fix(shopinbit): back off pollers on error and pause when backgrounded

diff --git a/lib/pages/shopinbit/shopinbit_car_research_payment_view.dart b/lib/pages/shopinbit/shopinbit_car_research_payment_view.dart
index 7f34843..d8f78bd 100644
--- a/lib/pages/shopinbit/shopinbit_car_research_payment_view.dart
+++ b/lib/pages/shopinbit/shopinbit_car_research_payment_view.dart
@@ -42,8 +42,14 @@ class ShopInBitCarResearchPaymentView extends ConsumerStatefulWidget {
 }
 
 class _ShopInBitCarResearchPaymentViewState
-    extends ConsumerState<ShopInBitCarResearchPaymentView> {
+    extends ConsumerState<ShopInBitCarResearchPaymentView>
+    with WidgetsBindingObserver {
   Timer? _pollTimer;
+
+  static const Duration _kBasePollInterval = Duration(seconds: 15);
+  static const Duration _kMaxPollInterval = Duration(seconds: 120);
+  Duration _pollInterval = _kBasePollInterval;
+
   Map<String, dynamic>? _status;
   _PaymentFlowState _flowState = _PaymentFlowState.idle;
   String _statusString = "ready_to_pay";
@@ -183,23 +189,59 @@ class _ShopInBitCarResearchPaymentViewState
   @override
   void initState() {
     super.initState();
+    WidgetsBinding.instance.addObserver(this);
     final links = widget.invoice.paymentLinks;
     _methods = links.keys.map((k) => k.toUpperCase()).toList();
     _addresses = links.values.toList();
     // Kick off an immediate poll then start periodic polling.
     unawaited(_pollStatus());
-    _pollTimer = Timer.periodic(
-      const Duration(seconds: 15),
-      (_) => unawaited(_pollStatus()),
-    );
+    _scheduleNextPoll();
   }
 
   @override
   void dispose() {
+    WidgetsBinding.instance.removeObserver(this);
     _pollTimer?.cancel();
     super.dispose();
   }
 
+  @override
+  void didChangeAppLifecycleState(AppLifecycleState state) {
+    // Don't poll while backgrounded; resume fresh when we come back.
+    if (state == AppLifecycleState.resumed) {
+      if (!_isTerminal && _flowState != _PaymentFlowState.finalizing) {
+        _pollInterval = _kBasePollInterval;
+        _scheduleNextPoll();
+      }
+    } else {
+      _pollTimer?.cancel();
+    }
+  }
+
+  void _scheduleNextPoll() {
+    _pollTimer?.cancel();
+    _pollTimer = Timer(_pollInterval, _pollTick);
+  }
+
+  Duration _nextBackoff(Duration current) {
+    final Duration next = current * 2;
+    return next > _kMaxPollInterval ? _kMaxPollInterval : next;
+  }
+
+  /// Periodic driver: poll once, then reschedule with backoff on failure and
+  /// reset on success. Stops once the flow is terminal or finalizing.
+  Future<void> _pollTick() async {
+    final bool ok = await _pollStatus();
+    if (!mounted) return;
+    if (_isTerminal ||
+        _flowState == _PaymentFlowState.finalizing ||
+        _flowState == _PaymentFlowState.complete) {
+      return;
+    }
+    _pollInterval = ok ? _kBasePollInterval : _nextBackoff(_pollInterval);
+    _scheduleNextPoll();
+  }
+
   void _popToTickets() {
     Navigator.of(context).popUntil((route) {
       final name = route.settings.name;
@@ -266,7 +308,9 @@ class _ShopInBitCarResearchPaymentViewState
     }
   }
 
-  Future<void> _pollStatus() async {
+  /// Fetch invoice status once and apply it. Returns false on any failure so
+  /// the periodic driver can back off instead of polling at full rate.
+  Future<bool> _pollStatus() async {
     try {
       final resp = await ref
           .read(pShopinBitService)
@@ -283,9 +327,9 @@ class _ShopInBitCarResearchPaymentViewState
             ),
           );
         }
-        return;
+        return false;
       }
-      if (!mounted) return;
+      if (!mounted) return true;
       Logging.instance.i(
         "CarResearch status response (payment_view): ${resp.value}",
       );
@@ -302,6 +346,7 @@ class _ShopInBitCarResearchPaymentViewState
         _pollTimer?.cancel();
         await _finalizePayment();
       }
+      return true;
     } catch (e, s) {
       Logging.instance.e(
         "ticket status polling issue",
@@ -317,6 +362,7 @@ class _ShopInBitCarResearchPaymentViewState
           ),
         );
       }
+      return false;
     }
   }
 
