feat(app): undo deleting a card

Deleting a card, from the list or while studying, asks first ("Delete
flashcard?"), then offers Undo for a few seconds ("Flashcard deleted").
Meanwhile the card leaves every list and session; once the time to
undo is over, its revisions are blanked and it is deleted for good, as
notes and studysets already are (CardDeletions, a DelayedDeletions).
Undo while studying puts the card back into the round where it was.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

halkyon_learn_flutter/lib/l10n/app_de.arb

@@ -372,6 +372,9 @@
   "cardUnbury": "Zurückstellung aufheben",
   "cardTileBuried": "Karteikarte bis morgen zurückgestellt",
   "cardTileUnburied": "Karteikarte nicht mehr zurückgestellt",
+  "cardDeleteTitle": "Karteikarte löschen?",
+  "cardDeleteMessage": "Diese Karteikarte wird aus dem Lernset entfernt. Du kannst dies für einige Sekunden rückgängig machen.",
+  "cardDeleted": "Karteikarte gelöscht",
   "cardFilterTooltip": "Filter",
   "cardFilterTitle": "Filter",
   "cardFilterTag": "Tag",

halkyon_learn_flutter/lib/l10n/app_en.arb

@@ -413,6 +413,9 @@
   "cardUnbury": "Unbury",
   "cardTileBuried": "Flashcard buried until tomorrow",
   "cardTileUnburied": "Flashcard unburied",
+  "cardDeleteTitle": "Delete flashcard?",
+  "cardDeleteMessage": "This flashcard will be removed from the studyset. You can undo this for a few seconds.",
+  "cardDeleted": "Flashcard deleted",
   "cardFilterTooltip": "Filter",
   "cardFilterTitle": "Filter",
   "cardFilterTag": "Tag",

halkyon_learn_flutter/lib/l10n/app_localizations.dart

@@ -2266,6 +2266,24 @@ abstract class AppLocalizations {
   /// **'Flashcard unburied'**
   String get cardTileUnburied;
 
+  /// No description provided for @cardDeleteTitle.
+  ///
+  /// In en, this message translates to:
+  /// **'Delete flashcard?'**
+  String get cardDeleteTitle;
+
+  /// No description provided for @cardDeleteMessage.
+  ///
+  /// In en, this message translates to:
+  /// **'This flashcard will be removed from the studyset. You can undo this for a few seconds.'**
+  String get cardDeleteMessage;
+
+  /// No description provided for @cardDeleted.
+  ///
+  /// In en, this message translates to:
+  /// **'Flashcard deleted'**
+  String get cardDeleted;
+
   /// No description provided for @cardFilterTooltip.
   ///
   /// In en, this message translates to:

halkyon_learn_flutter/lib/l10n/app_localizations_de.dart

@@ -1320,6 +1320,16 @@ class AppLocalizationsDe extends AppLocalizations {
   @override
   String get cardTileUnburied => 'Karteikarte nicht mehr zurückgestellt';
 
+  @override
+  String get cardDeleteTitle => 'Karteikarte löschen?';
+
+  @override
+  String get cardDeleteMessage =>
+      'Diese Karteikarte wird aus dem Lernset entfernt. Du kannst dies für einige Sekunden rückgängig machen.';
+
+  @override
+  String get cardDeleted => 'Karteikarte gelöscht';
+
   @override
   String get cardFilterTooltip => 'Filter';
 

halkyon_learn_flutter/lib/l10n/app_localizations_en.dart

@@ -1311,6 +1311,16 @@ class AppLocalizationsEn extends AppLocalizations {
   @override
   String get cardTileUnburied => 'Flashcard unburied';
 
