fix(api): derive habit DueDate from the user's timezone, not UTC (#243)

src/Orbit.Application/Chat/Tools/Implementations/CreateHabitTool.cs

@@ -188,10 +188,10 @@
 
         return Habit.Create(new HabitCreateParams(
             userId, title, frequencyUnit, frequencyQuantity,
+            JsonArgumentParser.ParseDateOnly(args, "due_date") ?? today,
             JsonArgumentParser.GetOptionalString(args, "description"),
             Days: JsonArgumentParser.ParseDays(args),
             IsBadHabit: isBadHabit,
-            DueDate: JsonArgumentParser.ParseDateOnly(args, "due_date") ?? today,
             DueTime: JsonArgumentParser.ParseTimeOnly(args, "due_time"),
             ReminderEnabled: JsonArgumentParser.GetOptionalBool(args, "reminder_enabled") ?? false,
             ReminderTimes: JsonArgumentParser.ParseIntArray(args, "reminder_times"),
@@ -244,10 +244,10 @@
             JsonArgumentParser.GetOptionalString(sub, TitleProperty) ?? "Untitled",
             JsonArgumentParser.ParseFrequencyUnit(sub) ?? parentFreqUnit,
             JsonArgumentParser.GetOptionalInt(sub, "frequency_quantity") ?? parentFreqQty,
+            JsonArgumentParser.ParseDateOnly(sub, "due_date") ?? parentDueDate,
             JsonArgumentParser.GetOptionalString(sub, "description"),
             Days: subDays,
             IsBadHabit: JsonArgumentParser.GetOptionalBool(sub, "is_bad_habit") ?? false,
-            DueDate: JsonArgumentParser.ParseDateOnly(sub, "due_date") ?? parentDueDate,
             ParentHabitId: parentId,
             Emoji: JsonArgumentParser.GetOptionalString(sub, "emoji"),
             ChecklistItems: JsonArgumentParser.ParseChecklistItems(sub)));
@@ -329,7 +329,7 @@
         string.IsNullOrEmpty(s) ? s : char.ToUpper(s[0]) + s[1..].ToLower();
 
     private static readonly System.Text.RegularExpressions.Regex HabitWordRegex =
         new(@"\bhabit\b", System.Text.RegularExpressions.RegexOptions.IgnoreCase | System.Text.RegularExpressions.RegexOptions.Compiled);
 
     private static bool IsHabitFlavoredTitle(string title)
     {

src/Orbit.Application/Habits/Commands/BulkCreateHabitsCommand.cs

@@ -49,7 +49,7 @@
 
 public enum BulkItemStatus { Success, Failed }
 
 public partial class BulkCreateHabitsCommandHandler(
     IGenericRepository<Habit> habitRepository,
     IGenericRepository<GoogleCalendarSyncSuggestion> suggestionRepository,
     IGenericRepository<Tag> tagRepository,
@@ -122,11 +122,11 @@
                 item.Title,
                 item.FrequencyUnit,
                 item.FrequencyQuantity,
+                item.DueDate ?? userToday,
                 item.Description,
                 Emoji: item.Emoji,
                 Days: item.Days,
                 IsBadHabit: item.IsBadHabit,
-                DueDate: item.DueDate ?? userToday,
                 DueTime: item.DueTime,
                 DueEndTime: item.DueEndTime,
                 ReminderEnabled: item.ReminderEnabled,
@@ -163,11 +163,11 @@
                         subItem.Title,
                         subItem.FrequencyUnit ?? item.FrequencyUnit,
                         subItem.FrequencyQuantity ?? item.FrequencyQuantity,
+                        subItem.DueDate ?? item.DueDate ?? userToday,
                         subItem.Description,
                         Emoji: subItem.Emoji,
                         Days: subItem.Days ?? item.Days,
                         IsBadHabit: subItem.IsBadHabit,
-                        DueDate: subItem.DueDate ?? item.DueDate ?? userToday,
                         ParentHabitId: parentHabit.Id,
                         IsGeneral: item.IsGeneral,
                         IsFlexible: subItem.IsFlexible,

src/Orbit.Application/Habits/Commands/CreateHabitCommand.cs

@@ -41,7 +41,7 @@
     IMemoryCache cache,
     ILogger<CreateHabitCommandHandler> logger) : IRequestHandler<CreateHabitCommand, Result<Guid>>
 {
     public async Task<Result<Guid>> Handle(CreateHabitCommand request, CancellationToken cancellationToken)
     {
         var opts = request.Options ?? new HabitCommandOptions();
 
