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");
         });
     }