diff --git a/Data.SeaHavenIndustries/Migrations/20260730150000_WoIsAddOn.cs b/Data.SeaHavenIndustries/Migrations/20260730150000_WoIsAddOn.cs
new file mode 100644
index 0000000..92484c0
--- /dev/null
+++ b/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");
+        }
+    }
+}
diff --git a/Data.SeaHavenIndustries/Migrations/20260813193000_SH121_BoardSearchFacets.cs b/Data.SeaHavenIndustries/Migrations/20260813193000_SH121_BoardSearchFacets.cs
new file mode 100644
index 0000000..c5fe2cd
--- /dev/null
+++ b/Data.SeaHavenIndustries/Migrations/20260813193000_SH121_BoardSearchFacets.cs
@@ -0,0 +1,29 @@
+using Data.SeaHavenIndustries;
+using Microsoft.EntityFrameworkCore.Infrastructure;
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace Data.SeaHavenIndustries.Migrations
+{
+    /// <inheritdoc />
+    /// <summary>
+    /// SH-121 originally added <c>IsAddOn</c> for search facets. Column + legacy backfill
+    /// now live in <c>20260730150000_WoIsAddOn</c> (SH-184). This migration is a no-op so
+    /// both PRs can land without a duplicate column.
+    /// </summary>
+    [DbContext(typeof(ApplicationDbContext))]
+    [Migration("20260813193000_SH121_BoardSearchFacets")]
+    public partial class SH121_BoardSearchFacets : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+        }
+    }
+}
diff --git a/Data.SeaHavenIndustries/Migrations/ApplicationDbContextModelSnapshot.cs b/Data.SeaHavenIndustries/Migrations/ApplicationDbContextModelSnapshot.cs
index 813853c..e938918 100644
--- a/Data.SeaHavenIndustries/Migrations/ApplicationDbContextModelSnapshot.cs
+++ b/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");
 
diff --git a/Data.SeaHavenIndustries/Models/WorkerOrder.cs b/Data.SeaHavenIndustries/Models/WorkerOrder.cs
index 59f2390..b2d1989 100644
--- a/Data.SeaHavenIndustries/Models/WorkerOrder.cs
+++ b/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. Board/search facet.</summary>
+        public bool IsAddOn { get; set; }
         public OperationalFlags OperationalFlags { get; set; }
 
         // --- Completion slice ---
diff --git a/SeaHaven.DataServices/Helpers/WorkOrderBoardProjection.cs b/SeaHaven.DataServices/Helpers/WorkOrderBoardProjection.cs
index 3d43fe3..2b31222 100644
--- a/SeaHaven.DataServices/Helpers/WorkOrderBoardProjection.cs
+++ b/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,
diff --git a/SeaHaven.DataServices/Helpers/WorkOrderBoardQueryFilters.cs b/SeaHaven.DataServices/Helpers/WorkOrderBoardQueryFilters.cs
index ba41941..44f965b 100644
--- a/SeaHaven.DataServices/Helpers/WorkOrderBoardQueryFilters.cs
+++ b/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.ScheduledDate.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(
diff --git a/SeaHaven.DataServices/Helpers/WorkOrderBoardSearchFacetFilters.cs b/SeaHaven.DataServices/Helpers/WorkOrderBoardSearchFacetFilters.cs
new file mode 100644
index 0000000..08b2c2d
--- /dev/null
+++ b/SeaHaven.DataServices/Helpers/WorkOrderBoardSearchFacetFilters.cs
@@ -0,0 +1,166 @@
+using Data.SeaHavenIndustries;
+using Data.SeaHavenIndustries.Enums;
+using Microsoft.EntityFrameworkCore;
+
+namespace SeaHaven.DataServices.Helpers
+{
+    /// <summary>
+    /// SH-121/SH-196 advanced search facets (severity, indicators, flag, internal WO#, uplift).
+    /// </summary>
+    public static class WorkOrderBoardSearchFacetFilters
+    {
+        private static readonly WorkOrderType[] SeverityEligibleTypes =
+        {
+            WorkOrderType.Emergency,
+            WorkOrderType.Reactive,
+        };
+
+        private static readonly string[] RevokedUpliftStatuses =
+        {
+            "Withdrawn",
+            "Cancelled",
+        };
+
+        public static IQueryable<WorkOrder> ApplySeverityFilter(
+            IQueryable<WorkOrder> query,
+            IReadOnlyList<int>? severities)
+        {
+            if (severities == null || severities.Count == 0)
+                return query;
+
+            var allowed = severities
+                .Where(s => s is >= 1 and <= 5)
+                .Select(s => s.ToString())
+                .Distinct()
+                .ToList();
+
+            if (allowed.Count == 0)
+                return query;
+
+            return query.Where(w =>
+                w.WorkOrderType != null
+                && SeverityEligibleTypes.Contains(w.WorkOrderType.Value)
+                && w.Severity != null
+                && allowed.Contains(w.Severity));
+        }
+
+        public static IQueryable<WorkOrder> ApplyRescheduledFilter(
+            IQueryable<WorkOrder> query,
+            bool rescheduled)
+        {
+            if (!rescheduled)
+                return query;
+
+            return query.Where(w => w.RescheduleCount >= 2);
+        }
+
+        public static IQueryable<WorkOrder> ApplyCarriedOverFilter(
+            IQueryable<WorkOrder> query,
+            bool carriedOver)
+        {
+            if (!carriedOver)
+                return query;
+
+            return query.Where(w => w.CarriedOver >= 2);
+        }
+
+        public static IQueryable<WorkOrder> ApplyAddOnFilter(
+            IQueryable<WorkOrder> query,
+            bool addOn)
+        {
+            if (!addOn)
+                return query;
+
+            return query.Where(w => w.IsAddOn);
+        }
+
+        public static IQueryable<WorkOrder> ApplyFlagColorFilter(
+            IQueryable<WorkOrder> query,
+            IReadOnlyList<string>? flagColors)
+        {
+            if (flagColors == null || flagColors.Count == 0)
+                return query;
+
+            var normalized = flagColors
+                .Where(c => !string.IsNullOrWhiteSpace(c))
+                .Select(c => c.Trim().ToUpperInvariant())
+                .Distinct()
+                .ToList();
+
+            if (normalized.Count == 0)
+                return query;
+
+            return query.Where(w =>
+                w.FlagColor != null && normalized.Contains(w.FlagColor.ToUpper()));
+        }
+
+        public static IQueryable<WorkOrder> ApplyInternalOnlyFilter(
+            IQueryable<WorkOrder> query,
+            bool internalOnly)
+        {
+            if (!internalOnly)
+                return query;
+
+            return query.Where(w =>
+                w.InternalWONumber != null
+                && EF.Functions.Like(w.InternalWONumber, "SH%"));
+        }
+
+        public static IQueryable<WorkOrder> ApplyUpliftFilter(
+            IQueryable<WorkOrder> query,
+            ApplicationDbContext context,
+            bool hasUplift,
+            IReadOnlyList<string>? upliftStatuses)
+        {
+            if (!hasUplift)
+                return query;
+
+            var mappedStatuses = MapUpliftStatuses(upliftStatuses);
+
+            return query.Where(w => context.DispatchUpliftRequests.Any(u =>
+                (u.IsDeleted == null || u.IsDeleted == false)
+                && u.Status != "Expired"
+                && !RevokedUpliftStatuses.Contains(u.Status)
+                && u.Dispatch != null
+                && (u.Dispatch.IsDeleted == null || u.Dispatch.IsDeleted == false)
+                && (
+                    u.Dispatch.WorkOrderId == w.Id
+                    || u.Dispatch.DispatchWorkOrders!.Any(link => link.WorkOrderId == w.Id))
+                && (mappedStatuses.Count == 0 || mappedStatuses.Contains(u.Status))));
+        }
+
+        internal static List<string> MapUpliftStatuses(IReadOnlyList<string>? upliftStatuses)
+        {
+            if (upliftStatuses == null || upliftStatuses.Count == 0)
+                return new List<string>();
+
+            var mapped = new List<string>();
+            foreach (var raw in upliftStatuses)
+            {
+                if (string.IsNullOrWhiteSpace(raw))
+                    continue;
+
+                switch (raw.Trim().ToLowerInvariant())
+                {
+                    case "pending":
+                        mapped.Add("Pending");
+                        mapped.Add("ChangesRequested");
+                        break;
+                    case "approved":
+                        mapped.Add("Approved");
+                        break;
+                    case "auto_approved":
+                        mapped.Add("NoApprovalRequired");
+                        break;
+                    case "rejected":
+                        mapped.Add("Rejected");
+                        mapped.Add("Denied");
+                        break;
+                }
+            }
+
+            return mapped.Distinct(StringComparer.Ordinal).ToList();
+        }
+    }
+
+}
diff --git a/SeaHaven.DataServices/Helpers/WorkOrderBoardSearchFilter.cs b/SeaHaven.DataServices/Helpers/WorkOrderBoardSearchFilter.cs
index d6cf28d..441802b 100644
--- a/SeaHaven.DataServices/Helpers/WorkOrderBoardSearchFilter.cs
+++ b/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.ScheduledDate != null
diff --git a/SeaHaven.DataServices/Implementation/WorkOrderAdvancedSearchDataService.cs b/SeaHaven.DataServices/Implementation/WorkOrderAdvancedSearchDataService.cs
index de1f4d2..1d4892d 100644
--- a/SeaHaven.DataServices/Implementation/WorkOrderAdvancedSearchDataService.cs
+++ b/SeaHaven.DataServices/Implementation/WorkOrderAdvancedSearchDataService.cs
@@ -28,6 +28,14 @@ namespace SeaHaven.DataServices.Implementation
             baseQuery = WorkOrderBoardQueryFilters.ApplyPmTypeFilter(baseQuery, query.PmTypes);
             baseQuery = WorkOrderBoardQueryFilters.ApplyVendorFilter(baseQuery, query.VendorIds);
             baseQuery = WorkOrderBoardQueryFilters.ApplyDocStatusFilter(baseQuery, query.DocStatuses);
+            baseQuery = WorkOrderBoardSearchFacetFilters.ApplySeverityFilter(baseQuery, query.Severities);
+            baseQuery = WorkOrderBoardSearchFacetFilters.ApplyRescheduledFilter(baseQuery, query.Rescheduled);
+            baseQuery = WorkOrderBoardSearchFacetFilters.ApplyCarriedOverFilter(baseQuery, query.CarriedOver);
+            baseQuery = WorkOrderBoardSearchFacetFilters.ApplyAddOnFilter(baseQuery, query.AddOn);
+            baseQuery = WorkOrderBoardSearchFacetFilters.ApplyFlagColorFilter(baseQuery, query.FlagColors);
+            baseQuery = WorkOrderBoardSearchFacetFilters.ApplyInternalOnlyFilter(baseQuery, query.InternalOnly);
+            baseQuery = WorkOrderBoardSearchFacetFilters.ApplyUpliftFilter(
+                baseQuery, _context, query.HasUplift, query.UpliftStatuses);
 