@@ -90,11 +90,11 @@
             request.Title,
             request.FrequencyUnit,
             request.FrequencyQuantity,
+            dueDate,
             request.Description,
             Emoji: request.Emoji,
             Days: opts.Days,
             IsBadHabit: request.IsBadHabit,
-            DueDate: dueDate,
             DueTime: opts.DueTime,
             DueEndTime: opts.DueEndTime,
             ReminderEnabled: opts.ReminderEnabled,
@@ -145,7 +145,7 @@
                 subTitle,
                 request.FrequencyUnit,
                 request.FrequencyQuantity,
-                DueDate: request.DueDate ?? dueDate,
+                request.DueDate ?? dueDate,
                 ParentHabitId: parentId,
                 IsGeneral: request.IsGeneral,
                 EndDate: opts.EndDate,

src/Orbit.Application/Habits/Commands/CreateSubHabitCommand.cs

@@ -66,11 +66,11 @@ public async Task<Result<Guid>> Handle(CreateSubHabitCommand request, Cancellati
             request.Title,
             request.FrequencyUnit ?? parent.FrequencyUnit,
             request.FrequencyQuantity ?? parent.FrequencyQuantity,
+            childDueDate,
             request.Description,
             Emoji: request.Emoji,
             Days: opts.Days,
             IsBadHabit: request.IsBadHabit,
-            DueDate: childDueDate,
             DueTime: opts.DueTime,
             DueEndTime: opts.DueEndTime,
             ParentHabitId: parent.Id,

src/Orbit.Application/Habits/Commands/DuplicateHabitCommand.cs

@@ -130,11 +130,11 @@ private static Result<Habit> CloneHabit(
             source.Title,
             source.FrequencyUnit,
             source.FrequencyQuantity,
+            source.DueDate,
             source.Description,
             Emoji: source.Emoji,
             Days: source.Days.ToList(),
             IsBadHabit: source.IsBadHabit,
-            DueDate: source.DueDate,
             DueTime: source.DueTime,
             DueEndTime: source.DueEndTime,
             ParentHabitId: parentHabitId,

src/Orbit.Application/Profile/Commands/ApplyOnboardingCommand.cs

@@ -57,7 +57,7 @@
 /// by construction — an already-onboarded user is a no-op (<c>Applied:false</c>) — so the client can
 /// flush unconditionally after any successful auth and retry safely under the concurrency pipeline.
 /// </summary>
 public class ApplyOnboardingCommandHandler(
     IGenericRepository<User> userRepository,
     IGenericRepository<Habit> habitRepository,
     IGenericRepository<Goal> goalRepository,
@@ -67,7 +67,7 @@
     IUnitOfWork unitOfWork,
     IMemoryCache cache) : IRequestHandler<ApplyOnboardingCommand, Result<ApplyOnboardingResponse>>
 {
     public async Task<Result<ApplyOnboardingResponse>> Handle(
         ApplyOnboardingCommand request, CancellationToken cancellationToken)
     {
         var result = await unitOfWork.ExecuteInTransactionAsync(async ct =>
@@ -155,11 +155,11 @@
                 item.Title,
                 item.FrequencyUnit,
                 item.FrequencyQuantity,
+                item.DueDate ?? today,
                 item.Description,
                 Emoji: item.Emoji,
                 Days: item.Days,
                 IsBadHabit: item.IsBadHabit,
-                DueDate: item.DueDate ?? today,
                 DueTime: item.DueTime,
                 ReminderEnabled: item.ReminderEnabled,
                 ReminderTimes: item.ReminderTimes,

src/Orbit.Domain/Entities/Habit.cs

@@ -11,10 +11,10 @@ public record HabitCreateParams(
     string Title,
     FrequencyUnit? FrequencyUnit,
     int? FrequencyQuantity,
+    DateOnly DueDate,
     string? Description = null,
     IReadOnlyList<System.DayOfWeek>? Days = null,
     bool IsBadHabit = false,
-    DateOnly? DueDate = null,
     TimeOnly? DueTime = null,
     TimeOnly? DueEndTime = null,
     Guid? ParentHabitId = null,
@@ -129,8 +129,6 @@ public static Result<Habit> Create(HabitCreateParams p)
         if (reminderValidation is not null)
             return Result.Failure<Habit>(reminderValidation);
 
