Phase 3 scaffold: chat engine (WebSocket, FCM, pricing, timer, extension, history)

- Backend: WebSocket plugin, chat/pricing/timer/extension/closure/notification services
- Client app: ChatBloc, pricing dialog, chat screen with message status, extension/goodbye flow, history
- Mitra app: MitraChatBloc, ExtensionBloc, chat screen, extension accept/reject, history
- Control center: free trial, extension timeout, early end config toggles
- DB migration: chat_messages, session_closures, session_extensions, customer_transactions tables

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

client_app/lib/core/pairing/pairing_bloc.dart

@@ -12,6 +12,16 @@ abstract class PairingEvent extends Equatable {
 }
 
 class RequestPairing extends PairingEvent {}
+
+class RequestPairingWithTier extends PairingEvent {
+  final int? durationMinutes;
+  final int? price;
+  final bool isFreeTrial;
+  RequestPairingWithTier({this.durationMinutes, this.price, this.isFreeTrial = false});
+  @override
+  List<Object?> get props => [durationMinutes, price, isFreeTrial];
+}
+
 class CancelPairing extends PairingEvent {}
 
 class _PairingStatusUpdate extends PairingEvent {
@@ -71,29 +81,42 @@ class PairingBloc extends Bloc<PairingEvent, PairingState> {
 
   PairingBloc({required this.apiClient}) : super(PairingInitial()) {
     on<RequestPairing>(_onRequestPairing);
+    on<RequestPairingWithTier>(_onRequestPairingWithTier);
     on<CancelPairing>(_onCancelPairing);
     on<_PairingStatusUpdate>(_onStatusUpdate);
     on<_PairingTimeout>(_onTimeout);
   }
 
   Future<void> _onRequestPairing(RequestPairing event, Emitter<PairingState> emit) async {
-    // Reset to initial so BlocListener can detect new errors
+    await _doPairingRequest(emit, {});
+  }
+
+  Future<void> _onRequestPairingWithTier(RequestPairingWithTier event, Emitter<PairingState> emit) async {
+    final body = <String, dynamic>{};
+    if (event.isFreeTrial) {
+      body['is_free_trial'] = true;
+    } else {
+      body['duration_minutes'] = event.durationMinutes;
+      body['price'] = event.price;
+    }
+    await _doPairingRequest(emit, body);
+  }
+
+  Future<void> _doPairingRequest(Emitter<PairingState> emit, Map<String, dynamic> body) async {
     if (state is! PairingInitial) {
       emit(PairingInitial());
     }
     try {
-      final response = await apiClient.post('/api/client/chat/request');
+      final response = await apiClient.post('/api/client/chat/request', data: body);
       final data = response['data'] as Map<String, dynamic>;
       final sessionId = data['id'] as String;
 
       emit(PairingSearching(sessionId));
 
-      // Start 60s local timeout as a safety net
       _timeoutTimer = Timer(const Duration(seconds: 60), () {
         add(_PairingTimeout());
       });
 
-      // Listen to SSE for status updates
       _listenToSSE(sessionId);
     } on DioException catch (e) {
       final code = e.response?.data?['error']?['code'];
@@ -101,6 +124,8 @@ class PairingBloc extends Bloc<PairingEvent, PairingState> {
         emit(PairingNoBestie());
       } else if (code == 'ALREADY_ACTIVE') {
         emit(PairingError('Kamu sudah memiliki sesi aktif.'));
+      } else if (code == 'FREE_TRIAL_INELIGIBLE') {
+        emit(PairingError('Kamu tidak memenuhi syarat untuk free trial.'));
       } else {
         emit(PairingError('Gagal memulai. Coba lagi.'));
       }