diff --git a/SeaHaven.Services/Helpers/LifecycleStatusMapper.cs b/SeaHaven.Services/Helpers/LifecycleStatusMapper.cs
new file mode 100644
index 0000000..348048f
--- /dev/null
+++ b/SeaHaven.Services/Helpers/LifecycleStatusMapper.cs
@@ -0,0 +1,34 @@
+using Data.SeaHavenIndustries.Enums;
+
+namespace SeaHaven.Services.Helpers
+{
+    public static class LifecycleStatusMapper
+    {
+        public static LifecycleStatus? FromLegacyStatus(string? status)
+        {
+            if (string.IsNullOrWhiteSpace(status)) return null;
+
+            return status.Trim().ToLowerInvariant() switch
+            {
+                "open" => LifecycleStatus.Incomplete,
+                "inprogress" or "in progress" => LifecycleStatus.InProgress,
+                "completed" or "complete" => LifecycleStatus.Complete,
+                "cancelled" or "canceled" => LifecycleStatus.Canceled,
+                "onhold" or "on hold" => LifecycleStatus.OnHold,
+                "scheduled" => LifecycleStatus.Scheduled,
+                "pendingvendor" or "pending vendor" => LifecycleStatus.PendingVendor,
+                "pendingapproval" or "pending approval" => LifecycleStatus.PendingApproval,
+                "needsreview" or "needs review" => LifecycleStatus.NeedsReview,
+                "closed" => LifecycleStatus.Closed,
+                _ => LifecycleStatus.NeedsReview
+            };
+        }
+
+        public static LifecycleStatus? ParseLifecycleStatus(string? value)
+        {
+            if (string.IsNullOrWhiteSpace(value)) return null;
+            if (Enum.TryParse<LifecycleStatus>(value, true, out var parsed)) return parsed;
+            return FromLegacyStatus(value);
+        }
+    }
+}
diff --git a/SeaHaven.Services/Helpers/WorkOrderNumberNormalizer.cs b/SeaHaven.Services/Helpers/WorkOrderNumberNormalizer.cs
new file mode 100644
index 0000000..59f8494
--- /dev/null
+++ b/SeaHaven.Services/Helpers/WorkOrderNumberNormalizer.cs
@@ -0,0 +1,37 @@
+using System.Text.RegularExpressions;
+
+namespace SeaHaven.Services.Helpers
+{
+    public static class WorkOrderNumberNormalizer
+    {
+        private const int RequiredLength = 11;
+
+        public static bool TryNormalize(string? input, out string normalized, out string? error)
+        {
+            normalized = "";
+            error = null;
+
+            if (string.IsNullOrWhiteSpace(input))
+            {
+                error = "WO number is required.";
+                return false;
+            }
+
+            var digits = Regex.Replace(input.Trim(), @"\D", "");
+            if (digits.Length == 0)
+            {
+                error = "WO number must contain digits.";
+                return false;
+            }
+
+            if (digits.Length > RequiredLength)
+            {
+                error = $"WO number cannot exceed {RequiredLength} digits.";
+                return false;
+            }
+
+            normalized = digits.PadLeft(RequiredLength, '0');
+            return true;
+        }
+    }
+}
diff --git a/SeaHaven.Services/Implementation/SyncFieldMergePolicy.cs b/SeaHaven.Services/Implementation/SyncFieldMergePolicy.cs
new file mode 100644
index 0000000..6d564e3
--- /dev/null
+++ b/SeaHaven.Services/Implementation/SyncFieldMergePolicy.cs
@@ -0,0 +1,92 @@
+using Data.SeaHavenIndustries;
+using SeaHaven.Services.Interfaces;
+
+namespace SeaHaven.Services.Implementation
+{
+    public class SyncFieldMergePolicy : ISyncFieldMergePolicy
+    {
+        private static readonly HashSet<string> ShocOwnedFieldSet = new(StringComparer.OrdinalIgnoreCase)
+        {
+            "LifecycleStatus", "AssignTo", "ScheduledDate", "ScheduledEnd", "TargetWeek", "ScheduleWeekOnly",
+            "DueDate", "Description", "WorkerOrderTitle", "SiteCode", "Building", "LocationId",
+            "WorkOrderType", "DocStatus", "Trade", "Problem", "Priority", "InternalWONumber", "Status"
+        };
+
+        private readonly IWorkOrderFieldLockService _fieldLocks;
+        private readonly IWorkOrderAuditService _audit;
+
+        public SyncFieldMergePolicy(IWorkOrderFieldLockService fieldLocks, IWorkOrderAuditService audit)
+        {
+            _fieldLocks = fieldLocks;
+            _audit = audit;
+        }
+
+        public IReadOnlySet<string> ShocOwnedFields => ShocOwnedFieldSet;
+
+        public bool CanSyncOverwrite(int workOrderId, string fieldName)
+            => !_fieldLocks.IsLockedAsync(workOrderId, fieldName).GetAwaiter().GetResult();
+
+        public async Task<bool> TryApplyAsync(WorkOrderSyncContext context, string fieldName, object? incomingValue)
+        {
+            if (incomingValue == null) return false;
+
+            if (await context.FieldLocks.IsLockedAsync(context.WorkOrder.Id, fieldName))
