fix(api): keep schedule Instances/ScheduledDates consistent + Stripe session idempotency (#403 follow-up)

src/Orbit.Application/Habits/Queries/GetHabitScheduleQuery.cs

@@ -214,6 +214,8 @@ private async Task<Result<PaginatedResponse<HabitScheduleItem>>> HandleScheduled
 
         var dateFrom = request.DateFrom.Value;
         var dateTo = request.DateTo.Value;
+        if (dateTo.DayNumber - dateFrom.DayNumber > AppConstants.MaxInstanceHorizonDays)
+            dateTo = dateFrom.AddDays(AppConstants.MaxInstanceHorizonDays);
 
         var filtered = HabitScheduleFilters.FilterScheduledHabits(topLevel, dateFrom, dateTo, request.IncludeOverdue, lookup, weekStartDay);
 

src/Orbit.Infrastructure/Services/StripeBillingService.cs

@@ -75,8 +75,10 @@ public async Task<string> CreateCheckoutSessionAsync(
                 options.AllowPromotionCodes = true;
             }
 
+            var idempotencyKey = $"orbit-checkout-{userId}-{priceId}-{referralCouponId ?? "std"}";
             var session = await StripeRetryPolicy.ExecuteWithRetryAsync(
-                () => clients.CheckoutSessions.CreateAsync(options, cancellationToken: cancellationToken),
+                () => clients.CheckoutSessions.CreateAsync(
+                    options, new RequestOptions { IdempotencyKey = idempotencyKey }, cancellationToken),
                 cancellationToken);
             return session.Url;
         }
@@ -90,12 +92,13 @@ public async Task<string> CreatePortalSessionAsync(string customerId, string ret
     {
         try
         {
+            var idempotencyKey = $"orbit-portal-{customerId}";
             var session = await StripeRetryPolicy.ExecuteWithRetryAsync(
                 () => clients.PortalSessions.CreateAsync(new Stripe.BillingPortal.SessionCreateOptions
                 {
                     Customer = customerId,
                     ReturnUrl = returnUrl,
-                }, cancellationToken: cancellationToken),
+                }, new RequestOptions { IdempotencyKey = idempotencyKey }, cancellationToken),
                 cancellationToken);
             return session.Url;
         }

tests/Orbit.Application.Tests/Queries/Habits/GetHabitScheduleQueryHandlerTests.cs

@@ -83,6 +83,26 @@ public async Task Handle_SingleDailyHabitInRange_ReturnsHabit()
         result.Value.Items[0].Title.Should().Be("Test Habit");
     }
 
+    [Fact]
+    public async Task Handle_RangeExceedingHorizon_BoundsScheduledDatesAndInstancesConsistently()
+    {
+        var habit = CreateTestHabit(dueDate: Today);
+        SetupHabits(habit);
+        var query = new GetHabitScheduleQuery(UserId, Today, Today.AddDays(200));
+
+        var result = await _handler.Handle(query, CancellationToken.None);
+
+        result.IsSuccess.Should().BeTrue();
+        result.Value.Items.Should().HaveCount(1);
+        var item = result.Value.Items[0];
+        var horizonEnd = Today.AddDays(AppConstants.MaxInstanceHorizonDays);
+
+        item.ScheduledDates.Should().NotBeEmpty();
+        item.ScheduledDates.Max().Should().Be(horizonEnd);
+        item.Instances.Should().NotBeEmpty();
+        item.Instances.Select(i => i.Date).Max().Should().Be(horizonEnd);
+    }
+
     [Fact]
     public async Task Handle_OneTimeTaskOverdue_WhenIncludeOverdue_ReturnsAsOverdue()
     {