diff --git a/Codex Documentation/Current Software Plan/V1_BLOCKS_07_10_UPDATED/V1_BLOCK_09_Persistence_Preparation.md b/Codex Documentation/Current Software Plan/V1_BLOCKS_07_10_UPDATED/V1_BLOCK_09_Persistence_Preparation.md
index 4666bec..19fd59a 100644
--- a/Codex Documentation/Current Software Plan/V1_BLOCKS_07_10_UPDATED/V1_BLOCK_09_Persistence_Preparation.md	
+++ b/Codex Documentation/Current Software Plan/V1_BLOCKS_07_10_UPDATED/V1_BLOCK_09_Persistence_Preparation.md	
@@ -1,6 +1,6 @@
 # V1 Block 09 — Persistence Preparation
 
-Status: In progress — Chunk 9.1 complete
+Status: In progress — Chunks 9.1 and 9.2 complete
 
 Purpose: Prepare the domain layer for future MongoDB-backed persistence without adding a MongoDB driver, network behavior, sync behavior, or database runtime dependency too early.
 
@@ -84,6 +84,21 @@ Acceptance criteria:
 - Any unresolved persistence detail is documented as a TODO in the plan or architecture notes.
 - No alternative-database references remain in the active persistence plan.
 
+Completed:
+
+- Added persistence edge-case regression tests for stable task, project, and locked-block IDs across copy/update helpers.
+- Added UTC ISO-8601 DateTime persistence convention helpers and tests.
+- Added enum persistence-name mapping tests, including `RewardLevel.notSet` remaining distinct from `RewardLevel.veryLow`.
+- Added nullable-field preservation and explicit schedule-clearing tests.
+- Added backlog age source tests documenting `Task.createdAt` as the current staleness source.
+- Added in-memory repository round-trip and unmodifiable-read tests.
+- Added MongoDB-oriented document field-name constants and tests for task/statistics, project, locked-block, override, scheduling snapshot, and embedded scheduling structures.
+- Verified with `dart format lib test`, `dart analyze`, and `dart test`.
+
+TODO for Chunk 9.3:
+
+- Define document mapping behavior for clearing nullable non-schedule fields before adding model serialization helpers. Current explicit clear behavior only covers task schedule placement through `Task.copyWith(clearSchedule: true)`.
+
 BREAKPOINT: Stop here. Confirm `high` mode before model serialization changes.
 
 ## Chunk 9.3 — MongoDB-document-safe models
diff --git a/Codex Documentation/Current Software Plan/V1_BLOCK_09_Persistence_Preparation.md b/Codex Documentation/Current Software Plan/V1_BLOCK_09_Persistence_Preparation.md
index 4666bec..19fd59a 100644
--- a/Codex Documentation/Current Software Plan/V1_BLOCK_09_Persistence_Preparation.md	
+++ b/Codex Documentation/Current Software Plan/V1_BLOCK_09_Persistence_Preparation.md	
@@ -1,6 +1,6 @@
 # V1 Block 09 — Persistence Preparation
 
-Status: In progress — Chunk 9.1 complete
+Status: In progress — Chunks 9.1 and 9.2 complete
 
 Purpose: Prepare the domain layer for future MongoDB-backed persistence without adding a MongoDB driver, network behavior, sync behavior, or database runtime dependency too early.
 
@@ -84,6 +84,21 @@ Acceptance criteria:
 - Any unresolved persistence detail is documented as a TODO in the plan or architecture notes.
 - No alternative-database references remain in the active persistence plan.
 