-        var effectiveDueDate = p.DueDate ?? DateOnly.FromDateTime(DateTime.UtcNow);
-
         return Result.Success(new Habit
         {
             UserId = p.UserId,
@@ -143,9 +141,9 @@ public static Result<Habit> Create(HabitCreateParams p)
             IsBadHabit = p.IsBadHabit,
             IsGeneral = p.IsGeneral,
             IsFlexible = p.IsFlexible,
-            DueDate = effectiveDueDate,
+            DueDate = p.DueDate,
             OriginalDayOfMonth = p.FrequencyUnit is Enums.FrequencyUnit.Month or Enums.FrequencyUnit.Year
-                ? effectiveDueDate.Day
+                ? p.DueDate.Day
                 : null,
             DueTime = p.DueTime,
             DueEndTime = p.DueEndTime,

src/Orbit.Domain/Entities/HabitInvariants.cs

@@ -41,16 +41,15 @@ internal static class HabitInvariants
     public static AppError? ValidateDateOptions(
         TimeOnly? dueTime, TimeOnly? dueEndTime,
         DateOnly? endDate, FrequencyUnit? frequencyUnit,
-        bool isGeneral, DateOnly? dueDate)
+        bool isGeneral, DateOnly dueDate)
     {
         if (dueEndTime.HasValue && dueTime.HasValue && dueEndTime.Value <= dueTime.Value)
             return DomainErrors.EndTimeBeforeStartTime;
 
         if (endDate.HasValue && frequencyUnit is null && !isGeneral)
             return DomainErrors.OneTimeTaskHasEndDate;
 
-        var effectiveDueDate = dueDate ?? DateOnly.FromDateTime(DateTime.UtcNow);
-        if (endDate.HasValue && endDate.Value < effectiveDueDate)
+        if (endDate.HasValue && endDate.Value < dueDate)
             return DomainErrors.EndDateBeforeStartDate;
 
         return null;

tests/Orbit.Application.Tests/Chat/QueryHabitsToolTests.cs

@@ -454,7 +454,7 @@ private static Habit CreateHabit(
         string? emoji = null)
     {
         var habit = Habit.Create(new HabitCreateParams(UserId, title, freq, qty,
-            DueDate: dueDate, IsBadHabit: isBadHabit, IsGeneral: isGeneral,
+            DueDate: dueDate ?? DateOnly.FromDateTime(DateTime.UtcNow), IsBadHabit: isBadHabit, IsGeneral: isGeneral,
             ParentHabitId: parentId, Emoji: emoji)).Value;
         if (position.HasValue) habit.SetPosition(position.Value);
         return habit;

tests/Orbit.Application.Tests/Commands/Calendar/RunCalendarAutoSyncCommandHandlerTests.cs

@@ -185,6 +185,7 @@ public async Task Handle_Success_DedupesAgainstExistingHabits()
 
         var existingHabit = Habit.Create(new HabitCreateParams(
             user.Id, "Daily standup", FrequencyUnit.Day, 1,
+            DueDate: DateOnly.FromDateTime(DateTime.UtcNow),
             GoogleEventId: "evt_a")).Value;
         _habitRepo.FindAsync(Arg.Any<Expression<Func<Habit, bool>>>(), Arg.Any<CancellationToken>())
             .Returns(new List<Habit> { existingHabit }.AsReadOnly());
@@ -659,7 +660,7 @@ public async Task Handle_UniqueViolationButNoNewSuggestions_Propagates()
             .Returns(new GoogleTokenRefreshOutcome("new_access", GoogleTokenRefreshResult.Success, null));
 
         var existingHabit = Habit.Create(new HabitCreateParams(
-            user.Id, "Standup", FrequencyUnit.Day, 1, GoogleEventId: "evt_a")).Value;
+            user.Id, "Standup", FrequencyUnit.Day, 1, DueDate: DateOnly.FromDateTime(DateTime.UtcNow), GoogleEventId: "evt_a")).Value;
         _habitRepo.FindAsync(Arg.Any<Expression<Func<Habit, bool>>>(), Arg.Any<CancellationToken>())
             .Returns(new List<Habit> { existingHabit }.AsReadOnly());
         _fetcher.FetchAsync(Arg.Any<string>(), Arg.Any<IReadOnlyCollection<string>?>(), Arg.Any<DateTime?>(), Arg.Any<CancellationToken>())

tests/Orbit.Application.Tests/Commands/Goals/LinkHabitsToGoalCommandHandlerTests.cs

