fix(CLI-40): scrub the credential from the redacted error's structured reply, route MXACCESS_FAILURE to MxAccess (Rust), fix Go Subscribe terminal-error drop

Code-review follow-up on the CLI-40/41/44 branch.

ISSUE 1 (all five, critical): the message-only scrub still leaked the
server-echoed credential through the redacted error's structured reply accessor
(.NET Reply/Statuses, Java reply()/protocolStatus(), Go MxAccessError.Reply via
errors.As, Rust reply()/into_reply(), Python raw_reply). The redacted error now
carries a scrubbed clone of the reply (protocol_status.message,
diagnostic_message, statuses[].diagnostic_text), with per-language tests asserting
the reply accessor no longer contains the credential.

ISSUE 2 (Rust, critical): ensure_command_success routed MXACCESS_FAILURE to
Error::Command (unlike the other four clients), bypassing attach_secrets and
leaking via derived Debug/Display. MXACCESS_FAILURE now routes to Error::MxAccess,
fixing the cross-client inconsistency.

ISSUE 3 (Go, important): the CLI-44 terminal send was unconditionally
non-blocking, dropping a genuine terminal error under a full buffer on the
never-drop SubscribeEvents path. It is now reserved-slot-non-blocking only for the
cancel-on-overflow path and blocking for the never-drop path.

New shared fixture authenticate-user.echoed-credential-mxaccess-failure.reply.json
wired into all five suites. Minors: whitespace-secret guard on .NET/Java redact
helpers; Java preserves exception subtype on redaction; redaction-helper unit
tests (Go/Java/.NET). Docs (ClientBehaviorFixtures.md, ClientLibrariesDesign.md)
updated to make the structured-field claim true.

clients/dotnet/ZB.MOM.WW.MxGateway.Client.Tests/MxGatewaySecretRedactionTests.cs

@@ -0,0 +1,96 @@
+using ZB.MOM.WW.MxGateway.Contracts.Proto;
+
+namespace ZB.MOM.WW.MxGateway.Client.Tests;
+
+/// <summary>
+/// Unit tests for <see cref="MxGatewaySecretRedaction"/> — the exact-substring scrub applied to
+/// diagnostic text and rebuilt exceptions before they leave the client on a failure path.
+/// </summary>
+public sealed class MxGatewaySecretRedactionTests
+{
+    [Fact]
+    public void Redact_ReplacesEveryOccurrenceOfSecret()
+    {
+        string result = MxGatewaySecretRedaction.Redact(
+            "pw=hunter2 retry pw=hunter2 again hunter2",
+            "hunter2");
+
+        Assert.DoesNotContain("hunter2", result, StringComparison.Ordinal);
+        Assert.Equal("pw=<redacted> retry pw=<redacted> again <redacted>", result);
+    }
+
+    [Fact]
+    public void Redact_ScrubsBothSecretsWhenOneIsSubstringOfTheOther()
+    {
+        // "secret" is a substring of "secretPassword"; both must be fully scrubbed regardless of
+        // supplied order — no residual leak of either verbatim value.
+        string result = MxGatewaySecretRedaction.Redact(
+            "a=secretPassword b=secret",
+            "secret",
+            "secretPassword");
+
+        Assert.DoesNotContain("secretPassword", result, StringComparison.Ordinal);
+        Assert.DoesNotContain("secret", result, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void Redact_WithNullSecretsArray_ReturnsMessageUnchanged()
+    {
+        const string message = "nothing to scrub here";
+
+        string result = MxGatewaySecretRedaction.Redact(message, null!);
+
+        Assert.Equal(message, result);
+    }
+
+    [Fact]
+    public void Redact_WithEmptySecretsArray_ReturnsMessageUnchanged()
+    {
+        const string message = "nothing to scrub here";
+
+        string result = MxGatewaySecretRedaction.Redact(message);
+
+        Assert.Equal(message, result);
+    }
+
+    [Fact]
+    public void Redact_IgnoresWhitespaceOnlySecret()
+    {
+        // A whitespace-only secret must not over-redact the internal spaces of the message.
+        const string message = "user operator logged in";
+
+        string result = MxGatewaySecretRedaction.Redact(message, " ");
+
+        Assert.Equal(message, result);
+    }
+
+    [Fact]
+    public void Redacted_PreservesConcreteSubtypeAndDoesNotChainSecretBearingOriginal()
+    {
+        const string secret = "hunter2";
+        Exception transportCause = new InvalidOperationException("transport reset");
+        MxGatewaySessionException original = new(
+            $"session rejected credential '{secret}'",
+            "session-1",
+            "correlation-1",
+            new ProtocolStatus { Code = ProtocolStatusCode.SessionNotReady, Message = $"echoed '{secret}'" },
+            hResult: -1,
+            statuses: [new MxStatusProxy { DiagnosticText = $"denied '{secret}'" }],
+            innerException: transportCause);
+
+        MxGatewayException redacted = MxGatewaySecretRedaction.Redacted(original, secret);
+
+        // Concrete runtime type is preserved.
+        Assert.IsType<MxGatewaySessionException>(redacted);
+        // The secret is gone from the message and every structured accessor.
+        Assert.DoesNotContain(secret, redacted.Message, StringComparison.Ordinal);
+        Assert.DoesNotContain(secret, redacted.ToString(), StringComparison.Ordinal);
+        Assert.DoesNotContain(secret, redacted.ProtocolStatus!.Message, StringComparison.Ordinal);
+        Assert.All(redacted.Statuses, status =>
+            Assert.DoesNotContain(secret, status.DiagnosticText, StringComparison.Ordinal));
+        Assert.Contains("<redacted>", redacted.Message, StringComparison.Ordinal);
+        // The secret-bearing original is NOT chained; the original's transport cause is carried.
+        Assert.NotSame(original, redacted.InnerException);
+        Assert.Same(transportCause, redacted.InnerException);
+    }
+}

clients/dotnet/ZB.MOM.WW.MxGateway.Client.Tests/MxGatewaySessionReplyContractTests.cs

@@ -32,6 +32,44 @@ public sealed class MxGatewaySessionReplyContractTests
         Assert.DoesNotContain(password, exception.ToString(), StringComparison.Ordinal);
     }
 
+    /// <summary>
+    /// CLI-40: the redacted exception must not leak the echoed credential through any structured
+    /// accessor either — <see cref="MxAccessException.Reply"/> (protocol message, diagnostic
+    /// message, and each MXSTATUS_PROXY diagnostic text) and <see cref="MxGatewayException.Statuses"/>
+    /// all carry the server-echoed credential verbatim before the fix. Both the OK+negative-HRESULT
+    /// and the MXACCESS_FAILURE reply route to <see cref="MxAccessException"/>, so both must scrub.
+    /// </summary>
+    /// <param name="fixture">The echoed-credential reply fixture to drive.</param>
+    [Theory]
+    [InlineData("authenticate-user.echoed-credential.reply.json")]
+    [InlineData("authenticate-user.echoed-credential-mxaccess-failure.reply.json")]
+    public async Task AuthenticateUserAsync_RedactsEchoedCredentialInStructuredAccessors(string fixture)
+    {
+        const string password = "sup3rSecretVerify9f3a2b";
+        FakeGatewayTransport transport = CreateTransport();
+        transport.AddInvokeReply(ReadReplyFixture(fixture));
+        await using MxGatewayClient client = CreateClient(transport);
+        MxGatewaySession session = await client.OpenSessionAsync();
+
+        MxAccessException exception = await Assert.ThrowsAsync<MxAccessException>(
+            async () => await session.AuthenticateUserAsync(12, "operator", password));
+
+        Assert.DoesNotContain(password, exception.Message, StringComparison.Ordinal);
+        Assert.Contains("<redacted>", exception.Message, StringComparison.Ordinal);
+        Assert.DoesNotContain(password, exception.ToString(), StringComparison.Ordinal);
+        Assert.DoesNotContain(password, exception.Reply.ProtocolStatus.Message, StringComparison.Ordinal);
+        Assert.DoesNotContain(password, exception.Reply.DiagnosticMessage, StringComparison.Ordinal);
+        foreach (MxStatusProxy status in exception.Reply.Statuses)
+        {
+            Assert.DoesNotContain(password, status.DiagnosticText, StringComparison.Ordinal);
+        }
+
+        foreach (MxStatusProxy status in exception.Statuses)
+        {
+            Assert.DoesNotContain(password, status.DiagnosticText, StringComparison.Ordinal);
+        }
+    }
+
     /// <summary>
     /// CLI-41: an OK reply that carries neither the typed AuthenticateUser payload nor an
     /// int32 return_value is a malformed reply, surfaced as a typed exception rather than an NRE.