             var normalizedSearch = WorkOrderBoardSearchFilter.NormalizeSearch(query.Search);
             if (normalizedSearch != null)
diff --git a/SeaHaven.DataServices/Implementation/WorkOrderDomainJobDataService.cs b/SeaHaven.DataServices/Implementation/WorkOrderDomainJobDataService.cs
index 65d98bc..ca15639 100644
--- a/SeaHaven.DataServices/Implementation/WorkOrderDomainJobDataService.cs
+++ b/SeaHaven.DataServices/Implementation/WorkOrderDomainJobDataService.cs
@@ -120,7 +120,7 @@ namespace SeaHaven.DataServices.Implementation
                 var batch = await _context.workOrders
                     .Where(w => w.IsDeleted != true)
                     .Where(w => w.istemplate != true)
-                    .Where(w => w.ScheduledDate != null)
+                    .Where(w => w.DueDate != null)
                     .OrderBy(w => w.Id)
                     .Skip(skip)
                     .Take(batchSize)
@@ -132,7 +132,7 @@ namespace SeaHaven.DataServices.Implementation
                 foreach (var workOrder in batch)
                 {
                     examinedCount++;
-                    var shouldBePastDue = workOrder.ScheduledDate!.Value.Date < today
+                    var shouldBePastDue = workOrder.DueDate!.Value.Date < today
                         && !TerminalStatuses.Contains(workOrder.LifecycleStatus);
                     var hasFlag = workOrder.OperationalFlags.HasFlag(OperationalFlags.PastDue);
 
