feat(audit): stamp SourceNode at site SqliteAuditWriter from INodeIdentityProvider

Caller-provided SourceNode wins (preserves reconciled rows from other nodes);
otherwise the writer fills it from the local INodeIdentityProvider.NodeName.
Reads from the provider on every write — singleton lifetime means zero overhead.

src/ScadaLink.AuditLog/Site/SqliteAuditWriter.cs

@@ -42,6 +42,7 @@ public class SqliteAuditWriter : IAuditWriter, ISiteAuditQueue, IAsyncDisposable
     private readonly SqliteConnection _connection;
     private readonly SqliteAuditWriterOptions _options;
     private readonly ILogger<SqliteAuditWriter> _logger;
+    private readonly INodeIdentityProvider _nodeIdentity;
     private readonly object _writeLock = new();
     private readonly Channel<PendingAuditEvent> _writeQueue;
     private readonly Task _writerLoop;
@@ -50,13 +51,16 @@ public class SqliteAuditWriter : IAuditWriter, ISiteAuditQueue, IAsyncDisposable
     public SqliteAuditWriter(
         IOptions<SqliteAuditWriterOptions> options,
         ILogger<SqliteAuditWriter> logger,
+        INodeIdentityProvider nodeIdentity,
         string? connectionStringOverride = null)
     {
         ArgumentNullException.ThrowIfNull(options);
         ArgumentNullException.ThrowIfNull(logger);
+        ArgumentNullException.ThrowIfNull(nodeIdentity);
 
         _options = options.Value;
         _logger = logger;
+        _nodeIdentity = nodeIdentity;
 
         var connectionString = connectionStringOverride
             ?? $"Data Source={_options.DatabasePath};Cache=Shared";
@@ -325,7 +329,15 @@ public class SqliteAuditWriter : IAuditWriter, ISiteAuditQueue, IAsyncDisposable
                     pKind.Value = e.Kind.ToString();
                     pCorrelationId.Value = (object?)e.CorrelationId?.ToString() ?? DBNull.Value;
                     pSourceSiteId.Value = (object?)e.SourceSiteId ?? DBNull.Value;
-                    pSourceNode.Value = (object?)e.SourceNode ?? DBNull.Value;
+                    // SourceNode-stamping: caller-provided value wins (preserves
+                    // rows reconciled in from other nodes via the same writer);
+                    // otherwise stamp from the local INodeIdentityProvider. The
+                    // event record itself is NOT mutated — stamping is at write
+                    // time only. If the provider also returns null (unconfigured
+                    // node), the row's SourceNode stays NULL — operators see
+                    // "needs config" via the schema, not a magic fallback string.
+                    var sourceNode = e.SourceNode ?? _nodeIdentity.NodeName;
+                    pSourceNode.Value = (object?)sourceNode ?? DBNull.Value;
                     pSourceInstanceId.Value = (object?)e.SourceInstanceId ?? DBNull.Value;
                     pSourceScript.Value = (object?)e.SourceScript ?? DBNull.Value;
                     pActor.Value = (object?)e.Actor ?? DBNull.Value;

tests/ScadaLink.AuditLog.Tests/AddAuditLogTests.cs

@@ -7,6 +7,7 @@ using ScadaLink.AuditLog.Central;
 using ScadaLink.AuditLog.Configuration;
 using ScadaLink.AuditLog.Site;
 using ScadaLink.AuditLog.Site.Telemetry;
+using ScadaLink.AuditLog.Tests.TestSupport;
 using ScadaLink.Commons.Interfaces.Services;
 using ScadaLink.HealthMonitoring;
 
