Phase 3.7: paid pairing flow + returning chat + extension flip

- Backend: payment_sessions + pairing_failures tables; payment.service.js
  and pairing-failure.service.js (new); rewritten pairing.service.js
  (payment-gated blast + targeted "Curhat lagi" + cancel + fallback);
  rewritten extension.service.js (data-driven auto-approve with offline
  safeguard, charge-at-approval); pricing.service.js (extension tiers
  without free trial); mitra-status.service.js (countAvailableMitras
  cached path); 60s sweeper for stale payment sessions
- Backend routes: client.payment.routes, client.mitra-availability.routes,
  internal/failed-pairings.routes; client.chat.routes rewritten for
  payment-gated start + /returning + /cancel + /fallback-to-blast;
  internal/config.routes adds 4 new keys with Valkey invalidate publish
- client_app: mitra-availability poll, payment screen + notifier, pairing
  notifier rewrite (PairingTargetedWaiting + PairingFailed states),
  targeted-waiting overlay + bestie-unavailable dialog, "Curhat lagi"
  CTA, failed-pairing terminal, extension via payment-session
- mitra_app: PairingRequestType enum, returning-chat 20s countdown
  auto-dismiss, extension card "otomatis disetujui" copy
- control_center: 4 new config rows in Settings, Failed Pairings page
  (filter + paginate + action menu), sidebar + route registered
- Test infrastructure: Vitest backend (7/7 pass), Playwright CC (4/4
  pass), Maestro mobile scaffold (CLI install pending)
- Bugs found via Playwright + fixed: LoginPage labels not associated
  with inputs (a11y); backend internal CORS missing PATCH/PUT/DELETE
  in allow-methods (silent settings breakage in browsers since Stage 4)
- Docs: phase3.7.md PRD, phase3.7-plan.md, phase3.7-questions.md (Q&A),
  phase3.7-testing.md (E2E checklist), phase3.7-test-run-2026-05-03.md
  (today's run results)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

client_app/lib/core/chat/chat_notifier.g.dart

@@ -6,7 +6,7 @@ part of 'chat_notifier.dart';
 // RiverpodGenerator
 // **************************************************************************
 
-String _$chatHash() => r'30e0aa41d2022e5bb080877e23fcb0a0c0c4b927';
+String _$chatHash() => r'35388d2977db9cee4307697524620b22691c54f5';
 
 /// See also [Chat].
 @ProviderFor(Chat)

client_app/lib/core/chat/session_closure_notifier.dart

@@ -1,5 +1,4 @@
 import 'package:dio/dio.dart';
-import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:riverpod_annotation/riverpod_annotation.dart';
 import '../api/api_client_provider.dart';
 import 'active_session_notifier.dart';
@@ -41,14 +40,42 @@ class SessionClosure extends _$SessionClosure {
   @override
   SessionClosureData build() => const ClosureInitialData();
 
+  /// Extension request is a 3-step flow with the extension cost held in its
+  /// own `payment_session` (never combined with a free trial). Server-side,
+  /// the extension service refuses requests without an
+  /// `extension_payment_session_id` on a confirmed, is_extension payment session.
+  ///
+  /// 1. POST `/api/client/payment-sessions` with `is_extension: true`
+  /// 2. POST `/api/client/payment-sessions/:id/confirm`
+  /// 3. POST `/api/client/chat/session/:sessionId/extend` with the
+  ///    extension_payment_session_id from step 2.
+  ///
+  /// Charge timing is server-side: only on actual approve / auto-approve.
+  /// If the mitra explicitly rejects within 10s the payment is failed back, no charge.
   Future<void> requestExtension(String sessionId, {required int durationMinutes, required int price}) async {
     state = const ExtendingWaitingMitraData();
     try {
-      await ref.read(apiClientProvider).post('/api/client/chat/session/$sessionId/extend', data: {
+      final api = ref.read(apiClientProvider);
+
+      final createResp = await api.post('/api/client/payment-sessions/', data: {
+        'duration_minutes': durationMinutes,
+        'is_extension': true,
+      });
+      final paymentSessionId = (createResp['data'] as Map<String, dynamic>)['id'] as String;
+
+      // Backend rejects truly empty bodies on confirm, so always send `{}`.
+      await api.post(
+        '/api/client/payment-sessions/$paymentSessionId/confirm',
+        data: const <String, dynamic>{},
+      );
+
+      // Trigger the extension request. The actual approve/reject round-trip is
+      // owned by the chat WS — ChatNotifier surfaces it.
+      await api.post('/api/client/chat/session/$sessionId/extend', data: {
         'duration_minutes': durationMinutes,
         'price': price,
+        'extension_payment_session_id': paymentSessionId,
       });
-      // Response will come via WebSocket (ChatBloc/ChatNotifier handles it)
     } catch (e) {
       state = const ClosureErrorData('Gagal meminta perpanjangan.');
     }