diff --git a/SeaHaven.DataServices/Interfaces/WorkOrderAdvancedSearchModels.cs b/SeaHaven.DataServices/Interfaces/WorkOrderAdvancedSearchModels.cs
index d1ef77f..b965e86 100644
--- a/SeaHaven.DataServices/Interfaces/WorkOrderAdvancedSearchModels.cs
+++ b/SeaHaven.DataServices/Interfaces/WorkOrderAdvancedSearchModels.cs
@@ -15,6 +15,14 @@ namespace SeaHaven.DataServices.Interfaces
         IReadOnlyList<string>? PmTypes,
         IReadOnlyList<int>? VendorIds,
         IReadOnlyList<DocStatus>? DocStatuses,
+        IReadOnlyList<int>? Severities,
+        bool Rescheduled,
+        bool CarriedOver,
+        bool AddOn,
+        IReadOnlyList<string>? FlagColors,
+        bool InternalOnly,
+        bool HasUplift,
+        IReadOnlyList<string>? UpliftStatuses,
         bool MyWorkOrders,
         string? CurrentUserId,
         int Page,
diff --git a/SeaHaven.DataServices/Interfaces/WorkOrderBoardModels.cs b/SeaHaven.DataServices/Interfaces/WorkOrderBoardModels.cs
index ca27ca0..ad46340 100644
--- a/SeaHaven.DataServices/Interfaces/WorkOrderBoardModels.cs
+++ b/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,
diff --git a/SeaHaven.Services/DTOs/WorkOrderBoardDTOs.cs b/SeaHaven.Services/DTOs/WorkOrderBoardDTOs.cs
index de3fe67..1a2c9c2 100644
--- a/SeaHaven.Services/DTOs/WorkOrderBoardDTOs.cs
+++ b/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; }
diff --git a/SeaHaven.Services/DTOs/WorkOrderBoardRequestDTOs.cs b/SeaHaven.Services/DTOs/WorkOrderBoardRequestDTOs.cs
index 3ca672c..0f7d976 100644
--- a/SeaHaven.Services/DTOs/WorkOrderBoardRequestDTOs.cs
+++ b/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)
@@ -63,6 +68,14 @@ namespace SeaHaven.Services.DTOs
         public List<string>? PmTypes { get; set; }
         public List<int>? VendorIds { get; set; }
         public List<DocStatus>? DocStatuses { get; set; }
+        public List<int>? Severities { get; set; }
+        public bool Rescheduled { get; set; }
+        public bool CarriedOver { get; set; }
+        public bool AddOn { get; set; }
+        public List<string>? FlagColors { get; set; }
+        public bool InternalOnly { get; set; }
+        public bool HasUplift { get; set; }
+        public List<string>? UpliftStatuses { get; set; }
         public bool MyWorkOrders { get; set; }
         public string? SortBy { get; set; }
         public string? SortDir { get; set; }
diff --git a/SeaHaven.Services/Helpers/WorkOrderAddonCutoff.cs b/SeaHaven.Services/Helpers/WorkOrderAddonCutoff.cs
new file mode 100644
index 0000000..db81e62
--- /dev/null
+++ b/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);
+        }
+    }
+}
diff --git a/SeaHaven.Services/Helpers/WorkOrderBoardMutationRules.cs b/SeaHaven.Services/Helpers/WorkOrderBoardMutationRules.cs
index 3067947..3589d36 100644
--- a/SeaHaven.Services/Helpers/WorkOrderBoardMutationRules.cs
+++ b/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);
diff --git a/SeaHaven.Services/Helpers/WorkOrderDerivedFields.cs b/SeaHaven.Services/Helpers/WorkOrderDerivedFields.cs
index b64d16c..c7ac473 100644
--- a/SeaHaven.Services/Helpers/WorkOrderDerivedFields.cs
+++ b/SeaHaven.Services/Helpers/WorkOrderDerivedFields.cs
@@ -1,4 +1,4 @@
-using Data.SeaHavenIndustries;
+using Data.SeaHavenIndustries;
 using Data.SeaHavenIndustries.Enums;
 
 namespace SeaHaven.Services.Helpers
@@ -6,7 +6,8 @@ namespace SeaHaven.Services.Helpers
     public static class WorkOrderDerivedFields
     {
         /// <summary>
-        /// Past due overlay — never a WorkOrderType. Matches SHOC board design.
+        /// Past due overlay from Schedule On — never a WorkOrderType. Matches SHOC board design (SH-185).
+        /// Changing Due Date alone must never trigger or clear it.
         /// </summary>
         public static bool IsPastDue(WorkOrder workOrder, DateOnly? asOf = null)
         {
@@ -21,7 +22,7 @@ namespace SeaHaven.Services.Helpers
         }
 
         /// <summary>
-        /// Board read-model past-due check. Phase 1 compares UTC calendar dates;
+        /// Board read-model past-due check against ScheduledDate. Compares UTC calendar dates;
         /// business/location timezone support is planned for a later phase.
         /// </summary>
         public static bool IsPastDue(
diff --git a/SeaHaven.Services/Implementation/WorkOrderAdvancedSearchService.cs b/SeaHaven.Services/Implementation/WorkOrderAdvancedSearchService.cs
index a4d332d..f1e79cf 100644
--- a/SeaHaven.Services/Implementation/WorkOrderAdvancedSearchService.cs
+++ b/SeaHaven.Services/Implementation/WorkOrderAdvancedSearchService.cs
@@ -51,6 +51,14 @@ namespace SeaHaven.Services.Implementation
                 query.PmTypes,
                 query.VendorIds,
                 query.DocStatuses,
+                query.Severities,
+                query.Rescheduled,
+                query.CarriedOver,
+                query.AddOn,
+                query.FlagColors,
+                query.InternalOnly,
+                query.HasUplift,
+                query.UpliftStatuses,
                 query.MyWorkOrders,
                 currentUserId,
                 page,
diff --git a/SeaHaven.Services/Implementation/WorkOrderBoardCreateService.cs b/SeaHaven.Services/Implementation/WorkOrderBoardCreateService.cs
index ee32e53..acba7d6 100644
--- a/SeaHaven.Services/Implementation/WorkOrderBoardCreateService.cs
+++ b/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),
diff --git a/SeaHaven.Services/Implementation/WorkOrderBoardService.cs b/SeaHaven.Services/Implementation/WorkOrderBoardService.cs
index 04bf63c..a2bda0c 100644
--- a/SeaHaven.Services/Implementation/WorkOrderBoardService.cs
+++ b/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.ScheduledDate, row.LifecycleStatus, utcNow),
                 SiteCode = row.SiteCode,
diff --git a/SeaHaven.Services/Implementation/WorkOrderBoardUpdateService.cs b/SeaHaven.Services/Implementation/WorkOrderBoardUpdateService.cs
index 3e8c108..126d01e 100644
--- a/SeaHaven.Services/Implementation/WorkOrderBoardUpdateService.cs
+++ b/SeaHaven.Services/Implementation/WorkOrderBoardUpdateService.cs
@@ -63,7 +63,7 @@ namespace SeaHaven.Services.Implementation
 
                 var isPastDue = WorkOrderDerivedFields.IsPastDue(workOrder.ScheduledDate, workOrder.LifecycleStatus);
                 if (WorkOrderBoardMutationRules.ShouldBlockStatusChangeWhenPastDue(canonicalField, isPastDue))
-                    throw new WorkOrderBoardValidationException("PastDueStatusBlocked", "Status cannot be changed while work order is past due. Reschedule first.");
+                    throw new WorkOrderBoardValidationException("PastDueStatusBlocked", "Status cannot be changed while work order is past due. Update Schedule On first.");
 
                 _mutationData.SetExpectedWorkOrderVersion(workOrder, workOrderVersion);
 
