Resolve all 46 low-severity architecture review findings

src/ZB.MOM.WW.ScadaBridge.DataConnectionLayer/Adapters/RealOpcUaClient.cs

@@ -675,9 +675,16 @@ public class RealOpcUaClient : IOpcUaClient
         List<DataShard> touched,
         CancellationToken cancellationToken)
     {
-        foreach (var (index, nodeId, startNode) in resolved)
+        // Plan once for this chunk while the apply gate keeps shard occupancy stable.
+        var placement = MonitoredItemShardPlanner.Plan(
+            _dataShards.Select(s => s.ItemCount).ToArray(), ItemsPerShard, resolved.Count);
+        for (var itemIndex = 0; itemIndex < resolved.Count; itemIndex++)
         {
-            var shard = await PlaceOnDataShardAsync(cancellationToken);
+            var (index, nodeId, startNode) = resolved[itemIndex];
+            var shardIndex = placement[itemIndex];
+            var shard = shardIndex < _dataShards.Count
+                ? _dataShards[shardIndex]
+                : await CreateDataShardAsync(cancellationToken);
             var handle = Guid.NewGuid().ToString();
             var monitoredItem = new MonitoredItem(shard.Subscription.DefaultItem)
             {
@@ -760,20 +767,6 @@ public class RealOpcUaClient : IOpcUaClient
             created.Count);
     }
 
-    /// <summary>
-    /// Returns the shard this item belongs on per
-    /// <see cref="MonitoredItemShardPlanner"/> — first shard with free capacity, else a
-    /// freshly created one. Callers must hold <see cref="_applyGate"/>.
-    /// </summary>
-    private async Task<DataShard> PlaceOnDataShardAsync(CancellationToken cancellationToken)
-    {
-        var index = MonitoredItemShardPlanner.Plan(
-            _dataShards.Select(s => s.ItemCount).ToList(), ItemsPerShard, 1)[0];
-        return index < _dataShards.Count
-            ? _dataShards[index]
-            : await CreateDataShardAsync(cancellationToken);
-    }
-
     /// <summary>
     /// Drops a monitored item that failed to create from the shard it was placed on.
     /// Callers must hold <see cref="_applyGate"/>. No ApplyChanges is issued: the server

src/ZB.MOM.WW.ScadaBridge.DataConnectionLayer/MxGatewayGlobalOptionsValidator.cs

@@ -0,0 +1,15 @@
+using Microsoft.Extensions.Options;
+
+namespace ZB.MOM.WW.ScadaBridge.DataConnectionLayer;
+
+/// <summary>Validates the MxGateway client identity before connections start.</summary>
+public sealed class MxGatewayGlobalOptionsValidator : IValidateOptions<MxGatewayGlobalOptions>
+{
+    /// <inheritdoc />
+    public ValidateOptionsResult Validate(string? name, MxGatewayGlobalOptions options)
+    {
+        if (string.IsNullOrWhiteSpace(options.ClientNamePrefix))
+            return ValidateOptionsResult.Fail("ScadaBridge:MxGateway:ClientNamePrefix must not be blank.");
+        return ValidateOptionsResult.Success;
+    }
+}

src/ZB.MOM.WW.ScadaBridge.DataConnectionLayer/OpcUaGlobalOptionsValidator.cs

@@ -0,0 +1,15 @@
+using Microsoft.Extensions.Options;
+
+namespace ZB.MOM.WW.ScadaBridge.DataConnectionLayer;
+
+/// <summary>Validates the OPC UA application identity before connections start.</summary>
+public sealed class OpcUaGlobalOptionsValidator : IValidateOptions<OpcUaGlobalOptions>
+{
+    /// <inheritdoc />
+    public ValidateOptionsResult Validate(string? name, OpcUaGlobalOptions options)
+    {
+        if (string.IsNullOrWhiteSpace(options.ApplicationName))
+            return ValidateOptionsResult.Fail("ScadaBridge:OpcUa:ApplicationName must not be blank.");
+        return ValidateOptionsResult.Success;
+    }
+}

src/ZB.MOM.WW.ScadaBridge.DataConnectionLayer/ServiceCollectionExtensions.cs

@@ -24,16 +24,18 @@ public static class ServiceCollectionExtensions
         services.TryAddEnumerable(
             ServiceDescriptor.Singleton<IValidateOptions<DataConnectionOptions>, DataConnectionOptionsValidator>());
 
-        // OpcUaGlobalOptions / MxGatewayGlobalOptions carry only string identity/path
-        // fields (no numeric or duration knobs), so there is nothing to range-validate
-        // — no dedicated validator is registered for them. Canonical sections are
-        // ScadaBridge:OpcUa / ScadaBridge:MxGateway (NF8): the bare "OpcUa"/"MxGateway"
-        // sections exist in no appsettings, so binding them read nothing.
+        // Validate identities before the first connection attempts to register with a server.
         services.AddOptions<OpcUaGlobalOptions>()
-            .BindConfiguration("ScadaBridge:OpcUa");
+            .BindConfiguration("ScadaBridge:OpcUa")
+            .ValidateOnStart();
+        services.TryAddEnumerable(
+            ServiceDescriptor.Singleton<IValidateOptions<OpcUaGlobalOptions>, OpcUaGlobalOptionsValidator>());
 
         services.AddOptions<MxGatewayGlobalOptions>()
-            .BindConfiguration("ScadaBridge:MxGateway");
+            .BindConfiguration("ScadaBridge:MxGateway")
+            .ValidateOnStart();
+        services.TryAddEnumerable(
+            ServiceDescriptor.Singleton<IValidateOptions<MxGatewayGlobalOptions>, MxGatewayGlobalOptionsValidator>());
 
         // Register the factory for protocol extensibility
         services.AddSingleton<IDataConnectionFactory, DataConnectionFactory>();