diff --git a/tests/GameCult.Networking.Tests/CultNetClientWriteCompletionTests.cs b/tests/GameCult.Networking.Tests/CultNetClientWriteCompletionTests.cs
new file mode 100644
index 00000000..8641a082
--- /dev/null
+++ b/tests/GameCult.Networking.Tests/CultNetClientWriteCompletionTests.cs
@@ -0,0 +1,100 @@
+#nullable enable
+using System;
+using System.Collections.Concurrent;
+using System.Net;
+using System.Net.Sockets;
+using System.Threading;
+using System.Threading.Tasks;
+using NUnit.Framework;
+
+namespace GameCult.Networking.Tests
+{
+    /// <summary>
+    /// Heimdall's invariant: no client treats a reliable-transport ack as write admission. A put completes
+    /// only on its result frame (write_not_authorized, or the success reply). The C# schema client has no
+    /// completion call: SendCultNet returns once the put is queued, and the outcome reaches the caller only
+    /// as the result frame, through OnCultNet. These tests serve it a peer that acknowledges the put and
+    /// refuses it, the ack before the refusal and after it, and require the refusal to arrive as the outcome.
+    /// </summary>
+    public class CultNetClientWriteCompletionTests
+    {
+        private const uint ConnectionId = 0x10203197;
+
+        // Acknowledges the first reliable schema frame it receives and answers it with write_not_authorized,
+        // the second packet 150 ms after the first. The refusal carries no acknowledgement of its own.
+        private static Task RefusingPeer(Socket socket, bool refusalFirst, CancellationToken stop)
+        {
+            return Task.Run(() =>
+            {
+                var session = new CultNetRudpSession(new CultNetRudpSessionOptions { ConnectionId = ConnectionId, ResendDelayMs = 25 });
+                var buffer = new byte[65535];
+                EndPoint from = new IPEndPoint(IPAddress.Any, 0);
+                var answered = false;
+                while (!stop.IsCancellationRequested)
+                {
+                    if (!socket.Poll(10_000, SelectMode.SelectRead))
+                        continue;
+                    var received = socket.ReceiveFrom(buffer, ref from);
+                    var packet = CultNetRudpPacketCodec.Decode(buffer.AsSpan(0, received).ToArray());
+                    void Send(CultNetRudpPacket p) => socket.SendTo(CultNetRudpPacketCodec.Encode(p), from);
+                    if (packet.PacketType == CultNetRudpPacketType.Connect)
+                    {
+                        Send(session.AcceptConnect(packet));
+                        continue;
+                    }
+                    var result = session.Receive(packet, 1);
+                    if (result.Reply != null)
+                        Send(result.Reply);
+                    if (answered || result.Delivered.Count == 0)
+                        continue;
+                    answered = true;
+                    var ack = session.CreateAckForReceived(packet.Sequence);
+                    var refusal = session.Send("schema", CultNetSchemaMessageSerialization.Serialize(new CultNetErrorMessage
+                    {
+                        Error = "write_not_authorized: the catalog refused the document",
+                        Code = "write_not_authorized"
+                    }), new CultNetRudpSendOptions { Reliable = true, Ordered = true });
+                    refusal.Ack = 0;
+                    refusal.AckMask = 0;
+                    if (refusalFirst)
+                    {
+                        Send(refusal);
+                        Thread.Sleep(150);
+                        Send(ack);
+                    }
+                    else
+                    {
+                        Send(ack);
+                        Thread.Sleep(150);
+                        Send(refusal);
+                    }
+                }
+            });
+        }
+
+        [TestCase(false, TestName = "AckThenRefusal")]
+        [TestCase(true, TestName = "RefusalThenAck")]
+        public async Task ARefusedPutIsReportedRefusedWhateverTheOrderOfItsAck(bool refusalFirst)
+        {
+            using var serverSocket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
+            serverSocket.Bind(new IPEndPoint(IPAddress.Loopback, 0));
+            using var stop = new CancellationTokenSource();
+            var peer = RefusingPeer(serverSocket, refusalFirst, stop.Token);
+            using var client = new RudpCultNetSchemaClient("completion", ConnectionId);
+            var outcomes = new BlockingCollection<CultNetErrorMessage>();
+            client.OnCultNet<CultNetErrorMessage>(outcomes.Add);
+            client.Connect("127.0.0.1", ((IPEndPoint)serverSocket.LocalEndPoint!).Port);
+            var deadline = DateTime.UtcNow.AddSeconds(3);
+            while (!client.Connected && DateTime.UtcNow < deadline)
+                await Task.Delay(5);
+            Assert.That(client.Connected, "fixture: the client connected");
+
+            client.SendCultNet(new CultNetDocumentPutRawMessage { MessageId = "completion" });
+
+            Assert.That(outcomes.TryTake(out var refusal, 3000), Is.True, "the result frame reached the caller");
+            Assert.That(refusal!.Code, Is.EqualTo("write_not_authorized"));
+            stop.Cancel();
+            await peer;
+        }
+    }
+}