@@ -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.ScheduleWeekOnly => new List<FieldChange> { ApplyBoolField(value, auditField, v => workOrder.ScheduleWeekOnly = v, () => workOrder.ScheduleWeekOnly) },
+                WorkOrderBoardFieldNames.TargetWeek => ApplyTargetWeek(workOrder, value, auditField),
+                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),
@@ -232,7 +232,7 @@ namespace SeaHaven.Services.Implementation
             if (string.Equals(value.Trim(), "Overdue", StringComparison.OrdinalIgnoreCase))
                 throw new WorkOrderBoardValidationException(
                     "InvalidValue",
-                    "Overdue is not a work order type; it is derived from scheduledDate (isPastDue).");
+                    "Overdue is not a work order type; it is derived from dueDate (isPastDue).");
 
             if (!WorkOrderTypeMapper.TryParseFeLabel(value, out var parsed))
                 throw new WorkOrderBoardValidationException("InvalidValue", $"Invalid workOrderType: {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)
-                return FieldChange.Unchanged(auditField);
+            if (old != newVal)
+            {
+                workOrder.TargetWeek = parsed;
+                changes.Add(FieldChange.ForField(auditField, old, newVal));
+            }
 
-            workOrder.TargetWeek = parsed;
-            return 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(
diff --git a/SeaHaven.Services/Implementation/WorkOrderDetailService.cs b/SeaHaven.Services/Implementation/WorkOrderDetailService.cs
index 0bb6eac..9da5034 100644
--- a/SeaHaven.Services/Implementation/WorkOrderDetailService.cs
+++ b/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,
diff --git a/SeaHaven.Services/Validation/WorkOrderBoardCreateValidation.cs b/SeaHaven.Services/Validation/WorkOrderBoardCreateValidation.cs
index 8d0564d..8d7b1d5 100644
--- a/SeaHaven.Services/Validation/WorkOrderBoardCreateValidation.cs
+++ b/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.")
diff --git a/SeaHavenIndustries.Tests/WorkOrderAddonCutoffTests.cs b/SeaHavenIndustries.Tests/WorkOrderAddonCutoffTests.cs
new file mode 100644
index 0000000..d860482
--- /dev/null
+++ b/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);
+    }
+}
diff --git a/SeaHavenIndustries.Tests/WorkOrderBoardConcurrencyTests.cs b/SeaHavenIndustries.Tests/WorkOrderBoardConcurrencyTests.cs
index 16f8e9e..d1014b6 100644
--- a/SeaHavenIndustries.Tests/WorkOrderBoardConcurrencyTests.cs
+++ b/SeaHavenIndustries.Tests/WorkOrderBoardConcurrencyTests.cs
@@ -141,8 +141,11 @@ public class WorkOrderBoardConcurrencyTests
             WorkOrderVersion = Convert.ToBase64String(wo!.RowVersion!)
         }, "actor-1");
 
-        var auditCount = await context.WorkOrderAuditLogs.CountAsync();
-        Assert.Equal(2, auditCount);
+        var audits = await context.WorkOrderAuditLogs.ToListAsync();
+        Assert.Equal(3, audits.Count);
+        Assert.Contains(audits, a => a.FieldName == "IsAddOn");
+        Assert.Contains(audits, a => a.FieldName == "ScheduledDate");
+        Assert.Contains(audits, a => a.FieldName == "RescheduleCount");
     }
 
     [Fact]
diff --git a/SeaHavenIndustries.Tests/WorkOrderBoardCreateServiceTests.cs b/SeaHavenIndustries.Tests/WorkOrderBoardCreateServiceTests.cs
index bd5f2bf..16cd08d 100644
--- a/SeaHavenIndustries.Tests/WorkOrderBoardCreateServiceTests.cs
+++ b/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
+        }, WorkOrderAccountTestHelpers.AccountUser(), "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
+        }, WorkOrderAccountTestHelpers.AccountUser(), "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
+        }, WorkOrderAccountTestHelpers.AccountUser(), "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"
+            }, WorkOrderAccountTestHelpers.AccountUser(), "actor-1"));
+
+        Assert.Contains(ex.Errors, e => e.PropertyName == "WorkOrderType");
+    }
 }
diff --git a/SeaHavenIndustries.Tests/WorkOrderBoardMutationRulesTests.cs b/SeaHavenIndustries.Tests/WorkOrderBoardMutationRulesTests.cs
index 933aa80..4cda7f8 100644
--- a/SeaHavenIndustries.Tests/WorkOrderBoardMutationRulesTests.cs
+++ b/SeaHavenIndustries.Tests/WorkOrderBoardMutationRulesTests.cs
@@ -22,6 +22,8 @@ public class WorkOrderBoardMutationRulesTests
             WorkOrderBoardFieldNames.LifecycleStatus, isPastDue: true));
         Assert.False(WorkOrderBoardMutationRules.ShouldBlockStatusChangeWhenPastDue(
             WorkOrderBoardFieldNames.ScheduledDate, isPastDue: true));
+        Assert.False(WorkOrderBoardMutationRules.ShouldBlockStatusChangeWhenPastDue(
+            WorkOrderBoardFieldNames.DueDate, isPastDue: true));
     }
 
     [Fact]
diff --git a/SeaHavenIndustries.Tests/WorkOrderBoardSearchTests.cs b/SeaHavenIndustries.Tests/WorkOrderBoardSearchTests.cs
index 780c25c..9da4328 100644
--- a/SeaHavenIndustries.Tests/WorkOrderBoardSearchTests.cs
+++ b/SeaHavenIndustries.Tests/WorkOrderBoardSearchTests.cs
@@ -342,7 +342,8 @@ public class WorkOrderAdvancedSearchServiceTests
             {
                 Id = 1,
                 WorkOrderType = WorkOrderType.PM,
-                ScheduledDate = today.AddDays(-3),
+                DueDate = today.AddDays(-3),
+                ScheduledDate = today.AddDays(5),
                 LifecycleStatus = LifecycleStatus.Scheduled,
                 InternalWONumber = "10000000001"
             },
@@ -358,7 +359,8 @@ public class WorkOrderAdvancedSearchServiceTests
             {
                 Id = 3,
                 WorkOrderType = WorkOrderType.Reactive,
-                ScheduledDate = today.AddDays(1),
+                DueDate = today.AddDays(1),
+                ScheduledDate = today.AddDays(-5),
                 LifecycleStatus = LifecycleStatus.Scheduled,
                 InternalWONumber = "10000000003"
             });
@@ -377,7 +379,7 @@ public class WorkOrderAdvancedSearchServiceTests
         }, WorkOrderAccountTestHelpers.OrgWideAdmin(), null);
 
         Assert.Equal(1, result.TotalCount);
-        Assert.Equal(1, result.Items.First().Id);
+        Assert.Equal(3, result.Items.First().Id);
         Assert.True(result.Items.First().IsPastDue);
     }
 