@@ -31,6 +32,10 @@ public class AddAuditLogTests
         var services = new ServiceCollection();
         services.AddSingleton<ILoggerFactory, NullLoggerFactory>();
         services.AddSingleton(typeof(ILogger<>), typeof(NullLogger<>));
+        // INodeIdentityProvider is registered by the Host's
+        // SiteServiceRegistration in production; AddAuditLog assumes its
+        // presence so SqliteAuditWriter and CentralAuditWriter can resolve.
+        services.AddSingleton<INodeIdentityProvider>(new FakeNodeIdentityProvider());
         services.AddAuditLog(config);
         return services.BuildServiceProvider();
     }

tests/ScadaLink.AuditLog.Tests/Integration/DatabaseSyncEmissionEndToEndTests.cs

@@ -9,6 +9,7 @@ using ScadaLink.AuditLog.Central;
 using ScadaLink.AuditLog.Site;
 using ScadaLink.AuditLog.Site.Telemetry;
 using ScadaLink.AuditLog.Tests.Integration.Infrastructure;
+using ScadaLink.AuditLog.Tests.TestSupport;
 using ScadaLink.Commons.Entities.Audit;
 using ScadaLink.Commons.Interfaces.Repositories;
 using ScadaLink.Commons.Interfaces.Services;
@@ -114,6 +115,7 @@ public class DatabaseSyncEmissionEndToEndTests : TestKit, IClassFixture<MsSqlMig
                 ChannelCapacity = 1024,
             }),
             NullLogger<SqliteAuditWriter>.Instance,
+            new FakeNodeIdentityProvider(),
             connectionStringOverride:
                 $"Data Source=file:auditlog-e1-{Guid.NewGuid():N}?mode=memory&cache=shared");
 

tests/ScadaLink.AuditLog.Tests/Integration/ExecutionIdCorrelationTests.cs

@@ -9,6 +9,7 @@ using ScadaLink.AuditLog.Central;
 using ScadaLink.AuditLog.Site;
 using ScadaLink.AuditLog.Site.Telemetry;
 using ScadaLink.AuditLog.Tests.Integration.Infrastructure;
+using ScadaLink.AuditLog.Tests.TestSupport;
 using ScadaLink.Commons.Interfaces.Repositories;
 using ScadaLink.Commons.Interfaces.Services;
 using ScadaLink.Commons.Types.Audit;
@@ -111,6 +112,7 @@ public class ExecutionIdCorrelationTests : TestKit, IClassFixture<MsSqlMigration
                 ChannelCapacity = 1024,
             }),
             NullLogger<SqliteAuditWriter>.Instance,
+            new FakeNodeIdentityProvider(),
             connectionStringOverride:
                 $"Data Source=file:auditlog-execid-{Guid.NewGuid():N}?mode=memory&cache=shared");
 

tests/ScadaLink.AuditLog.Tests/Integration/Infrastructure/CombinedTelemetryHarness.cs

@@ -10,6 +10,7 @@ using ScadaLink.Commons.Interfaces;
 using ScadaLink.Commons.Interfaces.Repositories;
 using ScadaLink.Commons.Interfaces.Services;
 using ScadaLink.Commons.Messages.Integration;
+using ScadaLink.AuditLog.Tests.TestSupport;
 using ScadaLink.ConfigurationDatabase;
 using ScadaLink.ConfigurationDatabase.Repositories;
 using ScadaLink.ConfigurationDatabase.Tests.Migrations;
@@ -78,6 +79,7 @@ public sealed class CombinedTelemetryHarness : IAsyncDisposable
                 ChannelCapacity = 1024,
             }),
             NullLogger<SqliteAuditWriter>.Instance,
+            new FakeNodeIdentityProvider(),
             connectionStringOverride:
                 $"Data Source=file:cachedcall-g-{Guid.NewGuid():N}?mode=memory&cache=shared");
 

tests/ScadaLink.AuditLog.Tests/Integration/OutageReconciliationTests.cs

@@ -6,6 +6,7 @@ using Microsoft.Extensions.Logging.Abstractions;
 using Microsoft.Extensions.Options;
 using ScadaLink.AuditLog.Central;
 using ScadaLink.AuditLog.Site;
+using ScadaLink.AuditLog.Tests.TestSupport;
 using ScadaLink.Commons.Entities.Audit;
 using ScadaLink.Commons.Interfaces.Repositories;
 using ScadaLink.Commons.Interfaces.Services;
@@ -148,6 +149,7 @@ public class OutageReconciliationTests : TestKit, IClassFixture<MsSqlMigrationFi
                 ChannelCapacity = 4096,
             }),
             NullLogger<SqliteAuditWriter>.Instance,
+            new FakeNodeIdentityProvider(),
             connectionStringOverride:
                 $"Data Source=file:outage-{Guid.NewGuid():N}?mode=memory&cache=shared");
 

