refactor(logging): isolate native log transport

test/native_log_source_test.dart

@@ -0,0 +1,62 @@
+import 'dart:convert';
+
+import 'package:flutter/services.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:spotiflac_android/services/native_log_source.dart';
+
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+  const channel = MethodChannel('com.zarz.spotiflac/backend');
+  const source = NativeLogSource(channel: channel);
+  final messenger =
+      TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger;
+
+  tearDown(() => messenger.setMockMethodCallHandler(channel, null));
+
+  for (final encoded in [false, true]) {
+    test('reads native logs and cursor (JSON=$encoded)', () async {
+      final payload = {
+        'logs': [
+          {'level': 'ERROR', 'tag': 'Native', 'message': 'failed'},
+        ],
+        'next_index': 8,
+      };
+      messenger.setMockMethodCallHandler(channel, (call) async {
+        expect(call.method, 'getLogsSince');
+        expect(call.arguments, {'index': 3});
+        return encoded ? jsonEncode(payload) : payload;
+      });
+      expect(await source.getSince(3), payload);
+    });
+  }
+
+  test('keeps the native logging controls on the existing channel', () async {
+    final calls = <MethodCall>[];
+    messenger.setMockMethodCallHandler(channel, (call) async {
+      calls.add(call);
+      return null;
+    });
+    await source.setLoggingEnabled(true);
+    await source.setLoggingEnabled(false);
+    await source.clear();
+    expect(calls.map((call) => call.method), [
+      'setLoggingEnabled',
+      'setLoggingEnabled',
+      'clearLogs',
+    ]);
+    expect(calls[0].arguments, {'enabled': true});
+    expect(calls[1].arguments, {'enabled': false});
+  });
+
+  test('reports malformed batches instead of silently losing logs', () async {
+    messenger.setMockMethodCallHandler(channel, (_) async => '[]');
+    await expectLater(source.getSince(0), throwsFormatException);
+  });
+
+  test('propagates transport failures to the polling error boundary', () async {
+    messenger.setMockMethodCallHandler(channel, (_) async {
+      throw PlatformException(code: 'backend_unavailable');
+    });
+    await expectLater(source.getSince(0), throwsA(isA<PlatformException>()));
+  });
+}