+  @override
+  String get cardDeleteTitle => 'Delete flashcard?';
+
+  @override
+  String get cardDeleteMessage =>
+      'This flashcard will be removed from the studyset. You can undo this for a few seconds.';
+
+  @override
+  String get cardDeleted => 'Flashcard deleted';
+
   @override
   String get cardFilterTooltip => 'Filter';
 

halkyon_learn_flutter/lib/src/app/app_router.dart

@@ -106,6 +106,7 @@ GoRouter buildRouter({String initialLocation = RoutePaths.home}) => GoRouter(
             create: (context) => StudySessionBloc(
               person.studysets,
               person.cards,
+              person.cardDeletions,
               person.reviews,
               person.tags,
               person.settings,

halkyon_learn_flutter/lib/src/core/dependencies/dependencies.dart

@@ -23,6 +23,7 @@ import 'package:halkyon_learn_flutter/src/feature/anki/data/anki_package_reader.
 import 'package:halkyon_learn_flutter/src/feature/auth/data/auth_repository.dart';
 import 'package:halkyon_learn_flutter/src/feature/auth/data/serverpod_auth_gateway.dart';
 import 'package:halkyon_learn_flutter/src/feature/auth/model/auth_status.dart';
+import 'package:halkyon_learn_flutter/src/feature/card/data/card_deletions.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/data/card_repository.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/data/sync_card_gateway.dart';
 import 'package:halkyon_learn_flutter/src/feature/geo_map/data/geo_map_repository.dart';
@@ -255,6 +256,7 @@ Future<PersonDependencies> _openPerson(
     pdfSources,
   );
   final noteDeletions = NoteDeletions(notes);
+  final cardDeletions = CardDeletions(cards);
   final pathDeletions = LearningPathDeletions(paths);
   final stepDeletions = StepDeletions(paths);
   final pdfDeletions = PdfDeletions(pdfSources);
@@ -273,6 +275,7 @@ Future<PersonDependencies> _openPerson(
     assets: assets,
     deletions: deletions,
     noteDeletions: noteDeletions,
+    cardDeletions: cardDeletions,
     pathDeletions: pathDeletions,
     stepDeletions: stepDeletions,
     pdfDeletions: pdfDeletions,
@@ -285,6 +288,7 @@ Future<PersonDependencies> _openPerson(
         // finish while their repositories are open.
         await deletions.dispose();
         await noteDeletions.dispose();
+        await cardDeletions.dispose();
         await pathDeletions.dispose();
         await stepDeletions.dispose();
         await pdfDeletions.dispose();

halkyon_learn_flutter/lib/src/core/dependencies/person_dependencies.dart

@@ -1,5 +1,6 @@
 import 'package:halkyon_learn_flutter/src/core/asset/data/asset_repository.dart';
 import 'package:halkyon_learn_flutter/src/core/sync/sync_service.dart';
+import 'package:halkyon_learn_flutter/src/feature/card/data/card_deletions.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/data/card_repository.dart';
 import 'package:halkyon_learn_flutter/src/feature/learning_path/data/learning_path_deletions.dart';
 import 'package:halkyon_learn_flutter/src/feature/learning_path/data/learning_path_repository.dart';
@@ -60,6 +61,9 @@ class PersonDependencies({
   /// The note deletions that can still be undone.
   required final NoteDeletions noteDeletions,
 
+  /// The card deletions that can still be undone.
+  required final CardDeletions cardDeletions,
+
   /// The learning path deletions that can still be undone.
   required final LearningPathDeletions pathDeletions,
 

halkyon_learn_flutter/lib/src/feature/card/bloc/card_list_bloc.dart

@@ -1,6 +1,7 @@
 import 'package:clock/clock.dart';
 import 'package:equatable/equatable.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
+import 'package:halkyon_learn_flutter/src/feature/card/data/card_deletions.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/data/card_repository.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/model/card.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/model/card_content.dart';
@@ -17,14 +18,12 @@ class CardListBloc(
   final CardRepository _cards,
   final TagRepository _tags,
   final ReviewRepository _reviews,
+  final CardDeletions _deletions,
   final String _studysetId,
 ) extends Bloc<CardListEvent, CardListState> {
   this : super(const CardListStateLoading()) {
     on<CardListEventStarted>(_onStarted);
     on<CardListEventMoved>(_onMoved);
-    on<CardListEventDeleteRequested>(
-      (event, emit) => _cards.delete(event.card),
-    );
     on<CardListEventReported>(
       (event, emit) => _cards.saveEdit(
         event.card.id,
@@ -59,6 +58,9 @@ class CardListBloc(
   List<Card>? _cardsNow;
   var _tagging = Tagging.empty;
   var _buried = <String>{};
+
+  /// The cards whose deletion can still be undone: they don't show.
+  var _deleted = <String>{};
   String? _tagFilter;
 
