feat(db): add SourceNode column + IX_AuditLog_Node_Occurred index to AuditLog

src/ScadaLink.ConfigurationDatabase/Configurations/AuditLogEntityTypeConfiguration.cs

@@ -70,6 +70,14 @@ public class AuditLogEntityTypeConfiguration : IEntityTypeConfiguration<AuditEve
             .HasMaxLength(256)
             .IsUnicode(false);
 
+        // SourceNode (Audit Log #23, SourceNode-stamping): node-local identifier of the
+        // cluster member that produced the row (e.g. "node-a", "central-a"). NULL is
+        // valid for reconciled rows from a retired node and for direct-write rows
+        // produced before this feature shipped. ASCII — varchar(64), no unicode.
+        builder.Property(e => e.SourceNode)
+            .HasColumnType("varchar(64)")
+            .HasMaxLength(64);
+
         // Bounded unicode message column.
         builder.Property(e => e.ErrorMessage)
             .HasMaxLength(1024);
@@ -97,6 +105,14 @@ public class AuditLogEntityTypeConfiguration : IEntityTypeConfiguration<AuditEve
             .HasFilter("[ParentExecutionId] IS NOT NULL")
             .HasDatabaseName("IX_AuditLog_ParentExecution");
 
+        // SourceNode composite index (Audit Log #23, SourceNode-stamping): backs
+        // per-node Central UI / health-dashboard queries (e.g. "rows produced by
+        // central-a, newest first"). Created via raw SQL in the migration so it lands
+        // on the ps_AuditLog_Month(OccurredAtUtc) partition scheme like every other
+        // IX_AuditLog_* index — keeps the partition-switch purge path intact.
+        builder.HasIndex(e => new { e.SourceNode, e.OccurredAtUtc })
+            .HasDatabaseName("IX_AuditLog_Node_Occurred");
+
         builder.HasIndex(e => new { e.Channel, e.Status, e.OccurredAtUtc })
             .IsDescending(false, false, true)
             .HasDatabaseName("IX_AuditLog_Channel_Status_Occurred");

src/ScadaLink.ConfigurationDatabase/Configurations/NotificationOutboxConfiguration.cs

@@ -47,6 +47,11 @@ public class NotificationOutboxConfiguration : IEntityTypeConfiguration<Notifica
 
         builder.Property(n => n.SourceScript).HasMaxLength(200);
 
+        // SourceNode (Audit Log #23, SourceNode-stamping): mapped in a follow-on migration
+        // (AddNotificationSourceNode). Ignored here for now so the AddAuditLogSourceNode
+        // migration only touches AuditLog. Removed in the AddNotificationSourceNode commit.
+        builder.Ignore(n => n.SourceNode);
+
         // OriginExecutionId (Audit Log #23): nullable uniqueidentifier carried from the
         // site so the dispatcher can echo it onto NotifyDeliver audit rows. No index —
         // it is never a query predicate on this table, only copied onto audit events.

src/ScadaLink.ConfigurationDatabase/Configurations/SiteCallEntityTypeConfiguration.cs

@@ -59,6 +59,11 @@ public class SiteCallEntityTypeConfiguration : IEntityTypeConfiguration<SiteCall
         builder.Property(s => s.LastError)
             .HasMaxLength(1024);
 
+        // SourceNode (Audit Log #23, SourceNode-stamping): mapped in a follow-on migration
+        // (AddSiteCallSourceNode). Ignored here for now so the AddAuditLogSourceNode
+        // migration only touches AuditLog. Removed in the AddSiteCallSourceNode commit.
+        builder.Ignore(s => s.SourceNode);
+
         // Indexes — names locked for reconciliation/migration discoverability.
         // Source_Created backs "calls from this site" (Central UI Site Calls page,
         // filter by SourceSite, newest first).

src/ScadaLink.ConfigurationDatabase/Migrations/20260523201754_AddAuditLogSourceNode.cs

