feat(notification-outbox): add NotificationOutboxActor ingest

src/ScadaLink.NotificationOutbox/Messages/InternalMessages.cs

@@ -0,0 +1,29 @@
+using Akka.Actor;
+
+namespace ScadaLink.NotificationOutbox.Messages;
+
+/// <summary>
+/// Actor-internal message types for the <see cref="NotificationOutboxActor"/>. These are
+/// never sent across the network — they bridge the actor's async repository/delivery work
+/// back onto the actor's own mailbox so handlers run single-threaded on the actor.
+/// </summary>
+internal static class InternalMessages
+{
+    /// <summary>
+    /// Result of an asynchronous ingest persistence attempt, piped back to the actor.
+    /// Carries the original <paramref name="Sender"/> so the actor can ack the site that
+    /// submitted the notification once the insert completes.
+    /// </summary>
+    /// <param name="NotificationId">Id of the notification that was submitted.</param>
+    /// <param name="Sender">Original submitter to receive the ack.</param>
+    /// <param name="Succeeded">
+    /// True if persistence completed without error — covers both a fresh insert and an
+    /// already-existing row (idempotent re-submission). False only when the repository threw.
+    /// </param>
+    /// <param name="Error">Failure detail when <paramref name="Succeeded"/> is false; otherwise null.</param>
+    internal sealed record IngestPersisted(
+        string NotificationId,
+        IActorRef Sender,
+        bool Succeeded,
+        string? Error);
+}