feat(work-orders): persist IsAddOn frozen at create (SH-126)

Add set-once IsAddOn with server cutoff at create, board DTO exposure, legacy type-7 backfill, and Types=AddOn search compat. Aligns with FE PR #61 frozen contract.

Data.SeaHavenIndustries/Migrations/20260730150000_WoIsAddOn.cs

@@ -0,0 +1,37 @@
+using Data.SeaHavenIndustries;
+using Microsoft.EntityFrameworkCore.Infrastructure;
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace Data.SeaHavenIndustries.Migrations
+{
+    /// <inheritdoc />
+    [DbContext(typeof(ApplicationDbContext))]
+    [Migration("20260730150000_WoIsAddOn")]
+    public partial class WoIsAddOn : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AddColumn<bool>(
+                name: "IsAddOn",
+                table: "workOrders",
+                type: "bit",
+                nullable: false,
+                defaultValue: false);
+
+            // Legacy WorkOrderType.AddOn (7) → flag; do not remap type (real type unknown).
+            migrationBuilder.Sql(
+                "UPDATE workOrders SET IsAddOn = 1 WHERE WorkOrderType = 7;");
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropColumn(
+                name: "IsAddOn",
+                table: "workOrders");
+        }
+    }
+}

Data.SeaHavenIndustries/Migrations/ApplicationDbContextModelSnapshot.cs

@@ -2458,6 +2458,9 @@ namespace Data.SeaHavenIndustries.Migrations
                         .HasMaxLength(11)
                         .HasColumnType("nvarchar(11)");
 
+                    b.Property<bool>("IsAddOn")
+                        .HasColumnType("bit");
+
                     b.Property<bool?>("IsDeleted")
                         .HasColumnType("bit");
 

Data.SeaHavenIndustries/Models/WorkerOrder.cs

@@ -80,6 +80,8 @@ namespace Data.SeaHavenIndustries
         // --- Analytics slice ---
         public int RescheduleCount { get; set; }
         public int CarriedOver { get; set; }
+        /// <summary>Recalculated on schedule set/change/clear (SH-184); create hint when unscheduled.</summary>
+        public bool IsAddOn { get; set; }
         public OperationalFlags OperationalFlags { get; set; }
 
         // --- Completion slice ---

SeaHaven.DataServices/Helpers/WorkOrderBoardProjection.cs

@@ -18,6 +18,7 @@ namespace SeaHaven.DataServices.Helpers
                     w.InternalWONumber,
                     w.RescheduleCount,
                     w.CarriedOver,
+                    w.IsAddOn,
                     w.WorkOrderType,
                     w.SiteCode,
                     LocationName = w.Locations != null ? w.Locations.Name : null,
@@ -99,6 +100,7 @@ namespace SeaHaven.DataServices.Helpers
                     w.InternalWONumber,
                     w.RescheduleCount,
                     w.CarriedOver,
+                    w.IsAddOn,
                     w.WorkOrderType,
                     w.SiteCode,
                     w.LocationName,

SeaHaven.DataServices/Helpers/WorkOrderBoardQueryFilters.cs

@@ -66,8 +66,10 @@ namespace SeaHaven.DataServices.Helpers
 
             var today = (utcNow ?? DateTime.UtcNow).Date;
             var typeFilters = hasTypes ? types!.ToList() : new List<WorkOrderType>();
+            var includeAddOnFlag = typeFilters.Contains(WorkOrderType.AddOn);
 
             // Keep past-due predicate inline — EF cannot translate local method calls.
+            // Types=AddOn also matches IsAddOn (legacy type 7 OR flag on a real type).
             if (overdue && !hasTypes)
             {
                 return query.Where(w =>
@@ -84,10 +86,13 @@ namespace SeaHaven.DataServices.Helpers
                      && w.DueDate.Value.Date < today
                      && w.LifecycleStatus != LifecycleStatus.Completed
                      && w.LifecycleStatus != LifecycleStatus.Canceled)
-                    || (w.WorkOrderType != null && typeFilters.Contains(w.WorkOrderType.Value)));
+                    || (w.WorkOrderType != null && typeFilters.Contains(w.WorkOrderType.Value))
+                    || (includeAddOnFlag && w.IsAddOn));
             }
 
