diff --git a/src/ScadaLink.SiteRuntime/Actors/ScriptExecutionActor.cs b/src/ScadaLink.SiteRuntime/Actors/ScriptExecutionActor.cs
index ce4f6e4..85cea1c 100644
--- a/src/ScadaLink.SiteRuntime/Actors/ScriptExecutionActor.cs
+++ b/src/ScadaLink.SiteRuntime/Actors/ScriptExecutionActor.cs
@@ -125,7 +125,10 @@ public class ScriptExecutionActor : ReceiveActor
                     databaseGateway,
                     storeAndForward,
                     siteCommunicationActor,
-                    siteId);
+                    siteId,
+                    // Notification Outbox (FU3): stamp the executing script onto outbound
+                    // notifications using the Site Event Logging "Source" convention.
+                    sourceScript: $"ScriptActor:{scriptName}");
 
                 var globals = new ScriptGlobals
                 {
diff --git a/src/ScadaLink.SiteRuntime/Scripts/ScriptRuntimeContext.cs b/src/ScadaLink.SiteRuntime/Scripts/ScriptRuntimeContext.cs
index 273e59b..ba00063 100644
--- a/src/ScadaLink.SiteRuntime/Scripts/ScriptRuntimeContext.cs
+++ b/src/ScadaLink.SiteRuntime/Scripts/ScriptRuntimeContext.cs
@@ -66,6 +66,15 @@ public class ScriptRuntimeContext
     /// </summary>
     private readonly string _siteId;
 
+    /// <summary>
+    /// Notification Outbox (FU3): identifier of the script currently executing in this
+    /// context — stamped onto <c>NotificationSubmit.SourceScript</c> for the central
+    /// audit trail. Uses the Site Event Logging "Source" convention
+    /// (<c>"ScriptActor:&lt;scriptName&gt;"</c>). Null when no single script owns the
+    /// context (e.g. alarm on-trigger paths that do not wire the Notify outbox).
+    /// </summary>
+    private readonly string? _sourceScript;
+
     public ScriptRuntimeContext(
         IActorRef instanceActor,
         IActorRef self,
@@ -79,7 +88,8 @@ public class ScriptRuntimeContext
         IDatabaseGateway? databaseGateway = null,
         StoreAndForwardService? storeAndForward = null,
         ICanTell? siteCommunicationActor = null,
-        string siteId = "")
+        string siteId = "",
+        string? sourceScript = null)
     {
         _instanceActor = instanceActor;
         _self = self;
@@ -94,6 +104,7 @@ public class ScriptRuntimeContext
         _storeAndForward = storeAndForward;
         _siteCommunicationActor = siteCommunicationActor;
         _siteId = siteId;
+        _sourceScript = sourceScript;
     }
 
     /// <summary>
@@ -209,7 +220,7 @@ public class ScriptRuntimeContext
     /// <c>Notify.Status(id)</c> queries the delivery status of that notification.
     /// </summary>
     public NotifyHelper Notify => new(
-        _storeAndForward, _siteCommunicationActor, _siteId, _instanceName, _askTimeout, _logger);
+        _storeAndForward, _siteCommunicationActor, _siteId, _instanceName, _sourceScript, _askTimeout, _logger);
 
     /// <summary>
     /// Helper class for Scripts.CallShared() syntax.
@@ -356,6 +367,7 @@ public class ScriptRuntimeContext
         private readonly ICanTell? _siteCommunicationActor;
         private readonly string _siteId;
         private readonly string _instanceName;
+        private readonly string? _sourceScript;
         private readonly TimeSpan _askTimeout;
         private readonly ILogger _logger;
 
@@ -364,6 +376,7 @@ public class ScriptRuntimeContext
             ICanTell? siteCommunicationActor,
             string siteId,
             string instanceName,
+            string? sourceScript,
             TimeSpan askTimeout,
             ILogger logger)
         {
@@ -371,6 +384,7 @@ public class ScriptRuntimeContext
             _siteCommunicationActor = siteCommunicationActor;
             _siteId = siteId;
             _instanceName = instanceName;
+            _sourceScript = sourceScript;
             _askTimeout = askTimeout;
             _logger = logger;
         }
@@ -381,7 +395,7 @@ public class ScriptRuntimeContext
         public NotifyTarget To(string listName)
         {
             return new NotifyTarget(
-                listName, _storeAndForward, _siteId, _instanceName, _logger);
+                listName, _storeAndForward, _siteId, _instanceName, _sourceScript, _logger);
         }
 
