feat(mesh-phase4): retire DB-reachability from ServiceLevel on DB-less nodes

Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW

src/Server/ZB.MOM.WW.OtOpcUa.Runtime/ServiceCollectionExtensions.cs

@@ -326,10 +326,19 @@ public static class ServiceCollectionExtensions
             // (durable AVEVA sink is infra-gated); a deployment binding a real IHistoryWriter overrides.
             var historyWriter = resolver.GetService<IHistoryWriter>() ?? NullHistoryWriter.Instance;
 
-            var dbHealth = system.ActorOf(
-                DbHealthProbeActor.Props(dbFactory),
-                DbHealthProbeActorName);
-            registry.Register<DbHealthProbeActorKey>(dbHealth);
+            // Per-cluster mesh Phase 4: a driver-only node has NO ConfigDb (LocalDb is its config
+            // store), so dbFactory is null and there is nothing to probe. Skip spawning the probe
+            // entirely — spawning it with a null factory would NRE on the first SELECT 1 — and do not
+            // register its marker key. OpcUaPublishActor then runs in dbLess mode (DbReachable retired,
+            // treated constant-true) so a healthy DB-less node still publishes full ServiceLevel.
+            IActorRef? dbHealth = null;
+            if (dbFactory is not null)
+            {
+                dbHealth = system.ActorOf(
+                    DbHealthProbeActor.Props(dbFactory),
+                    DbHealthProbeActorName);
+                registry.Register<DbHealthProbeActorKey>(dbHealth);
+            }
 
             // Dependency mux must be spawned before DriverHostActor so the host can forward
             // AttributeValuePublished into it from the very first driver spawn.
@@ -436,7 +445,8 @@ public static class ServiceCollectionExtensions
                     localNode: roleInfo.LocalNode,
                     dbFactory: dbFactory,
                     applier: applier,
-                    dbHealthProbe: dbHealth),
+                    dbHealthProbe: dbHealth,
+                    dbLess: dbFactory is null),
                 OpcUaPublishActorName);
             registry.Register<OpcUaPublishActorKey>(publishActor);
 
@@ -452,7 +462,14 @@ public static class ServiceCollectionExtensions
                 // ackRouter: under ClusterClient mode the node comm actor relays ApplyAcks across
                 // the boundary; under Dps it stays null and the host publishes on the
                 // deployment-acks topic exactly as before.
-                DriverHostActor.Props(dbFactory, roleInfo.LocalNode,
+                // dbFactory! — KNOWN INTERIM. A driver-only node genuinely passes a null factory here
+                // (ConfigDb is now gated on hasAdmin, and driver-only nodes are forced to FetchAndCache),
+                // so DriverHostActor's ConfigDb-touching paths — scripted-alarm state persistence
+                // (EfAlarmConditionStateStore) and UpsertNodeDeploymentState — fault-and-swallow until
+                // Task 4 makes the factory nullable + guards those sites (and removes this !) and Task 6
+                // re-homes the alarm store to LocalDb. Inert in practice: no driver-only node is
+                // configured to boot until the Task 10 rig change.
+                DriverHostActor.Props(dbFactory!, roleInfo.LocalNode,
                     ackRouter: useClusterClient ? nodeComm : null,
                     driverFactory: driverFactory, localRoles: roleInfo.LocalRoles,
                     dependencyMux: mux,