-            return query.Where(w => w.WorkOrderType != null && typeFilters.Contains(w.WorkOrderType.Value));
+            return query.Where(w =>
+                (w.WorkOrderType != null && typeFilters.Contains(w.WorkOrderType.Value))
+                || (includeAddOnFlag && w.IsAddOn));
         }
 
         public static IQueryable<WorkOrder> ApplyTypeFilter(

SeaHaven.DataServices/Helpers/WorkOrderBoardSearchFilter.cs

@@ -58,6 +58,7 @@ namespace SeaHaven.DataServices.Helpers
                 || (w.WorkOrderType == WorkOrderType.Inspection && "inspection".Contains(s))
                 || (w.WorkOrderType == WorkOrderType.Reactive && "reactive".Contains(s))
                 || (w.WorkOrderType == WorkOrderType.AddOn && ("add-on".Contains(s) || "addon".Contains(s)))
+                || (w.IsAddOn && ("add-on".Contains(s) || "addon".Contains(s)))
                 || (w.WorkOrderType == WorkOrderType.Other && "other".Contains(s))
                 || ("overdue".Contains(s)
                     && w.DueDate != null

SeaHaven.DataServices/Interfaces/WorkOrderBoardModels.cs

@@ -18,6 +18,7 @@ namespace SeaHaven.DataServices.Interfaces
         string? InternalWONumber,
         int RescheduleCount,
         int CarriedOver,
+        bool IsAddOn,
         WorkOrderType? WorkOrderType,
         string? SiteCode,
         string? LocationName,

SeaHaven.Services/DTOs/WorkOrderBoardDTOs.cs

@@ -27,6 +27,7 @@ namespace SeaHaven.Services.DTOs
         public string? WoNumber { get; set; }
         public int RescheduleCount { get; set; }
         public int CarriedOver { get; set; }
+        public bool IsAddOn { get; set; }
         public WorkOrderType? WorkOrderType { get; set; }
         public bool IsPastDue { get; set; }
         public string? SiteCode { get; set; }

SeaHaven.Services/DTOs/WorkOrderBoardRequestDTOs.cs

@@ -14,6 +14,11 @@ namespace SeaHaven.Services.DTOs
     {
         public string? WoNumber { get; set; }
         public WorkOrderType WorkOrderType { get; set; }
+        /// <summary>
+        /// Manual Add-On override when unscheduled. Ignored when ScheduledDate or TargetWeek is set
+        /// (server computes from cutoff).
+        /// </summary>
+        public bool? IsAddOn { get; set; }
         public string? SiteCode { get; set; }
         /// <summary>
         /// Optional CRM customer name. Required when the caller is org-wide (no account_id)

SeaHaven.Services/Helpers/WorkOrderAddonCutoff.cs

@@ -0,0 +1,77 @@
+namespace SeaHaven.Services.Helpers
+{
+    /// <summary>
+    /// Server-side Add-On cutoff: Saturday 23:59:59 UTC of the week prior to the schedule week.
+    /// SH-184: recalculated whenever scheduling is set, changed, or cleared; audited on change.
+    /// Create may accept a client hint when unscheduled; schedule present ignores override.
+    /// </summary>
+    public static class WorkOrderAddonCutoff
+    {
+        /// <summary>
+        /// Cutoff = Monday-of(anchor) − 2 days, end of day UTC (prior-week Saturday 23:59:59).
+        /// </summary>
+        public static DateTime GetAddonCutoffUtc(DateTime anchor)
+        {
+            var monday = WorkOrderBoardMutationRules.GetWeekStartMonday(anchor);
+            var saturday = monday.Date.AddDays(-2);
+            return DateTime.SpecifyKind(
+                saturday.AddHours(23).AddMinutes(59).AddSeconds(59),
+                DateTimeKind.Utc);
+        }
+
+        public static DateTime GetAddonCutoffUtc(DateOnly anchor)
+            => GetAddonCutoffUtc(anchor.ToDateTime(TimeOnly.MinValue, DateTimeKind.Utc));
+
+        /// <summary>
+        /// With schedule (ScheduledDate or TargetWeek): IsAddOn when createdAtUtc is after cutoff.
+        /// Without schedule: client <paramref name="manualOverride"/> (default false).
+        /// </summary>
+        public static bool ComputeIsAddOnAtCreation(
+            DateTime createdAtUtc,
+            DateTime? scheduledDate,
+            DateOnly? targetWeek,
+            bool? manualOverride)
+        {
+            return ComputeFromScheduleAnchor(createdAtUtc, scheduledDate, targetWeek, manualOverride);
+        }
+
+        /// <summary>
+        /// SH-184 authoritative recalc after schedule set/change/clear. No manual override on patch.
+        /// Cleared schedule yields false.
+        /// </summary>
+        public static bool RecalculateIsAddOnFromSchedule(
+            DateTime createdAtUtc,
+            DateTime? scheduledDate,
+            DateOnly? targetWeek)
+            => ComputeFromScheduleAnchor(createdAtUtc, scheduledDate, targetWeek, manualOverride: false);
+
+        private static bool ComputeFromScheduleAnchor(
+            DateTime createdAtUtc,
+            DateTime? scheduledDate,
+            DateOnly? targetWeek,
+            bool? manualOverride)
+        {
+            DateTime? anchor = null;
+            if (scheduledDate.HasValue)
+                anchor = scheduledDate.Value;
+            else if (targetWeek.HasValue)
+                anchor = targetWeek.Value.ToDateTime(TimeOnly.MinValue, DateTimeKind.Utc);
+
+            if (!anchor.HasValue)
+                return manualOverride ?? false;
+
+            var cutoff = GetAddonCutoffUtc(anchor.Value);
+            var created = NormalizeUtc(createdAtUtc);
+            return created > cutoff;
+        }
+
+        private static DateTime NormalizeUtc(DateTime value)
+        {
+            if (value.Kind == DateTimeKind.Utc)
+                return value;
+            if (value.Kind == DateTimeKind.Local)
+                return value.ToUniversalTime();
+            return DateTime.SpecifyKind(value, DateTimeKind.Utc);
+        }
+    }
+}