@@ -392,6 +394,7 @@ public class WorkOrderAdvancedSearchServiceTests
             {
                 Id = 1,
                 WorkOrderType = WorkOrderType.PM,
+                DueDate = today.AddDays(5),
                 ScheduledDate = today.AddDays(-3),
                 LifecycleStatus = LifecycleStatus.Scheduled,
                 InternalWONumber = "10000000001"
@@ -408,6 +411,7 @@ public class WorkOrderAdvancedSearchServiceTests
             {
                 Id = 3,
                 WorkOrderType = WorkOrderType.Reactive,
+                DueDate = today.AddDays(1),
                 ScheduledDate = today.AddDays(1),
                 LifecycleStatus = LifecycleStatus.Scheduled,
                 InternalWONumber = "10000000003"
@@ -444,7 +448,8 @@ public class WorkOrderAdvancedSearchServiceTests
             {
                 Id = 1,
                 WorkOrderType = WorkOrderType.Other,
-                ScheduledDate = today.AddDays(5),
+                DueDate = today.AddDays(5),
+                ScheduledDate = today.AddDays(-5),
                 LifecycleStatus = LifecycleStatus.Scheduled,
                 InternalWONumber = "10000000001"
             },
@@ -452,7 +457,8 @@ public class WorkOrderAdvancedSearchServiceTests
             {
                 Id = 2,
                 WorkOrderType = WorkOrderType.PM,
-                ScheduledDate = today.AddDays(-3),
+                DueDate = today.AddDays(-3),
+                ScheduledDate = today.AddDays(5),
                 LifecycleStatus = LifecycleStatus.Scheduled,
                 InternalWONumber = "10000000002"
             },
@@ -460,6 +466,7 @@ public class WorkOrderAdvancedSearchServiceTests
             {
                 Id = 3,
                 WorkOrderType = WorkOrderType.Reactive,
+                DueDate = today.AddDays(-2),
                 ScheduledDate = today.AddDays(-2),
                 LifecycleStatus = LifecycleStatus.Completed,
                 InternalWONumber = "10000000003"
@@ -468,6 +475,7 @@ public class WorkOrderAdvancedSearchServiceTests
             {
                 Id = 4,
                 WorkOrderType = WorkOrderType.Reactive,
+                DueDate = today.AddDays(-1),
                 ScheduledDate = today.AddDays(-1),
                 LifecycleStatus = LifecycleStatus.Canceled,
                 InternalWONumber = "10000000004"
@@ -490,9 +498,9 @@ public class WorkOrderAdvancedSearchServiceTests
 
         var overdue = Assert.Single(result.Items);
         Assert.Equal(0, result.Page);
-        Assert.Equal(2, overdue.Id);
+        Assert.Equal(1, overdue.Id);
         Assert.True(overdue.IsPastDue);
-        Assert.DoesNotContain(result.Items, i => i.Id == 1);
+        Assert.DoesNotContain(result.Items, i => i.Id == 2);
         Assert.DoesNotContain(result.Items, i => i.Id == 3);
         Assert.DoesNotContain(result.Items, i => i.Id == 4);
     }
@@ -605,4 +613,220 @@ 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,
+            WorkOrderAccountTestHelpers.Resolver(context));
+
+        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 }
+        }, WorkOrderAccountTestHelpers.OrgWideAdmin(), 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);
+    }
+
+    [Fact]
+    public async Task SearchAsync_SeverityFilter_ReturnsEmergencyReactiveOnly()
+    {
+        await using var context = CreateContext();
+        var weekStart = new DateOnly(2026, 6, 22);
+
+        context.workOrders.AddRange(
+            new WorkOrder
+            {
+                Id = 1,
+                WorkOrderType = WorkOrderType.Emergency,
+                Severity = "1",
+                ScheduledDate = new DateTime(2026, 6, 23),
+                LifecycleStatus = LifecycleStatus.Scheduled,
+                InternalWONumber = "10000000001",
+            },
+            new WorkOrder
+            {
+                Id = 2,
+                WorkOrderType = WorkOrderType.Reactive,
+                Severity = "2",
+                ScheduledDate = new DateTime(2026, 6, 24),
+                LifecycleStatus = LifecycleStatus.Scheduled,
+                InternalWONumber = "10000000002",
+            },
+            new WorkOrder
+            {
+                Id = 3,
+                WorkOrderType = WorkOrderType.PM,
+                Severity = "1",
+                ScheduledDate = new DateTime(2026, 6, 25),
+                LifecycleStatus = LifecycleStatus.Scheduled,
+                InternalWONumber = "10000000003",
+            });
+
+        await context.SaveChangesAsync();
+
+        var dataService = new WorkOrderAdvancedSearchDataService(context);
+        var service = new SeaHaven.Services.Implementation.WorkOrderAdvancedSearchService(
+            dataService,
+            WorkOrderAccountTestHelpers.Resolver(context));
+
+        var result = await service.SearchAsync(
+            new SeaHaven.Services.DTOs.WorkOrderAdvancedSearchQueryDto
+            {
+                DatePreset = SeaHaven.Services.Helpers.WorkOrderAdvancedSearchDatePreset.Custom,
+                DateFrom = weekStart,
+                DateTo = weekStart.AddDays(6),
+                Severities = new List<int> { 1 },
+            },
+            WorkOrderAccountTestHelpers.OrgWideAdmin(),
+            null);
+
+        Assert.Equal(1, result.TotalCount);
+        Assert.Equal(1, result.Items.Single().Id);
