test: pin add-on across week-only toggles and date-less edits

Keep the add-on recalculation on the week-only toggle so a future schedule
side effect cannot leave a stale tag, and cover that a toggle and an edit
without Schedule On leave Add-On unchanged.

SeaHaven.Services/Implementation/WorkOrderBoardUpdateService.cs

@@ -823,12 +823,15 @@ namespace SeaHaven.Services.Implementation
             return changes;
         }
 
-        // Toggling week-only mode keeps the scheduled week, so Add-On is unchanged (SH-412).
-        private static List<FieldChange> ApplyScheduleWeekOnly(WorkOrder workOrder, string? value, string auditField)
+        private List<FieldChange> ApplyScheduleWeekOnly(WorkOrder workOrder, string? value, string auditField)
         {
+            var previousDate = workOrder.ScheduledDate;
+            var previousTargetWeek = workOrder.TargetWeek;
             var change = ApplyBoolField(value, auditField, v => workOrder.ScheduleWeekOnly = v, () => workOrder.ScheduleWeekOnly);
             var changes = new List<FieldChange> { change };
             changes.AddRange(ApplyAutoScheduleSideEffects(workOrder));
+            if (change.HasChanged)
+                AppendIsAddOnRecalculation(workOrder, previousDate, previousTargetWeek, changes);
             return changes;
         }
 

SeaHavenIndustries.Tests/WorkOrderBoardUpdateServiceTests.cs

@@ -2267,6 +2267,42 @@ public class WorkOrderBoardUpdateServiceTests
         Assert.True(persisted.IsAddOn);
     }
 
+    [Theory]
+    [InlineData(true, "true")]
+    [InlineData(false, "true")]
+    [InlineData(true, "false")]
+    [InlineData(false, "false")]
+    public async Task PatchField_ScheduleWeekOnlyToggle_KeepsIsAddOn(bool isAddOn, string weekOnly)
+    {
+        var (context, service) = CreateSut(new FixedTimeProvider());
+        var wo = new WorkOrder
+        {
+            Id = 1,
+            LifecycleStatus = weekOnly == "true" ? LifecycleStatus.Scheduled : LifecycleStatus.Pending,
+            WorkOrderType = WorkOrderType.PM,
+            ScheduledDate = new DateTime(2026, 6, 25),
+            ScheduleWeekOnly = weekOnly != "true",
+            CreatedDate = new DateTime(2026, 6, 1, 0, 0, 0, DateTimeKind.Utc),
+            IsAddOn = isAddOn,
+            RowVersion = new byte[] { 1, 0, 0, 0, 0, 0, 0, 1 }
+        };
+        context.workOrders.Add(wo);
+        await context.SaveChangesAsync();
+
+        var result = await service.PatchFieldAsync(1, new WorkOrderBoardPatchRequestDto
+        {
+            Field = WorkOrderBoardFieldNames.ScheduleWeekOnly,
+            Value = weekOnly,
+            WorkOrderVersion = ToVersion(wo)
+        }, "actor-1");
+
+        Assert.Equal(isAddOn, result.IsAddOn);
+        var persisted = await context.workOrders.SingleAsync(w => w.Id == 1);
+        Assert.Equal(new DateTime(2026, 6, 25), persisted.ScheduledDate);
+        Assert.Equal(isAddOn, persisted.IsAddOn);
+        Assert.Empty(await context.WorkOrderAuditLogs.Where(a => a.FieldName == "IsAddOn").ToListAsync());
+    }
+
     [Theory]
     [InlineData("2026-07-08", false, "2026-06-25", true)]  // into the current week, past its cutoff
     [InlineData("2026-06-24", true, "2026-07-01", false)]  // into next week, before its cutoff

SeaHavenIndustries.Tests/WorkOrderEditAddonRescheduleTests.cs

@@ -129,6 +129,36 @@ public sealed class WorkOrderEditAddonRescheduleTests
         Assert.DoesNotContain("IsAddOn", audit.FieldName);
     }
 
+    [Fact]
+    public async Task EditWorkorder_WithoutScheduledDate_LeavesScheduleAndAddOnUntouched()
+    {
+        // The edit form sends only changed fields: a null Schedule On means "not sent", never
+        // "clear". Clearing happens through the board patch, which turns Add-On off.
+        await using var context = CreateContext();
+        context.workOrders.Add(new WorkOrder
+        {
+            Id = 1,
+            CreatedDate = new DateTime(2026, 6, 23, 0, 0, 0, DateTimeKind.Utc),
+            ScheduledDate = new DateTime(2026, 6, 24),
+            IsAddOn = true
+        });
+        await context.SaveChangesAsync();
+
+        var result = await CreateController(context, new FixedTimeProvider()).Editworkorder(new EditWorkorder_DTO
+        {
+            Id = 1,
+            DueDate = new DateTime(2026, 6, 30)
+        });
+
+        Assert.IsType<OkObjectResult>(result);
+        var persisted = await context.workOrders.SingleAsync(x => x.Id == 1);
+        Assert.Equal(new DateTime(2026, 6, 24), persisted.ScheduledDate);
+        Assert.True(persisted.IsAddOn);
+        Assert.DoesNotContain(
+            await context.WorkOrderAuditLogs.Where(x => x.WorkOrderId == 1).ToListAsync(),
+            x => x.FieldName?.Contains("IsAddOn", StringComparison.Ordinal) == true);
+    }
+
     [Fact]
     public async Task EditWorkorder_FirstSchedule_SetsOriginalWeekAndPromotesIncomplete()
     {