feat(auditlog): AuditLogPartitionMaintenanceService monthly roll-forward (#23 M6)

src/ScadaLink.AuditLog/ServiceCollectionExtensions.cs

@@ -1,6 +1,7 @@
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.DependencyInjection.Extensions;
+using Microsoft.Extensions.Hosting;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
 using ScadaLink.AuditLog.Central;
@@ -43,6 +44,9 @@ public static class ServiceCollectionExtensions
     /// <summary>Configuration section bound to <see cref="SiteAuditTelemetryOptions"/>.</summary>
     public const string SiteTelemetrySectionName = "AuditLog:SiteTelemetry";
 
+    /// <summary>Configuration section bound to <see cref="AuditLogPartitionMaintenanceOptions"/>.</summary>
+    public const string PartitionMaintenanceSectionName = "AuditLog:PartitionMaintenance";
+
     /// <summary>
     /// Registers the Audit Log (#23) component services: options, the site
     /// SQLite writer chain (primary + ring fallback + failure-counter sink),
@@ -216,4 +220,37 @@ public static class ServiceCollectionExtensions
             ServiceDescriptor.Singleton<IAuditRedactionFailureCounter, HealthMetricsAuditRedactionFailureCounter>());
         return services;
     }
+
+    /// <summary>
+    /// Audit Log (#23) M6-T5 Bundle D — central-only registration for the
+    /// <see cref="AuditLogPartitionMaintenanceService"/> hosted service plus
+    /// its <see cref="AuditLogPartitionMaintenanceOptions"/> binding. Must be
+    /// called from the Central role's composition root (not from a site
+    /// composition root); the underlying <c>IPartitionMaintenance</c>
+    /// implementation is registered by <c>AddConfigurationDatabase</c> and
+    /// only exists on the central node.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// Separated from <see cref="AddAuditLog"/> because <c>AddAuditLog</c> is
+    /// also invoked from site composition roots — silently starting a
+    /// hosted service that resolves an unregistered dependency on a site
+    /// would fail every tick. Keeping the central-only registration in its
+    /// own helper preserves the "every <c>Add*</c> call is safe to issue
+    /// from any composition root" invariant.
+    /// </para>
+    /// </remarks>
+    public static IServiceCollection AddAuditLogCentralMaintenance(
+        this IServiceCollection services,
+        IConfiguration config)
+    {
+        ArgumentNullException.ThrowIfNull(services);
+        ArgumentNullException.ThrowIfNull(config);
+
+        services.AddOptions<AuditLogPartitionMaintenanceOptions>()
+            .Bind(config.GetSection(PartitionMaintenanceSectionName));
+        services.AddHostedService<AuditLogPartitionMaintenanceService>();
+
+        return services;
+    }
 }