   Future<void> _onStarted(
@@ -79,6 +81,15 @@ class CardListBloc(
         _reviews.changes,
         onData: (_) => add(const CardListEventBuriedRead()),
       ),
+      emit.onEach(
+        _deletions.watchPending(),
+        onData: (pending) {
+          _deleted = pending;
+          if (_loaded() case final loaded?) {
+            emit(loaded);
+          }
+        },
+      ),
       emit.forEach(
         _tags.watch(),
         onData: (tagging) {
@@ -99,7 +110,10 @@ class CardListBloc(
   /// The list as it stands, or null while the cards are being read.
   CardListStateLoaded? _loaded() => switch (_cardsNow) {
     final cards? => CardListStateLoaded(
-      cards,
+      [
+        for (final card in cards)
+          if (!_deleted.contains(card.id)) card,
+      ],
       tagging: _tagging,
       tagFilter: _tagFilter,
       buried: _buried,
@@ -129,15 +143,6 @@ final class const CardListEventMoved(
   List<Object?> get props => [card, toIndex];
 }
 
-/// Delete [card]; the person has confirmed it.
-final class const CardListEventDeleteRequested(
-  /// The card to delete.
-  final Card card,
-) extends CardListEvent {
-  @override
-  List<Object?> get props => [card];
-}
-
 /// Show only the cards with the tag [tagId], or all when it is null.
 final class const CardListEventTagFilterChanged(
   /// The tag's id.

halkyon_learn_flutter/lib/src/feature/card/data/card_deletions.dart

@@ -0,0 +1,10 @@
+import 'package:halkyon_learn_flutter/src/core/async/delayed_deletions.dart';
+import 'package:halkyon_learn_flutter/src/feature/card/data/card_repository.dart';
+
+/// The person's card deletions, which can be undone for a moment (see
+/// [DelayedDeletions]). Once the time to undo is over, the card's revisions
+/// are blanked and it is deleted.
+class CardDeletions(CardRepository cards, {super.undoWindow})
+    extends DelayedDeletions {
+  this : super(cards.deleteById, logName: 'Cards');
+}

halkyon_learn_flutter/lib/src/feature/card/data/card_repository.dart

@@ -245,9 +245,12 @@ class CardRepository(final CardGateway _gateway) {
 
   /// Deletes [card]. Its revisions are blanked first: the sync engine keeps
   /// deleted rows until the whole space is deleted (ADR 0002, rule 2).
-  Future<void> delete(Card card) async {
+  Future<void> delete(Card card) => deleteById(card.id);
-    await _gateway.blankRevisions(card.id);
+
-    await _gateway.deleteCard(card.id);
+  /// Deletes the card [id]: its revisions blanked first (ADR 0002, rule 2).
+  Future<void> deleteById(String id) async {
+    await _gateway.blankRevisions(id);
+    await _gateway.deleteCard(id);
     _changes.add(null);
   }
 

halkyon_learn_flutter/lib/src/feature/card/widget/card_list.dart

@@ -1,6 +1,7 @@
 import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:go_router/go_router.dart';
 import 'package:halkyon_learn_flutter/l10n/app_localizations.dart';
+import 'package:halkyon_learn_flutter/src/core/dependencies/person_scope.dart';
 import 'package:halkyon_learn_flutter/src/core/router/route_paths.dart';
 import 'package:halkyon_learn_flutter/src/core/widget/adaptive_sheet.dart';
 import 'package:halkyon_learn_flutter/src/core/widget/confirm_dialog.dart';
@@ -40,9 +41,13 @@ class const CardList({
 }) extends StatelessWidget {
   @override
   Widget build(BuildContext context) => BlocProvider(
-    create: (context) =>
+    create: (context) => CardListBloc(
-        CardListBloc(cards, tags, reviews, studysetId)
+      cards,
-          ..add(const CardListEventStarted()),
+      tags,
+      reviews,
+      PersonScope.of(context).cardDeletions,
+      studysetId,
+    )..add(const CardListEventStarted()),
     child: BlocBuilder<CardListBloc, CardListState>(
       builder: (context, state) => switch (state) {
         CardListStateLoading() => const SizedBox.shrink(),
@@ -321,16 +326,24 @@ class const _Cards(
               _bury(context, card, buried: buried.contains(card.id)),
           onOpen: () => context.push(RoutePaths.card(studysetId, card.id)),
           onDelete: () async {
-            final bloc = context.read<CardListBloc>();
             final l10n = AppLocalizations.of(context);
-            if (await confirmDestructiveAction(
+            final deletions = PersonScope.of(context).cardDeletions;
-              context,
+            if (!await confirmDestructiveAction(
-              title: l10n.composerDeleteTitle,
+                  context,
-              message: l10n.composerDeleteSavedMessage,
+                  title: l10n.cardDeleteTitle,
-              confirmLabel: l10n.composerDelete,
+                  message: l10n.cardDeleteMessage,
-            )) {
+                  confirmLabel: l10n.cardTileDelete,
-              bloc.add(CardListEventDeleteRequested(card));
+                ) ||
+                !context.mounted) {
+              return;
             }
+            // The deletion outlives the tile.
+            deletions.delete(card.id);
+            showUndoSnackBar(
+              context,
+              message: l10n.cardDeleted,
+              onUndo: () => deletions.undo(card.id),
+            );
           },
         ),
     ],