+            {
+                var current = GetFieldValue(context.WorkOrder, fieldName);
+                await context.Audit.LogSyncRejectedAsync(
+                    context.WorkOrder.Id,
+                    fieldName,
+                    current,
+                    incomingValue.ToString());
+                return false;
+            }
+
+            ApplyField(context.WorkOrder, fieldName, incomingValue);
+            return true;
+        }
+
+        private static string? GetFieldValue(WorkOrder wo, string fieldName) => fieldName switch
+        {
+            "Description" => wo.Description,
+            "WorkerOrderTitle" => wo.WorkerOrderTitle,
+            "Status" => wo.Status,
+            "DueDate" => wo.DueDate?.ToString("O"),
+            "SiteCode" => wo.SiteCode,
+            "Building" => wo.Building,
+            "Priority" => wo.Priority,
+            "Severity" => wo.Severity,
+            _ => null
+        };
+
+        private static void ApplyField(WorkOrder wo, string fieldName, object incomingValue)
+        {
+            switch (fieldName)
+            {
+                case "Description":
+                    wo.Description = incomingValue.ToString();
+                    break;
+                case "WorkerOrderTitle":
+                    wo.WorkerOrderTitle = incomingValue.ToString();
+                    break;
+                case "Status":
+                    wo.Status = incomingValue.ToString();
+                    break;
+                case "DueDate" when incomingValue is DateTime dt:
+                    wo.DueDate = dt;
+                    break;
+                case "SiteCode":
+                    wo.SiteCode = incomingValue.ToString();
+                    break;
+                case "Building":
+                    wo.Building = incomingValue.ToString();
+                    break;
+                case "Priority":
+                    wo.Priority = incomingValue.ToString();
+                    break;
+                case "Severity":
+                    wo.Severity = incomingValue.ToString();
+                    break;
+            }
+        }
+    }
+}
diff --git a/SeaHaven.Services/Implementation/WorkOrderAuditService.cs b/SeaHaven.Services/Implementation/WorkOrderAuditService.cs
new file mode 100644
index 0000000..4543c91
--- /dev/null
+++ b/SeaHaven.Services/Implementation/WorkOrderAuditService.cs
@@ -0,0 +1,69 @@
+using Data.SeaHavenIndustries;
+using Data.SeaHavenIndustries.Enums;
+using Microsoft.EntityFrameworkCore;
+using SeaHaven.Services.Interfaces;
+
+namespace SeaHaven.Services.Implementation
+{
+    public class WorkOrderAuditService : IWorkOrderAuditService
+    {
+        private readonly ApplicationDbContext _context;
+        private readonly IWorkOrderFieldLockService _fieldLocks;
+
+        public WorkOrderAuditService(ApplicationDbContext context, IWorkOrderFieldLockService fieldLocks)
+        {
+            _context = context;
+            _fieldLocks = fieldLocks;
+        }
+
+        public Task LogStatusChangedAsync(int workOrderId, string? oldStatus, string? newStatus, string? actorId)
+            => LogAsync(workOrderId, AuditActionType.StatusChanged, AuditEventType.Manual,
+                AuditActorType.Dispatcher, "LifecycleStatus", oldStatus, newStatus, actorId);
+
+        public Task LogAssignmentChangedAsync(int workOrderId, string? oldValue, string? newValue, string? actorId)
+            => LogAsync(workOrderId, AuditActionType.AssignmentChanged, AuditEventType.Manual,
+                AuditActorType.Dispatcher, "AssignTo", oldValue, newValue, actorId);
+
+        public Task LogSyncRejectedAsync(int workOrderId, string fieldName, string? oldValue, string? newValue)
+            => LogAsync(workOrderId, AuditActionType.SyncRejected, AuditEventType.Sync,
+                AuditActorType.Sync, fieldName, oldValue, newValue);
+
+        public async Task LogAsync(
+            int workOrderId,
+            AuditActionType action,
+            AuditEventType eventType,
+            AuditActorType actorType,
+            string fieldName,
+            string? oldValue,
+            string? newValue,
+            string? actorId = null,
+            int? dispatchId = null,
+            string? correlationId = null)
+        {
+            _context.WorkOrderAuditLogs.Add(new WorkOrderAuditLog
+            {
+                WorkOrderId = workOrderId,
+                UserId = actorId,
+                FieldName = fieldName,
+                OldValue = oldValue ?? "",
+                NewValue = newValue ?? "",
+                Action = action.ToString(),
+                EventType = eventType.ToString(),