+    }
+
+    [Fact]
+    public async Task SearchAsync_InternalOnly_ReturnsShPrefixRows()
+    {
+        await using var context = CreateContext();
+        var weekStart = new DateOnly(2026, 6, 22);
+
+        context.workOrders.AddRange(
+            new WorkOrder
+            {
+                Id = 1,
+                InternalWONumber = "SH-1001",
+                ScheduledDate = new DateTime(2026, 6, 23),
+                LifecycleStatus = LifecycleStatus.Scheduled,
+            },
+            new WorkOrder
+            {
+                Id = 2,
+                InternalWONumber = "10000000002",
+                ScheduledDate = new DateTime(2026, 6, 24),
+                LifecycleStatus = LifecycleStatus.Scheduled,
+            });
+
+        await context.SaveChangesAsync();
+
+        var dataService = new WorkOrderAdvancedSearchDataService(context);
+        var service = new SeaHaven.Services.Implementation.WorkOrderAdvancedSearchService(
+            dataService,
+            WorkOrderAccountTestHelpers.Resolver(context));
+
+        var result = await service.SearchAsync(
+            new SeaHaven.Services.DTOs.WorkOrderAdvancedSearchQueryDto
+            {
+                DatePreset = SeaHaven.Services.Helpers.WorkOrderAdvancedSearchDatePreset.Custom,
+                DateFrom = weekStart,
+                DateTo = weekStart.AddDays(6),
+                InternalOnly = true,
+            },
+            WorkOrderAccountTestHelpers.OrgWideAdmin(),
+            null);
+
+        Assert.Equal(1, result.TotalCount);
+        Assert.Equal("SH-1001", result.Items.Single().WoNumber);
+    }
+
+    [Fact]
+    public async Task SearchAsync_HasUpliftWithPendingStatus_FiltersRows()
+    {
+        await using var context = CreateContext();
+        var weekStart = new DateOnly(2026, 6, 22);
+
+        context.Vendors.Add(new Vendor { Id = 1, CompanyName = "Acme HVAC" });
+        context.Dispatches.Add(new Dispatch { Id = 10, VendorId = 1, WorkOrderId = 1 });
+        context.Dispatches.Add(new Dispatch { Id = 11, VendorId = 1, WorkOrderId = 2 });
+        context.workOrders.AddRange(
+            new WorkOrder
+            {
+                Id = 1,
+                InternalWONumber = "10000000001",
+                ScheduledDate = new DateTime(2026, 6, 23),
+                LifecycleStatus = LifecycleStatus.Scheduled,
+                PrimaryDispatchId = 10,
+            },
+            new WorkOrder
+            {
+                Id = 2,
+                InternalWONumber = "10000000002",
+                ScheduledDate = new DateTime(2026, 6, 24),
+                LifecycleStatus = LifecycleStatus.Scheduled,
+                PrimaryDispatchId = 11,
+            });
+        context.DispatchUpliftRequests.Add(new DispatchUpliftRequest
+        {
+            Id = 100,
+            DispatchId = 10,
+            RequestedNTE = 1500m,
+            Status = "Pending",
+            RequiredTier = 1,
+            NotificationStatus = "Pending",
+        });
+
+        await context.SaveChangesAsync();
+
+        var dataService = new WorkOrderAdvancedSearchDataService(context);
+        var service = new SeaHaven.Services.Implementation.WorkOrderAdvancedSearchService(
+            dataService,
+            WorkOrderAccountTestHelpers.Resolver(context));
+
+        var result = await service.SearchAsync(
+            new SeaHaven.Services.DTOs.WorkOrderAdvancedSearchQueryDto
+            {
+                DatePreset = SeaHaven.Services.Helpers.WorkOrderAdvancedSearchDatePreset.Custom,
+                DateFrom = weekStart,
+                DateTo = weekStart.AddDays(6),
+                HasUplift = true,
+                UpliftStatuses = new List<string> { "pending" },
+            },
+            WorkOrderAccountTestHelpers.OrgWideAdmin(),
+            null);
+
+        Assert.Equal(1, result.TotalCount);
+        Assert.Equal(1, result.Items.Single().Id);
+    }
 }
diff --git a/SeaHavenIndustries.Tests/WorkOrderBoardServiceTests.cs b/SeaHavenIndustries.Tests/WorkOrderBoardServiceTests.cs
index 92c4d36..32a890c 100644
--- a/SeaHavenIndustries.Tests/WorkOrderBoardServiceTests.cs
+++ b/SeaHavenIndustries.Tests/WorkOrderBoardServiceTests.cs
@@ -391,6 +391,7 @@ public class WorkOrderBoardServiceTests
         {
             Id = 1,
             InternalWONumber = "10000000001",
+            DueDate = new DateTime(2026, 6, 20),
             ScheduledDate = new DateTime(2026, 6, 24, 12, 0, 0, DateTimeKind.Utc),
             LifecycleStatus = LifecycleStatus.Scheduled
         });
@@ -411,6 +412,37 @@ 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),
+            WorkOrderAccountTestHelpers.Resolver(context));
+        var response = await boardService.GetBoardAsync(new WorkOrderBoardQueryDto
+        {
+            WeekStart = weekStart
+        }, WorkOrderAccountTestHelpers.OrgWideAdmin(), 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()
     {
diff --git a/SeaHavenIndustries.Tests/WorkOrderBoardUpdateServiceTests.cs b/SeaHavenIndustries.Tests/WorkOrderBoardUpdateServiceTests.cs
index b775ee6..c76632a 100644
--- a/SeaHavenIndustries.Tests/WorkOrderBoardUpdateServiceTests.cs
+++ b/SeaHavenIndustries.Tests/WorkOrderBoardUpdateServiceTests.cs
@@ -55,7 +55,11 @@ public class WorkOrderBoardUpdateServiceTests
         }, "actor-1");
 