tests/ScadaLink.AuditLog.Tests/Integration/ParentExecutionIdCorrelationTests.cs

@@ -16,6 +16,7 @@ using ScadaLink.AuditLog.Central;
 using ScadaLink.AuditLog.Site;
 using ScadaLink.AuditLog.Site.Telemetry;
 using ScadaLink.AuditLog.Tests.Integration.Infrastructure;
+using ScadaLink.AuditLog.Tests.TestSupport;
 using ScadaLink.Commons.Entities.Audit;
 using ScadaLink.Commons.Interfaces.Repositories;
 using ScadaLink.Commons.Interfaces.Services;
@@ -166,6 +167,7 @@ public class ParentExecutionIdCorrelationTests : TestKit, IClassFixture<MsSqlMig
                 ChannelCapacity = 1024,
             }),
             NullLogger<SqliteAuditWriter>.Instance,
+            new FakeNodeIdentityProvider(),
             connectionStringOverride:
                 $"Data Source=file:auditlog-parentexec-{Guid.NewGuid():N}?mode=memory&cache=shared");
         var ring = new RingBufferFallback();

tests/ScadaLink.AuditLog.Tests/Integration/SyncCallEmissionEndToEndTests.cs

@@ -7,6 +7,7 @@ using ScadaLink.AuditLog.Central;
 using ScadaLink.AuditLog.Site;
 using ScadaLink.AuditLog.Site.Telemetry;
 using ScadaLink.AuditLog.Tests.Integration.Infrastructure;
+using ScadaLink.AuditLog.Tests.TestSupport;
 using ScadaLink.Commons.Entities.Audit;
 using ScadaLink.Commons.Interfaces.Repositories;
 using ScadaLink.Commons.Interfaces.Services;
@@ -91,12 +92,13 @@ public class SyncCallEmissionEndToEndTests : TestKit, IClassFixture<MsSqlMigrati
         });
 
     private static SqliteAuditWriter CreateInMemorySqliteWriter() =>
-        // The 3rd constructor argument is connectionStringOverride. A unique
+        // The 4th constructor argument is connectionStringOverride. A unique
         // shared-cache in-memory URI keeps the schema scoped to this writer
         // instance and torn down when the writer is disposed.
         new SqliteAuditWriter(
             InMemorySqliteOptions(),
             NullLogger<SqliteAuditWriter>.Instance,
+            new FakeNodeIdentityProvider(),
             connectionStringOverride: $"Data Source=file:auditlog-h-{Guid.NewGuid():N}?mode=memory&cache=shared");
 
     private static IOptions<SiteAuditTelemetryOptions> FastTelemetryOptions() =>

tests/ScadaLink.AuditLog.Tests/Payload/FilterIntegrationTests.cs

@@ -11,6 +11,7 @@ using ScadaLink.AuditLog.Central;
 using ScadaLink.AuditLog.Configuration;
 using ScadaLink.AuditLog.Payload;
 using ScadaLink.AuditLog.Site;
+using ScadaLink.AuditLog.Tests.TestSupport;
 using ScadaLink.Commons.Entities.Audit;
 using ScadaLink.Commons.Interfaces.Repositories;
 using ScadaLink.Commons.Interfaces.Services;
@@ -89,6 +90,7 @@ public class FilterIntegrationTests
         var sqliteWriter = new SqliteAuditWriter(
             Microsoft.Extensions.Options.Options.Create(new SqliteAuditWriterOptions { DatabasePath = dataSource }),
             NullLogger<SqliteAuditWriter>.Instance,
+            new FakeNodeIdentityProvider(),
             connectionStringOverride: $"Data Source={dataSource};Cache=Shared");
         await using var _disposeSqlite = sqliteWriter;
 

tests/ScadaLink.AuditLog.Tests/Site/SqliteAuditWriterBacklogStatsTests.cs

@@ -1,6 +1,7 @@
 using Microsoft.Extensions.Logging.Abstractions;
 using Microsoft.Extensions.Options;
 using ScadaLink.AuditLog.Site;
+using ScadaLink.AuditLog.Tests.TestSupport;
 using ScadaLink.Commons.Entities.Audit;
 using ScadaLink.Commons.Types.Enums;
 
