diff --git a/src/Azos.Sky.Server/Fabric/Server/FiberMemory.cs b/src/Azos.Sky.Server/Fabric/Server/FiberMemory.cs
index 805df68b4..5981f254a 100644
--- a/src/Azos.Sky.Server/Fabric/Server/FiberMemory.cs
+++ b/src/Azos.Sky.Server/Fabric/Server/FiberMemory.cs
@@ -162,10 +162,12 @@ public void Crash(Exception error)
     /// Creates s snapshot of data changes which can be commited back into <see cref="IFiberStoreShard"/>
     /// using <see cref="IFiberStoreShard.CheckInAsync(FiberMemoryDelta)"/>.
     /// This only succeeds if the <see cref="Status"/> is <see cref="MemoryStatus.LockedForCaller"/>
-    /// otherwise Delta can not be obtained
+    /// otherwise Delta can not be obtained.
+    /// Performs validation and throws if slots are in invalid state
     /// </summary>
-    public FiberMemoryDelta MakeDeltaSnapshot(FiberStep? nextStep, FiberState currentState)
+    public FiberMemoryDelta MakeDeltaSnapshot(IApplication app, FiberStep? nextStep, FiberState currentState)
     {
+      app.NonNull(nameof(app));
       (m_Status == MemoryStatus.LockedForCaller).IsTrue("Delta obtained for LockedForCaller memory");
 
       var result = new FiberMemoryDelta
@@ -188,7 +190,24 @@ public FiberMemoryDelta MakeDeltaSnapshot(FiberStep? nextStep, FiberState curren
         result.NextSliceInterval = nxt.NextSliceInterval;
         result.ExitCode = nxt.ExitCode;
         result.Result = nxt.Result;
-        result.Changes = currentState.SlotChanges.ToArray();
+
+        var changes = currentState.SlotChanges.ToArray();
+        foreach(var change in changes)
+        {
+          app.InjectInto(change.Value);
+
+          var error = change.Value.Validate();
+          if (error != null)
+          {
+            throw new FabricStateValidationException(
+              "Validation error for state slot `{0}.{1}` validation failed: {2}".Args(
+                 currentState.GetType().DisplayNameWithExpandedGenericArgs(),
+                 change.Value.GetType().DisplayNameWithExpandedGenericArgs(),
+              error.ToMessageWithType()), error);
+          }
+        }
+
+        result.Changes = changes;
       }
 
       return  result;
diff --git a/src/Azos.Sky.Server/Fabric/Server/FiberProcessorDaemon.cs b/src/Azos.Sky.Server/Fabric/Server/FiberProcessorDaemon.cs
index e071a2602..ae77eea16 100644
--- a/src/Azos.Sky.Server/Fabric/Server/FiberProcessorDaemon.cs
+++ b/src/Azos.Sky.Server/Fabric/Server/FiberProcessorDaemon.cs
@@ -403,7 +403,7 @@ private async Task processFiberQuantumUnsafe(ShardMapping shard, Guid logRel)
         var (wasHandled, nextStep, fiberState) = await processFiberQuantumCore(memory).ConfigureAwait(false);//<===================== FIBER SLICE gets called
         if (!wasHandled) return;//get out asap
 
-        var delta = memory.MakeDeltaSnapshot(nextStep, fiberState);
+        var delta = memory.MakeDeltaSnapshot(App, nextStep, fiberState);//this can throw on invalid state
 
         var saveErrorCount = 0;
         while(true)
diff --git a/src/Azos.Sky/Fabric/Exceptions.cs b/src/Azos.Sky/Fabric/Exceptions.cs
index f183f4405..23c8c0007 100644
--- a/src/Azos.Sky/Fabric/Exceptions.cs
+++ b/src/Azos.Sky/Fabric/Exceptions.cs
@@ -48,6 +48,18 @@ public FabricProcessorException(string message, Exception inner) : base(message,
     protected FabricProcessorException(SerializationInfo info, StreamingContext context) : base(info, context) { }
   }
 