halkyon_learn_flutter/lib/src/feature/study/bloc/study_session_bloc.dart

@@ -4,6 +4,7 @@ import 'dart:math' as math;
 import 'package:clock/clock.dart';
 import 'package:equatable/equatable.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
+import 'package:halkyon_learn_flutter/src/feature/card/data/card_deletions.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/data/card_repository.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/model/card.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/model/card_content.dart';
@@ -35,6 +36,7 @@ import 'package:halkyon_learn_flutter/src/feature/tag/model/tagging.dart';
 class StudySessionBloc(
   final StudysetRepository _studysets,
   final CardRepository _cards,
+  final CardDeletions _deletions,
   final ReviewRepository _reviews,
   final TagRepository _tags,
   final SettingsRepository _settings,
@@ -67,6 +69,7 @@ class StudySessionBloc(
     on<StudySessionEventCardEdited>(_onCardEdited);
     on<StudySessionEventReported>(_onReported);
     on<StudySessionEventCardDeleted>(_onCardDeleted);
+    on<StudySessionEventDeleteUndone>(_onDeleteUndone);
     on<StudySessionEventBackFirstToggled>((event, emit) async {
       // A session focused on a side turns for itself; the settings stay as
       // they are.
@@ -103,6 +106,9 @@ class StudySessionBloc(
 
   /// The card set aside last in this round, and when, to undo it.
   ({Card card, DateTime at, int index})? _lastBuried;
+
+  /// The card deleted last in this round, and where it was, to undo it.
+  ({Card card, int index})? _lastDeleted;
   final _ratings = <String, Rating>{};
   final _graduated = <String>{};
   var _cramIndex = 0;
@@ -159,6 +165,7 @@ class StudySessionBloc(
     _graduated.clear();
     _undoable.clear();
     _lastBuried = null;
+    _lastDeleted = null;
     _cramIndex = 0;
     final groups = await _groups();
     _cardsById = {
@@ -245,7 +252,9 @@ class StudySessionBloc(
     for (final studysetId in studied) {
       final group = [
         for (final card in await _cards.cardsOf(studysetId))
-          if (tagged == null || tagged.contains(card.id)) card,
+          if ((tagged == null || tagged.contains(card.id)) &&
+              !_deletions.pending.contains(card.id))
+            card,
       ];
       for (final card in group) {
         _studysetOf[card.id] = studysetId;
@@ -554,8 +563,30 @@ class StudySessionBloc(
     Emitter<StudySessionState> emit,
   ) async {
     if (state case final StudySessionStateShowing showing) {
-      await _cards.delete(showing.card);
+      final card = showing.card;
-      await _leave(emit, showing.card.id);
+      // Deleted for good once the time to undo it is over.
+      _deletions.delete(card.id);
+      _lastDeleted = (card: card, index: _round.indexOf(card.id));
+      await _leave(emit, card.id);
+    }
+  }
+
+  void _onDeleteUndone(
+    StudySessionEventDeleteUndone event,
+    Emitter<StudySessionState> emit,
+  ) {
+    final deleted = _lastDeleted;
+    _lastDeleted = null;
+    if (deleted == null) {
+      return;
+    }
+    final (:card, :index) = deleted;
+    _deletions.undo(card.id);
+    // Back where it was in the round under way; the card on screen stays.
+    if (state case final StudySessionStateShowing showing) {
+      _cardsById[card.id] = card;
+      _round.insert(index.clamp(0, _round.length), card.id);
+      _reshow(emit, showing);
     }
   }
 