         Assert.Equal(LifecycleStatus.Scheduled, result.LifecycleStatus);
-        Assert.Equal(2, await context.WorkOrderAuditLogs.CountAsync());
+        var audits = await context.WorkOrderAuditLogs.ToListAsync();
+        Assert.Equal(3, audits.Count);
+        Assert.Contains(audits, a => a.FieldName == "IsAddOn");
+        Assert.Contains(audits, a => a.FieldName == "ScheduledDate");
+        Assert.Contains(audits, a => a.Action == AuditActionType.StatusChanged.ToString());
     }
 
     [Fact]
@@ -91,6 +95,7 @@ public class WorkOrderBoardUpdateServiceTests
         {
             Id = 1,
             LifecycleStatus = LifecycleStatus.Scheduled,
+            DueDate = DateTime.UtcNow.Date.AddDays(5),
             ScheduledDate = DateTime.UtcNow.Date.AddDays(-3),
             RowVersion = new byte[] { 1, 0, 0, 0, 0, 0, 0, 1 }
         };
@@ -106,6 +111,149 @@ public class WorkOrderBoardUpdateServiceTests
             }, "actor-1"));
 
         Assert.Equal("PastDueStatusBlocked", ex.Code);
+        Assert.Contains("Schedule On", ex.Message, StringComparison.Ordinal);
+        Assert.DoesNotContain("due date", ex.Message, StringComparison.OrdinalIgnoreCase);
+    }
+
+    [Fact]
+    public async Task PatchField_FutureSchedule_ClearsPastDueAndAllowsStatusChange()
+    {
+        var (context, service) = CreateSut();
+        var wo = new WorkOrder
+        {
+            Id = 1,
+            LifecycleStatus = LifecycleStatus.Scheduled,
+            DueDate = DateTime.UtcNow.Date.AddDays(-3),
+            ScheduledDate = DateTime.UtcNow.Date.AddDays(-1),
+            RowVersion = new byte[] { 1, 0, 0, 0, 0, 0, 0, 1 }
+        };
+        context.workOrders.Add(wo);
+        await context.SaveChangesAsync();
+
+        var futureSchedule = DateTime.UtcNow.Date.AddDays(7).ToString("yyyy-MM-dd");
+        var row = await service.PatchFieldAsync(1, new WorkOrderBoardPatchRequestDto
+        {
+            Field = WorkOrderBoardFieldNames.ScheduledDate,
+            Value = futureSchedule,
+            WorkOrderVersion = ToVersion(wo)
+        }, "actor-1");
+
+        Assert.False(row.IsPastDue);
+        Assert.Equal(DateTime.UtcNow.Date.AddDays(7), row.ScheduledDate!.Value.Date);
+
+        wo = await context.workOrders.SingleAsync(w => w.Id == 1);
+        var afterStatus = await service.PatchFieldAsync(1, new WorkOrderBoardPatchRequestDto
+        {
+            Field = WorkOrderBoardFieldNames.LifecycleStatus,
+            Value = "Complete",
+            WorkOrderVersion = ToVersion(wo)
+        }, "actor-1");
+
+        Assert.Equal(LifecycleStatus.Completed, afterStatus.LifecycleStatus);
+        Assert.False(afterStatus.IsPastDue);
+    }
+
+    [Fact]
+    public async Task PatchField_DueDateAlone_DoesNotClearPastDue()
+    {
+        var (context, service) = CreateSut();
+        var wo = new WorkOrder
+        {
+            Id = 1,
+            LifecycleStatus = LifecycleStatus.Scheduled,
+            DueDate = DateTime.UtcNow.Date.AddDays(-3),
+            ScheduledDate = DateTime.UtcNow.Date.AddDays(-1),
+            RowVersion = new byte[] { 1, 0, 0, 0, 0, 0, 0, 1 }
+        };
+        context.workOrders.Add(wo);
+        await context.SaveChangesAsync();
+
+        var futureDue = DateTime.UtcNow.Date.AddDays(10).ToString("yyyy-MM-dd");
+        var afterDue = await service.PatchFieldAsync(1, new WorkOrderBoardPatchRequestDto
+        {
+            Field = WorkOrderBoardFieldNames.DueDate,
+            Value = futureDue,
+            WorkOrderVersion = ToVersion(wo)
+        }, "actor-1");
+
+        Assert.True(afterDue.IsPastDue);
+        Assert.Equal(DateTime.UtcNow.Date.AddDays(-1), afterDue.ScheduledDate!.Value.Date);
+
+        wo = await context.workOrders.SingleAsync(w => w.Id == 1);
+        var ex = await Assert.ThrowsAsync<WorkOrderBoardValidationException>(() =>
+            service.PatchFieldAsync(1, new WorkOrderBoardPatchRequestDto
+            {
+                Field = WorkOrderBoardFieldNames.LifecycleStatus,
+                Value = "Complete",
+                WorkOrderVersion = ToVersion(wo)
+            }, "actor-1"));
+
+        Assert.Equal("PastDueStatusBlocked", ex.Code);
+        Assert.Contains("Schedule On", ex.Message, StringComparison.Ordinal);
+        Assert.DoesNotContain("due date", ex.Message, StringComparison.OrdinalIgnoreCase);
+    }
+
+    [Fact]
+    public async Task PatchField_DueDate_DoesNotChangeScheduledDate()
+    {
+        var (context, service) = CreateSut();
+        var scheduled = new DateTime(2026, 6, 20);
+        var wo = new WorkOrder
+        {
+            Id = 1,
+            LifecycleStatus = LifecycleStatus.Scheduled,
+            DueDate = new DateTime(2026, 6, 18),
+            ScheduledDate = scheduled,
+            RescheduleCount = 2,
+            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.DueDate,
+            Value = "2026-07-01",
+            WorkOrderVersion = ToVersion(wo)
+        }, "actor-1");
+
+        Assert.Equal(new DateTime(2026, 7, 1), result.DueDate!.Value.Date);
+        Assert.Equal(scheduled, result.ScheduledDate);
+        Assert.Equal(2, result.RescheduleCount);
+
+        var persisted = await context.workOrders.SingleAsync(w => w.Id == 1);
+        Assert.Equal(scheduled, persisted.ScheduledDate);
+        Assert.Equal(2, persisted.RescheduleCount);
+    }
+
+    [Fact]
+    public async Task PatchField_ScheduledDate_DoesNotChangeDueDate()
+    {
+        var (context, service) = CreateSut();
+        var due = new DateTime(2026, 6, 18);
+        var wo = new WorkOrder
+        {
+            Id = 1,
+            LifecycleStatus = LifecycleStatus.Scheduled,
+            DueDate = due,
+            ScheduledDate = new DateTime(2026, 6, 20),
+            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.Equal(new DateTime(2026, 6, 25), result.ScheduledDate!.Value.Date);
+        Assert.Equal(due, result.DueDate);
+
+        var persisted = await context.workOrders.SingleAsync(w => w.Id == 1);
+        Assert.Equal(due, persisted.DueDate);
     }
 
     [Fact]
@@ -132,7 +280,7 @@ public class WorkOrderBoardUpdateServiceTests
 
         Assert.Equal("InvalidValue", ex.Code);
         Assert.Contains("isPastDue", ex.Message, StringComparison.Ordinal);
-        Assert.Contains("scheduledDate", ex.Message, StringComparison.OrdinalIgnoreCase);
+        Assert.Contains("dueDate", ex.Message, StringComparison.OrdinalIgnoreCase);
     }
 
     [Fact]
@@ -853,4 +1001,93 @@ 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());
+    }
 }
diff --git a/SeaHavenIndustries.Tests/WorkOrderDerivedFieldsTests.cs b/SeaHavenIndustries.Tests/WorkOrderDerivedFieldsTests.cs
index 0d1f61c..2dd8c6b 100644
--- a/SeaHavenIndustries.Tests/WorkOrderDerivedFieldsTests.cs
+++ b/SeaHavenIndustries.Tests/WorkOrderDerivedFieldsTests.cs
@@ -6,28 +6,80 @@ namespace SeaHavenIndustries.Tests;
 
 public class WorkOrderDerivedFieldsTests
 {
+    private static readonly DateOnly Today = DateOnly.FromDateTime(DateTime.UtcNow);
+    private static readonly DateTime Past = DateTime.UtcNow.Date.AddDays(-2);
+    private static readonly DateTime Future = DateTime.UtcNow.Date.AddDays(3);
+    private static readonly DateTime TodayDate = DateTime.UtcNow.Date;
+
     [Fact]
-    public void IsPastDue_WhenScheduledBeforeTodayAndNotTerminal_ReturnsTrue()
+    public void IsPastDue_WhenSchedulePastAndDueFuture_ReturnsTrue()
     {
         var wo = new WorkOrder
         {
-            ScheduledDate = DateTime.UtcNow.AddDays(-2),
+            DueDate = Future,
+            ScheduledDate = Past,
             LifecycleStatus = LifecycleStatus.Scheduled
         };
 
-        Assert.True(WorkOrderDerivedFields.IsPastDue(wo, DateOnly.FromDateTime(DateTime.UtcNow)));
+        Assert.True(WorkOrderDerivedFields.IsPastDue(wo, Today));
+        Assert.True(WorkOrderDerivedFields.IsPastDue(wo.ScheduledDate, wo.LifecycleStatus));
     }
 
     [Fact]
-    public void IsPastDue_WhenCompleted_ReturnsFalse()
+    public void IsPastDue_WhenScheduleFutureAndDuePast_ReturnsFalse()
     {
         var wo = new WorkOrder
         {
-            ScheduledDate = DateTime.UtcNow.AddDays(-2),
-            LifecycleStatus = LifecycleStatus.Completed
+            DueDate = Past,
+            ScheduledDate = Future,
+            LifecycleStatus = LifecycleStatus.Scheduled
         };
 