@@ -0,0 +1,59 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace ScadaLink.ConfigurationDatabase.Migrations
+{
+    /// <summary>
+    /// Adds the <c>SourceNode</c> column to the centralized <c>AuditLog</c> table (#23,
+    /// SourceNode-stamping). <c>SourceNode</c> identifies the cluster node that produced the
+    /// audit row (e.g. <c>node-a</c>, <c>central-a</c>) — ASCII-only, so <c>varchar(64)</c>
+    /// not <c>nvarchar</c>. <c>NULL</c> is valid (reconciled rows from a retired node,
+    /// central direct-write rows pre-this-feature).
+    ///
+    /// The change is purely additive:
+    /// 1. <c>SourceNode varchar(64) NULL</c> is added with no default, so the operation
+    ///    is a metadata-only <c>ALTER TABLE … ADD</c> — it does NOT rewrite the
+    ///    monthly-partitioned <c>AuditLog</c> table, and historical rows stay <c>NULL</c>.
+    /// 2. <c>IX_AuditLog_Node_Occurred (SourceNode, OccurredAtUtc)</c> is created via raw
+    ///    SQL so it lands on the <c>ps_AuditLog_Month(OccurredAtUtc)</c> partition scheme,
+    ///    matching every other <c>IX_AuditLog_*</c> index. Keeping it partition-aligned
+    ///    preserves the partition-switch purge path (see
+    ///    AuditLogRepository.SwitchOutPartitionAsync).
+    /// </summary>
+    public partial class AddAuditLogSourceNode : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AddColumn<string>(
+                name: "SourceNode",
+                table: "AuditLog",
+                type: "varchar(64)",
+                maxLength: 64,
+                nullable: true);
+
+            // Raw SQL so the index is created on the partition scheme — EF's
+            // CreateIndex cannot express the ON ps_AuditLog_Month(OccurredAtUtc)
+            // clause. Mirrors IX_AuditLog_ParentExecution (aligned, unfiltered here:
+            // NULL SourceNode is a legitimate query target, e.g. "rows produced
+            // before stamping shipped" — no HasFilter on this index).
+            migrationBuilder.Sql(@"
+CREATE NONCLUSTERED INDEX IX_AuditLog_Node_Occurred
+ON dbo.AuditLog (SourceNode, OccurredAtUtc)
+ON ps_AuditLog_Month(OccurredAtUtc);");
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.Sql(@"
+IF EXISTS (SELECT 1 FROM sys.indexes WHERE name = 'IX_AuditLog_Node_Occurred' AND object_id = OBJECT_ID('dbo.AuditLog'))
+    DROP INDEX IX_AuditLog_Node_Occurred ON dbo.AuditLog;");
+
+            migrationBuilder.DropColumn(
+                name: "SourceNode",
+                table: "AuditLog");
+        }
+    }
+}

src/ScadaLink.ConfigurationDatabase/Migrations/ScadaLinkDbContextModelSnapshot.cs

@@ -113,6 +113,10 @@ namespace ScadaLink.ConfigurationDatabase.Migrations
                         .IsUnicode(false)
                         .HasColumnType("varchar(128)");
 
+                    b.Property<string>("SourceNode")
+                        .HasMaxLength(64)
+                        .HasColumnType("varchar(64)");
+
                     b.Property<string>("SourceScript")
                         .HasMaxLength(128)
                         .IsUnicode(false)
@@ -156,6 +160,9 @@ namespace ScadaLink.ConfigurationDatabase.Migrations
                         .HasDatabaseName("IX_AuditLog_ParentExecution")
                         .HasFilter("[ParentExecutionId] IS NOT NULL");
 
+                    b.HasIndex("SourceNode", "OccurredAtUtc")
+                        .HasDatabaseName("IX_AuditLog_Node_Occurred");
+
                     b.HasIndex("SourceSiteId", "OccurredAtUtc")
                         .IsDescending(false, true)
                         .HasDatabaseName("IX_AuditLog_Site_Occurred");

src/ScadaLink.ConfigurationDatabase/Repositories/AuditLogRepository.cs

@@ -273,13 +273,14 @@ VALUES
                 PayloadTruncated   bit              NOT NULL,
                 Extra              nvarchar(max)    NULL,
                 ForwardState       varchar(32)      NULL,
-                -- ExecutionId and ParentExecutionId are last (in this ordinal order)
-                -- because each was added to the live AuditLog table by a later
-                -- ALTER TABLE ADD migration; the staging table must match the live
-                -- table column shape ordinal-for-ordinal or
-                -- ALTER TABLE ... SWITCH PARTITION fails.
+                -- ExecutionId, ParentExecutionId, and SourceNode are last (in this
+                -- ordinal order) because each was added to the live AuditLog table
+                -- by a later ALTER TABLE ADD migration; the staging table must
+                -- match the live table column shape ordinal-for-ordinal or
+                -- ALTER TABLE ... SWITCH PARTITION fails (msg 4904/4915).
                 ExecutionId        uniqueidentifier NULL,
                 ParentExecutionId  uniqueidentifier NULL,
+                SourceNode         varchar(64)      NULL,
                 CONSTRAINT PK_{stagingTableName} PRIMARY KEY CLUSTERED (EventId, OccurredAtUtc)
             ) ON [PRIMARY];