+                ActorType = actorType.ToString(),
+                DispatchId = dispatchId,
+                CorrelationId = correlationId,
+                CreatedAt = DateTime.UtcNow
+            });
+
+            if (eventType == AuditEventType.Manual &&
+                (action == AuditActionType.FieldChanged ||
+                 action == AuditActionType.StatusChanged ||
+                 action == AuditActionType.AssignmentChanged))
+            {
+                await _fieldLocks.LockFieldAsync(workOrderId, fieldName, actorId);
+            }
+
+            await _context.SaveChangesAsync();
+        }
+    }
+}
diff --git a/SeaHaven.Services/Implementation/WorkOrderFieldLockService.cs b/SeaHaven.Services/Implementation/WorkOrderFieldLockService.cs
new file mode 100644
index 0000000..d132ea8
--- /dev/null
+++ b/SeaHaven.Services/Implementation/WorkOrderFieldLockService.cs
@@ -0,0 +1,37 @@
+using Data.SeaHavenIndustries;
+using Microsoft.EntityFrameworkCore;
+using SeaHaven.Services.Interfaces;
+
+namespace SeaHaven.Services.Implementation
+{
+    public class WorkOrderFieldLockService : IWorkOrderFieldLockService
+    {
+        private readonly ApplicationDbContext _context;
+
+        public WorkOrderFieldLockService(ApplicationDbContext context)
+        {
+            _context = context;
+        }
+
+        public async Task<bool> IsLockedAsync(int workOrderId, string fieldName)
+        {
+            return await _context.WorkOrderFieldLocks
+                .AnyAsync(l => l.WorkOrderId == workOrderId && l.FieldName == fieldName);
+        }
+
+        public async Task LockFieldAsync(int workOrderId, string fieldName, string? userId)
+        {
+            var exists = await IsLockedAsync(workOrderId, fieldName);
+            if (exists) return;
+
+            _context.WorkOrderFieldLocks.Add(new WorkOrderFieldLock
+            {
+                WorkOrderId = workOrderId,
+                FieldName = fieldName,
+                LockedAt = DateTime.UtcNow,
+                LockedByUserId = userId
+            });
+            await _context.SaveChangesAsync();
+        }
+    }
+}
diff --git a/SeaHaven.Services/Interfaces/ISyncFieldMergePolicy.cs b/SeaHaven.Services/Interfaces/ISyncFieldMergePolicy.cs
new file mode 100644
index 0000000..96b401d
--- /dev/null
+++ b/SeaHaven.Services/Interfaces/ISyncFieldMergePolicy.cs
@@ -0,0 +1,18 @@
+namespace SeaHaven.Services.Interfaces
+{
+    public interface ISyncFieldMergePolicy
+    {
+        IReadOnlySet<string> ShocOwnedFields { get; }
+
+        bool CanSyncOverwrite(int workOrderId, string fieldName);
+
+        Task<bool> TryApplyAsync(WorkOrderSyncContext context, string fieldName, object? incomingValue);
+    }
+
+    public class WorkOrderSyncContext
+    {
+        public required Data.SeaHavenIndustries.WorkOrder WorkOrder { get; init; }
+        public required SeaHaven.Services.Interfaces.IWorkOrderFieldLockService FieldLocks { get; init; }
+        public required SeaHaven.Services.Interfaces.IWorkOrderAuditService Audit { get; init; }
+    }
+}
diff --git a/SeaHaven.Services/Interfaces/IWorkOrderAuditService.cs b/SeaHaven.Services/Interfaces/IWorkOrderAuditService.cs
new file mode 100644
index 0000000..bb83d5a
--- /dev/null
+++ b/SeaHaven.Services/Interfaces/IWorkOrderAuditService.cs
@@ -0,0 +1,23 @@
+using Data.SeaHavenIndustries.Enums;
+
+namespace SeaHaven.Services.Interfaces
+{
+    public interface IWorkOrderAuditService
+    {
+        Task LogAsync(
+            int workOrderId,
+            AuditActionType action,
+            AuditEventType eventType,
+            AuditActorType actorType,
+            string fieldName,
+            string? oldValue,
+            string? newValue,
+            string? actorId = null,
+            int? dispatchId = null,
+            string? correlationId = null);
+
+        Task LogStatusChangedAsync(int workOrderId, string? oldStatus, string? newStatus, string? actorId);
+        Task LogAssignmentChangedAsync(int workOrderId, string? oldValue, string? newValue, string? actorId);
+        Task LogSyncRejectedAsync(int workOrderId, string fieldName, string? oldValue, string? newValue);
+    }
+}
diff --git a/SeaHaven.Services/Interfaces/IWorkOrderFieldLockService.cs b/SeaHaven.Services/Interfaces/IWorkOrderFieldLockService.cs
new file mode 100644
index 0000000..2254724
--- /dev/null
+++ b/SeaHaven.Services/Interfaces/IWorkOrderFieldLockService.cs
@@ -0,0 +1,8 @@
+namespace SeaHaven.Services.Interfaces
+{
+    public interface IWorkOrderFieldLockService
+    {
+        Task LockFieldAsync(int workOrderId, string fieldName, string? userId);
+        Task<bool> IsLockedAsync(int workOrderId, string fieldName);
+    }
+}