SeaHaven.Services/Helpers/WorkOrderBoardMutationRules.cs

@@ -36,7 +36,7 @@ namespace SeaHaven.Services.Helpers
                 ? DateOnly.FromDateTime(GetWeekStartMonday(scheduledDate.Value))
                 : null;
 
-        private static DateTime GetWeekStartMonday(DateTime date)
+        public static DateTime GetWeekStartMonday(DateTime date)
         {
             var diff = (7 + (date.DayOfWeek - DayOfWeek.Monday)) % 7;
             return date.Date.AddDays(-diff);

SeaHaven.Services/Implementation/WorkOrderBoardCreateService.cs

@@ -106,6 +106,12 @@ namespace SeaHaven.Services.Implementation
 
             WorkOrderBoardFieldMutations.SetInitialLifecycleStatus(workOrder);
 
+            workOrder.IsAddOn = WorkOrderAddonCutoff.ComputeIsAddOnAtCreation(
+                workOrder.CreatedDate!.Value,
+                request.ScheduledDate,
+                request.TargetWeek,
+                request.IsAddOn);
+
             var changes = new List<WorkOrderBoardFieldMutations.BoardFieldChange>
             {
                 WorkOrderBoardFieldMutations.BoardFieldChange.Changed("InternalWONumber", "", woNumber),

SeaHaven.Services/Implementation/WorkOrderBoardService.cs

@@ -93,6 +93,7 @@ namespace SeaHaven.Services.Implementation
                 WoNumber = row.InternalWONumber,
                 RescheduleCount = row.RescheduleCount,
                 CarriedOver = row.CarriedOver,
+                IsAddOn = row.IsAddOn,
                 WorkOrderType = row.WorkOrderType,
                 IsPastDue = WorkOrderDerivedFields.IsPastDue(row.DueDate, row.LifecycleStatus, utcNow),
                 SiteCode = row.SiteCode,

