fix(localdb): fault live sync session on cap-prune; keepalive + newest-wins sync guard (0.3.2, ScadaBridge arch-review P4-1 + P4-3)

ZB.MOM.WW.LocalDb/src/ZB.MOM.WW.LocalDb.Replication/LocalDbOplogGapException.cs

@@ -0,0 +1,23 @@
+namespace ZB.MOM.WW.LocalDb.Replication;
+
+/// <summary>
+/// Thrown by a live sync session when the oplog horizon has moved ABOVE the position that session
+/// is streaming from: a cap prune deleted deltas it had not yet sent, so every later delta it could
+/// ship would land on the far side of a hole the peer will never receive.
+/// </summary>
+/// <remarks>
+/// This is not a transport failure and not a data error — it is the session discovering that its own
+/// incremental position has become unsound. Nothing can repair it in-session (the deleted rows are
+/// gone), so the session tears itself down; the same prune set <c>needs_snapshot</c>, which makes the
+/// reconnect handshake serve a snapshot instead of deltas. Catching this and continuing would
+/// reintroduce exactly the silent divergence it exists to stop.
+/// </remarks>
+public sealed class LocalDbOplogGapException : Exception
+{
+    /// <summary>Creates the exception with a message describing the gap.</summary>
+    public LocalDbOplogGapException(string message) : base(message) { }
+
+    /// <summary>Creates the exception with a message and the underlying cause.</summary>
+    public LocalDbOplogGapException(string message, Exception innerException)
+        : base(message, innerException) { }
+}