+Completed:
+
+- Added persistence edge-case regression tests for stable task, project, and locked-block IDs across copy/update helpers.
+- Added UTC ISO-8601 DateTime persistence convention helpers and tests.
+- Added enum persistence-name mapping tests, including `RewardLevel.notSet` remaining distinct from `RewardLevel.veryLow`.
+- Added nullable-field preservation and explicit schedule-clearing tests.
+- Added backlog age source tests documenting `Task.createdAt` as the current staleness source.
+- Added in-memory repository round-trip and unmodifiable-read tests.
+- Added MongoDB-oriented document field-name constants and tests for task/statistics, project, locked-block, override, scheduling snapshot, and embedded scheduling structures.
+- Verified with `dart format lib test`, `dart analyze`, and `dart test`.
+
+TODO for Chunk 9.3:
+
+- Define document mapping behavior for clearing nullable non-schedule fields before adding model serialization helpers. Current explicit clear behavior only covers task schedule placement through `Task.copyWith(clearSchedule: true)`.
+
 BREAKPOINT: Stop here. Confirm `high` mode before model serialization changes.
 
 ## Chunk 9.3 — MongoDB-document-safe models
diff --git a/lib/scheduler_core.dart b/lib/scheduler_core.dart
index 2153565..4e8606d 100644
--- a/lib/scheduler_core.dart
+++ b/lib/scheduler_core.dart
@@ -20,6 +20,7 @@ export 'src/models.dart';
 export 'src/backlog.dart';
 export 'src/child_tasks.dart';
 export 'src/locked_time.dart';
+export 'src/persistence_contract.dart';
 export 'src/quick_capture.dart';
 export 'src/repositories.dart';
 export 'src/scheduling_engine.dart';
diff --git a/lib/src/locked_time.dart b/lib/src/locked_time.dart
index 30a7f78..a035637 100644
--- a/lib/src/locked_time.dart
+++ b/lib/src/locked_time.dart
@@ -136,6 +136,33 @@ class LockedBlock {
 
   /// Convenience check for whether this block expands through recurrence.
   bool get isRecurring => recurrence != null;
+
+  /// Return a copy with selected locked-block details changed.
+  LockedBlock copyWith({
+    String? id,
+    String? name,
+    ClockTime? startTime,
+    ClockTime? endTime,
+    DateTime? date,
+    LockedBlockRecurrence? recurrence,
+    bool? hiddenByDefault,
+    String? projectId,
+    DateTime? createdAt,
+    DateTime? updatedAt,
+  }) {
+    return LockedBlock(
+      id: id ?? this.id,
+      name: name ?? this.name,
+      startTime: startTime ?? this.startTime,
+      endTime: endTime ?? this.endTime,
+      date: date ?? this.date,
+      recurrence: recurrence ?? this.recurrence,
+      hiddenByDefault: hiddenByDefault ?? this.hiddenByDefault,
+      projectId: projectId ?? this.projectId,
+      createdAt: createdAt ?? this.createdAt,
+      updatedAt: updatedAt ?? this.updatedAt,
+    );
+  }
 }
 
 /// Concrete locked-time occurrence for one calendar day.
diff --git a/lib/src/models.dart b/lib/src/models.dart
index bbb5a6d..c931cac 100644
--- a/lib/src/models.dart
+++ b/lib/src/models.dart
@@ -464,6 +464,31 @@ class ProjectProfile {
       updatedAt: updatedAt ?? createdAt,
     );
   }
+
+  /// Return a copy with selected project defaults changed.
+  ProjectProfile copyWith({
+    String? id,
+    String? name,
+    String? colorKey,
+    PriorityLevel? defaultPriority,
+    RewardLevel? defaultReward,
+    DifficultyLevel? defaultDifficulty,
+    ReminderProfile? defaultReminderProfile,
+    int? defaultDurationMinutes,
+  }) {
+    return ProjectProfile(
+      id: id ?? this.id,
+      name: name ?? this.name,
+      colorKey: colorKey ?? this.colorKey,
+      defaultPriority: defaultPriority ?? this.defaultPriority,
+      defaultReward: defaultReward ?? this.defaultReward,
+      defaultDifficulty: defaultDifficulty ?? this.defaultDifficulty,
+      defaultReminderProfile:
+          defaultReminderProfile ?? this.defaultReminderProfile,
+      defaultDurationMinutes:
+          defaultDurationMinutes ?? this.defaultDurationMinutes,
+    );
+  }
 }
 