SeaHaven.Services/Implementation/WorkOrderBoardUpdateService.cs

@@ -147,8 +147,8 @@ namespace SeaHaven.Services.Implementation
                 WorkOrderBoardFieldNames.AssignTo => ApplyAssignTo(workOrder, value, auditField),
                 WorkOrderBoardFieldNames.DueDate => new List<FieldChange> { ApplyDateField(value, auditField, v => workOrder.DueDate = v, () => workOrder.DueDate) },
                 WorkOrderBoardFieldNames.ScheduledDate => ApplyScheduledDate(workOrder, value, auditField),
-                WorkOrderBoardFieldNames.TargetWeek => new List<FieldChange> { ApplyTargetWeek(workOrder, value, auditField) },
+                WorkOrderBoardFieldNames.TargetWeek => ApplyTargetWeek(workOrder, value, auditField),
-                WorkOrderBoardFieldNames.ScheduleWeekOnly => new List<FieldChange> { ApplyBoolField(value, auditField, v => workOrder.ScheduleWeekOnly = v, () => workOrder.ScheduleWeekOnly) },
+                WorkOrderBoardFieldNames.ScheduleWeekOnly => ApplyScheduleWeekOnly(workOrder, value, auditField),
                 WorkOrderBoardFieldNames.VendorId => new List<FieldChange> { await ApplyVendorIdAsync(dispatch!, value, auditField) },
                 WorkOrderBoardFieldNames.ApptDate => new List<FieldChange> { ApplyApptDate(dispatch!, value, auditField) },
                 WorkOrderBoardFieldNames.ApptTime => ApplyApptTime(workOrder, dispatch!, value),
@@ -437,10 +437,11 @@ namespace SeaHaven.Services.Implementation
             }
 
             changes.AddRange(ApplyAutoScheduleSideEffects(workOrder));
+            AppendIsAddOnRecalculation(workOrder, changes);
             return changes;
         }
 
-        private static FieldChange ApplyTargetWeek(WorkOrder workOrder, string? value, string auditField)
+        private static List<FieldChange> ApplyTargetWeek(WorkOrder workOrder, string? value, string auditField)
         {
             DateOnly? parsed = null;
             if (!string.IsNullOrWhiteSpace(value))
@@ -450,13 +451,42 @@ namespace SeaHaven.Services.Implementation
                 parsed = d;
             }
 
+            var changes = new List<FieldChange>();
             var old = workOrder.TargetWeek?.ToString("yyyy-MM-dd");
             var newVal = parsed?.ToString("yyyy-MM-dd");
-            if (old == newVal)
+            if (old != newVal)
-                return FieldChange.Unchanged(auditField);
+            {
-
                 workOrder.TargetWeek = parsed;
-            return FieldChange.ForField(auditField, old, newVal);
+                changes.Add(FieldChange.ForField(auditField, old, newVal));
+            }
+
+            AppendIsAddOnRecalculation(workOrder, changes);
+            return changes;
+        }
+
+        private static List<FieldChange> ApplyScheduleWeekOnly(WorkOrder workOrder, string? value, string auditField)
+        {
+            var change = ApplyBoolField(value, auditField, v => workOrder.ScheduleWeekOnly = v, () => workOrder.ScheduleWeekOnly);
+            var changes = new List<FieldChange> { change };
+            if (change.HasChanged)
+                AppendIsAddOnRecalculation(workOrder, changes);
+            return changes;
+        }
+
+        private static void AppendIsAddOnRecalculation(WorkOrder workOrder, List<FieldChange> changes)
+        {
+            var createdAt = workOrder.CreatedDate ?? DateTime.UtcNow;
+            var oldValue = workOrder.IsAddOn.ToString();
+            var newIsAddOn = WorkOrderAddonCutoff.RecalculateIsAddOnFromSchedule(
+                createdAt,
+                workOrder.ScheduledDate,
+                workOrder.TargetWeek);
+
+            if (workOrder.IsAddOn == newIsAddOn)
+                return;
+
+            workOrder.IsAddOn = newIsAddOn;
+            changes.Add(FieldChange.ForField("IsAddOn", oldValue, newIsAddOn.ToString()));
         }
 
         private static FieldChange ApplyBoolField(

SeaHaven.Services/Implementation/WorkOrderDetailService.cs

@@ -95,6 +95,7 @@ namespace SeaHaven.Services.Implementation
                 WoNumber = row.WoNumber,
                 RescheduleCount = row.RescheduleCount,
                 CarriedOver = row.CarriedOver,
+                IsAddOn = row.IsAddOn,
                 WorkOrderType = row.WorkOrderType,
                 IsPastDue = row.IsPastDue,
                 SiteCode = row.SiteCode,

SeaHaven.Services/Validation/WorkOrderBoardCreateValidation.cs

@@ -1,4 +1,5 @@
 using FluentValidation;
+using Data.SeaHavenIndustries.Enums;
 using SeaHaven.Services.DTOs;
 
 namespace SeaHaven.Services.Validation
@@ -12,7 +13,9 @@ namespace SeaHaven.Services.Validation
         public WorkOrderBoardCreateValidation()
         {
             RuleFor(x => x.WorkOrderType)
-                .IsInEnum().WithMessage("workOrderType is required and must be a valid value.");
+                .IsInEnum().WithMessage("workOrderType is required and must be a valid value.")
+                .Must(t => t != WorkOrderType.AddOn)
+                .WithMessage("workOrderType AddOn is not allowed on create; use isAddOn with a real type.");
 
             RuleFor(x => x.SiteCode)
                 .NotEmpty().WithMessage("siteCode is required.")