clients/dotnet/ZB.MOM.WW.MxGateway.Client/MxGatewaySecretRedaction.cs

@@ -1,3 +1,5 @@
+using ZB.MOM.WW.MxGateway.Contracts.Proto;
+
 namespace ZB.MOM.WW.MxGateway.Client;
 
 /// <summary>
@@ -13,9 +15,10 @@ internal static class MxGatewaySecretRedaction
     private const string Marker = "<redacted>";
 
     /// <summary>
-    /// Replaces every non-null, non-empty secret in <paramref name="secrets"/> with the
+    /// Replaces every usable secret in <paramref name="secrets"/> with the redaction marker
-    /// redaction marker (ordinal comparison). Returns the message unchanged when it is null or
+    /// (ordinal comparison). Returns the message unchanged when it is null or empty, or when no
-    /// empty, or when no usable secret is supplied.
+    /// usable secret is supplied. A secret that is null, empty, or whitespace-only is ignored so
+    /// it cannot over-redact ordinary separator characters in the message.
     /// </summary>
     /// <param name="message">The diagnostic message to scrub.</param>
     /// <param name="secrets">The secret values to remove from the message.</param>
@@ -30,7 +33,7 @@ internal static class MxGatewaySecretRedaction
         string result = message;
         foreach (string? secret in secrets)
         {
-            if (!string.IsNullOrEmpty(secret))
+            if (!string.IsNullOrWhiteSpace(secret))
             {
                 result = result.Replace(secret, Marker, StringComparison.Ordinal);
             }
@@ -39,6 +42,81 @@ internal static class MxGatewaySecretRedaction
         return result;
     }
 
+    /// <summary>
+    /// Returns a scrubbed clone of <paramref name="reply"/>: the protocol-status message, the
+    /// reply-level diagnostic message, and each MXSTATUS_PROXY diagnostic text have every verbatim
+    /// secret replaced with the redaction marker. The original is left untouched. MXAccess can echo
+    /// a submitted credential into any of these fields, so a redacted exception must carry the
+    /// scrubbed reply rather than the secret-bearing original.
+    /// </summary>
+    /// <param name="reply">The reply to clone and scrub.</param>
+    /// <param name="secrets">The secret values to remove.</param>
+    /// <returns>A scrubbed clone of the reply.</returns>
+    internal static MxCommandReply RedactReply(MxCommandReply reply, params string?[] secrets)
+    {
+        ArgumentNullException.ThrowIfNull(reply);
+
+        MxCommandReply clone = reply.Clone();
+        if (clone.ProtocolStatus is not null)
+        {
+            clone.ProtocolStatus.Message = Redact(clone.ProtocolStatus.Message, secrets);
+        }
+
+        clone.DiagnosticMessage = Redact(clone.DiagnosticMessage, secrets);
+        foreach (MxStatusProxy status in clone.Statuses)
+        {
+            status.DiagnosticText = Redact(status.DiagnosticText, secrets);
+        }
+
+        return clone;
+    }
+
+    /// <summary>
+    /// Returns a scrubbed clone of <paramref name="status"/> (its message with every verbatim
+    /// secret removed), or <see langword="null"/> when the input is null.
+    /// </summary>
+    /// <param name="status">The protocol status to clone and scrub.</param>
+    /// <param name="secrets">The secret values to remove.</param>
+    /// <returns>A scrubbed clone, or <see langword="null"/>.</returns>
+    internal static ProtocolStatus? RedactStatus(ProtocolStatus? status, params string?[] secrets)
+    {
+        if (status is null)
+        {
+            return null;
+        }
+
+        ProtocolStatus clone = status.Clone();
+        clone.Message = Redact(clone.Message, secrets);
+        return clone;
+    }
+
+    /// <summary>
+    /// Returns a list of scrubbed clones of <paramref name="statuses"/> — each MXSTATUS_PROXY's
+    /// diagnostic text has every verbatim secret removed. The originals are left untouched.
+    /// </summary>
+    /// <param name="statuses">The statuses to clone and scrub.</param>
+    /// <param name="secrets">The secret values to remove.</param>
+    /// <returns>A list of scrubbed clones.</returns>
+    internal static IReadOnlyList<MxStatusProxy> RedactStatuses(
+        IReadOnlyList<MxStatusProxy> statuses,
+        params string?[] secrets)
+    {
+        if (statuses is null || statuses.Count is 0)
+        {
+            return statuses ?? [];
+        }
+
+        MxStatusProxy[] result = new MxStatusProxy[statuses.Count];
+        for (int i = 0; i < statuses.Count; i++)
+        {
+            MxStatusProxy clone = statuses[i].Clone();
+            clone.DiagnosticText = Redact(clone.DiagnosticText, secrets);
+            result[i] = clone;
+        }
+
+        return result;
+    }
+
     /// <summary>
     /// Returns an exception equivalent to <paramref name="ex"/> but with any verbatim secret
     /// scrubbed from its message. When nothing changes, the original exception is returned
@@ -57,28 +135,95 @@ internal static class MxGatewaySecretRedaction
         ArgumentNullException.ThrowIfNull(ex);
 
         string redacted = Redact(ex.Message, secrets);
-        if (string.Equals(redacted, ex.Message, StringComparison.Ordinal))
+        bool messageChanged = !string.Equals(redacted, ex.Message, StringComparison.Ordinal);
+        Exception? cause = ex.InnerException;
+
+        // MxAccessException derives its structured fields from the raw reply, so scrubbing must
+        // clone and redact that reply — the message alone changing is not enough, because the reply
+        // can carry the echoed secret even when the message does not.
+        if (ex is MxAccessException access)
+        {
+            if (!messageChanged && !ReplyContainsSecret(access.Reply, secrets))
+            {
+                return ex;
+            }
+
+            return new MxAccessException(redacted, RedactReply(access.Reply, secrets), cause);
+        }
+
+        // Other subtypes carry the secret through ProtocolStatus.Message and Statuses[].DiagnosticText.
+        if (!messageChanged
+            && !ContainsSecret(ex.ProtocolStatus?.Message, secrets)
+            && !StatusesContainSecret(ex.Statuses, secrets))
         {
             return ex;
         }
 