@@ -32,8 +32,8 @@ public LinkHabitsToGoalCommandHandlerTests()
     public async Task Handle_ValidLink_LinksHabitsToGoal()
     {
         var goal = Goal.Create(UserId, "Goal", 100, "km").Value;
-        var habit1 = Habit.Create(new HabitCreateParams(UserId, "Habit 1", FrequencyUnit.Day, 1)).Value;
-        var habit2 = Habit.Create(new HabitCreateParams(UserId, "Habit 2", FrequencyUnit.Day, 1)).Value;
+        var habit1 = Habit.Create(new HabitCreateParams(UserId, "Habit 1", FrequencyUnit.Day, 1, DueDate: DateOnly.FromDateTime(DateTime.UtcNow))).Value;
+        var habit2 = Habit.Create(new HabitCreateParams(UserId, "Habit 2", FrequencyUnit.Day, 1, DueDate: DateOnly.FromDateTime(DateTime.UtcNow))).Value;
 
         _goalRepo.FindOneTrackedAsync(
             Arg.Any<Expression<Func<Goal, bool>>>(),
@@ -91,7 +91,7 @@ public async Task Handle_TooManyHabits_ReturnsFailure()
     public async Task Handle_EmptyHabitList_ClearsExistingLinks()
     {
         var goal = Goal.Create(UserId, "Goal", 100, "km").Value;
-        var existingHabit = Habit.Create(new HabitCreateParams(UserId, "Existing", FrequencyUnit.Day, 1)).Value;
+        var existingHabit = Habit.Create(new HabitCreateParams(UserId, "Existing", FrequencyUnit.Day, 1, DueDate: DateOnly.FromDateTime(DateTime.UtcNow))).Value;
         goal.AddHabit(existingHabit);
 
         _goalRepo.FindOneTrackedAsync(
@@ -117,8 +117,8 @@ public async Task Handle_EmptyHabitList_ClearsExistingLinks()
     public async Task Handle_ReplacesExistingLinks()
     {
         var goal = Goal.Create(UserId, "Goal", 100, "km").Value;
-        var oldHabit = Habit.Create(new HabitCreateParams(UserId, "Old", FrequencyUnit.Day, 1)).Value;
-        var newHabit = Habit.Create(new HabitCreateParams(UserId, "New", FrequencyUnit.Day, 1)).Value;
+        var oldHabit = Habit.Create(new HabitCreateParams(UserId, "Old", FrequencyUnit.Day, 1, DueDate: DateOnly.FromDateTime(DateTime.UtcNow))).Value;
+        var newHabit = Habit.Create(new HabitCreateParams(UserId, "New", FrequencyUnit.Day, 1, DueDate: DateOnly.FromDateTime(DateTime.UtcNow))).Value;
         goal.AddHabit(oldHabit);
 
         _goalRepo.FindOneTrackedAsync(
@@ -161,7 +161,7 @@ public async Task Handle_PaywalledUser_ReturnsPayGateFailure()
     public async Task Handle_ForeignOrMissingHabitId_ReturnsFailureWithoutClearing()
     {
         var goal = Goal.Create(UserId, "Goal", 100, "km").Value;
-        var existingHabit = Habit.Create(new HabitCreateParams(UserId, "Existing", FrequencyUnit.Day, 1)).Value;
+        var existingHabit = Habit.Create(new HabitCreateParams(UserId, "Existing", FrequencyUnit.Day, 1, DueDate: DateOnly.FromDateTime(DateTime.UtcNow))).Value;
         goal.AddHabit(existingHabit);
 
         _goalRepo.FindOneTrackedAsync(

tests/Orbit.Application.Tests/Commands/Habits/BulkDeleteHabitsCommandHandlerTests.cs