@@ -757,6 +788,9 @@ final class const StudySessionEventReported(
   List<Object?> get props => [report];
 }
 
+/// Take back deleting the last card: it is studied again.
+final class const StudySessionEventDeleteUndone() extends StudySessionEvent;
+
 /// Delete the card on screen, and go on with the next.
 final class const StudySessionEventCardDeleted() extends StudySessionEvent;
 

halkyon_learn_flutter/lib/src/feature/study/widget/study_screen.dart

@@ -286,12 +286,22 @@ class const _Showing(
       onDelete: () async {
         final bloc = context.read<StudySessionBloc>();
         if (await confirmDestructiveAction(
-          context,
+              context,
-          title: l10n.composerDeleteTitle,
+              title: l10n.cardDeleteTitle,
-          message: l10n.composerDeleteSavedMessage,
+              message: l10n.cardDeleteMessage,
-          confirmLabel: l10n.composerDelete,
+              confirmLabel: l10n.cardTileDelete,
-        )) {
+            ) &&
+            context.mounted) {
           bloc.add(const StudySessionEventCardDeleted());
+          showUndoSnackBar(
+            context,
+            message: l10n.cardDeleted,
+            onUndo: () {
+              if (!bloc.isClosed) {
+                bloc.add(const StudySessionEventDeleteUndone());
+              }
+            },
+          );
         }
       },
     );

halkyon_learn_flutter/test/core/dependencies/person_scope_test.dart

@@ -6,6 +6,7 @@ import 'package:halkyon_learn_flutter/src/core/dependencies/person_dependencies.
 import 'package:halkyon_learn_flutter/src/core/dependencies/person_scope.dart';
 import 'package:halkyon_learn_flutter/src/core/sync/sync_service.dart';
 import 'package:halkyon_learn_flutter/src/feature/auth/model/auth_status.dart';
+import 'package:halkyon_learn_flutter/src/feature/card/data/card_deletions.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/data/card_repository.dart';
 import 'package:halkyon_learn_flutter/src/feature/learning_path/data/learning_path_deletions.dart';
 import 'package:halkyon_learn_flutter/src/feature/learning_path/data/learning_path_repository.dart';
@@ -62,6 +63,7 @@ PersonDependencies personDependencies({Future<void> Function()? onDispose}) {
     assets: assets,
     deletions: StudysetDeletions(studysets, cards, notes, paths, pdfSources),
     noteDeletions: NoteDeletions(notes),
+    cardDeletions: CardDeletions(cards),
     pathDeletions: LearningPathDeletions(paths),
     stepDeletions: StepDeletions(paths),
     pdfDeletions: PdfDeletions(pdfSources),

halkyon_learn_flutter/test/feature/card/bloc/card_blocs_test.dart

@@ -1,6 +1,7 @@
 import 'package:flutter_test/flutter_test.dart';
 import 'package:halkyon_learn_flutter/src/core/content/rich_content.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/bloc/card_list_bloc.dart';
+import 'package:halkyon_learn_flutter/src/feature/card/data/card_deletions.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/data/card_repository.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/model/card_content.dart';
 import 'package:halkyon_learn_flutter/src/feature/study/data/review_repository.dart';
@@ -22,14 +23,17 @@ void main() {
   late CardRepository cards;
   late TagRepository tags;
   late ReviewRepository reviews;
+  late CardDeletions deletions;
 
   setUp(() {
     gateway = FakeCardGateway();
     cards = CardRepository(gateway);
     tags = TagRepository(FakeTagGateway(), cardChanges: cards.changes);
     reviews = ReviewRepository(FakeReviewGateway());
+    deletions = CardDeletions(cards, undoWindow: Duration.zero);
   });
   tearDown(() async {
+    await deletions.dispose();
     await reviews.dispose();
     await tags.dispose();
     await cards.dispose();
@@ -40,7 +44,7 @@ void main() {
       'a card reported or buried shows so, and either is taken back',
       () async {
         final id = await cards.create('japanese', card('猫', 'cat'));
-        final bloc = CardListBloc(cards, tags, reviews, 'japanese')
+        final bloc = CardListBloc(cards, tags, reviews, deletions, 'japanese')
           ..add(const CardListEventStarted());
         addTearDown(bloc.close);
         Future<CardListStateLoaded> next(
@@ -70,7 +74,7 @@ void main() {
 