-        Exception? cause = ex.InnerException;
+        ProtocolStatus? status = RedactStatus(ex.ProtocolStatus, secrets);
+        IReadOnlyList<MxStatusProxy> statuses = RedactStatuses(ex.Statuses, secrets);
         return ex switch
         {
-            MxAccessException access => new MxAccessException(redacted, access.Reply, cause),
             MxGatewaySessionException => new MxGatewaySessionException(
-                redacted, ex.SessionId, ex.CorrelationId, ex.ProtocolStatus, ex.HResultCode, ex.Statuses, cause),
+                redacted, ex.SessionId, ex.CorrelationId, status, ex.HResultCode, statuses, cause),
             MxGatewayWorkerException => new MxGatewayWorkerException(
-                redacted, ex.SessionId, ex.CorrelationId, ex.ProtocolStatus, ex.HResultCode, ex.Statuses, cause),
+                redacted, ex.SessionId, ex.CorrelationId, status, ex.HResultCode, statuses, cause),
             MxGatewayAuthenticationException => new MxGatewayAuthenticationException(
-                redacted, ex.SessionId, ex.CorrelationId, ex.ProtocolStatus, ex.HResultCode, ex.Statuses, cause),
+                redacted, ex.SessionId, ex.CorrelationId, status, ex.HResultCode, statuses, cause),
             MxGatewayAuthorizationException => new MxGatewayAuthorizationException(
-                redacted, ex.SessionId, ex.CorrelationId, ex.ProtocolStatus, ex.HResultCode, ex.Statuses, cause),
+                redacted, ex.SessionId, ex.CorrelationId, status, ex.HResultCode, statuses, cause),
             MxGatewayMalformedReplyException => new MxGatewayMalformedReplyException(
-                redacted, ex.SessionId, ex.CorrelationId, ex.ProtocolStatus, ex.HResultCode, ex.Statuses, cause),
+                redacted, ex.SessionId, ex.CorrelationId, status, ex.HResultCode, statuses, cause),
             MxGatewayCommandException => new MxGatewayCommandException(
-                redacted, ex.SessionId, ex.CorrelationId, ex.ProtocolStatus, ex.HResultCode, ex.Statuses, cause),
+                redacted, ex.SessionId, ex.CorrelationId, status, ex.HResultCode, statuses, cause),
             _ => new MxGatewayException(redacted, cause),
         };
     }
+
+    private static bool ContainsSecret(string? text, string?[] secrets)
+    {
+        if (string.IsNullOrEmpty(text) || secrets is null)
+        {
+            return false;
+        }
+
+        foreach (string? secret in secrets)
+        {
+            if (!string.IsNullOrWhiteSpace(secret) && text.Contains(secret, StringComparison.Ordinal))
+            {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    private static bool StatusesContainSecret(IReadOnlyList<MxStatusProxy> statuses, string?[] secrets)
+    {
+        if (statuses is null)
+        {
+            return false;
+        }
+
+        foreach (MxStatusProxy status in statuses)
+        {
+            if (ContainsSecret(status.DiagnosticText, secrets))
+            {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    private static bool ReplyContainsSecret(MxCommandReply reply, string?[] secrets)
+    {
+        if (reply is null)
+        {
+            return false;
+        }
+
+        return ContainsSecret(reply.ProtocolStatus?.Message, secrets)
+            || ContainsSecret(reply.DiagnosticMessage, secrets)
+            || StatusesContainSecret(reply.Statuses, secrets);
+    }
 }

clients/go/mxgateway/client_session_test.go

@@ -264,6 +264,74 @@ func TestEventsFullBufferTerminalErrorKeepsRootCause(t *testing.T) {
 	}
 }
 
+// TestSubscribeEventsFullBufferDeliversTerminalError is the CLI-44 regression for
+// the never-drop Subscribe path. SubscribeEvents/SubscribeEventsAfter use
+// cancelWhenResultBufferFull=false, so ordinary sends are blocking and uncapped and
+// can fill every slot in the results channel — including the reserved terminal slot.
+// A genuine terminal Recv error must still be delivered as the final result, never
+// silently dropped. The server sends eventBufferSize+eventBufferReservedSlots events
+// (filling every slot) and then returns a genuine gRPC error; with an unconditional
+// non-blocking terminal send the error is dropped, so this fails red until the send
+// path blocks for the never-drop mode.
+func TestSubscribeEventsFullBufferDeliversTerminalError(t *testing.T) {
+	fake := &fakeGatewayServer{
+		streamStarted:     make(chan struct{}),
+		streamDone:        make(chan struct{}),
+		streamEventCount:  eventBufferSize + eventBufferReservedSlots,
+		streamTerminalErr: status.Error(codes.Internal, "boom"),
+	}
+	client, cleanup := newBufconnClient(t, fake)
+	defer cleanup()
+	session := NewSessionForID(client, "session-1")
+
+	subscription, err := session.SubscribeEvents(context.Background())
+	if err != nil {
+		t.Fatalf("SubscribeEvents() error = %v", err)
+	}
+	defer subscription.Close()
+	<-fake.streamStarted
+
+	// Wait for the server to finish sending every event and return the terminal
+	// error, so the producer goroutine has filled every buffered slot before the
+	// terminal result is processed. That is what makes the dropped-terminal bug
+	// observable: with the buffer full, an unconditional non-blocking send discards
+	// the terminal error.
+	select {
+	case <-fake.streamDone:
+	case <-time.After(2 * time.Second):
+		t.Fatal("event stream did not stop after terminal error")
+	}
+	time.Sleep(250 * time.Millisecond)
+
+	// Drain fully. Every data event, then the terminal gRPC error as the final
+	// result, must arrive; the channel must not close without yielding it.
+	events := subscription.Events()
+	var last EventResult
+	gotResult := false
+	for {
+		select {
+		case res, ok := <-events:
+			if !ok {
+				if !gotResult {
+					t.Fatal("events channel closed without yielding any result")
+				}
+				var gwErr *GatewayError
+				if !errors.As(last.Err, &gwErr) {
+					t.Fatalf("final event result err is %T (%v), want the terminal *GatewayError; it was dropped", last.Err, last.Err)
+				}
+				if code := status.Code(last.Err); code != codes.Internal {
+					t.Fatalf("final event result gRPC code = %s, want %s", code, codes.Internal)
+				}
+				return
+			}
+			last = res
+			gotResult = true
+		case <-time.After(2 * time.Second):
+			t.Fatal("events channel did not close after terminal error")
+		}
+	}
+}
+
 func TestEventsSurfacesReplayGapSentinelAsTypedSignal(t *testing.T) {
 	fake := &fakeGatewayServer{
 		streamStarted: make(chan struct{}),