 /// Starter time range value used by scheduling helpers.
diff --git a/lib/src/persistence_contract.dart b/lib/src/persistence_contract.dart
new file mode 100644
index 0000000..5899269
--- /dev/null
+++ b/lib/src/persistence_contract.dart
@@ -0,0 +1,319 @@
+// MongoDB-oriented persistence contract helpers.
+//
+// This file defines stable names and conventions that future document mapping
+// code should use. It deliberately does not serialize domain models or import a
+// MongoDB client.
+
+/// DateTime storage convention for future document persistence.
+abstract final class PersistenceDateTimeConvention {
+  /// Human-readable convention kept close to the helper for tests and docs.
+  static const description =
+      'Store DateTime values as UTC ISO-8601 strings and compare as UTC instants.';
+
+  /// Convert a DateTime into the persisted string convention.
+  static String toStoredString(DateTime value) {
+    return value.toUtc().toIso8601String();
+  }
+
+  /// Parse a persisted DateTime string back into a UTC DateTime.
+  static DateTime fromStoredString(String value) {
+    return DateTime.parse(value).toUtc();
+  }
+
+  /// Compare two DateTime values by their UTC instant.
+  static int compare(DateTime left, DateTime right) {
+    return left.toUtc().compareTo(right.toUtc());
+  }
+}
+
+/// Stable enum-name mapping plan for future document persistence.
+extension PersistenceEnumName on Enum {
+  /// Persist enum values by their Dart enum name.
+  String get persistenceName => name;
+}
+
+/// Shared MongoDB document field names.
+abstract final class DocumentFields {
+  /// MongoDB primary id field.
+  static const id = '_id';
+}
+
+/// Document field names for [Task] documents.
+abstract final class TaskDocumentFields {
+  static const id = DocumentFields.id;
+  static const title = 'title';
+  static const projectId = 'projectId';
+  static const type = 'type';
+  static const status = 'status';
+  static const priority = 'priority';
+  static const reward = 'reward';
+  static const difficulty = 'difficulty';
+  static const durationMinutes = 'durationMinutes';
+  static const scheduledStart = 'scheduledStart';
+  static const scheduledEnd = 'scheduledEnd';
+  static const parentTaskId = 'parentTaskId';
+  static const backlogTags = 'backlogTags';
+  static const createdAt = 'createdAt';
+  static const updatedAt = 'updatedAt';
+  static const stats = 'stats';
+
+  static const all = <String>{
+    id,
+    title,
+    projectId,
+    type,
+    status,
+    priority,
+    reward,
+    difficulty,
+    durationMinutes,
+    scheduledStart,
+    scheduledEnd,
+    parentTaskId,
+    backlogTags,
+    createdAt,
+    updatedAt,
+    stats,
+  };
+}
+
+/// Document field names for [TaskStatistics] embedded documents.
+abstract final class TaskStatisticsDocumentFields {
+  static const skippedDuringBurnoutCount = 'skippedDuringBurnoutCount';
+  static const manuallyPushedCount = 'manuallyPushedCount';
+  static const autoPushedCount = 'autoPushedCount';
+  static const movedToBacklogCount = 'movedToBacklogCount';
+  static const restoredFromBacklogCount = 'restoredFromBacklogCount';
+  static const missedCount = 'missedCount';
+  static const cancelledCount = 'cancelledCount';
+  static const completedLateCount = 'completedLateCount';
+  static const completedDuringLockedHoursCount =
+      'completedDuringLockedHoursCount';
+  static const completedDuringLockedHoursMinutes =
+      'completedDuringLockedHoursMinutes';
+
+  static const all = <String>{
+    skippedDuringBurnoutCount,
+    manuallyPushedCount,
+    autoPushedCount,
+    movedToBacklogCount,
+    restoredFromBacklogCount,
+    missedCount,
+    cancelledCount,
+    completedLateCount,
+    completedDuringLockedHoursCount,
+    completedDuringLockedHoursMinutes,
+  };
+}
+