     test('lists the cards and follows every change', () async {
       await cards.create('japanese', card('猫', 'cat'));
-      final bloc = CardListBloc(cards, tags, reviews, 'japanese')
+      final bloc = CardListBloc(cards, tags, reviews, deletions, 'japanese')
         ..add(const CardListEventStarted());
       addTearDown(bloc.close);
 
@@ -100,7 +104,7 @@ void main() {
     test('moves a card', () async {
       await cards.create('japanese', card('a', ''));
       await cards.create('japanese', card('b', ''));
-      final bloc = CardListBloc(cards, tags, reviews, 'japanese')
+      final bloc = CardListBloc(cards, tags, reviews, deletions, 'japanese')
         ..add(const CardListEventStarted());
       addTearDown(bloc.close);
       final loaded = await bloc.stream.firstWhere(
@@ -137,7 +141,7 @@ void main() {
       await tags.setTagsOf(ids[0], {noun});
       await tags.setTagsOf(ids[1], {noun});
       await tags.setTagsOf(ids[2], {verb});
-      bloc = CardListBloc(cards, tags, reviews, 'japanese')
+      bloc = CardListBloc(cards, tags, reviews, deletions, 'japanese')
         ..add(const CardListEventStarted());
     });
     tearDown(() => bloc.close());

halkyon_learn_flutter/test/feature/card/widget/card_widgets_test.dart

@@ -110,10 +110,8 @@ void main() {
     expect(find.text('Changed on two devices'), findsOneWidget);
   });
 
-  testWidgets("a card's options delete it, after asking", (tester) async {
+  /// Deletes the card shown through its options, saying yes.
-    final id = await cards.create('japanese', card('猫', 'cat'));
+  Future<void> delete(WidgetTester tester) async {
-    await showList(tester);
-
     await tester.tap(
       find.descendant(
         of: find.byType(CardTile),
@@ -126,11 +124,38 @@ void main() {
     await tester.pump();
     await tester.pump();
     await tester.pumpAndSettle();
+    expect(find.text('Delete flashcard?'), findsOneWidget);
     await tester.tap(find.widgetWithText(FilledButton, 'Delete'));
     await tester.pumpAndSettle();
+  }
 
-    expect(gateway.deletions, ['blank $id', 'delete $id']);
+  testWidgets("a card's options delete it, after asking; once the time to "
+      'undo is over, for good', (tester) async {
+    final id = await cards.create('japanese', card('猫', 'cat'));
+    await showList(tester);
+
+    await delete(tester);
+
+    expect(find.text('Flashcard deleted'), findsOneWidget);
     expect(find.text('No flashcards yet'), findsOneWidget);
+    expect(gateway.deletions, isEmpty);
+    await tester.pump(const Duration(seconds: 5));
+    await tester.pumpAndSettle();
+    expect(gateway.deletions, ['blank $id', 'delete $id']);
+  });
+
+  testWidgets('Undo keeps a card deleted a moment ago', (tester) async {
+    await cards.create('japanese', card('猫', 'cat'));
+    await showList(tester);
+
+    await delete(tester);
+    await tester.tap(find.text('Undo'));
+    await tester.pumpAndSettle();
+    await tester.pump(const Duration(seconds: 5));
+    await tester.pumpAndSettle();
+
+    expect(find.text('猫'), findsOneWidget);
+    expect(gateway.deletions, isEmpty);
   });
 
   testWidgets("a card's options report it and bury it, each shown on the "