clients/go/mxgateway/command_reply_fixtures_test.go

@@ -127,3 +127,71 @@ func TestAuthenticateUserScrubsEchoedCredentialFromError(t *testing.T) {
 		t.Fatalf("surfaced error missing redaction marker: %q", message)
 	}
 }
+
+// TestAuthenticateUserScrubsEchoedCredentialFromStructuredReply is the CLI-40
+// follow-up: redacting only the rendered Error() string is not enough. The typed
+// *MxAccessError still carries the raw command reply, whose ProtocolStatus.Message,
+// DiagnosticMessage, and Statuses[].DiagnosticText echo the credential verbatim. A
+// logger dumping structured fields would reintroduce the leak, so the reply the
+// typed error carries must be a scrubbed clone. Both the OK+negative-HRESULT and the
+// MXACCESS_FAILURE fixtures route to *MxAccessError (via EnsureProtocolSuccess), so
+// both must be scrubbed identically.
+func TestAuthenticateUserScrubsEchoedCredentialFromStructuredReply(t *testing.T) {
+	const credential = "sup3rSecretVerify9f3a2b"
+	fixtures := []string{
+		"authenticate-user.echoed-credential.reply.json",
+		"authenticate-user.echoed-credential-mxaccess-failure.reply.json",
+	}
+	for _, fixture := range fixtures {
+		t.Run(fixture, func(t *testing.T) {
+			fake := &fakeGatewayServer{
+				invokeReply: loadCommandReplyFixture(t, fixture),
+			}
+			client, cleanup := newBufconnClient(t, fake)
+			defer cleanup()
+			session := NewSessionForID(client, "session-1")
+
+			_, err := session.AuthenticateUser(context.Background(), 12, "operator", credential)
+			if err == nil {
+				t.Fatal("AuthenticateUser() error = nil, want an MXAccess failure")
+			}
+
+			var mxErr *MxAccessError
+			if !errors.As(err, &mxErr) {
+				t.Fatalf("AuthenticateUser() error = %v (%T), want *MxAccessError", err, err)
+			}
+
+			reply := mxErr.Reply
+			if reply == nil {
+				t.Fatal("MxAccessError.Reply is nil, want the scrubbed command reply")
+			}
+			if got := reply.GetProtocolStatus().GetMessage(); strings.Contains(got, credential) {
+				t.Fatalf("MxAccessError.Reply.ProtocolStatus.Message leaked the credential: %q", got)
+			}
+			if got := reply.GetDiagnosticMessage(); strings.Contains(got, credential) {
+				t.Fatalf("MxAccessError.Reply.DiagnosticMessage leaked the credential: %q", got)
+			}
+			for i, status := range reply.GetStatuses() {
+				if got := status.GetDiagnosticText(); strings.Contains(got, credential) {
+					t.Fatalf("MxAccessError.Reply.Statuses[%d].DiagnosticText leaked the credential: %q", i, got)
+				}
+			}
+
+			// The wrapped CommandError's status/reply must be scrubbed too.
+			if mxErr.Command != nil {
+				if got := mxErr.Command.Status.GetMessage(); strings.Contains(got, credential) {
+					t.Fatalf("MxAccessError.Command.Status.Message leaked the credential: %q", got)
+				}
+				if cmdReply := mxErr.Command.Reply; cmdReply != nil {
+					if got := cmdReply.GetDiagnosticMessage(); strings.Contains(got, credential) {
+						t.Fatalf("MxAccessError.Command.Reply.DiagnosticMessage leaked the credential: %q", got)
+					}
+				}
+			}
+
+			if got := err.Error(); strings.Contains(got, credential) {
+				t.Fatalf("rendered error leaked the credential: %q", got)
+			}
+		})
+	}
+}

clients/go/mxgateway/errors.go

@@ -6,6 +6,7 @@ import (
 	"strings"
 
 	pb "gitea.dohertylan.com/dohertj2/mxaccessgw/clients/go/internal/generated"
+	"google.golang.org/protobuf/proto"
 )
 
 // redactedSecretMarker is the placeholder substituted for credential material in
@@ -49,20 +50,108 @@ func (e *secretRedactingError) Unwrap() error {
 	return e.err
 }
 
-// redactSecrets wraps err so any occurrence of a non-empty secret in the surfaced
+// scrubReplyStrings returns a clone of reply with every non-empty secret replaced
-// message is redacted, while errors.As / errors.Is still reach the wrapped typed
+// by redactedSecretMarker in the free-text fields a gateway diagnostic could echo a
-// error. It returns nil unchanged and skips wrapping when no non-empty secret is
+// credential into: ProtocolStatus.Message, DiagnosticMessage, and each
-// supplied, so non-secret-bearing calls keep their original error verbatim.
+// Statuses[].DiagnosticText. It clones with proto.Clone so the caller's original
+// reply is never mutated. A nil reply, or an empty/whitespace-only secret set, is a
+// no-op (nil in, nil out; a clone otherwise).
+func scrubReplyStrings(reply *pb.MxCommandReply, secrets []string) *pb.MxCommandReply {
+	if reply == nil {
+		return nil
+	}
+	clone, ok := proto.Clone(reply).(*pb.MxCommandReply)
+	if !ok {
+		return reply
+	}
+	for _, secret := range secrets {
+		if secret == "" {
+			continue
+		}
+		if clone.GetProtocolStatus() != nil {
+			clone.ProtocolStatus.Message = strings.ReplaceAll(clone.GetProtocolStatus().GetMessage(), secret, redactedSecretMarker)
+		}
+		clone.DiagnosticMessage = strings.ReplaceAll(clone.GetDiagnosticMessage(), secret, redactedSecretMarker)
+		for _, status := range clone.GetStatuses() {
+			status.DiagnosticText = strings.ReplaceAll(status.GetDiagnosticText(), secret, redactedSecretMarker)
+		}
+	}
+	return clone
+}
+
+// scrubProtocolStatusMessage returns a clone of status with every non-empty secret
+// redacted from its Message, leaving the original untouched.
+func scrubProtocolStatusMessage(status *ProtocolStatus, secrets []string) *ProtocolStatus {
+	if status == nil {
+		return nil
+	}
+	clone, ok := proto.Clone(status).(*ProtocolStatus)
+	if !ok {
+		return status
+	}
+	for _, secret := range secrets {
+		if secret != "" {
+			clone.Message = strings.ReplaceAll(clone.GetMessage(), secret, redactedSecretMarker)
+		}
+	}
+	return clone
+}
+
+// redactSecrets scrubs a non-empty secret set from the error it surfaces. When the
+// wrapped error is a typed *MxAccessError or *CommandError it is rebuilt carrying
+// scrubbed clones of its reply and protocol status, so a caller logging the typed
+// error's structured fields cannot reintroduce the credential the rendered message
+// hides. The rebuilt (or original, for other error types) value is then wrapped in
+// secretRedactingError as a belt-and-suspenders scrub of any remaining rendered
+// text. errors.As / errors.Is still reach the typed error through the wrapper. It
+// returns nil unchanged and skips all work when no non-empty secret is supplied, so
+// non-secret-bearing calls keep their original error verbatim.
 func redactSecrets(err error, secrets ...string) error {
 	if err == nil {
 		return nil
 	}
+	hasSecret := false
 	for _, secret := range secrets {
 		if secret != "" {
-			return &secretRedactingError{err: err, secrets: secrets}
+			hasSecret = true
+			break
 		}
 	}
-	return err
+	if !hasSecret {
+		return err
+	}
+
+	rebuilt := rebuildScrubbedError(err, secrets)
+	return &secretRedactingError{err: rebuilt, secrets: secrets}
+}
+
+// rebuildScrubbedError rebuilds the typed error carrying scrubbed clones of any
+// command reply / protocol status it holds, so credential text never survives in the
+// error's structured fields. Non-reply-bearing error types are returned unchanged.
+func rebuildScrubbedError(err error, secrets []string) error {
+	switch typed := err.(type) {
+	case *MxAccessError:
+		return &MxAccessError{
+			Command: scrubCommandError(typed.Command, secrets),
+			Reply:   scrubReplyStrings(typed.Reply, secrets),
+		}
+	case *CommandError:
+		return scrubCommandError(typed, secrets)
+	default:
+		return err
+	}
+}
+
+// scrubCommandError rebuilds a CommandError with a scrubbed Status and Reply.
+func scrubCommandError(cmd *CommandError, secrets []string) *CommandError {
+	if cmd == nil {
+		return nil
+	}
+	return &CommandError{
+		Op:     cmd.Op,
+		Status: scrubProtocolStatusMessage(cmd.Status, secrets),
+		Reply:  scrubReplyStrings(cmd.Reply, secrets),
+	}
 }
 