+  /// <summary>
+  /// Thrown to indicate state validation error
+  /// </summary>
+  [Serializable]
+  public class FabricStateValidationException : FabricProcessorException
+  {
+    public FabricStateValidationException() : base() { }
+    public FabricStateValidationException(string message) : base(message) { }
+    public FabricStateValidationException(string message, Exception inner) : base(message, inner) { }
+    protected FabricStateValidationException(SerializationInfo info, StreamingContext context) : base(info, context) { }
+  }
+
   /// <summary>
   /// Thrown to indicate errors when fibers are not derived from <see cref="Fiber{TParameters, TState}"/>
   /// </summary>
diff --git a/src/Azos.Sky/Fabric/FiberStep.cs b/src/Azos.Sky/Fabric/FiberStep.cs
index fc844d4a8..5e954c992 100644
--- a/src/Azos.Sky/Fabric/FiberStep.cs
+++ b/src/Azos.Sky/Fabric/FiberStep.cs
@@ -21,6 +21,9 @@ public struct FiberStep
   {
     public const string CONVENTION_STEP_METHOD_NAME_PREFIX = "Step_";
 
+    public static readonly Atom START = Atom.Encode("Start");
+
+
     public static readonly FiberStep ZERO = new FiberStep();
 
     private static readonly FiniteSetLookup<(Type t, Atom s), MethodInfo> STEP_MI_CACHE =
diff --git a/src/testing/Azos.Tests.Unit/Fabric/MemoryDeltaFormatTests.cs b/src/testing/Azos.Tests.Unit/Fabric/MemoryDeltaFormatTests.cs
index d585165d5..c2ced90ea 100644
--- a/src/testing/Azos.Tests.Unit/Fabric/MemoryDeltaFormatTests.cs
+++ b/src/testing/Azos.Tests.Unit/Fabric/MemoryDeltaFormatTests.cs
@@ -9,7 +9,7 @@
 using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
-
+using Azos.Apps;
 using Azos.Data;
 using Azos.Scripting;
 using Azos.Serialization.Bix;
@@ -73,7 +73,7 @@ public void Test01_Roundtrip_NextStep_NoResult()
       gotState.AccountNumber = 223322;//mutate state <====================
       Aver.IsTrue(got.HasDelta(gotState));
 
-      var delta = got.MakeDeltaSnapshot(FiberStep.ContinueImmediately(Atom.Encode("step2")), gotState);
+      var delta = got.MakeDeltaSnapshot(NOPApplication.Instance, FiberStep.ContinueImmediately(Atom.Encode("step2")), gotState);
 
       Aver.AreEqual("step2", delta.NextStep.Value);
       Aver.AreEqual(new TimeSpan(0), delta.NextSliceInterval);
@@ -156,7 +156,7 @@ public void Test02_Roundtrip_FinalStep_WithResult()
         String1 = "Dallas"
       };
 
-      var delta = got.MakeDeltaSnapshot(FiberStep.FinishWithResult(123, result), gotState);
+      var delta = got.MakeDeltaSnapshot(NOPApplication.Instance, FiberStep.FinishWithResult(123, result), gotState);
 
       Aver.IsTrue(delta.NextStep.IsZero);
       Aver.AreEqual(new TimeSpan(0), delta.NextSliceInterval);
@@ -241,7 +241,7 @@ public void Test03_Roundtrip_FinalStep_NoResult()
       Aver.IsTrue(got.HasDelta(gotState));
 
 
-      var delta = got.MakeDeltaSnapshot(FiberStep.Finish(321), gotState);
+      var delta = got.MakeDeltaSnapshot(NOPApplication.Instance, FiberStep.Finish(321), gotState);
 
       Aver.IsTrue(delta.NextStep.IsZero);
       Aver.AreEqual(new TimeSpan(0), delta.NextSliceInterval);
@@ -323,7 +323,7 @@ public void Test04_Roundtrip_Crash()
       Aver.IsFalse(got.HasDelta(gotState));
       got.Crash(new FabricException("Problem X"));//crash memory
 
-      var delta = got.MakeDeltaSnapshot(FiberStep.Finish(321), gotState);
+      var delta = got.MakeDeltaSnapshot(NOPApplication.Instance, FiberStep.Finish(321), gotState);
 
       Aver.IsTrue(delta.NextStep.IsZero);
       Aver.AreEqual(new TimeSpan(0), delta.NextSliceInterval);