feat(audit): EventId + CorrelationId columns + filtered unique index (F3 + F4)

ConfigAuditLog gains two nullable columns (EventId, CorrelationId) + a filtered
unique index UX_ConfigAuditLog_EventId. EF migration
20260526105027_AddConfigAuditLogEventIdColumns is additive (nullable + filtered
index = legacy rows backfill cleanly).

AuditWriterActor now writes EventId + CorrelationId into the dedicated columns
instead of synthesising a JSON wrapper into DetailsJson. Cross-restart dedup
is now real: a retry of an already-flushed batch hits the unique index and
SaveChanges throws; the existing catch drops the duplicate without losing the
rest of the batch.

WrapDetails helper deleted — F4 (its JSON hardening) becomes moot.

AuditWriterActorTests.Details_wrapper_embeds_eventId_and_correlationId renamed
+ rewritten to assert against the columns. All 29 ControlPlane tests pass,
all 95 v2 tests green.

src/Core/ZB.MOM.WW.OtOpcUa.Configuration/Entities/ConfigAuditLog.cs

@@ -22,4 +22,16 @@ public sealed class ConfigAuditLog
     public long? GenerationId { get; set; }
 
     public string? DetailsJson { get; set; }
+
+    /// <summary>
+    /// Stable per-event identifier from <c>AuditEvent.EventId</c>. Filtered unique index on
+    /// this column gives cross-restart idempotency for the batched AuditWriterActor: a flush
+    /// that retries after a process crash can re-send the same EventId without producing a
+    /// duplicate row. Nullable so pre-v2 rows backfill cleanly.
+    /// </summary>
+    public Guid? EventId { get; set; }
+
+    /// <summary>Correlation ID from <c>AuditEvent.CorrelationId</c> so an audit row joins to its
+    /// originating request/workflow. Nullable for the same backfill reason as <see cref="EventId"/>.</summary>
+    public Guid? CorrelationId { get; set; }
 }

src/Core/ZB.MOM.WW.OtOpcUa.Configuration/Migrations/20260526105027_AddConfigAuditLogEventIdColumns.cs

@@ -0,0 +1,50 @@
+using System;
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace ZB.MOM.WW.OtOpcUa.Configuration.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddConfigAuditLogEventIdColumns : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AddColumn<Guid>(
+                name: "CorrelationId",
+                table: "ConfigAuditLog",
+                type: "uniqueidentifier",
+                nullable: true);
+
+            migrationBuilder.AddColumn<Guid>(
+                name: "EventId",
+                table: "ConfigAuditLog",
+                type: "uniqueidentifier",
+                nullable: true);
+
+            migrationBuilder.CreateIndex(
+                name: "UX_ConfigAuditLog_EventId",
+                table: "ConfigAuditLog",
+                column: "EventId",
+                unique: true,
+                filter: "[EventId] IS NOT NULL");
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropIndex(
+                name: "UX_ConfigAuditLog_EventId",
+                table: "ConfigAuditLog");
+
+            migrationBuilder.DropColumn(
+                name: "CorrelationId",
+                table: "ConfigAuditLog");
+
+            migrationBuilder.DropColumn(
+                name: "EventId",
+                table: "ConfigAuditLog");
+        }
+    }
+}

src/Core/ZB.MOM.WW.OtOpcUa.Configuration/Migrations/OtOpcUaConfigDbContextModelSnapshot.cs

@@ -165,9 +165,15 @@ namespace ZB.MOM.WW.OtOpcUa.Configuration.Migrations
                         .HasMaxLength(64)
                         .HasColumnType("nvarchar(64)");
 
+                    b.Property<Guid?>("CorrelationId")
+                        .HasColumnType("uniqueidentifier");
+
                     b.Property<string>("DetailsJson")
                         .HasColumnType("nvarchar(max)");
 
+                    b.Property<Guid?>("EventId")
+                        .HasColumnType("uniqueidentifier");
+
                     b.Property<string>("EventType")
                         .IsRequired()
                         .HasMaxLength(64)
@@ -192,6 +198,11 @@ namespace ZB.MOM.WW.OtOpcUa.Configuration.Migrations
 
                     b.HasKey("AuditId");
 
+                    b.HasIndex("EventId")
+                        .IsUnique()
+                        .HasDatabaseName("UX_ConfigAuditLog_EventId")
+                        .HasFilter("[EventId] IS NOT NULL");
+
                     b.HasIndex("GenerationId")
                         .HasDatabaseName("IX_ConfigAuditLog_Generation")
                         .HasFilter("[GenerationId] IS NOT NULL");

src/Core/ZB.MOM.WW.OtOpcUa.Configuration/OtOpcUaConfigDbContext.cs

@@ -413,6 +413,8 @@ public sealed class OtOpcUaConfigDbContext(DbContextOptions<OtOpcUaConfigDbConte
             e.Property(x => x.ClusterId).HasMaxLength(64);
             e.Property(x => x.NodeId).HasMaxLength(64);
             e.Property(x => x.DetailsJson).HasColumnType("nvarchar(max)");
+            e.Property(x => x.EventId);
+            e.Property(x => x.CorrelationId);
 
