feat(inventory): auto-recover from a transient stream failure

Instead of showing a retry button on the first failure, silently re-open
the inventory stream with exponential backoff (250ms→4s, 6 attempts,
staying in the loading spinner). The startup DB-not-ready race clears in
well under a second, so the user just sees the spinner briefly and the
list appears — no tap needed. Only after the retry budget is exhausted do
we surface the manual-retry error.

Tests cover auto-recovery, no error flicker during retries, and the
give-up path (via fake_async to fast-forward the backoff).

apps/app_seeds/lib/state/inventory_cubit.dart

@@ -167,6 +167,18 @@ class InventoryCubit extends Cubit<InventoryState> {
   >?
   _sub;
 
+  /// Pending auto-retry, cancelled on a fresh (re)subscribe or on close.
+  Timer? _retryTimer;
+
+  /// Consecutive stream failures since the last good emission. Drives the
+  /// backoff and, once [_maxAutoRetries] is hit, the switch to a manual retry.
+  int _failures = 0;
+
+  /// How many times we silently re-open the stream before giving up and asking
+  /// the user. The startup DB-not-ready race clears in well under a second, so
+  /// a handful of backed-off attempts recovers it without the user noticing.
+  static const _maxAutoRetries = 6;
+
   /// (Re)opens the combined inventory subscription (list + draft tray). One
   /// subscription only: two separate StreamGroups here re-emit in a loop that
   /// hangs widget tests — see watchInventoryView.
@@ -174,26 +186,48 @@ class InventoryCubit extends Cubit<InventoryState> {
   /// The onError handler is load-bearing: without it a transient stream failure
   /// (e.g. the encrypted DB not yet ready at startup) would go unhandled and
   /// leave [InventoryState.loading] true forever — the "stuck spinner" that a
-  /// restart clears. On error we drop out of loading and surface [error] so the
-  /// UI can offer [retry].
+  /// restart clears. On error we auto-retry with backoff (staying in [loading]
+  /// so the user just sees the spinner briefly), and only surface [error] for a
+  /// manual [retry] once the transient window has clearly passed.
   void _subscribe() {
+    _retryTimer?.cancel();
     _sub?.cancel();
     _sub = _repo.watchInventoryView().listen(
-      (view) => emit(
+      (view) {
+        _failures = 0;
+        emit(
           state.copyWith(
             items: view.items,
             drafts: view.drafts,
             loading: false,
             error: () => null,
           ),
-      ),
-      onError: (Object e) =>
-          emit(state.copyWith(loading: false, error: () => '$e')),
+        );
+      },
+      onError: _onStreamError,
     );
   }
 
-  /// Re-opens the inventory stream after a failure, back to the loading state.
+  void _onStreamError(Object e) {
+    if (isClosed) return;
+    _failures++;
+    if (_failures <= _maxAutoRetries) {
+      // Exponential backoff capped at ~4s: 250ms, 500ms, 1s, 2s, 4s, 4s.
+      final delayMs = (250 * (1 << (_failures - 1))).clamp(250, 4000);
+      // Stay in loading — an auto-recovering spinner, not an error screen.
+      _retryTimer = Timer(Duration(milliseconds: delayMs), () {
+        if (!isClosed) _subscribe();
+      });
+    } else {
+      // Transient window has passed; hand it to the user.
+      emit(state.copyWith(loading: false, error: () => '$e'));
+    }
+  }
+
+  /// Re-opens the inventory stream on demand (from the manual retry button),
+  /// resetting the auto-retry budget and returning to the loading state.
   void retry() {
+    _failures = 0;
     emit(state.copyWith(loading: true, error: () => null));
     _subscribe();
   }
@@ -269,6 +303,7 @@ class InventoryCubit extends Cubit<InventoryState> {
 
   @override
   Future<void> close() async {
+    _retryTimer?.cancel();
     await _sub?.cancel();
     return super.close();
   }

apps/app_seeds/pubspec.yaml

@@ -86,6 +86,8 @@ dev_dependencies:
     sdk: flutter
 
   flutter_lints: ^6.0.0
+  # Virtual clock to fast-forward the inventory auto-retry backoff in tests.
+  fake_async: ^1.3.1
   build_runner: ^2.4.13
   drift_dev: ^2.28.0
   slang_build_runner: ^4.7.0

apps/app_seeds/test/state/inventory_cubit_test.dart

@@ -1,6 +1,7 @@
 import 'dart:typed_data';
 
 import 'package:commons_core/commons_core.dart';
+import 'package:fake_async/fake_async.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:tane/data/variety_repository.dart';
 import 'package:tane/db/database.dart';
@@ -9,20 +10,23 @@ import 'package:tane/state/inventory_cubit.dart';
 
 import '../support/test_support.dart';
 
