diff --git a/archreview/plans/R2-06-serverhistorian-failfast-plan.md.tasks.json b/archreview/plans/R2-06-serverhistorian-failfast-plan.md.tasks.json
index b50deccb..eb478c82 100644
--- a/archreview/plans/R2-06-serverhistorian-failfast-plan.md.tasks.json
+++ b/archreview/plans/R2-06-serverhistorian-failfast-plan.md.tasks.json
@@ -5,7 +5,7 @@
     {
       "id": "T1",
       "subject": "RED: misconfig repro test — HistorianGatewayClientAdapter.Create with empty/malformed Endpoint must throw a named InvalidOperationException (currently UriFormatException; test MUST fail on current code)",
-      "status": "pending",
+      "status": "completed",
       "blockedBy": []
     },
     {
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Gateway.Tests/HistorianGatewayClientAdapterTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Gateway.Tests/HistorianGatewayClientAdapterTests.cs
index 08dcc002..1a86a92e 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Gateway.Tests/HistorianGatewayClientAdapterTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Gateway.Tests/HistorianGatewayClientAdapterTests.cs
@@ -1,5 +1,6 @@
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Logging.Abstractions;
+using Shouldly;
 using Xunit;
 using ZB.MOM.WW.OtOpcUa.Runtime.Historian;
 
@@ -21,6 +22,38 @@ public sealed class HistorianGatewayClientAdapterTests
         Assert.NotNull(adapter);
     }
 
+    /// <summary>
+    /// archreview 06/S-11 — an enabled historian with an empty <c>Endpoint</c> must fail with a
+    /// named, config-key-carrying <see cref="InvalidOperationException"/> (defense-in-depth for any
+    /// caller that bypasses the Host's <c>ServerHistorianOptionsValidator</c>), not the raw
+    /// <see cref="UriFormatException"/> that <c>new Uri("")</c> throws deep in the factory. Current
+    /// code throws <see cref="UriFormatException"/> → this is the failing-first (RED) repro.
+    /// </summary>
+    [Fact]
+    public void Create_with_empty_endpoint_throws_named_config_error()
+    {
+        var opts = new ServerHistorianOptions { Enabled = true, Endpoint = "", ApiKey = "histgw_x_y" };
+
+        var ex = Should.Throw<InvalidOperationException>(
+            () => HistorianGatewayClientAdapter.Create(opts, NullLoggerFactory.Instance));
+        ex.Message.ShouldContain("ServerHistorian:Endpoint");
+    }
+
+    /// <summary>
+    /// archreview 06/S-11 companion — a non-empty but unparseable / non-absolute <c>Endpoint</c> must
+    /// also fail with the same named <see cref="InvalidOperationException"/>, not a raw
+    /// <see cref="UriFormatException"/>. RED on current code.
+    /// </summary>
+    [Fact]
+    public void Create_with_malformed_endpoint_throws_named_config_error()
+    {
+        var opts = new ServerHistorianOptions { Enabled = true, Endpoint = "not a uri", ApiKey = "histgw_x_y" };
+
+        var ex = Should.Throw<InvalidOperationException>(
+            () => HistorianGatewayClientAdapter.Create(opts, NullLoggerFactory.Instance));
+        ex.Message.ShouldContain("ServerHistorian:Endpoint");
+    }
+
     [Fact]
     public void Factory_builds_GatewayHistorianDataSource()
     {