diff --git a/lib/pages/shopinbit/shopinbit_payment_view.dart b/lib/pages/shopinbit/shopinbit_payment_view.dart
index f3b7ccf..f306982 100644
--- a/lib/pages/shopinbit/shopinbit_payment_view.dart
+++ b/lib/pages/shopinbit/shopinbit_payment_view.dart
@@ -15,6 +15,7 @@ import '../../themes/coin_icon_provider.dart';
 import '../../themes/stack_colors.dart';
 import '../../utilities/address_utils.dart';
 import '../../utilities/assets.dart';
+import '../../utilities/logger.dart';
 import '../../utilities/show_loading.dart';
 import '../../utilities/text_styles.dart';
 import '../../utilities/util.dart';
@@ -50,10 +51,15 @@ class ShopInBitPaymentView extends ConsumerStatefulWidget {
       _ShopInBitPaymentViewState();
 }
 
-class _ShopInBitPaymentViewState extends ConsumerState<ShopInBitPaymentView> {
+class _ShopInBitPaymentViewState extends ConsumerState<ShopInBitPaymentView>
+    with WidgetsBindingObserver {
   int _selectedMethod = 0;
   Timer? _pollTimer;
 
+  static const Duration _kBasePollInterval = Duration(seconds: 15);
+  static const Duration _kMaxPollInterval = Duration(seconds: 120);
+  Duration _pollInterval = _kBasePollInterval;
+
   PaymentInfo? _paymentInfo;
 
   // Derived from API payment_links keys, fallback to defaults
@@ -81,6 +87,7 @@ class _ShopInBitPaymentViewState extends ConsumerState<ShopInBitPaymentView> {
   @override
   void initState() {
     super.initState();
+    WidgetsBinding.instance.addObserver(this);
     _applyPaymentInfo(widget.paymentInfo);
     if (widget.apiTicketId != 0) {
       _startPolling();
@@ -89,10 +96,22 @@ class _ShopInBitPaymentViewState extends ConsumerState<ShopInBitPaymentView> {
 
   @override
   void dispose() {
+    WidgetsBinding.instance.removeObserver(this);
     _pollTimer?.cancel();
     super.dispose();
   }
 
+  @override
+  void didChangeAppLifecycleState(AppLifecycleState state) {
+    if (widget.apiTicketId == 0) return;
+    // Don't poll while backgrounded; resume fresh when we come back.
+    if (state == AppLifecycleState.resumed) {
+      if (!_isTerminal) _startPolling();
+    } else {
+      _pollTimer?.cancel();
+    }
+  }
+
   void _applyPaymentInfo(PaymentInfo info) {
     _paymentInfo = info;
     final links = info.paymentLinks;
@@ -104,25 +123,49 @@ class _ShopInBitPaymentViewState extends ConsumerState<ShopInBitPaymentView> {
 
   void _startPolling() {
     _pollTimer?.cancel();
-    _pollTimer = Timer.periodic(
-      const Duration(seconds: 15),
-      (_) => _pollPayment(),
-    );
+    _pollInterval = _kBasePollInterval;
+    _scheduleNextPoll();
+  }
+
+  void _scheduleNextPoll() {
+    _pollTimer?.cancel();
+    _pollTimer = Timer(_pollInterval, _pollPayment);
+  }
+
+  Duration _nextBackoff(Duration current) {
+    final Duration next = current * 2;
+    return next > _kMaxPollInterval ? _kMaxPollInterval : next;
   }
 
   Future<void> _pollPayment() async {
+    bool ok = false;
     try {
       final resp = await ref
           .read(pShopinBitService)
           .client
           .getPayment(widget.apiTicketId);
-      if (!resp.hasError && resp.value != null && mounted) {
-        setState(() => _applyPaymentInfo(resp.value!));
-        if (_isTerminal) {
-          _pollTimer?.cancel();
+      if (!resp.hasError && resp.value != null) {
+        ok = true;
+        if (mounted) {
+          setState(() => _applyPaymentInfo(resp.value!));
         }
       }
-    } catch (_) {}
+    } catch (e, s) {
+      Logging.instance.w(
+        "ShopInBit payment poll failed",
+        error: e,
+        stackTrace: s,
+      );
+    }
+    if (!mounted) return;
+    if (_isTerminal) {
+      _pollTimer?.cancel();
+      return;
+    }
+    // Back off on failure (e.g. a 429), reset to base on success, so a rate
+    // limit slows us down instead of getting hammered every 15s.
+    _pollInterval = ok ? _kBasePollInterval : _nextBackoff(_pollInterval);
+    _scheduleNextPoll();
   }
 