 // ErrSlowConsumer is the terminal error sent on the Events/EventsAfter

clients/go/mxgateway/errors_redaction_test.go

@@ -0,0 +1,115 @@
+package mxgateway
+
+import (
+	"errors"
+	"strings"
+	"testing"
+
+	pb "gitea.dohertylan.com/dohertj2/mxaccessgw/clients/go/internal/generated"
+)
+
+// TestScrubReplyStringsRedactsEveryOccurrence covers the multi-occurrence case:
+// one secret appearing across ProtocolStatus.Message, DiagnosticMessage, and every
+// Statuses[].DiagnosticText must be fully redacted with no residue.
+func TestScrubReplyStringsRedactsEveryOccurrence(t *testing.T) {
+	const secret = "hunter2"
+	reply := &pb.MxCommandReply{
+		ProtocolStatus:    &pb.ProtocolStatus{Message: "rejected hunter2 then hunter2 again"},
+		DiagnosticMessage: "echoed hunter2 back",
+		Statuses: []*pb.MxStatusProxy{
+			{DiagnosticText: "first hunter2"},
+			{DiagnosticText: "second hunter2 and hunter2"},
+		},
+	}
+
+	scrubbed := scrubReplyStrings(reply, []string{secret})
+
+	if strings.Contains(scrubbed.GetProtocolStatus().GetMessage(), secret) {
+		t.Fatalf("ProtocolStatus.Message still contains the secret: %q", scrubbed.GetProtocolStatus().GetMessage())
+	}
+	if strings.Contains(scrubbed.GetDiagnosticMessage(), secret) {
+		t.Fatalf("DiagnosticMessage still contains the secret: %q", scrubbed.GetDiagnosticMessage())
+	}
+	for i, status := range scrubbed.GetStatuses() {
+		if strings.Contains(status.GetDiagnosticText(), secret) {
+			t.Fatalf("Statuses[%d].DiagnosticText still contains the secret: %q", i, status.GetDiagnosticText())
+		}
+	}
+	if !strings.Contains(scrubbed.GetProtocolStatus().GetMessage(), redactedSecretMarker) {
+		t.Fatalf("ProtocolStatus.Message missing redaction marker: %q", scrubbed.GetProtocolStatus().GetMessage())
+	}
+
+	// The original reply must be untouched (scrubReplyStrings clones).
+	if !strings.Contains(reply.GetDiagnosticMessage(), secret) {
+		t.Fatal("scrubReplyStrings mutated the original reply instead of cloning it")
+	}
+}
+
+// TestScrubReplyStringsRedactsOverlappingSecrets covers two secrets where one is a
+// substring of the other: both must be fully redacted, with no partial leak of the
+// longer secret's non-shared remainder.
+func TestScrubReplyStringsRedactsOverlappingSecrets(t *testing.T) {
+	const shortSecret = "pass"
+	const longSecret = "password123"
+	reply := &pb.MxCommandReply{
+		DiagnosticMessage: "value was password123 and also pass",
+	}
+
+	scrubbed := scrubReplyStrings(reply, []string{longSecret, shortSecret})
+
+	got := scrubbed.GetDiagnosticMessage()
+	if strings.Contains(got, shortSecret) {
+		t.Fatalf("scrubbed message still contains a secret substring %q: %q", shortSecret, got)
+	}
+	if strings.Contains(got, longSecret) {
+		t.Fatalf("scrubbed message still contains %q: %q", longSecret, got)
+	}
+	// "123" is the longer secret's remainder past the shared "pass" prefix; it must
+	// not survive as a partial leak.
+	if strings.Contains(got, "123") {
+		t.Fatalf("scrubbed message leaked the longer secret's remainder: %q", got)
+	}
+}
+
+// TestRedactSecretsEmptyOrNilLeavesErrorUnchanged confirms the no-secret paths keep
+// the original typed error verbatim (no wrapping, no scrubbed clone).
+func TestRedactSecretsEmptyOrNilLeavesErrorUnchanged(t *testing.T) {
+	base := &MxAccessError{Reply: &pb.MxCommandReply{DiagnosticMessage: "boom"}}
+
+	if got := redactSecrets(base); got != error(base) {
+		t.Fatalf("redactSecrets with no secrets = %v, want the original error unchanged", got)
+	}
+	if got := redactSecrets(base, ""); got != error(base) {
+		t.Fatalf("redactSecrets with only an empty secret = %v, want the original error unchanged", got)
+	}
+	if got := redactSecrets(nil, "secret"); got != nil {
+		t.Fatalf("redactSecrets(nil, ...) = %v, want nil", got)
+	}
+}
+
+// TestRedactSecretsRebuildsTypedCommandError confirms a *CommandError (non-MXAccess
+// path) is rebuilt with a scrubbed Status and Reply, and errors.As still reaches it.
+func TestRedactSecretsRebuildsTypedCommandError(t *testing.T) {
+	const secret = "topSecretValue"
+	base := &CommandError{
+		Op:     "write secured",
+		Status: &pb.ProtocolStatus{Message: "rejected topSecretValue"},
+		Reply:  &pb.MxCommandReply{DiagnosticMessage: "echoed topSecretValue"},
+	}
+
+	redacted := redactSecrets(base, secret)
+
+	var cmdErr *CommandError
+	if !errors.As(redacted, &cmdErr) {
+		t.Fatalf("redactSecrets result %T does not unwrap to *CommandError", redacted)
+	}
+	if strings.Contains(cmdErr.Status.GetMessage(), secret) {
+		t.Fatalf("CommandError.Status.Message leaked the secret: %q", cmdErr.Status.GetMessage())
+	}
+	if strings.Contains(cmdErr.Reply.GetDiagnosticMessage(), secret) {
+		t.Fatalf("CommandError.Reply.DiagnosticMessage leaked the secret: %q", cmdErr.Reply.GetDiagnosticMessage())
+	}
+	if strings.Contains(redacted.Error(), secret) {
+		t.Fatalf("rendered error leaked the secret: %q", redacted.Error())
+	}
+}

clients/go/mxgateway/session.go

@@ -1073,8 +1073,8 @@ func (s *Session) subscribeEventsAfter(ctx context.Context, afterWorkerSequence
 			// A genuine terminal stream error must be reported as itself, even
 			// when the data slots are full. Routing it through sendEventResult
 			// would let the overflow branch substitute ErrSlowConsumer and lose
-			// the real gRPC status, so send it directly on the reserved slot.
+			// the real gRPC status, so send it directly, bypassing that branch.
-			sendTerminalEventResult(results, EventResult{Err: &GatewayError{Op: "stream events", Err: err}})
+			sendTerminalEventResult(streamCtx, results, EventResult{Err: &GatewayError{Op: "stream events", Err: err}}, cancelWhenResultBufferFull)
 			return
 		}
 	}()
@@ -1093,20 +1093,32 @@ func ensureBulkSize(name string, length int) error {
 	return nil
 }
 
-// sendTerminalEventResult enqueues a terminal EventResult with a non-blocking
+// sendTerminalEventResult enqueues a terminal EventResult, bypassing
-// send. The eventBufferReservedSlots reserve (beyond the eventBufferSize data
+// sendEventResult's overflow branch so a genuine stream error is reported verbatim
-// slots) guarantees the send lands unless a terminal result was already
+// rather than relabeled as ErrSlowConsumer. How it sends depends on the mode:
-// enqueued; because this goroutine is the sole producer, at most one terminal
-// send ever races for the reserved slot, so the select default only fires when
-// the reserve is already spent — never dropping a first terminal error.
 //
-// Unlike sendEventResult, this bypasses the overflow branch: a genuine terminal
+//   - cancelWhenBufferFull=true (Events/EventsAfter): ordinary data sends are capped
-// stream error is reported verbatim even when the data slots are full, rather
+//     at eventBufferSize, leaving eventBufferReservedSlots free, so a non-blocking
-// than being relabeled as ErrSlowConsumer.
+//     send always lands the terminal result. Because this goroutine is the sole
-func sendTerminalEventResult(results chan<- EventResult, result EventResult) {
+//     producer, at most one terminal send ever races for the reserved slot, so the
+//     select default only fires when the reserve is already spent — never dropping a
+//     first terminal error.
+//   - cancelWhenBufferFull=false (SubscribeEvents/SubscribeEventsAfter, never-drop):
+//     ordinary data sends are uncapped and blocking, so every slot including the
+//     reserve can hold data. A non-blocking send would then hit the full buffer and
+//     silently drop the terminal error, breaking the never-drop contract; instead
+//     block until the consumer drains a slot (or the stream context is cancelled).
+func sendTerminalEventResult(ctx context.Context, results chan<- EventResult, result EventResult, cancelWhenBufferFull bool) {
+	if cancelWhenBufferFull {
+		select {
+		case results <- result:
+		default:
+		}
+		return
+	}
 	select {
 	case results <- result:
-	default:
+	case <-ctx.Done():
 	}
 }
 

clients/java/zb-mom-ww-mxgateway-client/src/main/java/com/zb/mom/ww/mxgateway/client/MxGatewaySecrets.java

