现缩放功能：增加缩放功能检索和设置方法，更新UI以支持缩放调整，增强缩放比例的状态管理。

test/features/recording/view_model_recording_test.dart

@@ -2,6 +2,7 @@ import 'package:flutter/services.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:permission_handler/permission_handler.dart';
+import 'package:recording_tool/features/recording/platform/recording_channel_names.dart';
 import 'package:recording_tool/features/recording/view-model/view_model_recording.dart';
 
 void main() {
@@ -24,6 +25,11 @@ void main() {
   tearDown(() {
     TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger
         .setMockMethodCallHandler(SystemChannels.platform, null);
+    TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger
+        .setMockMethodCallHandler(
+          const MethodChannel(RecordingChannelNames.method),
+          null,
+        );
   });
 
   group('RecordingViewModel', () {
@@ -36,9 +42,89 @@ void main() {
       expect(model.clipboardRecordingModel.title, defaultClipboardTitle);
       expect(model.session.isPreviewReady, isFalse);
       expect(model.session.isRecording, isFalse);
+      expect(model.session.zoomRatio, 1.0);
+      expect(model.session.minZoomRatio, 1.0);
+      expect(model.session.maxZoomRatio, 3.0);
     });
   });
 
+  group('RecordingViewModel.setZoomRatio', () {
+    test('updates zoom ratio from native response', () async {
+      TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger
+          .setMockMethodCallHandler(
+            const MethodChannel(RecordingChannelNames.method),
+            (call) async {
+              expect(call.method, 'setZoomRatio');
+              expect(call.arguments, <String, dynamic>{'zoomRatio': 2.0});
+              return <String, dynamic>{
+                'zoomRatio': 2.0,
+                'minZoomRatio': 1.0,
+                'maxZoomRatio': 3.0,
+              };
+            },
+          );
+      final container = ProviderContainer();
+      addTearDown(container.dispose);
+
+      await container.read(recordingViewModelProvider.notifier).setZoomRatio(2);
+
+      final session = container.read(recordingViewModelProvider).session;
+      expect(session.zoomRatio, 2.0);
+      expect(session.minZoomRatio, 1.0);
+      expect(session.maxZoomRatio, 3.0);
+      expect(session.errorMessage, isNull);
+    });
+
+    test('clamps requested zoom ratio before invoking native', () async {
+      final calls = <MethodCall>[];
+      TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger
+          .setMockMethodCallHandler(
+            const MethodChannel(RecordingChannelNames.method),
+            (call) async {
+              calls.add(call);
+              return <String, dynamic>{
+                'zoomRatio': 1.0,
+                'minZoomRatio': 1.0,
+                'maxZoomRatio': 1.0,
+              };
+            },
+          );
+      final container = ProviderContainer();
+      addTearDown(container.dispose);
+
+      await container.read(recordingViewModelProvider.notifier).setZoomRatio(4);
+
+      expect(calls.single.arguments, <String, dynamic>{'zoomRatio': 3.0});
+      expect(container.read(recordingViewModelProvider).session.zoomRatio, 1.0);
+    });
+
+    test(
+      'keeps previous zoom ratio and stores error when native fails',
+      () async {
+        TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger
+            .setMockMethodCallHandler(
+              const MethodChannel(RecordingChannelNames.method),
+              (call) async {
+                throw PlatformException(
+                  code: 'ZOOM_FAILED',
+                  message: 'Zoom is unavailable',
+                );
+              },
+            );
+        final container = ProviderContainer();
+        addTearDown(container.dispose);
+
+        await container
+            .read(recordingViewModelProvider.notifier)
+            .setZoomRatio(2);
+
+        final session = container.read(recordingViewModelProvider).session;
+        expect(session.zoomRatio, 1.0);
+        expect(session.errorMessage, 'Zoom is unavailable');
+      },
+    );
+  });
+
   group('recordingGalleryPermissionsForHost', () {
     test('requests only add-only photo permission on iOS', () {
       final permissions = recordingGalleryPermissionsForHost(

test/features/recording/widget_recording_hud_test.dart

@@ -0,0 +1,80 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_screenutil/flutter_screenutil.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:recording_tool/features/recording/widgets/widget_recording_hud.dart';
+
+void main() {
+  Future<void> pumpHud(
+    WidgetTester tester, {
+    double zoomRatio = 1.0,
+    double minZoomRatio = 1.0,
+    double maxZoomRatio = 3.0,
+    ValueChanged<double>? onZoomSelected,
+  }) async {
+    await tester.pumpWidget(
+      ScreenUtilInit(
+        designSize: const Size(375, 812),
+        builder: (context, _) {
+          return MaterialApp(
+            home: Scaffold(
+              backgroundColor: Colors.black,
+              body: RecordingHudWidget(
+                hasDndAccess: true,
+                isBatteryOptimizedIgnored: true,
+                notificationsGranted: true,
+                isRecording: false,
+                isStartingRecording: false,
+                isTouchLocked: false,
+                zoomRatio: zoomRatio,
+                minZoomRatio: minZoomRatio,
+                maxZoomRatio: maxZoomRatio,
+                onStart: () async {},
+                onStop: () async {},
+                onOpenDnd: () {},
+                onOpenBattery: () {},
+                onToggleTouchLock: () {},
+                onZoomSelected: onZoomSelected ?? (_) {},
+              ),
+            ),
+          );
+        },
+      ),
+    );
+    await tester.pump();
+  }
+
+  testWidgets('shows preset zoom buttons', (tester) async {
+    await pumpHud(tester);
+
+    expect(find.text('1x'), findsOneWidget);
+    expect(find.text('2x'), findsOneWidget);
+    expect(find.text('3x'), findsOneWidget);
+  });
+
+  testWidgets('marks current zoom ratio as selected', (tester) async {
+    await pumpHud(tester, zoomRatio: 2.0);
+
+    final selectedButton = tester.widget<TextButton>(
+      find.ancestor(of: find.text('2x'), matching: find.byType(TextButton)),
+    );
+    expect(selectedButton.enabled, isFalse);
+  });
+
+  testWidgets('does not expose presets beyond max zoom ratio', (tester) async {
+    await pumpHud(tester, maxZoomRatio: 2.0);
+
+    expect(find.text('1x'), findsOneWidget);
+    expect(find.text('2x'), findsOneWidget);
+    expect(find.text('3x'), findsNothing);
+  });
+
+  testWidgets('tapping zoom preset reports selected ratio', (tester) async {
+    double? selected;
+    await pumpHud(tester, onZoomSelected: (ratio) => selected = ratio);
+
+    await tester.tap(find.text('2x'));
+    await tester.pump();
+
+    expect(selected, 2.0);
+  });
+}