Add bidirectional host bridge

test/runtime/host/runtime_host_bridge_test.dart

@@ -0,0 +1,93 @@
+import 'package:flame_lua_runtime/runtime/diagnostics/runtime_diagnostics.dart';
+import 'package:flame_lua_runtime/runtime/host/runtime_host_bridge.dart';
+import 'package:flame_lua_runtime/runtime/models/runtime_event.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  group('RuntimeHostBridgeManager', () {
+    test('calls registered host handler and emits result event', () async {
+      final events = <RuntimeEvent>[];
+      final manager = RuntimeHostBridgeManager(
+        bridge: RuntimeHostBridge(
+          handlers: {
+            'user.profile': (call) => {'name': 'Lua', 'id': call.data},
+          },
+        ),
+        eventSink: events.add,
+      );
+
+      await manager.callHost(
+        const RuntimeHostCall(id: 'call_1', method: 'user.profile', data: 7),
+      );
+
+      expect(events.single.type, RuntimeHostEventType.callResult);
+      expect(events.single.data['ok'], isTrue);
+      expect(events.single.data['result'], {'name': 'Lua', 'id': 7});
+    });
+
+    test(
+      'emits failed result and diagnostics when host handler throws',
+      () async {
+        final diagnostics = RuntimeDiagnostics();
+        final events = <RuntimeEvent>[];
+        final manager = RuntimeHostBridgeManager(
+          bridge: RuntimeHostBridge(
+            handlers: {'boom': (_) => throw StateError('boom')},
+          ),
+          eventSink: events.add,
+          diagnostics: diagnostics,
+        );
+
+        await manager.callHost(
+          const RuntimeHostCall(id: 'call_1', method: 'boom'),
+        );
+
+        expect(events.single.data['ok'], isFalse);
+        expect(events.single.data['error'], contains('boom'));
+        expect(
+          diagnostics.entries.single.type,
+          RuntimeDiagnosticType.hostBridgeError,
+        );
+      },
+    );
+
+    test('notifies host and emits Lua calls', () async {
+      RuntimeHostNotification? notification;
+      final events = <RuntimeEvent>[];
+      final manager = RuntimeHostBridgeManager(
+        bridge: RuntimeHostBridge(onNotify: (value) => notification = value),
+        eventSink: events.add,
+      );
+
+      expect(
+        manager.notifyHost(
+          const RuntimeHostNotification(
+            method: 'analytics',
+            data: {'level': 2},
+          ),
+        ),
+        isTrue,
+      );
+      expect(notification?.method, 'analytics');
+      expect(manager.notifyLua('pause', data: {'reason': 'host'}), isTrue);
+
+      expect(events.single.type, RuntimeHostEventType.notify);
+      expect(events.single.data['method'], 'pause');
+    });
+
+    test('completes Flutter-to-Lua call through host response', () async {
+      final events = <RuntimeEvent>[];
+      final manager = RuntimeHostBridgeManager(
+        bridge: const RuntimeHostBridge(),
+        eventSink: events.add,
+      );
+
+      final future = manager.callLua('select_avatar', data: {'current': 1});
+      final id = events.single.data['id']! as String;
+      expect(events.single.type, RuntimeHostEventType.call);
+      expect(manager.completeLuaCall(id, result: {'selected': 3}), isTrue);
+
+      expect(await future, {'selected': 3});
+    });
+  });
+}