@@ -63,9 +63,9 @@ public final class MxGatewaySecrets {
      * into a free-form failure message.
      *
      * @param message the message to scrub, may be {@code null}
-     * @param secrets the exact secret substrings to remove; {@code null}/empty
+     * @param secrets the exact secret substrings to remove; {@code null}, empty,
-     *     entries and a {@code null} array are ignored
+     *     and blank (whitespace-only) entries and a {@code null} array are ignored
-     * @return {@code message} unchanged when it is {@code null} or no non-empty
+     * @return {@code message} unchanged when it is {@code null} or no non-blank
      *     secret is supplied, otherwise the message with every secret occurrence
      *     replaced by {@code "<redacted>"}
      */
@@ -76,9 +76,11 @@ public final class MxGatewaySecrets {
 
         String result = message;
         for (String secret : secrets) {
-            if (secret != null && !secret.isEmpty()) {
+            if (secret == null || secret.isBlank()) {
-                result = result.replace(secret, "<redacted>");
+                // A blank "secret" would over-redact real whitespace; skip it.
+                continue;
             }
+            result = result.replace(secret, "<redacted>");
         }
         return result;
     }

clients/java/zb-mom-ww-mxgateway-client/src/main/java/com/zb/mom/ww/mxgateway/client/MxGatewaySession.java

@@ -31,6 +31,7 @@ import mxaccess_gateway.v1.MxaccessGateway.MxSparseElement;
 import mxaccess_gateway.v1.MxaccessGateway.MxStatusProxy;
 import mxaccess_gateway.v1.MxaccessGateway.MxValue;
 import mxaccess_gateway.v1.MxaccessGateway.OpenSessionReply;
+import mxaccess_gateway.v1.MxaccessGateway.ProtocolStatus;
 import mxaccess_gateway.v1.MxaccessGateway.ReadBulkCommand;
 import mxaccess_gateway.v1.MxaccessGateway.RegisterCommand;
 import mxaccess_gateway.v1.MxaccessGateway.RemoveItemBulkCommand;
@@ -1055,29 +1056,142 @@ public final class MxGatewaySession implements AutoCloseable {
      * it into a diagnostic; this guarantees it never survives in the exception
      * text a caller might log.
      *
-     * <p>On failure the original exception's message is scrubbed with
+     * <p>On failure both the exception's message <em>and</em> its structured
-     * {@link MxGatewaySecrets#redactExact}. If nothing changed (the common case
+     * context (the {@link ProtocolStatus} and {@link MxCommandReply} a caller can
-     * where the message never carried the secret), the original exception is
+     * inspect and log) are scrubbed with {@link MxGatewaySecrets#redactExact}: the
+     * gateway echoes the credential into {@code protocolStatus.message},
+     * {@code reply.diagnosticMessage}, and each {@code statuses[i].diagnosticText}.
+     * If nothing carried the secret (the common case) the original exception is
      * rethrown untouched. Otherwise it is re-thrown as the same concrete type
-     * carrying the redacted message; the secret-bearing original is not chained
+     * carrying the redacted message and scrubbed context; the secret-bearing
-     * as a cause, so it cannot leak through a printed stack trace.
+     * original is not chained as a cause, so it cannot leak through a printed
+     * stack trace.
      */
     private MxCommandReply invokeCommandRedacted(MxCommand command, String... secrets) {
         try {
             return invokeCommand(command);
         } catch (MxGatewayException ex) {
             String original = ex.getMessage();
-            String redacted = MxGatewaySecrets.redactExact(original, secrets);
+            String redactedMessage = MxGatewaySecrets.redactExact(original, secrets);
-            if (redacted == null || redacted.equals(original)) {
+            boolean messageChanged = redactedMessage != null && !redactedMessage.equals(original);
+
+            ProtocolStatus status = protocolStatusOf(ex);
+            ProtocolStatus scrubbedStatus = scrubProtocolStatus(status, secrets);
+            boolean statusChanged = status != null && !status.equals(scrubbedStatus);
+
+            MxCommandReply reply = replyOf(ex);
+            MxCommandReply scrubbedReply = scrubReply(reply, secrets);
+            boolean replyChanged = reply != null && !reply.equals(scrubbedReply);
+
+            if (!messageChanged && !statusChanged && !replyChanged) {
                 throw ex;
             }
-            if (ex instanceof MxAccessException mx) {
+
-                throw new MxAccessException(redacted, mx.protocolStatus(), mx.reply(), null);
+            String message = messageChanged ? redactedMessage : original;
-            }
+            throw rebuildRedacted(ex, message, scrubbedStatus, scrubbedReply);
-            throw new MxGatewayException(redacted);
         }
     }
 
+    /**
+     * Extracts the {@link ProtocolStatus} an exception carries, if any, so it can
+     * be scrubbed and re-attached to the rebuilt exception.
+     */
+    private static ProtocolStatus protocolStatusOf(MxGatewayException ex) {
+        if (ex instanceof MxGatewayCommandException command) {
+            return command.protocolStatus();
+        }
+        if (ex instanceof MxGatewaySessionException session) {
+            return session.protocolStatus();
+        }
+        if (ex instanceof MxGatewayWorkerException worker) {
+            return worker.protocolStatus();
+        }
+        return null;
+    }
+
+    /**
+     * Extracts the raw {@link MxCommandReply} an exception carries, if any.
+     */
+    private static MxCommandReply replyOf(MxGatewayException ex) {
+        if (ex instanceof MxGatewayCommandException command) {
+            return command.reply();
+        }
+        return null;
+    }
+
+    /**
+     * Rebuilds a gateway exception of the same concrete type with a redacted
+     * message and already-scrubbed context, mirroring the .NET client's
+     * type-switch. Only a truly-unknown subtype collapses to the base
+     * {@link MxGatewayException}. The original (secret-bearing) exception is
+     * deliberately not chained as a cause.
+     */
+    private static MxGatewayException rebuildRedacted(
+            MxGatewayException ex, String message, ProtocolStatus status, MxCommandReply reply) {
+        if (ex instanceof MxAccessException) {
+            return new MxAccessException(message, status, reply, null);
+        }
+        if (ex instanceof MxGatewayCommandException) {
+            return new MxGatewayCommandException(message, status, reply, null);
+        }
+        if (ex instanceof MxGatewaySessionException) {
+            return new MxGatewaySessionException(message, status, null);
+        }
+        if (ex instanceof MxGatewayWorkerException) {
+            return new MxGatewayWorkerException(message, status, null);
+        }
+        if (ex instanceof MxGatewayMalformedReplyException) {
+            return new MxGatewayMalformedReplyException(message);
+        }
+        if (ex instanceof MxGatewayAuthenticationException) {
+            return new MxGatewayAuthenticationException(message, null);
+        }
+        if (ex instanceof MxGatewayAuthorizationException) {
+            return new MxGatewayAuthorizationException(message, null);
+        }
+        return new MxGatewayException(message);
+    }
+
+    /**
+     * Produces a scrubbed clone of a command reply, removing any exact secret the
+     * gateway echoed into {@code protocolStatus.message},
+     * {@code diagnosticMessage}, or a status's {@code diagnosticText}.
+     *
+     * @param reply the reply to scrub, or {@code null}
+     * @param secrets the exact secrets to strip
+     * @return {@code null} when {@code reply} is {@code null}, otherwise a clone
+     *     with every echoed secret replaced by the redaction marker
+     */
+    private static MxCommandReply scrubReply(MxCommandReply reply, String... secrets) {
+        if (reply == null) {
+            return null;
+        }
+        MxCommandReply.Builder builder = reply.toBuilder();
+        if (builder.hasProtocolStatus()) {
+            builder.setProtocolStatus(scrubProtocolStatus(builder.getProtocolStatus(), secrets));
+        }
+        builder.setDiagnosticMessage(MxGatewaySecrets.redactExact(builder.getDiagnosticMessage(), secrets));
+        for (int index = 0; index < builder.getStatusesCount(); index++) {
+            MxStatusProxy.Builder status = builder.getStatuses(index).toBuilder();
+            status.setDiagnosticText(MxGatewaySecrets.redactExact(status.getDiagnosticText(), secrets));
+            builder.setStatuses(index, status);
+        }
+        return builder.build();
+    }
+
+    /**
+     * Produces a scrubbed clone of a protocol status, removing any exact secret
+     * the gateway echoed into its free-form {@code message}.
+     */
+    private static ProtocolStatus scrubProtocolStatus(ProtocolStatus status, String... secrets) {
+        if (status == null) {
+            return null;
+        }
+        return status.toBuilder()
+                .setMessage(MxGatewaySecrets.redactExact(status.getMessage(), secrets))
+                .build();
+    }
+
     /**
      * Extracts the string payload of a secured-write value so it can be scrubbed
      * from an echoed failure message. Only string-kind values carry a