SeaHavenIndustries.Tests/WorkOrderAddonCutoffTests.cs

@@ -0,0 +1,135 @@
+using SeaHaven.Services.Helpers;
+
+namespace SeaHavenIndustries.Tests;
+
+public class WorkOrderAddonCutoffTests
+{
+    // Schedule week Mon 2026-06-22 → cutoff Sat 2026-06-20 23:59:59 UTC
+    private static readonly DateTime ScheduleMonday = new(2026, 6, 22, 0, 0, 0, DateTimeKind.Utc);
+    private static readonly DateTime ExpectedCutoff = new(2026, 6, 20, 23, 59, 59, DateTimeKind.Utc);
+
+    [Fact]
+    public void GetAddonCutoffUtc_FromScheduledDate_IsPriorSaturdayEndOfDay()
+    {
+        // Wednesday in schedule week
+        var cutoff = WorkOrderAddonCutoff.GetAddonCutoffUtc(new DateTime(2026, 6, 24, 15, 0, 0, DateTimeKind.Utc));
+        Assert.Equal(ExpectedCutoff, cutoff);
+    }
+
+    [Fact]
+    public void GetAddonCutoffUtc_FromTargetWeekMonday_IsPriorSaturdayEndOfDay()
+    {
+        var cutoff = WorkOrderAddonCutoff.GetAddonCutoffUtc(new DateOnly(2026, 6, 22));
+        Assert.Equal(ExpectedCutoff, cutoff);
+    }
+
+    [Fact]
+    public void GetAddonCutoffUtc_FromMondayAnchor_MatchesGetWeekStartMondayMinusTwo()
+    {
+        var monday = WorkOrderBoardMutationRules.GetWeekStartMonday(ScheduleMonday);
+        Assert.Equal(ScheduleMonday.Date, monday.Date);
+        Assert.Equal(ExpectedCutoff, WorkOrderAddonCutoff.GetAddonCutoffUtc(ScheduleMonday));
+    }
+
+    [Fact]
+    public void Compute_AfterCutoff_ReturnsTrue_IgnoresManualFalse()
+    {
+        var created = new DateTime(2026, 6, 21, 0, 0, 0, DateTimeKind.Utc);
+        var result = WorkOrderAddonCutoff.ComputeIsAddOnAtCreation(
+            created,
+            scheduledDate: new DateTime(2026, 6, 24),
+            targetWeek: null,
+            manualOverride: false);
+
+        Assert.True(result);
+    }
+
+    [Fact]
+    public void Compute_BeforeCutoff_ReturnsFalse_IgnoresManualTrue()
+    {
+        var created = new DateTime(2026, 6, 20, 23, 59, 59, DateTimeKind.Utc);
+        var result = WorkOrderAddonCutoff.ComputeIsAddOnAtCreation(
+            created,
+            scheduledDate: new DateTime(2026, 6, 24),
+            targetWeek: null,
+            manualOverride: true);
+
+        Assert.False(result);
+    }
+
+    [Fact]
+    public void Compute_ExactlyAtCutoff_ReturnsFalse()
+    {
+        var result = WorkOrderAddonCutoff.ComputeIsAddOnAtCreation(
+            ExpectedCutoff,
+            scheduledDate: ScheduleMonday,
+            targetWeek: null,
+            manualOverride: true);
+
+        Assert.False(result);
+    }
+
+    [Fact]
+    public void Compute_TargetWeekOnly_UsesCutoff()
+    {
+        var after = WorkOrderAddonCutoff.ComputeIsAddOnAtCreation(
+            new DateTime(2026, 6, 21, 12, 0, 0, DateTimeKind.Utc),
+            scheduledDate: null,
+            targetWeek: new DateOnly(2026, 6, 22),
+            manualOverride: false);
+
+        var before = WorkOrderAddonCutoff.ComputeIsAddOnAtCreation(
+            new DateTime(2026, 6, 19, 12, 0, 0, DateTimeKind.Utc),
+            scheduledDate: null,
+            targetWeek: new DateOnly(2026, 6, 22),
+            manualOverride: true);
+
+        Assert.True(after);
+        Assert.False(before);
+    }
+
+    [Fact]
+    public void Compute_NoSchedule_UsesManualOverride()
+    {
+        Assert.True(WorkOrderAddonCutoff.ComputeIsAddOnAtCreation(
+            DateTime.UtcNow, null, null, manualOverride: true));
+        Assert.False(WorkOrderAddonCutoff.ComputeIsAddOnAtCreation(
+            DateTime.UtcNow, null, null, manualOverride: false));
+        Assert.False(WorkOrderAddonCutoff.ComputeIsAddOnAtCreation(
+            DateTime.UtcNow, null, null, manualOverride: null));
+    }
+
+    [Fact]
+    public void Compute_ScheduledDatePreferredOverTargetWeek()
+    {
+        // Target week far future (cutoff after created) would be false;
+        // scheduled date near past (cutoff before created) → true.
+        var created = new DateTime(2026, 7, 1, 0, 0, 0, DateTimeKind.Utc);
+        var result = WorkOrderAddonCutoff.ComputeIsAddOnAtCreation(
+            created,
+            scheduledDate: new DateTime(2026, 6, 24),
+            targetWeek: new DateOnly(2099, 1, 5),
+            manualOverride: false);
+
+        Assert.True(result);
+    }
+
+    [Fact]
+    public void RecalculateIsAddOnFromSchedule_NoSchedule_ReturnsFalse()
+    {
+        var created = new DateTime(2026, 6, 21, 0, 0, 0, DateTimeKind.Utc);
+        Assert.False(WorkOrderAddonCutoff.RecalculateIsAddOnFromSchedule(created, null, null));
+    }
+
+    [Fact]
+    public void RecalculateIsAddOnFromSchedule_AfterCutoff_ReturnsTrue()
+    {
+        var created = new DateTime(2026, 6, 21, 0, 0, 0, DateTimeKind.Utc);
+        var result = WorkOrderAddonCutoff.RecalculateIsAddOnFromSchedule(
+            created,
+            scheduledDate: new DateTime(2026, 6, 24),
+            targetWeek: null);
+
+        Assert.True(result);
+    }
+}