@@ -39,7 +40,8 @@ public class SqliteAuditWriterBacklogStatsTests : IDisposable
         var options = new SqliteAuditWriterOptions { DatabasePath = _dbPath };
         return new SqliteAuditWriter(
             Options.Create(options),
-            NullLogger<SqliteAuditWriter>.Instance);
+            NullLogger<SqliteAuditWriter>.Instance,
+            new FakeNodeIdentityProvider());
     }
 
     private static AuditEvent NewEvent(DateTime? occurredAtUtc = null) => new()

tests/ScadaLink.AuditLog.Tests/Site/SqliteAuditWriterSchemaTests.cs

@@ -2,6 +2,7 @@ using Microsoft.Data.Sqlite;
 using Microsoft.Extensions.Logging.Abstractions;
 using Microsoft.Extensions.Options;
 using ScadaLink.AuditLog.Site;
+using ScadaLink.AuditLog.Tests.TestSupport;
 using ScadaLink.Commons.Entities.Audit;
 using ScadaLink.Commons.Types.Enums;
 
@@ -31,6 +32,7 @@ public class SqliteAuditWriterSchemaTests
         var writer = new SqliteAuditWriter(
             Options.Create(options),
             NullLogger<SqliteAuditWriter>.Instance,
+            new FakeNodeIdentityProvider(),
             connectionStringOverride: $"Data Source={dataSource};Cache=Shared");
         return (writer, dataSource);
     }
@@ -200,6 +202,7 @@ public class SqliteAuditWriterSchemaTests
         return new SqliteAuditWriter(
             Options.Create(options),
             NullLogger<SqliteAuditWriter>.Instance,
+            new FakeNodeIdentityProvider(),
             connectionStringOverride: $"Data Source={dataSource};Cache=Shared");
     }
 

tests/ScadaLink.AuditLog.Tests/Site/SqliteAuditWriterWriteTests.cs

@@ -2,7 +2,9 @@ using Microsoft.Data.Sqlite;
 using Microsoft.Extensions.Logging.Abstractions;
 using Microsoft.Extensions.Options;
 using ScadaLink.AuditLog.Site;
+using ScadaLink.AuditLog.Tests.TestSupport;
 using ScadaLink.Commons.Entities.Audit;
+using ScadaLink.Commons.Interfaces.Services;
 using ScadaLink.Commons.Types.Enums;
 
 namespace ScadaLink.AuditLog.Tests.Site;
@@ -19,7 +21,8 @@ public class SqliteAuditWriterWriteTests
 {
     private static (SqliteAuditWriter writer, string dataSource) CreateWriter(
         string testName,
-        int? channelCapacity = null)
+        int? channelCapacity = null,
+        INodeIdentityProvider? nodeIdentity = null)
     {
         var dataSource = $"file:{testName}-{Guid.NewGuid():N}?mode=memory&cache=shared";
         var opts = new SqliteAuditWriterOptions { DatabasePath = dataSource };
@@ -28,9 +31,15 @@ public class SqliteAuditWriterWriteTests
             opts.ChannelCapacity = cap;
         }
 