-        Assert.False(WorkOrderDerivedFields.IsPastDue(wo, DateOnly.FromDateTime(DateTime.UtcNow)));
+        Assert.False(WorkOrderDerivedFields.IsPastDue(wo, Today));
+        Assert.False(WorkOrderDerivedFields.IsPastDue(wo.ScheduledDate, wo.LifecycleStatus));
+    }
+
+    [Fact]
+    public void IsPastDue_WhenScheduledDateNull_ReturnsFalse()
+    {
+        var wo = new WorkOrder
+        {
+            DueDate = Past,
+            ScheduledDate = null,
+            LifecycleStatus = LifecycleStatus.Scheduled
+        };
+
+        Assert.False(WorkOrderDerivedFields.IsPastDue(wo, Today));
+        Assert.False(WorkOrderDerivedFields.IsPastDue(null, LifecycleStatus.Scheduled));
+    }
+
+    [Fact]
+    public void IsPastDue_WhenScheduleEqualsToday_ReturnsFalse()
+    {
+        var wo = new WorkOrder
+        {
+            DueDate = Past,
+            ScheduledDate = TodayDate,
+            LifecycleStatus = LifecycleStatus.Scheduled
+        };
+
+        Assert.False(WorkOrderDerivedFields.IsPastDue(wo, Today));
+    }
+
+    [Theory]
+    [InlineData(LifecycleStatus.Completed)]
+    [InlineData(LifecycleStatus.Canceled)]
+    public void IsPastDue_WhenTerminal_ReturnsFalse(LifecycleStatus status)
+    {
+        var wo = new WorkOrder
+        {
+            DueDate = Past,
+            ScheduledDate = Past,
+            LifecycleStatus = status
+        };
+
+        Assert.False(WorkOrderDerivedFields.IsPastDue(wo, Today));
+        Assert.False(WorkOrderDerivedFields.IsPastDue(Past, status));
     }
 
     [Fact]
diff --git a/SeaHavenIndustries.Tests/WorkOrderPhase6Tests.cs b/SeaHavenIndustries.Tests/WorkOrderPhase6Tests.cs
index d6bd47e..1d7440e 100644
--- a/SeaHavenIndustries.Tests/WorkOrderPhase6Tests.cs
+++ b/SeaHavenIndustries.Tests/WorkOrderPhase6Tests.cs
@@ -111,6 +111,7 @@ public class WorkOrderDetailServiceTests
             Id = 1,
             InternalWONumber = "00000000001",
             LifecycleStatus = LifecycleStatus.Scheduled,
+            DueDate = DateTime.UtcNow.AddDays(3),
             ScheduledDate = DateTime.UtcNow.AddDays(-2),
             Trade = "HVAC PM",
             WorkOrderType = WorkOrderType.PM,
diff --git a/SeaHavenIndustries.Tests/WorkOrderWeekRolledTests.cs b/SeaHavenIndustries.Tests/WorkOrderWeekRolledTests.cs
index bff60ca..c299e21 100644
--- a/SeaHavenIndustries.Tests/WorkOrderWeekRolledTests.cs
+++ b/SeaHavenIndustries.Tests/WorkOrderWeekRolledTests.cs
@@ -240,12 +240,14 @@ public class WorkOrderWeekRolledTests
             new WorkOrder
             {
                 Id = 1,
+                DueDate = pastDate,
                 ScheduledDate = pastDate,
                 LifecycleStatus = LifecycleStatus.Scheduled
             },
             new WorkOrder
             {
                 Id = 2,
+                DueDate = pastDate,
                 ScheduledDate = pastDate,
                 LifecycleStatus = LifecycleStatus.Completed,
                 OperationalFlags = OperationalFlags.PastDue
@@ -253,6 +255,7 @@ public class WorkOrderWeekRolledTests
             new WorkOrder
             {
                 Id = 3,
+                DueDate = futureDate,
                 ScheduledDate = futureDate,
                 LifecycleStatus = LifecycleStatus.Scheduled,
                 OperationalFlags = OperationalFlags.PastDue
@@ -307,6 +310,7 @@ public class WorkOrderWeekRolledTests
         context.workOrders.Add(new WorkOrder
         {
             Id = 1,
+            DueDate = DateTime.UtcNow.Date.AddDays(5),
             ScheduledDate = pastDate,
             LifecycleStatus = LifecycleStatus.Scheduled,
             OperationalFlags = OperationalFlags.None
@@ -319,7 +323,7 @@ public class WorkOrderWeekRolledTests
 
         Assert.NotNull(row);
         Assert.True(row!.IsPastDue);
-        Assert.False(WorkOrderDerivedFields.IsPastDue(pastDate, LifecycleStatus.Scheduled) == false);
+        Assert.True(WorkOrderDerivedFields.IsPastDue(pastDate, LifecycleStatus.Scheduled));
     }
 
     [Fact]
@@ -331,6 +335,7 @@ public class WorkOrderWeekRolledTests
         context.workOrders.Add(new WorkOrder
         {
             Id = 1,
+            DueDate = DateTime.UtcNow.Date.AddDays(-3),
             ScheduledDate = futureDate,
             LifecycleStatus = LifecycleStatus.Scheduled,
             OperationalFlags = OperationalFlags.PastDue
diff --git a/docs/work-orders/phase-1/README.md b/docs/work-orders/phase-1/README.md
index 660bfb3..cc37218 100644
--- a/docs/work-orders/phase-1/README.md
+++ b/docs/work-orders/phase-1/README.md
@@ -88,10 +88,13 @@ Lista opções para o filtro/dropdown de assignee do board.
 ### isPastDue
 
 ```
-ScheduledDate < UTC hoje
-AND LifecycleStatus NOT IN (Complete, Canceled, Closed)
+DueDate != null
+AND DueDate < UTC hoje
+AND LifecycleStatus NOT IN (Completed, Canceled)
 ```
 
+`DueDate` null → `isPastDue = false`. Independent of `ScheduledDate` (Schedule On).
+
 Implementação: `SeaHaven.Services/Helpers/WorkOrderDerivedFields.cs`
 
 ### Vendor / Appt
@@ -154,6 +157,18 @@ Endpoints legados (`GetWorkOrderList`, `GetWorkorderById`, etc.) **não foram al
 
 ---
 
+## Add-On indicator (SH-184)
+
+- Coluna `IsAddOn` persistida; legacy `WorkOrderType.AddOn` (7) backfilled.
+- **Create:** cutoff preview (scheduled) ou hint manual quando unscheduled (`request.IsAddOn`).
+- **Patch schedule** (`scheduledDate`, `targetWeek`, `scheduleWeekOnly`): servidor **recalcula** `IsAddOn` e audita mudanças.
+- **Schedule cleared:** `IsAddOn = false`.
+- Search `Types=AddOn` matches legacy type 7 **or** `IsAddOn`.
+
+Contrato FE: [shoc-frontend-new PR #102](https://github.com/Sea-Haven-Industries/shoc-frontend-new/pull/102).
+
+---
+
 ## Próximo passo
 
 **Fase 2** — Inline edit + concorrência (dual RowVersion, audit por campo, PATCH granular).