             e.HasIndex(x => new { x.ClusterId, x.Timestamp })
                 .IsDescending(false, true)
@@ -420,6 +422,14 @@ public sealed class OtOpcUaConfigDbContext(DbContextOptions<OtOpcUaConfigDbConte
             e.HasIndex(x => x.GenerationId)
                 .HasFilter("[GenerationId] IS NOT NULL")
                 .HasDatabaseName("IX_ConfigAuditLog_Generation");
+            // Filtered unique index gives cross-restart idempotency for the AuditWriterActor:
+            // a retry of an already-flushed batch will hit this constraint and the catch in
+            // FlushBuffer drops the duplicate insert. Nullable + filter so legacy backfill rows
+            // (EventId=NULL) don't collide.
+            e.HasIndex(x => x.EventId)
+                .IsUnique()
+                .HasFilter("[EventId] IS NOT NULL")
+                .HasDatabaseName("UX_ConfigAuditLog_EventId");
         });
     }
 

src/Server/ZB.MOM.WW.OtOpcUa.ControlPlane/Audit/AuditWriterActor.cs

@@ -14,9 +14,11 @@ namespace ZB.MOM.WW.OtOpcUa.ControlPlane.Audit;
 /// - <see cref="FlushInterval"/> elapses with a non-empty buffer.
 /// - <c>PreRestart</c> / <c>PostStop</c> (supervisor swap or coordinated shutdown).
 ///
-/// Dedup is in-buffer only — once a batch is flushed, the actor accepts a duplicate
+/// Dedup is two-layer: in-buffer (the <see cref="Dictionary{TKey, TValue}"/> below collapses
-/// <see cref="AuditEvent.EventId"/> as a new row. True cross-restart idempotency needs an
+/// duplicate EventIds before flush) and at the database via the filtered unique index
-/// EventId column with a unique index on <c>ConfigAuditLog</c>; tracked as follow-up F3.
+/// <c>UX_ConfigAuditLog_EventId</c> (cross-restart safety — a retry of an already-flushed
+/// batch hits the constraint and we drop the duplicate insert without losing the rest of
+/// the batch).
 /// </summary>
 public sealed class AuditWriterActor : ReceiveActor, IWithTimers
 {
@@ -70,7 +72,9 @@ public sealed class AuditWriterActor : ReceiveActor, IWithTimers
                     Principal = evt.Actor,
                     EventType = $"{evt.Category}:{evt.Action}",
                     NodeId = evt.SourceNode.Value,
-                    DetailsJson = WrapDetails(evt),
+                    DetailsJson = evt.DetailsJson,
+                    EventId = evt.EventId,
+                    CorrelationId = evt.CorrelationId.Value,
                 });
             }
             db.SaveChanges();
@@ -82,17 +86,6 @@ public sealed class AuditWriterActor : ReceiveActor, IWithTimers
         }
     }
 
-    /// <summary>
-    /// Wraps caller-supplied details with the EventId + CorrelationId so audit consumers can
-    /// reconstruct the original message. Until ConfigAuditLog gains a first-class EventId column
-    /// (follow-up F3), this is the only place these correlation IDs are persisted.
-    /// </summary>
-    private static string WrapDetails(AuditEvent evt)
-    {
-        var details = evt.DetailsJson ?? "null";
-        return $"{{\"eventId\":\"{evt.EventId:N}\",\"correlationId\":\"{evt.CorrelationId.Value:N}\",\"details\":{details}}}";
-    }
-
     protected override void PreRestart(Exception reason, object message)
     {
         FlushBuffer();

tests/Server/ZB.MOM.WW.OtOpcUa.ControlPlane.Tests/AuditWriterActorTests.cs

@@ -78,7 +78,7 @@ public sealed class AuditWriterActorTests : ControlPlaneActorTestBase
     }
 
     [Fact]
-    public void Details_wrapper_embeds_eventId_and_correlationId()
+    public void EventId_and_CorrelationId_are_persisted_to_dedicated_columns()
     {
         var dbFactory = NewInMemoryDbFactory();
         var actor = Sys.ActorOf(AuditWriterActor.Props(dbFactory));
@@ -92,9 +92,9 @@ public sealed class AuditWriterActorTests : ControlPlaneActorTestBase
 
         using var db = dbFactory.CreateDbContext();
         var row = db.ConfigAuditLogs.Single();
-        row.DetailsJson.ShouldNotBeNull();
+        row.EventId.ShouldBe(eventId);
-        row.DetailsJson.ShouldContain(eventId.ToString("N"));
+        row.CorrelationId.ShouldNotBeNull();
-        row.DetailsJson.ShouldContain("\"correlationId\":");
+        row.DetailsJson.ShouldBe("{\"field\":\"value\"}");
         row.EventType.ShouldBe("Config:Edit");
         row.NodeId.ShouldBe("node-a");
     }