feat(health): surface AuditRedactionFailure in central snapshot (#23 M6)

src/ScadaLink.AuditLog/Central/CentralAuditRedactionFailureCounter.cs

@@ -0,0 +1,57 @@
+using ScadaLink.AuditLog.Payload;
+
+namespace ScadaLink.AuditLog.Central;
+
+/// <summary>
+/// Audit Log (#23) M6 Bundle E (T9) — bridges
+/// <see cref="IAuditRedactionFailureCounter"/> (incremented by
+/// <see cref="DefaultAuditPayloadFilter"/> every time a header / body / SQL
+/// parameter redactor stage throws and the filter has to over-redact the
+/// offending field) into <see cref="AuditCentralHealthSnapshot"/> so the
+/// failure surfaces on the central health surface as
+/// <c>AuditCentralHealthSnapshot.AuditRedactionFailure</c>.
+/// </summary>
+/// <remarks>
+/// <para>
+/// <b>Site vs central.</b> M5 Bundle C wired the SITE-side bridge
+/// (<see cref="ScadaLink.AuditLog.Site.HealthMetricsAuditRedactionFailureCounter"/>),
+/// which routes increments into the site health report payload's
+/// <c>AuditRedactionFailure</c> field. That handles redactor failures on the
+/// site SQLite hot-path (FallbackAuditWriter). M6 Bundle E (T9) adds the
+/// MIRROR bridge here so the same payload filter — when it runs on the
+/// central <see cref="CentralAuditWriter"/> /
+/// <see cref="AuditLogIngestActor"/> paths — surfaces its failures on the
+/// central dashboard rather than disappearing into a NoOp.
+/// </para>
+/// <para>
+/// <b>Registration shape.</b> Site composition roots call
+/// <see cref="ServiceCollectionExtensions.AddAuditLogHealthMetricsBridge"/>,
+/// which overrides the binding with the site bridge. Central composition
+/// roots call <see cref="ServiceCollectionExtensions.AddAuditLogCentralMaintenance"/>,
+/// which overrides with this central bridge. A node never wears both hats —
+/// site and central are distinct host roles — so the two bridges never
+/// fight over the same binding at runtime.
+/// </para>
+/// <para>
+/// <b>Why not a thin wrapper around the snapshot directly?</b> The snapshot
+/// itself <i>could</i> be the bound implementation (it already implements
+/// <see cref="IAuditRedactionFailureCounter"/>), but a dedicated class makes
+/// the central-vs-site asymmetry explicit at the DI boundary — readers of
+/// <see cref="ServiceCollectionExtensions.AddAuditLogCentralMaintenance"/>
+/// see "site → site bridge, central → central bridge", matching the
+/// <see cref="ScadaLink.AuditLog.Site.HealthMetricsAuditRedactionFailureCounter"/>
+/// shape one-for-one.
+/// </para>
+/// </remarks>
+public sealed class CentralAuditRedactionFailureCounter : IAuditRedactionFailureCounter
+{
+    private readonly AuditCentralHealthSnapshot _snapshot;
+
+    public CentralAuditRedactionFailureCounter(AuditCentralHealthSnapshot snapshot)
+    {
+        _snapshot = snapshot ?? throw new ArgumentNullException(nameof(snapshot));
+    }
+
+    /// <inheritdoc/>
+    public void Increment() => ((IAuditRedactionFailureCounter)_snapshot).Increment();
+}

src/ScadaLink.AuditLog/ServiceCollectionExtensions.cs

@@ -295,14 +295,18 @@ public static class ServiceCollectionExtensions
         services.Replace(ServiceDescriptor.Singleton<ICentralAuditWriteFailureCounter>(
             sp => sp.GetRequiredService<AuditCentralHealthSnapshot>()));
         // M6 Bundle E (T9): override the NoOp IAuditRedactionFailureCounter
-        // (registered by AddAuditLog) with the central snapshot binding so
-        // payload-filter throws on CentralAuditWriter / AuditLogIngestActor
-        // paths surface on the central dashboard. The site composition root
+        // (registered by AddAuditLog) with the CentralAuditRedactionFailureCounter
+        // bridge so payload-filter throws on CentralAuditWriter /
+        // AuditLogIngestActor paths surface on the central dashboard. The
+        // bridge is a thin wrapper around the AuditCentralHealthSnapshot
+        // singleton so all central redactor failures route into the same
+        // counter as CentralAuditWriteFailures. The site composition root
         // overrides this binding AGAIN via AddAuditLogHealthMetricsBridge —
         // central nodes do not call that bridge, so this is the final
-        // binding on a central host.
-        services.Replace(ServiceDescriptor.Singleton<IAuditRedactionFailureCounter>(
-            sp => sp.GetRequiredService<AuditCentralHealthSnapshot>()));
+        // binding on a central host. Mirrors the M5 Bundle C
+        // HealthMetricsAuditRedactionFailureCounter shape one-for-one.
+        services.Replace(ServiceDescriptor.Singleton<IAuditRedactionFailureCounter,
+            CentralAuditRedactionFailureCounter>());
 
         return services;
     }

tests/ScadaLink.AuditLog.Tests/Central/CentralAuditRedactionFailureCounterTests.cs

