feat(notif-outbox): add SourceNode to Notification entity + NotificationSubmit

src/ScadaLink.Commons/Entities/Notifications/Notification.cs

@@ -25,6 +25,15 @@ public class Notification
     /// <summary>Resolved delivery targets snapshotted at delivery time, for audit.</summary>
     public string? ResolvedTargets { get; set; }
     public string SourceSiteId { get; set; }
+
+    /// <summary>
+    /// The cluster node on which the notification was emitted — `node-a` / `node-b`
+    /// for site rows (qualified by <see cref="SourceSiteId"/>), `central-a` / `central-b`
+    /// for central-originated rows. Carried from the site on the
+    /// <see cref="Commons.Messages.Notification.NotificationSubmit"/> and persisted at
+    /// central; nullable so rows submitted before the column existed don't block ingest.
+    /// </summary>
+    public string? SourceNode { get; set; }
     public string? SourceInstanceId { get; set; }
     public string? SourceScript { get; set; }
 

src/ScadaLink.Commons/Messages/Notification/NotificationMessages.cs

@@ -18,6 +18,15 @@ namespace ScadaLink.Commons.Messages.Notification;
 /// <c>NotifyDeliver</c> audit rows. Additive trailing member — null for messages built
 /// before the field existed, or for non-routed runs.
 /// </param>
+/// <param name="SourceNode">
+/// The cluster node on which the notification was emitted — `node-a` / `node-b` for site
+/// submissions, `central-a` / `central-b` for central-originated rows. Stamped by the
+/// emitting node from <c>INodeIdentityProvider</c> and carried, inside the serialized
+/// payload, through the site store-and-forward buffer so the central dispatcher can
+/// persist it on the <c>Notifications</c> row and echo it onto the <c>NotifyDeliver</c>
+/// audit rows. Additive trailing member — null for messages built before the field
+/// existed.
+/// </param>
 public record NotificationSubmit(
     string NotificationId,
     string ListName,
@@ -28,7 +37,8 @@ public record NotificationSubmit(
     string? SourceScript,
     DateTimeOffset SiteEnqueuedAt,
     Guid? OriginExecutionId = null,
-    Guid? OriginParentExecutionId = null);
+    Guid? OriginParentExecutionId = null,
+    string? SourceNode = null);
 
 /// <summary>
 /// Central -> Site: ack sent after the notification row is persisted.

tests/ScadaLink.Commons.Tests/Entities/NotificationEntityTests.cs

@@ -51,6 +51,20 @@ public class NotificationEntityTests
         Assert.Equal(parentExecutionId, n.OriginParentExecutionId);
     }
 
+    [Fact]
+    public void SourceNode_DefaultsToNull_AndIsSettable()
+    {
+        // SourceNode identifies the cluster node that emitted the notification
+        // (site node-a/node-b or central-a/central-b). Additive nullable
+        // property — defaults to null on rows submitted before the column
+        // existed, and round-trips its value when set.
+        var n = new Notification("id-1", NotificationType.Email, "ops-team", "subj", "body", "SiteA");
+        Assert.Null(n.SourceNode);
+
+        n.SourceNode = "node-a";
+        Assert.Equal("node-a", n.SourceNode);
+    }
+
     [Fact]
     public void Constructor_NullArguments_Throw()
     {

tests/ScadaLink.Commons.Tests/Messages/NotificationMessagesTests.cs

@@ -126,6 +126,32 @@ public class NotificationMessagesTests
         Assert.Equal(parentExecutionId, roundTripped!.OriginParentExecutionId);
     }
 
+    [Fact]
+    public void NotificationSubmit_carries_SourceNode()
+    {
+        // SourceNode is an additive trailing member — old call sites and old
+        // serialized payloads leave it null. When supplied it round-trips
+        // through both construction and JSON (the buffered S&F payload IS a
+        // serialized NotificationSubmit).
+        var defaulted = new NotificationSubmit(
+            "notif-9", "Operators", "Subject", "Body",
+            "site-01", "inst-1", "OnAlarm", DateTimeOffset.UtcNow);
+        Assert.Null(defaulted.SourceNode);
+
+        var stamped = new NotificationSubmit(
+            "notif-10", "Operators", "Subject", "Body",
+            "site-01", "inst-1", "OnAlarm", DateTimeOffset.UtcNow,
+            OriginExecutionId: null,
+            OriginParentExecutionId: null,
+            SourceNode: "node-a");
+        Assert.Equal("node-a", stamped.SourceNode);
+
+        var json = System.Text.Json.JsonSerializer.Serialize(stamped);
+        var roundTripped = System.Text.Json.JsonSerializer.Deserialize<NotificationSubmit>(json);
+        Assert.NotNull(roundTripped);
+        Assert.Equal("node-a", roundTripped!.SourceNode);
+    }
+
     [Fact]
     public void NotificationSubmit_ValueEquality_EqualWhenAllFieldsMatch()
     {