Improve XML documentation coverage across src modules and sync generated analysis artifacts.

src/NATS.Server/Events/EventSubjects.cs

@@ -74,6 +74,13 @@ public static class EventSubjects
 /// Callback signature for system message handlers.
 /// Maps to Go's sysMsgHandler type in events.go:109.
 /// </summary>
+/// <param name="sub">Subscription metadata that matched the incoming system message.</param>
+/// <param name="client">Client connection context that delivered the message, when available.</param>
+/// <param name="account">Owning account context for account-scoped system events.</param>
+/// <param name="subject">System subject that triggered this callback.</param>
+/// <param name="reply">Reply inbox subject for request/reply system handlers.</param>
+/// <param name="headers">Optional message headers encoded by the publisher.</param>
+/// <param name="message">Raw system advisory or request payload bytes.</param>
 public delegate void SystemMessageHandler(
     Subscription? sub,
     INatsClient? client,