@@ -40,8 +40,8 @@ public BulkDeleteHabitsCommandHandlerTests()
     [Fact]
     public async Task Handle_ValidIds_DeletesAllHabits()
     {
-        var habit1 = Habit.Create(new HabitCreateParams(UserId, "Habit 1", FrequencyUnit.Day, 1)).Value;
-        var habit2 = Habit.Create(new HabitCreateParams(UserId, "Habit 2", FrequencyUnit.Day, 1)).Value;
+        var habit1 = Habit.Create(new HabitCreateParams(UserId, "Habit 1", FrequencyUnit.Day, 1, DueDate: DateOnly.FromDateTime(DateTime.UtcNow))).Value;
+        var habit2 = Habit.Create(new HabitCreateParams(UserId, "Habit 2", FrequencyUnit.Day, 1, DueDate: DateOnly.FromDateTime(DateTime.UtcNow))).Value;
 
         _habitRepo.FindTrackedAsync(
             Arg.Any<Expression<Func<Habit, bool>>>(),
@@ -66,7 +66,7 @@ await _unitOfWork.Received(1).ExecuteInTransactionAsync(
     [Fact]
     public async Task Handle_SomeNotFound_ReportsPartialFailure()
     {
-        var habit1 = Habit.Create(new HabitCreateParams(UserId, "Habit 1", FrequencyUnit.Day, 1)).Value;
+        var habit1 = Habit.Create(new HabitCreateParams(UserId, "Habit 1", FrequencyUnit.Day, 1, DueDate: DateOnly.FromDateTime(DateTime.UtcNow))).Value;
         var missingId = Guid.NewGuid();
 
         _habitRepo.FindTrackedAsync(
@@ -105,7 +105,7 @@ public async Task Handle_AllNotFound_ReportsAllFailed()
     [Fact]
     public async Task Handle_InvalidatesSummaryCache()
     {
-        var habit = Habit.Create(new HabitCreateParams(UserId, "Habit", FrequencyUnit.Day, 1)).Value;
+        var habit = Habit.Create(new HabitCreateParams(UserId, "Habit", FrequencyUnit.Day, 1, DueDate: DateOnly.FromDateTime(DateTime.UtcNow))).Value;
         _habitRepo.FindTrackedAsync(
             Arg.Any<Expression<Func<Habit, bool>>>(),
             Arg.Any<CancellationToken>())

tests/Orbit.Application.Tests/Commands/Habits/CreateHabitCommandHandlerTests.cs

@@ -324,6 +324,25 @@ await _habitRepo.Received(1).AddAsync(
             Arg.Any<CancellationToken>());
     }
 
+    [Fact]
+    public async Task Handle_UserTimezoneAheadOfUtc_UsesUserTodayNotUtcToday()
+    {
+        var utcToday = DateOnly.FromDateTime(DateTime.UtcNow);
+        var userToday = utcToday.AddDays(1);
+        _userDateService.GetUserTodayAsync(Arg.Any<Guid>(), Arg.Any<CancellationToken>())
+            .Returns(userToday);
+
+        var command = new CreateHabitCommand(
+            UserId, "Timezone Habit", null, FrequencyUnit.Day, 1);
+
+        var result = await _handler.Handle(command, CancellationToken.None);
+
+        result.IsSuccess.Should().BeTrue();
+        await _habitRepo.Received(1).AddAsync(
+            Arg.Is<Habit>(h => h.DueDate == userToday && h.DueDate != utcToday),
+            Arg.Any<CancellationToken>());
+    }
+
     [Fact]
     public async Task Handle_WithOptions_PassesDaysAndTimes()
     {

tests/Orbit.Application.Tests/Commands/Habits/DuplicateHabitCommandHandlerTests.cs

@@ -71,7 +71,7 @@ public async Task Handle_HabitNotFound_ReturnsFailure()
     [Fact]
     public async Task Handle_PayGateLimitReached_ReturnsPayGateFailure()
     {
-        var original = Habit.Create(new HabitCreateParams(UserId, "Habit", FrequencyUnit.Day, 1)).Value;
+        var original = Habit.Create(new HabitCreateParams(UserId, "Habit", FrequencyUnit.Day, 1, DueDate: DateOnly.FromDateTime(DateTime.UtcNow))).Value;
         SetupAllHabitsForUser(new List<Habit> { original });
 
