feat: add reload semantics for cluster and jetstream options

src/NATS.Server/Configuration/ConfigReloader.cs

@@ -11,7 +11,8 @@ namespace NATS.Server.Configuration;
 public static class ConfigReloader
 {
     // Non-reloadable options (match Go server — Host, Port, ServerName require restart)
-    private static readonly HashSet<string> NonReloadable = ["Host", "Port", "ServerName"];
+    private static readonly HashSet<string> NonReloadable =
+        ["Host", "Port", "ServerName", "Cluster", "JetStream.StoreDir"];
 
     // Logging-related options
     private static readonly HashSet<string> LoggingOptions =
@@ -102,6 +103,13 @@ public static class ConfigReloader
         CompareAndAdd(changes, "NoSystemAccount", oldOpts.NoSystemAccount, newOpts.NoSystemAccount);
         CompareAndAdd(changes, "SystemAccount", oldOpts.SystemAccount, newOpts.SystemAccount);
 
+        // Cluster and JetStream (restart-required boundaries)
+        if (!ClusterEquivalent(oldOpts.Cluster, newOpts.Cluster))
+            changes.Add(new ConfigChange("Cluster", isNonReloadable: true));
+
+        if (JetStreamStoreDirChanged(oldOpts.JetStream, newOpts.JetStream))
+            changes.Add(new ConfigChange("JetStream.StoreDir", isNonReloadable: true));
+
         return changes;
     }
 
@@ -338,4 +346,35 @@ public static class ConfigReloader
                 isNonReloadable: NonReloadable.Contains(name)));
         }
     }
+
+    private static bool ClusterEquivalent(ClusterOptions? oldCluster, ClusterOptions? newCluster)
+    {
+        if (oldCluster is null && newCluster is null)
+            return true;
+
+        if (oldCluster is null || newCluster is null)
+            return false;
+
+        if (!string.Equals(oldCluster.Name, newCluster.Name, StringComparison.Ordinal))
+            return false;
+
+        if (!string.Equals(oldCluster.Host, newCluster.Host, StringComparison.Ordinal))
+            return false;
+
+        if (oldCluster.Port != newCluster.Port)
+            return false;
+
+        return oldCluster.Routes.SequenceEqual(newCluster.Routes, StringComparer.Ordinal);
+    }
+
+    private static bool JetStreamStoreDirChanged(JetStreamOptions? oldJetStream, JetStreamOptions? newJetStream)
+    {
+        if (oldJetStream is null && newJetStream is null)
+            return false;
+
+        if (oldJetStream is null || newJetStream is null)
+            return true;
+
+        return !string.Equals(oldJetStream.StoreDir, newJetStream.StoreDir, StringComparison.Ordinal);
+    }
 }