+        // Default identity provider returns null — existing tests pre-date
+        // SourceNode stamping and have no expectation about it. New stamping
+        // tests pass a real provider via the parameter.
+        var identity = nodeIdentity ?? new FakeNodeIdentityProvider();
+
         var writer = new SqliteAuditWriter(
             Options.Create(opts),
             NullLogger<SqliteAuditWriter>.Instance,
+            identity,
             connectionStringOverride: $"Data Source={dataSource};Cache=Shared");
         return (writer, dataSource);
     }
@@ -386,4 +395,57 @@ public class SqliteAuditWriterWriteTests
         var row = Assert.Single(rows);
         Assert.Null(row.ExecutionId);
     }
+
+    // ----- SourceNode stamping (Tasks 11/12) ----- //
+
+    [Fact]
+    public async Task WriteAsync_StampsSourceNodeFromProvider_WhenEventHasNone()
+    {
+        var (writer, _) = CreateWriter(
+            nameof(WriteAsync_StampsSourceNodeFromProvider_WhenEventHasNone),
+            nodeIdentity: new FakeNodeIdentityProvider("node-a"));
+        await using var _w = writer;
+
+        var evt = NewEvent();
+        Assert.Null(evt.SourceNode); // sanity check — fresh event has no SourceNode
+        await writer.WriteAsync(evt);
+
+        var rows = await writer.ReadPendingAsync(limit: 10);
+        var row = Assert.Single(rows);
+        Assert.Equal("node-a", row.SourceNode);
+    }
+
+    [Fact]
+    public async Task WriteAsync_PreservesCallerProvidedSourceNode()
+    {
+        var (writer, _) = CreateWriter(
+            nameof(WriteAsync_PreservesCallerProvidedSourceNode),
+            nodeIdentity: new FakeNodeIdentityProvider("node-a"));
+        await using var _w = writer;
+
+        // Reconciled rows from another node arrive with their origin's
+        // SourceNode already populated; the writer must preserve it.
+        var evt = NewEvent() with { SourceNode = "node-z" };
+        await writer.WriteAsync(evt);
+
+        var rows = await writer.ReadPendingAsync(limit: 10);
+        var row = Assert.Single(rows);
+        Assert.Equal("node-z", row.SourceNode);
+    }
+
+    [Fact]
+    public async Task WriteAsync_LeavesSourceNodeNull_WhenProviderReturnsNull()
+    {
+        var (writer, _) = CreateWriter(
+            nameof(WriteAsync_LeavesSourceNodeNull_WhenProviderReturnsNull),
+            nodeIdentity: new FakeNodeIdentityProvider(nodeName: null));
+        await using var _w = writer;
+
+        var evt = NewEvent();
+        await writer.WriteAsync(evt);
+
+        var rows = await writer.ReadPendingAsync(limit: 10);
+        var row = Assert.Single(rows);
+        Assert.Null(row.SourceNode);
+    }
 }

tests/ScadaLink.AuditLog.Tests/TestSupport/FakeNodeIdentityProvider.cs

@@ -0,0 +1,20 @@
+using ScadaLink.Commons.Interfaces.Services;
+
+namespace ScadaLink.AuditLog.Tests.TestSupport;
+
+/// <summary>
+/// Test fake for <see cref="INodeIdentityProvider"/>. Returns the configured
+/// <see cref="NodeName"/> verbatim — including <c>null</c> — so tests can
+/// exercise both the "stamped" and "unconfigured" branches of the SourceNode
+/// stamping logic in <see cref="ScadaLink.AuditLog.Site.SqliteAuditWriter"/>
+/// and <see cref="ScadaLink.AuditLog.Central.CentralAuditWriter"/>.
+/// </summary>
+internal sealed class FakeNodeIdentityProvider : INodeIdentityProvider
+{
+    public string? NodeName { get; }
+
+    public FakeNodeIdentityProvider(string? nodeName = null)
+    {
+        NodeName = nodeName;
+    }
+}

tests/ScadaLink.IntegrationTests/AuditLog/SiteAuditPushFlowTests.cs

@@ -146,8 +146,10 @@ public class SiteAuditPushFlowTests : TestKit
         // + Pending queue). A temp file so it survives across DI scopes.
         var dbPath = Path.Combine(Path.GetTempPath(), $"auditpush-{Guid.NewGuid():N}.db");
         var writerOptions = Options.Create(new SqliteAuditWriterOptions { DatabasePath = dbPath });
+        var nodeIdentity = Substitute.For<ScadaLink.Commons.Interfaces.Services.INodeIdentityProvider>();
+        nodeIdentity.NodeName.Returns((string?)null);
         await using var writer = new SqliteAuditWriter(
-            writerOptions, NullLogger<SqliteAuditWriter>.Instance);
+            writerOptions, NullLogger<SqliteAuditWriter>.Instance, nodeIdentity);
 
         // Real SiteCommunicationActor. RegisterCentralClient is given the relay
         // standing in for the central ClusterClient.