diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.ControlPlane/AdminOperations/AdminOperationsActor.cs b/src/Server/ZB.MOM.WW.OtOpcUa.ControlPlane/AdminOperations/AdminOperationsActor.cs
index cea2f062..eb31b42e 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.ControlPlane/AdminOperations/AdminOperationsActor.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.ControlPlane/AdminOperations/AdminOperationsActor.cs
@@ -85,6 +85,10 @@ public sealed class AdminOperationsActor : ReceiveActor
             // derivation, cross-cluster/namespace binding, driver-namespace compat, signal collisions,
             // …) gates the deploy. A green build in this repo does not prove the config is valid; this
             // is the last guard before a bad address space (or a non-derived EquipmentId) ships.
+            // NOTE: a BadDuplicateExternalIdentifier rejection from the reservation pre-flight can
+            // (rarely) be a false positive if an external-id reservation release has not yet been
+            // committed/visible when the snapshot is read — operators seeing a spurious one should
+            // check ExternalIdReservation state before re-submitting.
             var draft = await DraftSnapshotFactory.FromConfigDbAsync(db);
             var errors = DraftValidator.Validate(draft);
             if (errors.Count > 0)
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.ControlPlane.Tests/AdminOperationsActorTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.ControlPlane.Tests/AdminOperationsActorTests.cs
index 8898c43c..39840f33 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.ControlPlane.Tests/AdminOperationsActorTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.ControlPlane.Tests/AdminOperationsActorTests.cs
@@ -141,6 +141,54 @@ public sealed class AdminOperationsActorTests : ControlPlaneActorTestBase
         verify.Deployments.Count().ShouldBe(0);
     }
 
+    /// <summary>Verifies that a DriverInstance whose NamespaceId lives in a different cluster
+    /// triggers <c>BadCrossClusterNamespaceBinding</c> and routes to the Rejected branch through
+    /// the actor — no coordinator dispatch, no Deployment row.
+    /// Seeded: Namespace in cluster "MAIN" + DriverInstance in cluster "SITE-A" referencing that
+    /// namespace. NamespaceKind.Equipment + DriverType "ModbusTcp" satisfies the compat rule so
+    /// only the cross-cluster rule fires.</summary>
+    [Fact]
+    public void StartDeployment_rejects_on_cross_cluster_namespace_binding()
+    {
+        const string nsId = "ns-main-equipment";
+
+        var dbFactory = NewInMemoryDbFactory();
+        using (var db = dbFactory.CreateDbContext())
+        {
+            db.Namespaces.Add(new Configuration.Entities.Namespace
+            {
+                NamespaceId  = nsId,
+                ClusterId    = "MAIN",
+                Kind         = Configuration.Enums.NamespaceKind.Equipment,
+                NamespaceUri = "urn:zb:main:equipment",
+            });
+            db.DriverInstances.Add(new Configuration.Entities.DriverInstance
+            {
+                DriverInstanceId = "drv-site-a-01",
+                ClusterId        = "SITE-A",
+                NamespaceId      = nsId,          // cross-cluster: drv is SITE-A, ns is MAIN
+                Name             = "site-a-modbus",
+                DriverType       = "ModbusTcp",   // compatible with Equipment ns — no compat error
+                DriverConfig     = "{}",
+            });
+            db.SaveChanges();
+        }
+
+        var coordinator = CreateTestProbe("coord");
+        var actor = Sys.ActorOf(AdminOperationsActor.Props(dbFactory, coordinator.Ref, Enumerable.Empty<IDriverProbe>()));
+
+        actor.Tell(new StartDeployment("joe", CorrelationId.NewId()));
+
+        coordinator.ExpectNoMsg(TimeSpan.FromMilliseconds(500));
+        var reply = ExpectMsg<StartDeploymentResult>(TimeSpan.FromSeconds(3));
+        reply.Outcome.ShouldBe(StartDeploymentOutcome.Rejected);
+        reply.Message.ShouldNotBeNull();
+        reply.Message.ShouldContain("BadCrossClusterNamespaceBinding");
+
+        using var verify = dbFactory.CreateDbContext();
+        verify.Deployments.Count().ShouldBe(0);
+    }
+
     /// <summary>Verifies that starting a deployment is refused when another is in flight.</summary>
     [Fact]
     public void StartDeployment_refuses_when_another_is_in_flight()