+/// Document field names for [ProjectProfile] documents.
+abstract final class ProjectDocumentFields {
+  static const id = DocumentFields.id;
+  static const name = 'name';
+  static const colorKey = 'colorKey';
+  static const defaultPriority = 'defaultPriority';
+  static const defaultReward = 'defaultReward';
+  static const defaultDifficulty = 'defaultDifficulty';
+  static const defaultReminderProfile = 'defaultReminderProfile';
+  static const defaultDurationMinutes = 'defaultDurationMinutes';
+
+  static const all = <String>{
+    id,
+    name,
+    colorKey,
+    defaultPriority,
+    defaultReward,
+    defaultDifficulty,
+    defaultReminderProfile,
+    defaultDurationMinutes,
+  };
+}
+
+/// Document field names for [ClockTime] embedded documents.
+abstract final class ClockTimeDocumentFields {
+  static const hour = 'hour';
+  static const minute = 'minute';
+
+  static const all = <String>{
+    hour,
+    minute,
+  };
+}
+
+/// Document field names for [LockedBlockRecurrence] embedded documents.
+abstract final class LockedBlockRecurrenceDocumentFields {
+  static const weekdays = 'weekdays';
+
+  static const all = <String>{
+    weekdays,
+  };
+}
+
+/// Document field names for [LockedBlock] documents.
+abstract final class LockedBlockDocumentFields {
+  static const id = DocumentFields.id;
+  static const name = 'name';
+  static const startTime = 'startTime';
+  static const endTime = 'endTime';
+  static const date = 'date';
+  static const recurrence = 'recurrence';
+  static const hiddenByDefault = 'hiddenByDefault';
+  static const projectId = 'projectId';
+  static const createdAt = 'createdAt';
+  static const updatedAt = 'updatedAt';
+
+  static const all = <String>{
+    id,
+    name,
+    startTime,
+    endTime,
+    date,
+    recurrence,
+    hiddenByDefault,
+    projectId,
+    createdAt,
+    updatedAt,
+  };
+}
+
+/// Document field names for [LockedBlockOverride] documents.
+abstract final class LockedBlockOverrideDocumentFields {
+  static const id = DocumentFields.id;
+  static const lockedBlockId = 'lockedBlockId';
+  static const date = 'date';
+  static const type = 'type';
+  static const name = 'name';
+  static const startTime = 'startTime';
+  static const endTime = 'endTime';
+  static const hiddenByDefault = 'hiddenByDefault';
+  static const projectId = 'projectId';
+  static const createdAt = 'createdAt';
+  static const updatedAt = 'updatedAt';
+
+  static const all = <String>{
+    id,
+    lockedBlockId,
+    date,
+    type,
+    name,
+    startTime,
+    endTime,
+    hiddenByDefault,
+    projectId,
+    createdAt,
+    updatedAt,
+  };
+}
+
+/// Document field names for [SchedulingStateSnapshot] documents.
+abstract final class SchedulingSnapshotDocumentFields {
+  static const id = DocumentFields.id;
+  static const capturedAt = 'capturedAt';
+  static const window = 'window';
+  static const tasks = 'tasks';
+  static const lockedIntervals = 'lockedIntervals';
+  static const requiredVisibleIntervals = 'requiredVisibleIntervals';
+  static const notices = 'notices';
+  static const changes = 'changes';
+  static const overlaps = 'overlaps';
+  static const operationName = 'operationName';
+
+  static const all = <String>{
+    id,
+    capturedAt,
+    window,
+    tasks,
+    lockedIntervals,
+    requiredVisibleIntervals,
+    notices,
+    changes,
+    overlaps,
+    operationName,
+  };
+}
+
+/// Document field names for [SchedulingWindow] embedded documents.
+abstract final class SchedulingWindowDocumentFields {
+  static const start = 'start';
+  static const end = 'end';
+
+  static const all = <String>{
+    start,
+    end,
+  };
+}
+
+/// Document field names for [TimeInterval] embedded documents.
+abstract final class TimeIntervalDocumentFields {
+  static const start = 'start';
