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/availability/mitra_availability_notifier.dart

@@ -0,0 +1,78 @@
+import 'dart:async';
+import 'package:riverpod_annotation/riverpod_annotation.dart';
+import '../api/api_client_provider.dart';
+
+part 'mitra_availability_notifier.g.dart';
+
+/// Customer-home availability poll.
+///
+/// Polls `GET /api/client/mitra-availability` every 5 seconds while the home
+/// screen is in the foreground. Polling is gated by the home screen calling
+/// [setActive] from `WidgetsBindingObserver.didChangeAppLifecycleState`:
+///   - resumed   → setActive(true)
+///   - paused/inactive → setActive(false)
+///
+/// On any HTTP error we emit `false` (never display stale state).
+///
+/// The endpoint also returns a `count`, but the customer UI must only read the
+/// binary `available` field — the count is for CC/debug only.
+@Riverpod(keepAlive: true)
+class MitraAvailability extends _$MitraAvailability {
+  Timer? _pollTimer;
+  bool _active = false;
+
+  @override
+  Future<bool> build() async {
+    ref.onDispose(_stopPolling);
+    // Default to disabled until the first poll returns. Never optimistically
+    // show the CTA as enabled.
+    return false;
+  }
+
+  /// Called by the home screen via `WidgetsBindingObserver` to gate polling
+  /// to the foregrounded state. Polling is paused on `paused` / `inactive`
+  /// and resumed on `resumed` (and an immediate poll fires on resume).
+  void setActive(bool active) {
+    if (_active == active) return;
+    _active = active;
+    if (_active) {
+      _startPolling();
+      // Fire-and-forget an immediate poll on resume so the CTA reflects
+      // current availability without waiting up to 5s.
+      // ignore: unawaited_futures
+      _pollOnce();
+    } else {
+      _stopPolling();
+    }
+  }
+
+  /// Manual one-shot refresh — used for pull-to-refresh on the home screen.
+  Future<void> refresh() => _pollOnce();
+
+  void _startPolling() {
+    _stopPolling();
+    _pollTimer = Timer.periodic(const Duration(seconds: 5), (_) => _pollOnce());
+  }
+
+  void _stopPolling() {
+    _pollTimer?.cancel();
+    _pollTimer = null;
+  }
+
+  Future<void> _pollOnce() async {
+    bool available;
+    try {
+      final api = ref.read(apiClientProvider);
+      final response = await api.get('/api/client/mitra-availability');
+      final data = response['data'] as Map<String, dynamic>?;
+      available = data?['available'] as bool? ?? false;
+    } catch (_) {
+      // Poll failure → default to disabled. Never keep the last-known state.
+      available = false;
+    }
+    // Skip the assignment when the value didn't change — Riverpod allocates a
+    // new AsyncData each call, which would re-notify all listeners every 5s.
+    if (state.valueOrNull == available) return;
+    state = AsyncData(available);
+  }
+}

client_app/lib/core/availability/mitra_availability_notifier.g.dart

@@ -0,0 +1,39 @@
+// GENERATED CODE - DO NOT MODIFY BY HAND
+
+part of 'mitra_availability_notifier.dart';
+
+// **************************************************************************
+// RiverpodGenerator
+// **************************************************************************
+
+String _$mitraAvailabilityHash() => r'7429862ccffbae1fc7bbe7368359e1624fe28ec9';
+
+/// Phase 3.7 §1: customer-home availability poll.
+///
+/// Polls `GET /api/client/mitra-availability` every 5 seconds while the home
+/// screen is in the foreground. Polling is gated by the home screen calling
+/// [setActive] from `WidgetsBindingObserver.didChangeAppLifecycleState`:
+///   - resumed   → setActive(true)
+///   - paused/inactive → setActive(false)
+///
+/// On any HTTP error we emit `false` (PRD §1.3: never display stale state).
+///
+/// The endpoint also returns a `count`, but per PRD §1.3 the customer UI must
+/// only read the binary `available` field — the count is for CC/debug only.
+///
+/// Copied from [MitraAvailability].
+@ProviderFor(MitraAvailability)
+final mitraAvailabilityProvider =
+    AsyncNotifierProvider<MitraAvailability, bool>.internal(
+  MitraAvailability.new,
+  name: r'mitraAvailabilityProvider',
+  debugGetCreateSourceHash: const bool.fromEnvironment('dart.vm.product')
+      ? null
+      : _$mitraAvailabilityHash,
+  dependencies: null,
+  allTransitiveDependencies: null,
+);
+
+typedef _$MitraAvailability = AsyncNotifier<bool>;
+// ignore_for_file: type=lint
+// ignore_for_file: subtype_of_sealed_class, invalid_use_of_internal_member, invalid_use_of_visible_for_testing_member, deprecated_member_use_from_same_package