         _payGate.CanCreateHabits(Arg.Any<Guid>(), Arg.Any<int>(), Arg.Any<CancellationToken>())
@@ -118,10 +118,10 @@ await _habitRepo.Received(1).AddAsync(
     public async Task Handle_WithChildren_DuplicatesChildHabits()
     {
         var parent = Habit.Create(new HabitCreateParams(
-            UserId, "Morning Routine", FrequencyUnit.Day, 1)).Value;
+            UserId, "Morning Routine", FrequencyUnit.Day, 1, DueDate: DateOnly.FromDateTime(DateTime.UtcNow))).Value;
         var child = Habit.Create(new HabitCreateParams(
             UserId, "Brush teeth", FrequencyUnit.Day, 1,
-            ParentHabitId: parent.Id)).Value;
+            ParentHabitId: parent.Id, DueDate: DateOnly.FromDateTime(DateTime.UtcNow))).Value;
 
         SetupAllHabitsForUser(new List<Habit> { parent, child });
 
@@ -138,10 +138,10 @@ public async Task Handle_WithChildren_DuplicatesChildHabits()
     public async Task Handle_WithChildren_SubHabitPayGated_ReturnsFailure()
     {
         var parent = Habit.Create(new HabitCreateParams(
-            UserId, "Routine", FrequencyUnit.Day, 1)).Value;
+            UserId, "Routine", FrequencyUnit.Day, 1, DueDate: DateOnly.FromDateTime(DateTime.UtcNow))).Value;
         var child = Habit.Create(new HabitCreateParams(
             UserId, "Sub", FrequencyUnit.Day, 1,
-            ParentHabitId: parent.Id)).Value;
+            ParentHabitId: parent.Id, DueDate: DateOnly.FromDateTime(DateTime.UtcNow))).Value;
 
         SetupAllHabitsForUser(new List<Habit> { parent, child });
 
@@ -159,7 +159,7 @@ public async Task Handle_WithChildren_SubHabitPayGated_ReturnsFailure()
     [Fact]
     public async Task Handle_InvalidatesSummaryCache()
     {
-        var original = Habit.Create(new HabitCreateParams(UserId, "Habit", FrequencyUnit.Day, 1)).Value;
+        var original = Habit.Create(new HabitCreateParams(UserId, "Habit", FrequencyUnit.Day, 1, DueDate: DateOnly.FromDateTime(DateTime.UtcNow))).Value;
         SetupAllHabitsForUser(new List<Habit> { original });
 
         var realToday = DateOnly.FromDateTime(DateTime.UtcNow);
@@ -199,10 +199,10 @@ public async Task Handle_CompletedOneTimeTask_PreservesCompletionOnDuplicate()
     public async Task Handle_CompletedOneTimeChild_PreservesCompletionOnDuplicatedChild()
     {
         var parent = Habit.Create(new HabitCreateParams(
-            UserId, "Plan trip", FrequencyUnit.Day, 1)).Value;
+            UserId, "Plan trip", FrequencyUnit.Day, 1, DueDate: DateOnly.FromDateTime(DateTime.UtcNow))).Value;
         var child = Habit.Create(new HabitCreateParams(
             UserId, "Book hotel", null, null,
-            ParentHabitId: parent.Id)).Value;
+            ParentHabitId: parent.Id, DueDate: DateOnly.FromDateTime(DateTime.UtcNow))).Value;
         child.Log(new DateOnly(2026, 6, 3)).IsSuccess.Should().BeTrue();
 
         SetupAllHabitsForUser(new List<Habit> { parent, child });
@@ -223,7 +223,7 @@ public async Task Handle_CompletedOneTimeChild_PreservesCompletionOnDuplicatedCh
     [Fact]
     public async Task Handle_UncompletedOneTimeTask_StaysUncompleted()
     {
-        var original = Habit.Create(new HabitCreateParams(UserId, "Renew passport", null, null)).Value;
+        var original = Habit.Create(new HabitCreateParams(UserId, "Renew passport", null, null, DueDate: DateOnly.FromDateTime(DateTime.UtcNow))).Value;
 
         SetupAllHabitsForUser(new List<Habit> { original });
         var added = CaptureAddedHabits();