+  static const end = 'end';
+  static const label = 'label';
+
+  static const all = <String>{
+    start,
+    end,
+    label,
+  };
+}
+
+/// Document field names for [SchedulingNotice] embedded documents.
+abstract final class SchedulingNoticeDocumentFields {
+  static const message = 'message';
+  static const type = 'type';
+  static const taskId = 'taskId';
+
+  static const all = <String>{
+    message,
+    type,
+    taskId,
+  };
+}
+
+/// Document field names for [SchedulingChange] embedded documents.
+abstract final class SchedulingChangeDocumentFields {
+  static const taskId = 'taskId';
+  static const previousStart = 'previousStart';
+  static const previousEnd = 'previousEnd';
+  static const nextStart = 'nextStart';
+  static const nextEnd = 'nextEnd';
+
+  static const all = <String>{
+    taskId,
+    previousStart,
+    previousEnd,
+    nextStart,
+    nextEnd,
+  };
+}
+
+/// Document field names for [SchedulingOverlap] embedded documents.
+abstract final class SchedulingOverlapDocumentFields {
+  static const taskId = 'taskId';
+  static const taskInterval = 'taskInterval';
+  static const blockedInterval = 'blockedInterval';
+
+  static const all = <String>{
+    taskId,
+    taskInterval,
+    blockedInterval,
+  };
+}
+
+/// Every field-name set currently committed for future document mapping.
+abstract final class PersistenceDocumentFieldSets {
+  static const all = <Set<String>>[
+    TaskDocumentFields.all,
+    TaskStatisticsDocumentFields.all,
+    ProjectDocumentFields.all,
+    ClockTimeDocumentFields.all,
+    LockedBlockRecurrenceDocumentFields.all,
+    LockedBlockDocumentFields.all,
+    LockedBlockOverrideDocumentFields.all,
+    SchedulingSnapshotDocumentFields.all,
+    SchedulingWindowDocumentFields.all,
+    TimeIntervalDocumentFields.all,
+    SchedulingNoticeDocumentFields.all,
+    SchedulingChangeDocumentFields.all,
+    SchedulingOverlapDocumentFields.all,
+  ];
+}
diff --git a/test/persistence_edge_cases_test.dart b/test/persistence_edge_cases_test.dart
new file mode 100644
index 0000000..c00c18c
--- /dev/null
+++ b/test/persistence_edge_cases_test.dart
@@ -0,0 +1,280 @@
+import 'package:adhd_scheduler_core/scheduler_core.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('Persistence edge-case regressions', () {
+    final createdAt = DateTime.utc(2026, 6, 22, 8);
+
+    test('task ids remain stable across copy and update operations', () {
+      final original = scheduledTask(
+        id: 'task-1',
+        createdAt: createdAt,
+      );
+
+      final updated = original.copyWith(
+        title: 'Updated title',
+        status: TaskStatus.active,
+        updatedAt: createdAt.add(const Duration(minutes: 5)),
+      );
+
+      expect(updated.id, original.id);
+      expect(updated.title, 'Updated title');
+      expect(updated.status, TaskStatus.active);
+    });
+
+    test('project ids remain stable across copy and update operations', () {
+      const original = ProjectProfile(
+        id: 'project-1',
+        name: 'Project',
+        colorKey: 'project-blue',
+      );
+
+      final updated = original.copyWith(
+        name: 'Renamed project',
+        colorKey: 'project-green',
+      );
+
+      expect(updated.id, original.id);
+      expect(updated.name, 'Renamed project');
+      expect(updated.colorKey, 'project-green');
+    });
+
+    test('locked block ids remain stable across copy and update operations',
+        () {
+      final original = LockedBlock(
+        id: 'locked-1',
+        name: 'Work',
+        startTime: const ClockTime(hour: 9, minute: 0),
+        endTime: const ClockTime(hour: 17, minute: 0),
+        recurrence: const LockedBlockRecurrence.weekly(
+          weekdays: {LockedWeekday.monday},
+        ),
+        createdAt: createdAt,
+        updatedAt: createdAt,