SeaHavenIndustries.Tests/WorkOrderBoardCreateServiceTests.cs

@@ -351,4 +351,77 @@ public class WorkOrderBoardCreateServiceTests
 
         Assert.Equal("VendorNotFound", ex.Code);
     }
+
+    [Fact]
+    public async Task Create_ScheduledAfterCutoff_SetsIsAddOnTrue_KeepsRealType()
+    {
+        // UtcNow (test run) is after cutoff for a 2026-06 schedule week.
+        var (context, service) = CreateSut();
+
+        var result = await service.CreateAsync(new WorkOrderBoardCreateRequestDto
+        {
+            WorkOrderType = WorkOrderType.PM,
+            SiteCode = "BK5",
+            ScheduledDate = new DateTime(2026, 6, 24),
+            IsAddOn = false
+        }, "actor-1");
+
+        Assert.True(result.IsAddOn);
+        Assert.Equal(WorkOrderType.PM, result.WorkOrderType);
+        var wo = await context.workOrders.SingleAsync(w => w.Id == result.Id);
+        Assert.True(wo.IsAddOn);
+        Assert.Equal(WorkOrderType.PM, wo.WorkOrderType);
+    }
+
+    [Fact]
+    public async Task Create_ScheduledBeforeCutoff_SetsIsAddOnFalse_IgnoresClientTrue()
+    {
+        // Far-future schedule → cutoff after UtcNow → not an add-on.
+        var (context, service) = CreateSut();
+
+        var result = await service.CreateAsync(new WorkOrderBoardCreateRequestDto
+        {
+            WorkOrderType = WorkOrderType.Reactive,
+            SiteCode = "BK5",
+            ScheduledDate = new DateTime(2099, 3, 10),
+            IsAddOn = true
+        }, "actor-1");
+
+        Assert.False(result.IsAddOn);
+        Assert.Equal(WorkOrderType.Reactive, result.WorkOrderType);
+        var wo = await context.workOrders.SingleAsync(w => w.Id == result.Id);
+        Assert.False(wo.IsAddOn);
+    }
+
+    [Fact]
+    public async Task Create_NoSchedule_ManualIsAddOnTrue()
+    {
+        var (context, service) = CreateSut();
+
+        var result = await service.CreateAsync(new WorkOrderBoardCreateRequestDto
+        {
+            WorkOrderType = WorkOrderType.PM,
+            SiteCode = "BK5",
+            IsAddOn = true
+        }, "actor-1");
+
+        Assert.True(result.IsAddOn);
+        var wo = await context.workOrders.SingleAsync(w => w.Id == result.Id);
+        Assert.True(wo.IsAddOn);
+    }
+
+    [Fact]
+    public async Task Create_WorkOrderTypeAddOn_ThrowsValidation()
+    {
+        var (_, service) = CreateSut();
+
+        var ex = await Assert.ThrowsAsync<FluentValidation.ValidationException>(() =>
+            service.CreateAsync(new WorkOrderBoardCreateRequestDto
+            {
+                WorkOrderType = WorkOrderType.AddOn,
+                SiteCode = "BK5"
+            }, "actor-1"));
+
+        Assert.Contains(ex.Errors, e => e.PropertyName == "WorkOrderType");
+    }
 }