clients/java/zb-mom-ww-mxgateway-client/src/main/java/com/zb/mom/ww/mxgateway/client/MxGatewaySessionException.java

@@ -20,6 +20,20 @@ public final class MxGatewaySessionException extends MxGatewayException {
         this.protocolStatus = protocolStatus;
     }
 
+    /**
+     * Creates a new session exception with an already-built, verbatim message.
+     * Used to re-surface a failure with a redacted message while preserving the
+     * (already scrubbed) protocol status.
+     *
+     * @param message the exact message to surface (already formatted/redacted)
+     * @param protocolStatus protocol status returned by the gateway
+     * @param cause underlying error, or {@code null}
+     */
+    protected MxGatewaySessionException(String message, ProtocolStatus protocolStatus, Throwable cause) {
+        super(message, cause);
+        this.protocolStatus = protocolStatus;
+    }
+
     /**
      * Returns the gateway protocol status that triggered this exception.
      *

clients/java/zb-mom-ww-mxgateway-client/src/main/java/com/zb/mom/ww/mxgateway/client/MxGatewayWorkerException.java

@@ -20,6 +20,20 @@ public final class MxGatewayWorkerException extends MxGatewayException {
         this.protocolStatus = protocolStatus;
     }
 
+    /**
+     * Creates a new worker exception with an already-built, verbatim message.
+     * Used to re-surface a failure with a redacted message while preserving the
+     * (already scrubbed) protocol status.
+     *
+     * @param message the exact message to surface (already formatted/redacted)
+     * @param protocolStatus protocol status returned by the gateway
+     * @param cause underlying error, or {@code null}
+     */
+    protected MxGatewayWorkerException(String message, ProtocolStatus protocolStatus, Throwable cause) {
+        super(message, cause);
+        this.protocolStatus = protocolStatus;
+    }
+
     /**
      * Returns the gateway protocol status that triggered this exception.
      *

clients/java/zb-mom-ww-mxgateway-client/src/test/java/com/zb/mom/ww/mxgateway/client/MxGatewayCredentialReplyTests.java

@@ -2,6 +2,7 @@ package com.zb.mom.ww.mxgateway.client;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
@@ -28,11 +29,23 @@ final class MxGatewayCredentialReplyTests {
 
     @Test
     void authenticateUserRedactsEchoedCredentialFromReplyDrivenError() throws Exception {
-        MxCommandReply reply = loadReply("authenticate-user.echoed-credential.reply.json");
+        assertCredentialFullyRedacted(
+                "authenticate-user.echoed-credential.reply.json", "auth-echo-session");
+    }
+
+    @Test
+    void authenticateUserRedactsEchoedCredentialFromMxAccessFailureReply() throws Exception {
+        assertCredentialFullyRedacted(
+                "authenticate-user.echoed-credential-mxaccess-failure.reply.json",
+                "auth-echo-failure-session");
+    }
+
+    private static void assertCredentialFullyRedacted(String fixture, String sessionId) throws Exception {
+        MxCommandReply reply = loadReply(fixture);
 
         try (InProcessGateway gateway = InProcessGateway.startReturning(reply);
                 MxGatewayClient client = gateway.client()) {
-            MxGatewaySession session = MxGatewaySession.forSessionId(client, "auth-echo-session");
+            MxGatewaySession session = MxGatewaySession.forSessionId(client, sessionId);
 
             MxAccessException error = assertThrows(
                     MxAccessException.class,
@@ -42,6 +55,22 @@ final class MxGatewayCredentialReplyTests {
                     "credential echoed by the gateway must not survive in the surfaced message");
             assertTrue(error.getMessage().contains("<redacted>"),
                     "the echoed credential must be replaced with the redaction marker");
+
+            // The rebuilt exception must not re-expose the credential through the
+            // structured reply/protocolStatus a caller can inspect and log.
+            MxCommandReply surfaced = error.reply();
+            assertNotNull(surfaced, "the redacted exception must preserve a reply for inspection");
+            assertFalse(surfaced.getProtocolStatus().getMessage().contains(CREDENTIAL),
+                    "reply protocol status message must not leak the echoed credential");
+            assertFalse(surfaced.getDiagnosticMessage().contains(CREDENTIAL),
+                    "reply diagnostic message must not leak the echoed credential");
+            for (int index = 0; index < surfaced.getStatusesCount(); index++) {
+                assertFalse(surfaced.getStatusesList().get(index).getDiagnosticText().contains(CREDENTIAL),
+                        "reply status diagnostic text must not leak the echoed credential");
+            }
+            assertNotNull(error.protocolStatus(), "the redacted exception must preserve a protocol status");
+            assertFalse(error.protocolStatus().getMessage().contains(CREDENTIAL),
+                    "exception protocol status must not leak the echoed credential");
         }
     }
 

clients/java/zb-mom-ww-mxgateway-client/src/test/java/com/zb/mom/ww/mxgateway/client/MxGatewaySecretsTests.java

@@ -0,0 +1,50 @@
+package com.zb.mom.ww.mxgateway.client;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
+
+import org.junit.jupiter.api.Test;
+
+final class MxGatewaySecretsTests {
+    @Test
+    void redactExactReplacesEveryOccurrenceOfASecret() {
+        String message = "verify s3cr3t, retry s3cr3t, done s3cr3t";
+
+        String result = MxGatewaySecrets.redactExact(message, "s3cr3t");
+
+        assertFalse(result.contains("s3cr3t"), "no occurrence of the secret may survive");
+        assertEquals("verify <redacted>, retry <redacted>, done <redacted>", result);
+    }
+
+    @Test
+    void redactExactFullyRedactsOverlappingSecretsWhenOneIsASubstringOfTheOther() {
+        String message = "password=hunter2 token=hunter2extra";
+
+        String result = MxGatewaySecrets.redactExact(message, "hunter2extra", "hunter2");
+
+        assertFalse(result.contains("hunter2"), "both the secret and its superstring must be fully redacted");
+        assertEquals("password=<redacted> token=<redacted>", result);
+    }
+
+    @Test
+    void redactExactWithNoSecretsReturnsMessageUnchanged() {
+        String message = "nothing to scrub here";
+
+        assertEquals(message, MxGatewaySecrets.redactExact(message));
+    }
+
+    @Test
+    void redactExactToleratesNullMessage() {
+        assertNull(MxGatewaySecrets.redactExact(null, "secret"));
+    }
+
+    @Test
+    void redactExactIgnoresBlankSecretSoRealSpacesAreNotOverRedacted() {
+        String message = "keep these spaces intact";
+
+        String result = MxGatewaySecrets.redactExact(message, " ", "");
+
+        assertEquals(message, result);
+    }
+}

clients/proto/fixtures/behavior/command-replies/authenticate-user.echoed-credential-mxaccess-failure.reply.json