+      );
+
+      final updated = original.copyWith(
+        name: 'Adjusted work',
+        hiddenByDefault: false,
+        updatedAt: createdAt.add(const Duration(minutes: 10)),
+      );
+
+      expect(updated.id, original.id);
+      expect(updated.name, 'Adjusted work');
+      expect(updated.hiddenByDefault, isFalse);
+    });
+
+    test('DateTime persistence uses UTC ISO-8601 strings and UTC comparison',
+        () {
+      final pacificTime = DateTime.parse('2026-06-22T09:00:00-07:00');
+      final sameInstantUtc = DateTime.utc(2026, 6, 22, 16);
+
+      final stored = PersistenceDateTimeConvention.toStoredString(pacificTime);
+      final restored = PersistenceDateTimeConvention.fromStoredString(stored);
+
+      expect(PersistenceDateTimeConvention.description, contains('UTC'));
+      expect(stored, '2026-06-22T16:00:00.000Z');
+      expect(restored, sameInstantUtc);
+      expect(
+        PersistenceDateTimeConvention.compare(pacificTime, sameInstantUtc),
+        0,
+      );
+    });
+
+    test('nullable task fields are preserved unless explicitly cleared', () {
+      final original = scheduledTask(
+        id: 'nullable-task',
+        createdAt: createdAt,
+      ).copyWith(
+        priority: PriorityLevel.high,
+        parentTaskId: 'parent',
+      );
+
+      final preserved = original.copyWith(title: 'Updated');
+      final clearedSchedule = original.copyWith(clearSchedule: true);
+
+      expect(preserved.priority, PriorityLevel.high);
+      expect(preserved.durationMinutes, original.durationMinutes);
+      expect(preserved.scheduledStart, original.scheduledStart);
+      expect(preserved.scheduledEnd, original.scheduledEnd);
+      expect(preserved.parentTaskId, 'parent');
+
+      expect(clearedSchedule.scheduledStart, isNull);
+      expect(clearedSchedule.scheduledEnd, isNull);
+      expect(clearedSchedule.id, original.id);
+    });
+
+    test('enum persistence names stay stable and distinguish not set values',
+        () {
+      expect(TaskType.flexible.persistenceName, 'flexible');
+      expect(TaskStatus.backlog.persistenceName, 'backlog');
+      expect(PriorityLevel.veryHigh.persistenceName, 'veryHigh');
+      expect(RewardLevel.notSet.persistenceName, 'notSet');
+      expect(RewardLevel.veryLow.persistenceName, 'veryLow');
+      expect(DifficultyLevel.veryHard.persistenceName, 'veryHard');
+      expect(ReminderProfile.gentle.persistenceName, 'gentle');
+      expect(BacklogTag.wishlist.persistenceName, 'wishlist');
+      expect(LockedWeekday.monday.persistenceName, 'monday');
+      expect(LockedBlockOverrideType.replace.persistenceName, 'replace');
+
+      expect(
+        RewardLevel.notSet.persistenceName,
+        isNot(RewardLevel.veryLow.persistenceName),
+      );
+    });
+
+    test('backlog age behavior uses task creation timestamp', () {
+      final oldButRecentlyUpdated = Task.quickCapture(
+        id: 'old',
+        title: 'Old backlog idea',
+        createdAt: DateTime.utc(2026, 5, 1),
+        updatedAt: DateTime.utc(2026, 6, 21),
+      );
+      final view = BacklogView(
+        tasks: [oldButRecentlyUpdated],
+        now: DateTime.utc(2026, 6, 22),
+      );
+
+      expect(view.filter(BacklogFilter.stale), [oldButRecentlyUpdated]);
+      expect(
+        view.stalenessMarkerFor(oldButRecentlyUpdated),
+        BacklogStalenessMarker.purple,
+      );
+    });
+
+    test('in-memory repositories round-trip scheduling fields', () async {
+      final task = scheduledTask(
+        id: 'scheduled',
+        createdAt: createdAt,
+      );
+      final repository = InMemoryTaskRepository();
+
+      await repository.save(task);
+      final saved = await repository.findById(task.id);
+
+      expect(saved, isNotNull);
+      expect(saved!.id, task.id);
