Phase 2 scaffold: mitra online status & pairing logic

Add mitra online/offline status with heartbeat-based auto-offline,
customer-mitra pairing via Valkey pub/sub blast, session management,
and control center dashboard with real-time stats.

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

client_app/lib/core/pairing/pairing_bloc.dart

@@ -0,0 +1,173 @@
+import 'dart:async';
+import 'dart:convert';
+import 'package:dio/dio.dart';
+import 'package:equatable/equatable.dart';
+import 'package:flutter_bloc/flutter_bloc.dart';
+import '../api/api_client.dart';
+
+// Events
+abstract class PairingEvent extends Equatable {
+  @override
+  List<Object?> get props => [];
+}
+
+class RequestPairing extends PairingEvent {}
+class CancelPairing extends PairingEvent {}
+
+class _PairingStatusUpdate extends PairingEvent {
+  final Map<String, dynamic> data;
+  _PairingStatusUpdate(this.data);
+  @override
+  List<Object?> get props => [data];
+}
+
+class _PairingTimeout extends PairingEvent {}
+
+// States
+abstract class PairingState extends Equatable {
+  @override
+  List<Object?> get props => [];
+}
+
+class PairingInitial extends PairingState {}
+class PairingSearching extends PairingState {
+  final String sessionId;
+  PairingSearching(this.sessionId);
+  @override
+  List<Object?> get props => [sessionId];
+}
+
+class PairingBestieFound extends PairingState {
+  final String sessionId;
+  final String mitraName;
+  PairingBestieFound({required this.sessionId, required this.mitraName});
+  @override
+  List<Object?> get props => [sessionId, mitraName];
+}
+
+class PairingActive extends PairingState {
+  final String sessionId;
+  final String mitraName;
+  PairingActive({required this.sessionId, required this.mitraName});
+  @override
+  List<Object?> get props => [sessionId, mitraName];
+}
+
+class PairingNoBestie extends PairingState {}
+class PairingCancelled extends PairingState {}
+
+class PairingError extends PairingState {
+  final String message;
+  PairingError(this.message);
+  @override
+  List<Object?> get props => [message];
+}
+
+// Bloc
+class PairingBloc extends Bloc<PairingEvent, PairingState> {
+  final ApiClient apiClient;
+  Timer? _timeoutTimer;
+  StreamSubscription? _sseSubscription;
+
+  PairingBloc({required this.apiClient}) : super(PairingInitial()) {
+    on<RequestPairing>(_onRequestPairing);
+    on<CancelPairing>(_onCancelPairing);
+    on<_PairingStatusUpdate>(_onStatusUpdate);
+    on<_PairingTimeout>(_onTimeout);
+  }
+
+  Future<void> _onRequestPairing(RequestPairing event, Emitter<PairingState> emit) async {
+    try {
+      final response = await apiClient.post('/api/client/chat/request');
+      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'];
+      if (code == 'NO_MITRA_AVAILABLE') {
+        emit(PairingNoBestie());
+      } else if (code == 'ALREADY_ACTIVE') {
+        emit(PairingError('Kamu sudah memiliki sesi aktif.'));
+      } else {
+        emit(PairingError('Gagal memulai. Coba lagi.'));
+      }
+    }
+  }
+
+  void _listenToSSE(String sessionId) {
+    final dio = Dio(BaseOptions(baseUrl: ApiClient.baseUrl));
+    // SSE endpoint — use responseType stream
+    dio.get(
+      '/api/client/chat/request/$sessionId/status',
+      options: Options(responseType: ResponseType.stream),
+    ).then((response) {
+      final stream = response.data.stream as Stream<List<int>>;
+      _sseSubscription = stream
+          .transform(utf8.decoder)
+          .transform(const LineSplitter())
+          .where((line) => line.startsWith('data: '))
+          .map((line) => jsonDecode(line.substring(6)) as Map<String, dynamic>)
+          .listen(
+            (data) => add(_PairingStatusUpdate(data)),
+            onError: (_) {},
+          );
+    }).catchError((_) {});
+  }
+
+  Future<void> _onStatusUpdate(_PairingStatusUpdate event, Emitter<PairingState> emit) async {
+    final data = event.data;
+    final type = data['type'] as String?;
+
+    if (type == 'paired') {
+      _cleanup();
+      final mitraName = data['mitra_display_name'] as String? ?? 'Bestie';
+      final sessionId = data['session_id'] as String;
+      emit(PairingBestieFound(sessionId: sessionId, mitraName: mitraName));
+
+      // Brief delay then transition to active
+      await Future.delayed(const Duration(seconds: 2));
+      emit(PairingActive(sessionId: sessionId, mitraName: mitraName));
+    } else if (type == 'expired') {
+      _cleanup();
+      emit(PairingNoBestie());
+    }
+  }
+
+  Future<void> _onCancelPairing(CancelPairing event, Emitter<PairingState> emit) async {
+    if (state is PairingSearching) {
+      final sessionId = (state as PairingSearching).sessionId;
+      try {
+        await apiClient.post('/api/client/chat/request/$sessionId/cancel');
+      } catch (_) {}
+      _cleanup();
+      emit(PairingCancelled());
+    }
+  }
+
+  Future<void> _onTimeout(_PairingTimeout event, Emitter<PairingState> emit) async {
+    _cleanup();
+    emit(PairingNoBestie());
+  }
+
+  void _cleanup() {
+    _timeoutTimer?.cancel();
+    _timeoutTimer = null;
+    _sseSubscription?.cancel();
+    _sseSubscription = null;
+  }
+
+  @override
+  Future<void> close() {
+    _cleanup();
+    return super.close();
+  }
+}