SeaHavenIndustries.Tests/WorkOrderBoardSearchTests.cs

@@ -613,4 +613,58 @@ public class WorkOrderAdvancedSearchServiceTests
 
         Assert.Contains("sortBy", ex.Message);
     }
+
+    [Fact]
+    public async Task SearchAsync_TypesAddOn_MatchesLegacyTypeOrIsAddOnFlag()
+    {
+        await using var context = CreateContext();
+        var today = DateTime.UtcNow.Date;
+
+        context.workOrders.AddRange(
+            new WorkOrder
+            {
+                Id = 1,
+                WorkOrderType = WorkOrderType.AddOn,
+                IsAddOn = false,
+                ScheduledDate = today.AddDays(1),
+                LifecycleStatus = LifecycleStatus.Scheduled,
+                InternalWONumber = "10000000001"
+            },
+            new WorkOrder
+            {
+                Id = 2,
+                WorkOrderType = WorkOrderType.PM,
+                IsAddOn = true,
+                ScheduledDate = today.AddDays(2),
+                LifecycleStatus = LifecycleStatus.Scheduled,
+                InternalWONumber = "10000000002"
+            },
+            new WorkOrder
+            {
+                Id = 3,
+                WorkOrderType = WorkOrderType.Reactive,
+                IsAddOn = false,
+                ScheduledDate = today.AddDays(3),
+                LifecycleStatus = LifecycleStatus.Scheduled,
+                InternalWONumber = "10000000003"
+            });
+
+        await context.SaveChangesAsync();
+
+        var dataService = new WorkOrderAdvancedSearchDataService(context);
+        var service = new SeaHaven.Services.Implementation.WorkOrderAdvancedSearchService(dataService);
+
+        var result = await service.SearchAsync(new SeaHaven.Services.DTOs.WorkOrderAdvancedSearchQueryDto
+        {
+            DatePreset = SeaHaven.Services.Helpers.WorkOrderAdvancedSearchDatePreset.Custom,
+            DateFrom = DateOnly.FromDateTime(today.AddMonths(-1)),
+            DateTo = DateOnly.FromDateTime(today.AddMonths(1)),
+            Types = new List<WorkOrderType> { WorkOrderType.AddOn }
+        }, null);
+
+        Assert.Equal(2, result.TotalCount);
+        Assert.Contains(result.Items, i => i.Id == 1 && i.WorkOrderType == WorkOrderType.AddOn);
+        Assert.Contains(result.Items, i => i.Id == 2 && i.IsAddOn && i.WorkOrderType == WorkOrderType.PM);
+        Assert.DoesNotContain(result.Items, i => i.Id == 3);
+    }
 }

SeaHavenIndustries.Tests/WorkOrderBoardServiceTests.cs

@@ -412,6 +412,35 @@ public class WorkOrderBoardServiceTests
         Assert.Equal("wednesday", response.Scheduled[0].DayGroup);
     }
 