+      expect(saved.scheduledStart, task.scheduledStart);
+      expect(saved.scheduledEnd, task.scheduledEnd);
+      expect(saved.durationMinutes, task.durationMinutes);
+      expect(saved.projectId, task.projectId);
+      expect(saved.reward, task.reward);
+      expect(saved.difficulty, task.difficulty);
+    });
+
+    test('repository read operations do not expose mutable collections',
+        () async {
+      final original = scheduledTask(
+        id: 'immutable',
+        createdAt: createdAt,
+      );
+      final repository = InMemoryTaskRepository([original]);
+
+      final savedList = await repository.findAll();
+
+      expect(() => savedList.add(original), throwsUnsupportedError);
+      expect((await repository.findAll()).map((task) => task.id), [
+        'immutable',
+      ]);
+      expect(original.scheduledStart, DateTime.utc(2026, 6, 22, 9));
+    });
+
+    test('document field sets preserve all task and statistics fields', () {
+      expect(TaskDocumentFields.all, {
+        '_id',
+        'title',
+        'projectId',
+        'type',
+        'status',
+        'priority',
+        'reward',
+        'difficulty',
+        'durationMinutes',
+        'scheduledStart',
+        'scheduledEnd',
+        'parentTaskId',
+        'backlogTags',
+        'createdAt',
+        'updatedAt',
+        'stats',
+      });
+      expect(TaskStatisticsDocumentFields.all, {
+        'skippedDuringBurnoutCount',
+        'manuallyPushedCount',
+        'autoPushedCount',
+        'movedToBacklogCount',
+        'restoredFromBacklogCount',
+        'missedCount',
+        'cancelledCount',
+        'completedLateCount',
+        'completedDuringLockedHoursCount',
+        'completedDuringLockedHoursMinutes',
+      });
+    });
+
+    test('document field sets cover project locked and snapshot documents', () {
+      expect(ProjectDocumentFields.all, containsAll(['_id', 'colorKey']));
+      expect(
+        LockedBlockDocumentFields.all,
+        containsAll(['_id', 'startTime', 'recurrence', 'hiddenByDefault']),
+      );
+      expect(
+        LockedBlockOverrideDocumentFields.all,
+        containsAll(['_id', 'lockedBlockId', 'type']),
+      );
+      expect(
+        SchedulingSnapshotDocumentFields.all,
+        containsAll([
+          '_id',
+          'capturedAt',
+          'window',
+          'tasks',
+          'lockedIntervals',
+          'requiredVisibleIntervals',
+          'notices',
+          'changes',
+          'overlaps',
+          'operationName',
+        ]),
+      );
+    });
+
+    test('document field names are stable and migration-friendly', () {
+      for (final fieldSet in PersistenceDocumentFieldSets.all) {
+        expect(fieldSet, isNotEmpty);
+        for (final fieldName in fieldSet) {
+          expect(fieldName, isNotEmpty);
+          expect(fieldName.trim(), fieldName);
+          expect(fieldName.contains('.'), isFalse, reason: fieldName);
+          expect(fieldName.startsWith(r'$'), isFalse, reason: fieldName);
+        }
+      }
+
+      expect(DocumentFields.id, '_id');
+      expect(TaskDocumentFields.projectId, 'projectId');
+      expect(TaskDocumentFields.scheduledStart, 'scheduledStart');
+      expect(TaskDocumentFields.scheduledEnd, 'scheduledEnd');
+    });
+  });
+}
+
+Task scheduledTask({
+  required String id,
+  required DateTime createdAt,
+}) {
+  return Task(
+    id: id,
+    title: 'Scheduled task',
+    projectId: 'project-1',
+    type: TaskType.flexible,
+    status: TaskStatus.planned,
+    priority: PriorityLevel.medium,
+    reward: RewardLevel.high,
+    difficulty: DifficultyLevel.medium,
+    durationMinutes: 30,
+    scheduledStart: DateTime.utc(2026, 6, 22, 9),
+    scheduledEnd: DateTime.utc(2026, 6, 22, 9, 30),
+    createdAt: createdAt,
+    updatedAt: createdAt,
+  );
+}