fix(cluster-infrastructure): resolve ClusterInfrastructure-002..006 — options validation, DI registration, down-if-alone

src/ScadaLink.ClusterInfrastructure/ServiceCollectionExtensions.cs

@@ -1,18 +1,47 @@
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.DependencyInjection.Extensions;
+using Microsoft.Extensions.Options;
 
 namespace ScadaLink.ClusterInfrastructure;
 
+/// <summary>
+/// DI registration for the Cluster Infrastructure component.
+/// </summary>
 public static class ServiceCollectionExtensions
 {
+    /// <summary>
+    /// Registers the Cluster Infrastructure services. This component owns the
+    /// cluster <em>configuration contract</em> (<see cref="ClusterOptions"/>); the
+    /// Akka.NET bootstrap itself lives in <c>ScadaLink.Host</c>
+    /// (see <c>Component-ClusterInfrastructure.md</c>).
+    /// <para>
+    /// Registering the <see cref="ClusterOptionsValidator"/> means a misconfigured
+    /// <c>ScadaLink:Cluster</c> section (e.g. <c>MinNrOfMembers: 2</c> or a quorum
+    /// split-brain strategy) throws an <see cref="OptionsValidationException"/> the
+    /// first time <see cref="IOptions{TOptions}"/> is resolved, rather than booting
+    /// into a broken cluster.
+    /// </para>
+    /// </summary>
     public static IServiceCollection AddClusterInfrastructure(this IServiceCollection services)
     {
-        // Phase 0: skeleton only
+        services.TryAddEnumerable(
+            ServiceDescriptor.Singleton<IValidateOptions<ClusterOptions>, ClusterOptionsValidator>());
         return services;
     }
 
+    /// <summary>
+    /// Reserved for cluster-infrastructure actor registration. This component does
+    /// not register any actors — the Akka.NET bootstrap and actor wiring live in
+    /// <c>ScadaLink.Host</c>. The method throws rather than silently returning
+    /// success so that any caller assuming this component registers actors fails
+    /// fast with a clear cause instead of failing later, far from here.
+    /// </summary>
+    /// <exception cref="NotImplementedException">Always thrown.</exception>
     public static IServiceCollection AddClusterInfrastructureActors(this IServiceCollection services)
     {
-        // Phase 0: placeholder for Akka actor registration
-        return services;
+        throw new NotImplementedException(
+            "ScadaLink.ClusterInfrastructure registers no actors. The Akka.NET actor system " +
+            "bootstrap and all cluster actor registration live in ScadaLink.Host " +
+            "(AkkaHostedService). Do not call AddClusterInfrastructureActors().");
     }
 }