         /// <summary>
@@ -453,6 +467,7 @@ public class ScriptRuntimeContext
         private readonly StoreAndForwardService? _storeAndForward;
         private readonly string _siteId;
         private readonly string _instanceName;
+        private readonly string? _sourceScript;
         private readonly ILogger _logger;
 
         internal NotifyTarget(
@@ -460,12 +475,14 @@ public class ScriptRuntimeContext
             StoreAndForwardService? storeAndForward,
             string siteId,
             string instanceName,
+            string? sourceScript,
             ILogger logger)
         {
             _listName = listName;
             _storeAndForward = storeAndForward;
             _siteId = siteId;
             _instanceName = instanceName;
+            _sourceScript = sourceScript;
             _logger = logger;
         }
 
@@ -504,9 +521,10 @@ public class ScriptRuntimeContext
                 // value is the best-effort site id known to the script runtime.
                 SourceSiteId: _siteId,
                 SourceInstanceId: _instanceName,
-                // SourceScript: the script runtime does not currently thread the script
-                // name down to the Notify helper; left null until that wiring exists.
-                SourceScript: null,
+                // SourceScript (FU3): identifier of the script that raised this
+                // notification, threaded down from the script-execution context for the
+                // central audit trail. Null when no single script owns the context.
+                SourceScript: _sourceScript,
                 SiteEnqueuedAt: DateTimeOffset.UtcNow);
 
             var payloadJson = JsonSerializer.Serialize(payload);
diff --git a/tests/ScadaLink.SiteRuntime.Tests/Scripts/NotifyHelperTests.cs b/tests/ScadaLink.SiteRuntime.Tests/Scripts/NotifyHelperTests.cs
index 95cf53b..e85e671 100644
--- a/tests/ScadaLink.SiteRuntime.Tests/Scripts/NotifyHelperTests.cs
+++ b/tests/ScadaLink.SiteRuntime.Tests/Scripts/NotifyHelperTests.cs
@@ -58,13 +58,16 @@ public class NotifyHelperTests : TestKit, IAsyncLifetime, IDisposable
         base.Dispose(disposing);
     }
 
-    private ScriptRuntimeContext.NotifyHelper CreateHelper(IActorRef siteCommunicationActor)
+    private ScriptRuntimeContext.NotifyHelper CreateHelper(
+        IActorRef siteCommunicationActor,
+        string? sourceScript = null)
     {
         return new ScriptRuntimeContext.NotifyHelper(
             _saf,
             siteCommunicationActor,
             "site-7",
             "Plant.Pump3",
+            sourceScript,
             TimeSpan.FromSeconds(3),
             NullLogger.Instance);
     }
@@ -113,6 +116,36 @@ public class NotifyHelperTests : TestKit, IAsyncLifetime, IDisposable
         Assert.Equal("Plant.Pump3", payload.SourceInstanceId);
     }
 
+    [Fact]
+    public async Task Send_WhenHelperHasSourceScript_StampsItOnTheNotificationSubmit()
+    {
+        var commProbe = CreateTestProbe();
+        var notify = CreateHelper(commProbe.Ref, sourceScript: "ScriptActor:MonitorSpeed");
+
+        var notificationId = await notify.To("Operators").Send("Pump alarm", "Pump 3 tripped");
+
+        var buffered = await _saf.GetMessageByIdAsync(notificationId);
+        Assert.NotNull(buffered);
+
+        var payload = JsonSerializer.Deserialize<NotificationSubmit>(buffered!.PayloadJson);
+        Assert.NotNull(payload);
+        // FU3: the executing script name is threaded down and stamped for the audit trail.
+        Assert.Equal("ScriptActor:MonitorSpeed", payload!.SourceScript);
+    }
+
+    [Fact]
+    public async Task Send_WhenHelperHasNoSourceScript_LeavesSourceScriptNull()
+    {
+        var commProbe = CreateTestProbe();
+        var notify = CreateHelper(commProbe.Ref, sourceScript: null);
+
+        var notificationId = await notify.To("Operators").Send("Pump alarm", "Pump 3 tripped");
+
+        var buffered = await _saf.GetMessageByIdAsync(notificationId);
+        var payload = JsonSerializer.Deserialize<NotificationSubmit>(buffered!.PayloadJson);
+        Assert.Null(payload!.SourceScript);
+    }
+
     [Fact]
     public async Task Status_WhenStillBufferedAtSite_ReportsForwarding()
     {