+    [Fact]
+    public async Task GetBoardAsync_MapsIsAddOn()
+    {
+        await using var context = CreateContext();
+        var weekStart = new DateOnly(2026, 6, 22);
+
+        context.workOrders.Add(new WorkOrder
+        {
+            Id = 1,
+            InternalWONumber = "10000000001",
+            WorkOrderType = WorkOrderType.PM,
+            IsAddOn = true,
+            ScheduledDate = new DateTime(2026, 6, 24, 12, 0, 0, DateTimeKind.Utc),
+            LifecycleStatus = LifecycleStatus.Scheduled
+        });
+
+        await context.SaveChangesAsync();
+
+        var boardService = new WorkOrderBoardService(new WorkOrderBoardDataService(context));
+        var response = await boardService.GetBoardAsync(new WorkOrderBoardQueryDto
+        {
+            WeekStart = weekStart
+        }, null);
+
+        Assert.Single(response.Scheduled);
+        Assert.True(response.Scheduled[0].IsAddOn);
+        Assert.Equal(WorkOrderType.PM, response.Scheduled[0].WorkOrderType);
+    }
+
     [Fact]
     public async Task GetBoardAsync_InvalidWeekWindow_Throws()
     {

SeaHavenIndustries.Tests/WorkOrderBoardUpdateServiceTests.cs

@@ -993,4 +993,93 @@ public class WorkOrderBoardUpdateServiceTests
         Assert.Null(result.CompletedDate);
         Assert.Null(context.workOrders.Single().CompletedDate);
     }
+
+    [Fact]
+    public async Task PatchField_ClearsIsAddOn_WhenScheduleCleared()
+    {
+        var (context, service) = CreateSut();
+        var wo = new WorkOrder
+        {
+            Id = 1,
+            LifecycleStatus = LifecycleStatus.Scheduled,
+            WorkOrderType = WorkOrderType.PM,
+            ScheduledDate = new DateTime(2026, 6, 20),
+            CreatedDate = new DateTime(2026, 6, 21, 0, 0, 0, DateTimeKind.Utc),
+            IsAddOn = true,
+            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.ScheduledDate,
+            Value = "",
+            WorkOrderVersion = ToVersion(wo)
+        }, "actor-1");
+
+        Assert.False(result.IsAddOn);
+        var persisted = await context.workOrders.SingleAsync(w => w.Id == 1);
+        Assert.False(persisted.IsAddOn);
+        Assert.Single(await context.WorkOrderAuditLogs.Where(a => a.FieldName == "IsAddOn").ToListAsync());
+    }
+
+    [Fact]
+    public async Task PatchField_ScheduledDate_RecalculatesIsAddOn_AfterCrossWeekMove()
+    {
+        var (context, service) = CreateSut();
+        var wo = new WorkOrder
+        {
+            Id = 1,
+            LifecycleStatus = LifecycleStatus.Scheduled,
+            WorkOrderType = WorkOrderType.PM,
+            ScheduledDate = new DateTime(2026, 6, 10),
+            CreatedDate = new DateTime(2026, 6, 21, 0, 0, 0, DateTimeKind.Utc),
+            IsAddOn = false,
+            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.ScheduledDate,
+            Value = "2026-06-25",
+            WorkOrderVersion = ToVersion(wo)
+        }, "actor-1");
+
+        Assert.True(result.IsAddOn);
+        var persisted = await context.workOrders.SingleAsync(w => w.Id == 1);
+        Assert.True(persisted.IsAddOn);
+    }
+
+    [Fact]
+    public async Task PatchField_WorkOrderType_DoesNotRecalculateIsAddOn()
+    {
+        var (context, service) = CreateSut();
+        var wo = new WorkOrder
+        {
+            Id = 1,
+            LifecycleStatus = LifecycleStatus.Scheduled,
+            WorkOrderType = WorkOrderType.PM,
+            IsAddOn = true,
+            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.WorkOrderType,
+            Value = "Reactive",
+            WorkOrderVersion = ToVersion(wo)
+        }, "actor-1");
+
+        Assert.Equal(WorkOrderType.Reactive, result.WorkOrderType);
+        Assert.True(result.IsAddOn);
+        var persisted = await context.workOrders.SingleAsync(w => w.Id == 1);
+        Assert.Equal(WorkOrderType.Reactive, persisted.WorkOrderType);
+        Assert.True(persisted.IsAddOn);
+        Assert.Empty(await context.WorkOrderAuditLogs.Where(a => a.FieldName == "IsAddOn").ToListAsync());
+    }
 }