diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Tests/Runtime/GatewayGalaxyLiveReopenAndWriteTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Tests/Runtime/GatewayGalaxyLiveReopenAndWriteTests.cs
index e0e7208f..f2a3cb1e 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Tests/Runtime/GatewayGalaxyLiveReopenAndWriteTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Tests/Runtime/GatewayGalaxyLiveReopenAndWriteTests.cs
@@ -124,6 +124,55 @@ public sealed class GatewayGalaxyLiveReopenAndWriteTests
             $"write-persist smoke: {WriteRef} {current} -> wrote {target} -> fresh-session read-back {persisted}");
     }
 
+    /// <summary>
+    ///     <b>Borrow</b> — the writer reuses a live MXAccess item handle the subscription registry
+    ///     already holds, so the first write to an already-subscribed tag skips a redundant AddItem.
+    ///     Proves the load-bearing premise (a subscription handle is usable for a no-login supervisory
+    ///     write that commits) AND the optimization (zero AddItem on the borrow path). Control: a writer
+    ///     with no registry source on the same session AddItems exactly once.
+    /// </summary>
+    [Fact]
+    public async Task Live_writer_borrows_subscription_handle_and_skips_AddItem()
+    {
+        var (endpoint, apiKey) = RequireLiveGatewayOrSkip();
+        var ct = TestContext.Current.CancellationToken;
+        var clientOptions = BuildClientOptions(endpoint, apiKey);
+
+        await using var session = new GalaxyMxSession(new GalaxyMxAccessOptions(ClientName: "OtOpcUaBorrowSmoke"));
+        await session.ConnectAsync(clientOptions, ct);
+
+        // Subscribe the tag so the registry holds the gateway's REAL item handle for it.
+        var subscriber = new GatewayGalaxySubscriber(session);
+        var subResults = await subscriber.SubscribeBulkAsync([WriteRef], bufferedUpdateIntervalMs: 0, ct);
+        var match = subResults.SingleOrDefault(r =>
+            string.Equals(r.TagAddress, WriteRef, StringComparison.OrdinalIgnoreCase) && r.WasSuccessful);
+        match.ShouldNotBeNull($"the gateway should accept a subscription on {WriteRef}");
+        match!.ItemHandle.ShouldBeGreaterThan(0, "a successful subscribe must return a positive item handle");
+
+        var registry = new SubscriptionRegistry();
+        registry.Register(1, [new TagBinding(WriteRef, match.ItemHandle)]);
+
+        // Borrow case: a writer wired to the registry must commit the write WITHOUT a fresh AddItem,
+        // and must NOT cache the borrowed handle (the registry owns its lifecycle).
+        var borrowingWriter = new GatewayGalaxyDataWriter(
+            session, writeUserId: 0, logger: null, subscribedHandleSource: registry.TryResolveItemHandle);
+        var borrowed = await borrowingWriter.WriteAsync(
+            [new WriteRequest(WriteRef, 2727.0f)], _ => SecurityClassification.FreeAccess, ct);
+        borrowed.ShouldHaveSingleItem().StatusCode.ShouldBe(0u, "the borrowed-handle write should commit Good (0)");
+        borrowingWriter.AddItemCallCount.ShouldBe(0, "the writer should reuse the subscription handle, not AddItem");
+        borrowingWriter.CachedItemHandleCount.ShouldBe(0, "a borrowed handle must not be cached in the writer");
+
+        // Control: a writer with NO source on the same session must AddItem exactly once for the same tag.
+        var plainWriter = new GatewayGalaxyDataWriter(session, writeUserId: 0);
+        var control = await plainWriter.WriteAsync(
+            [new WriteRequest(WriteRef, 3838.0f)], _ => SecurityClassification.FreeAccess, ct);
+        control.ShouldHaveSingleItem().StatusCode.ShouldBe(0u, "the control write should commit Good (0)");
+        plainWriter.AddItemCallCount.ShouldBe(1, "with no borrow source the writer must AddItem once");
+
+        TestContext.Current.SendDiagnosticMessage(
+            $"borrow smoke: subscribed {WriteRef} -> handle {match.ItemHandle}; borrowed write Good with AddItemCallCount=0; control AddItemCallCount=1");
+    }
+
     private static (string Endpoint, string ApiKey) RequireLiveGatewayOrSkip()
     {
         var endpoint = Environment.GetEnvironmentVariable("MXGW_ENDPOINT");