-/// A repository whose inventory stream errors until [healthy] is flipped —
-/// mimics the transient DB-not-ready failure that used to leave the spinner
-/// stuck forever.
+/// A repository whose inventory stream errors for the first
+/// [failuresBeforeHealthy] subscriptions, then behaves normally — mimics the
+/// transient DB-not-ready failure that used to leave the spinner stuck forever.
+/// The default never recovers, for the "give up" path.
 class _FailingRepository extends VarietyRepository {
   // ignore: use_super_parameters
-  _FailingRepository(AppDatabase db)
+  _FailingRepository(AppDatabase db, {this.failuresBeforeHealthy = 1 << 30})
     : super(db, idGen: IdGen(), nodeId: 'test-node');
 
-  bool healthy = false;
+  final int failuresBeforeHealthy;
+  int subscriptions = 0;
 
   @override
   Stream<({List<VarietyListItem> items, List<VarietyListItem> drafts})>
-  watchInventoryView() =>
-      healthy ? super.watchInventoryView() : Stream.error(StateError('boom'));
+  watchInventoryView() => subscriptions++ < failuresBeforeHealthy
+      ? Stream.error(StateError('boom'))
+      : super.watchInventoryView();
 }
 
 /// Waits until the cubit's state satisfies [predicate], whether it already
@@ -57,30 +61,49 @@ void main() {
   });
 
   group('stream failure', () {
-    test('a failing stream drops loading and surfaces an error, not a '
-        'forever-spinner', () async {
-      final failing = _FailingRepository(db);
+    test('a transient failure recovers on its own — no error, no manual retry',
+        () async {
+      // Fails the first two subscribes, then the DB is ready.
+      final failing = _FailingRepository(db, failuresBeforeHealthy: 2);
+      await failing.addQuickVariety(label: 'Maize');
       final failCubit = InventoryCubit(failing);
       addTearDown(failCubit.close);
 
-      final state = await waitFor(failCubit, (s) => s.error != null);
-      expect(state.loading, isFalse);
-      expect(state.error, contains('boom'));
+      // Auto-retry with backoff brings it back without ever showing an error.
+      final state = await waitFor(failCubit, (s) => !s.loading && s.error == null);
+      expect(state.items.single.label, 'Maize');
+      expect(failing.subscriptions, greaterThan(1));
     });
 
-    test('retry re-opens the stream and recovers once the DB is healthy',
+    test('stays in loading (spinner), never flips to error, while auto-retrying',
         () async {
-      final failing = _FailingRepository(db);
+      final failing = _FailingRepository(db, failuresBeforeHealthy: 2);
+      await failing.addQuickVariety(label: 'Maize');
       final failCubit = InventoryCubit(failing);
       addTearDown(failCubit.close);
-      await waitFor(failCubit, (s) => s.error != null);
 
-      await failing.addQuickVariety(label: 'Maize');
-      failing.healthy = true;
-      failCubit.retry();
+      final errors = <String?>[];
+      final sub = failCubit.stream.listen((s) => errors.add(s.error));
+      addTearDown(sub.cancel);
 
-      final state = await waitFor(failCubit, (s) => s.error == null && !s.loading);
-      expect(state.items.single.label, 'Maize');
+      await waitFor(failCubit, (s) => !s.loading && s.error == null);
+      expect(errors.every((e) => e == null), isTrue,
+          reason: 'no error state should be emitted during auto-recovery');
+    });
+
+    test('gives up after the retry budget and surfaces a manual-retry error',
+        () {
+      fakeAsync((async) {
+        final failing = _FailingRepository(db); // never recovers
+        final failCubit = InventoryCubit(failing);
+        addTearDown(failCubit.close);
+
+        // Fast-forward past all backoff windows (~12s of retries).
+        async.elapse(const Duration(seconds: 30));
+
+        expect(failCubit.state.loading, isFalse);
+        expect(failCubit.state.error, contains('boom'));
+      });
     });
   });