@@ -0,0 +1,99 @@
+using Akka.Actor;
+using Akka.TestKit.Xunit2;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Logging.Abstractions;
+using ScadaLink.AuditLog;
+using ScadaLink.AuditLog.Central;
+using ScadaLink.AuditLog.Payload;
+
+namespace ScadaLink.AuditLog.Tests.Central;
+
+/// <summary>
+/// Bundle E (M6-T9) coverage for the central-side payload-filter redactor
+/// failure bridge. M5 wired the SITE bridge
+/// (<c>HealthMetricsAuditRedactionFailureCounter</c>) that pushes increments
+/// into the site health report; M6 mirrors that with
+/// <see cref="CentralAuditRedactionFailureCounter"/> so the same payload
+/// filter — when it runs on the central writer paths — surfaces failures on
+/// the central <see cref="AuditCentralHealthSnapshot"/>.
+/// </summary>
+public class CentralAuditRedactionFailureCounterTests : TestKit
+{
+    [Fact]
+    public void Increment_Routes_To_Snapshot()
+    {
+        using var tracker = new SiteAuditTelemetryStalledTracker(Sys);
+        var snapshot = new AuditCentralHealthSnapshot(tracker);
+        var counter = new CentralAuditRedactionFailureCounter(snapshot);
+
+        counter.Increment();
+        counter.Increment();
+        counter.Increment();
+
+        Assert.Equal(3, snapshot.AuditRedactionFailure);
+    }
+
+    [Fact]
+    public void Construction_With_Null_Snapshot_Throws()
+    {
+        Assert.Throws<ArgumentNullException>(
+            () => new CentralAuditRedactionFailureCounter(null!));
+    }
+
+    [Fact]
+    public void AddAuditLogCentralMaintenance_Replaces_IAuditRedactionFailureCounter_With_CentralImpl()
+    {
+        // AddAuditLog registers NoOp; AddAuditLogCentralMaintenance is the
+        // override path. The replaced binding MUST resolve to the central
+        // bridge — a site host that wires AddAuditLogHealthMetricsBridge
+        // instead would resolve to the site bridge (covered in
+        // AddAuditLogTests).
+        var config = new ConfigurationBuilder()
+            .AddInMemoryCollection(new Dictionary<string, string?>
+            {
+                ["AuditLog:SiteWriter:DatabasePath"] = ":memory:",
+            })
+            .Build();
+
+        var services = new ServiceCollection();
+        services.AddSingleton<ILoggerFactory, NullLoggerFactory>();
+        services.AddSingleton(typeof(ILogger<>), typeof(NullLogger<>));
+        // The AuditCentralHealthSnapshot ctor takes the stalled tracker
+        // which itself needs an ActorSystem — register a real system
+        // (test-kit's Sys) so the DI graph composes.
+        services.AddSingleton<ActorSystem>(Sys);
+        services.AddAuditLog(config);
+        services.AddAuditLogCentralMaintenance(config);
+        using var provider = services.BuildServiceProvider();
+
+        var counter = provider.GetRequiredService<IAuditRedactionFailureCounter>();
+
+        Assert.IsType<CentralAuditRedactionFailureCounter>(counter);
+    }
+
+    [Fact]
+    public void AddAuditLog_Default_IAuditRedactionFailureCounter_Is_NoOp()
+    {
+        // Sanity check: without AddAuditLogCentralMaintenance the default
+        // remains the NoOp from M5 — the central bridge only takes effect
+        // when the central-only registration runs.
+        var config = new ConfigurationBuilder()
+            .AddInMemoryCollection(new Dictionary<string, string?>
+            {
+                ["AuditLog:SiteWriter:DatabasePath"] = ":memory:",
+            })
+            .Build();
+
+        var services = new ServiceCollection();
+        services.AddSingleton<ILoggerFactory, NullLoggerFactory>();
+        services.AddSingleton(typeof(ILogger<>), typeof(NullLogger<>));
+        services.AddAuditLog(config);
+        using var provider = services.BuildServiceProvider();
+
+        var counter = provider.GetRequiredService<IAuditRedactionFailureCounter>();
+
+        Assert.IsType<NoOpAuditRedactionFailureCounter>(counter);
+    }
+}