halkyon_learn_flutter/test/feature/study/bloc/study_session_bloc_test.dart

@@ -3,6 +3,7 @@ import 'dart:math' as math;
 import 'package:clock/clock.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:halkyon_learn_flutter/src/core/content/rich_content.dart';
+import 'package:halkyon_learn_flutter/src/feature/card/data/card_deletions.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/data/card_repository.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/model/card_content.dart';
 import 'package:halkyon_learn_flutter/src/feature/settings/data/settings_repository.dart';
@@ -35,6 +36,7 @@ void main() {
   late FakeStudysetGateway studysetGateway;
   late StudysetRepository studysets;
   late CardRepository cards;
+  late CardDeletions deletions;
   late FakeReviewGateway reviewGateway;
   late ReviewRepository reviews;
   late TagRepository tags;
@@ -49,6 +51,7 @@ void main() {
       );
     studysets = StudysetRepository(studysetGateway);
     cards = CardRepository(FakeCardGateway());
+    deletions = CardDeletions(cards, undoWindow: Duration.zero);
     reviewGateway = FakeReviewGateway();
     reviews = ReviewRepository(reviewGateway);
     tags = TagRepository(FakeTagGateway());
@@ -56,6 +59,7 @@ void main() {
     now = DateTime.utc(2026, 10, 5, 9);
   });
   tearDown(() async {
+    await deletions.dispose();
     await studysets.dispose();
     await cards.dispose();
     await tags.dispose();
@@ -66,6 +70,7 @@ void main() {
   StudySessionBloc session() => StudySessionBloc(
     studysets,
     cards,
+    deletions,
     reviews,
     tags,
     settings,
@@ -188,6 +193,8 @@ void main() {
         bloc.add(const StudySessionEventCardDeleted());
         expect((await showing(bloc, '犬')).pills, hasLength(1));
       });
+      // Deleted for good once the time to undo it is over.
+      await Future<void>.delayed(const Duration(milliseconds: 50));
 
       expect(
         (await cards.cardsOf('japanese')).map((each) => each.content.front),
@@ -794,6 +801,7 @@ void main() {
     StudySessionBloc focused(StudyFocus focus) => StudySessionBloc(
       studysets,
       cards,
+      deletions,
       reviews,
       tags,
       settings,

halkyon_learn_flutter/test/feature/study/widget/study_screen_test.dart

@@ -253,7 +253,11 @@ void main() {
     await tester.tap(find.widgetWithText(FilledButton, 'Delete'));
     await tester.pumpAndSettle();
 
+    expect(find.text('Flashcard deleted'), findsOneWidget);
     expect(find.textContaining('犬', findRichText: true), findsOneWidget);
+    // For good once the time to undo it is over.
+    await tester.pump(const Duration(seconds: 5));
+    await tester.pumpAndSettle();
     expect(await cards.cardsOf('japanese'), hasLength(1));
   });
 

halkyon_learn_flutter/test/support/test_dependencies.dart

@@ -20,6 +20,7 @@ import 'package:halkyon_learn_flutter/src/feature/anki/data/anki_package.dart';
 import 'package:halkyon_learn_flutter/src/feature/anki/data/anki_package_reader.dart';
 import 'package:halkyon_learn_flutter/src/feature/auth/data/auth_gateway.dart';
 import 'package:halkyon_learn_flutter/src/feature/auth/data/auth_repository.dart';
+import 'package:halkyon_learn_flutter/src/feature/card/data/card_deletions.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/data/card_gateway.dart';
 import 'package:halkyon_learn_flutter/src/feature/card/data/card_repository.dart';
 import 'package:halkyon_learn_flutter/src/feature/geo_map/data/geo_map_repository.dart';
@@ -170,6 +171,7 @@ Dependencies testDependencies({
           pdfSources,
         );
         final noteDeletions = NoteDeletions(notes);
+        final cardDeletions = CardDeletions(cards);
         final pathDeletions = LearningPathDeletions(paths);
         final stepDeletions = StepDeletions(paths);
         final pdfDeletions = PdfDeletions(pdfSources);
@@ -187,6 +189,7 @@ Dependencies testDependencies({
           assets: assets,
           deletions: deletions,
           noteDeletions: noteDeletions,
+          cardDeletions: cardDeletions,
           pathDeletions: pathDeletions,
           stepDeletions: stepDeletions,
           pdfDeletions: pdfDeletions,
@@ -194,6 +197,7 @@ Dependencies testDependencies({
           onDispose: () async {
             await deletions.dispose();
             await noteDeletions.dispose();
+            await cardDeletions.dispose();
             await pathDeletions.dispose();
             await stepDeletions.dispose();
             await pdfDeletions.dispose();