   Future<void> _refreshInvoice() async {
diff --git a/lib/pages/shopinbit/shopinbit_ticket_detail.dart b/lib/pages/shopinbit/shopinbit_ticket_detail.dart
index 8424551..49fac0e 100644
--- a/lib/pages/shopinbit/shopinbit_ticket_detail.dart
+++ b/lib/pages/shopinbit/shopinbit_ticket_detail.dart
@@ -13,6 +13,7 @@ import '../../services/shopinbit/src/models/message.dart';
 import '../../services/shopinbit/src/models/ticket.dart';
 import '../../themes/stack_colors.dart';
 import '../../utilities/assets.dart';
+import '../../utilities/logger.dart';
 import '../../utilities/text_styles.dart';
 import '../../utilities/util.dart';
 import '../../widgets/background.dart';
@@ -38,9 +39,14 @@ class ShopInBitTicketDetail extends ConsumerStatefulWidget {
       _ShopInBitTicketDetailState();
 }
 
-class _ShopInBitTicketDetailState extends ConsumerState<ShopInBitTicketDetail> {
+class _ShopInBitTicketDetailState extends ConsumerState<ShopInBitTicketDetail>
+    with WidgetsBindingObserver {
   late final TextEditingController _messageController;
 
+  static const Duration _kBasePollInterval = Duration(seconds: 30);
+  static const Duration _kMaxPollInterval = Duration(seconds: 120);
+  Duration _pollInterval = _kBasePollInterval;
+
   // Optimistically-shown messages the user just sent, kept until the next
   // refresh folds them into the persisted ticket row.
   final List<TicketMessage> _pending = [];
@@ -54,6 +60,7 @@ class _ShopInBitTicketDetailState extends ConsumerState<ShopInBitTicketDetail> {
     super.initState();
 
     _messageController = TextEditingController();
+    WidgetsBinding.instance.addObserver(this);
 
     // start with a refresh right away and then start polling for updates
     unawaited(_refresh().then((_) => _startPolling()));
@@ -61,15 +68,39 @@ class _ShopInBitTicketDetailState extends ConsumerState<ShopInBitTicketDetail> {
 
   @override
   void dispose() {
+    WidgetsBinding.instance.removeObserver(this);
     _pollingTimer?.cancel();
     _pollingTimer = null;
     _messageController.dispose();
     super.dispose();
   }
 
+  @override
+  void didChangeAppLifecycleState(AppLifecycleState state) {
+    // Don't poll while backgrounded; resume fresh when we come back.
+    if (state == AppLifecycleState.resumed) {
+      final ticket = ref.read(pShopInBitTicket(_id)).asData?.value;
+      final terminal =
+          ticket != null && TicketState.fromString(ticket.statusRaw).isTerminal;
+      if (!terminal) _startPolling();
+    } else {
+      _pollingTimer?.cancel();
+    }
+  }
+
   Timer? _pollingTimer;
   Future<void> _poll() async {
-    await _refresh();
+    bool ok = false;
+    try {
+      await _refresh();
+      ok = true;
+    } catch (e, s) {
+      Logging.instance.w(
+        "ShopInBit ticket poll failed",
+        error: e,
+        stackTrace: s,
+      );
+    }
     if (!mounted) return;
 
     // Stop polling once the ticket reaches a terminal state; nothing about a
@@ -79,11 +110,19 @@ class _ShopInBitTicketDetailState extends ConsumerState<ShopInBitTicketDetail> {
       return;
     }
 
-    _pollingTimer = Timer(const Duration(seconds: 30), _poll);
+    // Back off on failure (e.g. a 429), reset on success.
+    _pollInterval = ok ? _kBasePollInterval : _nextBackoff(_pollInterval);
+    _pollingTimer = Timer(_pollInterval, _poll);
+  }
+
+  Duration _nextBackoff(Duration current) {
+    final Duration next = current * 2;
+    return next > _kMaxPollInterval ? _kMaxPollInterval : next;
   }
 
   void _startPolling() {
     _pollingTimer?.cancel();
+    _pollInterval = _kBasePollInterval;
     unawaited(_poll());
   }