@@ -0,0 +1,22 @@
+{
+  "sessionId": "session-fixture",
+  "correlationId": "gateway-correlation-authenticate-echoed-mxaccess-failure",
+  "kind": "MX_COMMAND_KIND_AUTHENTICATE_USER",
+  "protocolStatus": {
+    "code": "PROTOCOL_STATUS_CODE_MXACCESS_FAILURE",
+    "message": "MXAccess AuthenticateUser rejected credential 'sup3rSecretVerify9f3a2b'."
+  },
+  "hresult": -2147024891,
+  "statuses": [
+    {
+      "success": 0,
+      "category": "MX_STATUS_CATEGORY_SECURITY_ERROR",
+      "detectedBy": "MX_STATUS_SOURCE_RESPONDING_NMX",
+      "detail": 5,
+      "rawCategory": 8,
+      "rawDetectedBy": 5,
+      "diagnosticText": "Authentication failed for password 'sup3rSecretVerify9f3a2b'."
+    }
+  ],
+  "diagnosticMessage": "MXAccess echoed the credential 'sup3rSecretVerify9f3a2b' back in its failure diagnostic."
+}

clients/proto/fixtures/behavior/manifest.json

@@ -53,7 +53,14 @@
       "category": "command_replies",
       "messageType": "mxaccess_gateway.v1.MxCommandReply",
       "path": "command-replies/authenticate-user.echoed-credential.reply.json",
-      "expectation": "When a gateway/MXAccess diagnostic echoes the caller's credential back, the surfaced error redacts the exact secret and never leaks the verbatim value."
+      "expectation": "When a gateway/MXAccess diagnostic echoes the caller's credential back (OK envelope, negative HRESULT), the surfaced error redacts the exact secret from both the rendered message and the structured reply accessors."
+    },
+    {
+      "id": "command-reply.authenticate-user.echoed-credential-mxaccess-failure",
+      "category": "command_replies",
+      "messageType": "mxaccess_gateway.v1.MxCommandReply",
+      "path": "command-replies/authenticate-user.echoed-credential-mxaccess-failure.reply.json",
+      "expectation": "The same echoed-credential redaction holds when the reply is coded PROTOCOL_STATUS_CODE_MXACCESS_FAILURE, which every client routes to its MXAccess error type."
     },
     {
       "id": "command-reply.authenticate-user.missing-payload",

clients/python/src/zb_mom_ww_mxgateway/session.py

@@ -919,19 +919,47 @@ def _value_secrets(value: MxValueInput) -> list[str]:
 
 
 def _redact_error(error: MxGatewayError, secrets: Sequence[str | None]) -> None:
-    """Scrub secret substrings from a raised error's message in place.
+    """Scrub secret substrings from a raised error's message and reply in place.
 
     Rewrites ``error.args[0]`` (the message returned by ``str(error)``) through
     the shared :func:`~zb_mom_ww_mxgateway.auth.redact_secret` seam so credential
-    text can never reach logs or be re-raised to a caller. The
+    text can never reach logs or be re-raised to a caller.
-    ``protocol_status`` / ``raw_reply`` context is left untouched — those hold the
+
-    gateway's own fields, which never echo the client-supplied secret.
+    A misbehaving MXAccess provider can echo the client-supplied credential back
+    verbatim in its failure diagnostics, so ``error.raw_reply`` (the protobuf
+    reply) can carry the secret in ``protocol_status.message``,
+    ``diagnostic_message``, and each ``statuses[].diagnostic_text``. A logger
+    dumping those structured fields would reintroduce the leak the message scrub
+    closes. When there is a secret to scrub and a reply is attached, this rebinds
+    ``error.raw_reply`` to a scrubbed deep copy so the raised exception carries no
+    credential text on any surface. The clone leaves the original reply untouched.
     """
     scrubbed = [secret for secret in secrets if secret]
     if not scrubbed:
         return
     if error.args and isinstance(error.args[0], str):
         error.args = (redact_secret(error.args[0], scrubbed), *error.args[1:])
+    if error.raw_reply is not None:
+        error.raw_reply = _redact_reply(error.raw_reply, scrubbed)
+
+
+def _redact_reply(reply: pb.MxCommandReply, secrets: Sequence[str]) -> pb.MxCommandReply:
+    """Return a deep copy of *reply* with credential text scrubbed from diagnostics.
+
+    Operates on a clone so the caller's original reply object is never mutated.
+    Only the free-text diagnostic fields that can echo a client-supplied secret
+    are scrubbed; the structured/enum fields the gateway itself sets are left as-is.
+    """
+    clone = type(reply)()
+    clone.CopyFrom(reply)
+    if clone.protocol_status.message:
+        clone.protocol_status.message = redact_secret(clone.protocol_status.message, secrets)
+    if clone.diagnostic_message:
+        clone.diagnostic_message = redact_secret(clone.diagnostic_message, secrets)
+    for status in clone.statuses:
+        if status.diagnostic_text:
+            status.diagnostic_text = redact_secret(status.diagnostic_text, secrets)
+    return clone
 
 
 from .client import GatewayClient  # noqa: E402

clients/python/tests/test_malformed_reply.py

@@ -82,15 +82,31 @@ async def test_add_buffered_item_missing_payload_raises_malformed_reply() -> Non
     assert captured.value.raw_reply is reply
 
 
+@pytest.mark.parametrize(
+    "fixture",
+    [
+        "command-replies/authenticate-user.echoed-credential.reply.json",
+        "command-replies/authenticate-user.echoed-credential-mxaccess-failure.reply.json",
+    ],
+)
 @pytest.mark.asyncio
-async def test_authenticate_user_echoed_credential_is_scrubbed() -> None:
+async def test_authenticate_user_echoed_credential_is_scrubbed(fixture: str) -> None:
     credential = "sup3rSecretVerify9f3a2b"
-    reply = _load_reply("command-replies/authenticate-user.echoed-credential.reply.json")
+    reply = _load_reply(fixture)
     session, _ = await _session_with([reply])
 
     with pytest.raises(MxAccessError) as captured:
         await session.authenticate_user(12, "operator", credential)
 
-    message = str(captured.value)
+    exc = captured.value
+    message = str(exc)
     assert credential not in message
     assert "[redacted]" in message
+
+    # The credential must not survive in the structured protobuf context either:
+    # a logger dumping raw_reply's fields would otherwise reintroduce the leak.
+    assert exc.raw_reply is not None
+    assert credential not in exc.raw_reply.protocol_status.message
+    assert credential not in exc.raw_reply.diagnostic_message
+    for status in exc.raw_reply.statuses:
+        assert credential not in status.diagnostic_text

clients/python/tests/test_typed_command_helpers.py

@@ -140,10 +140,19 @@ async def test_write_secured_surfaces_native_failure_without_prior_authenticate(
     with pytest.raises(MxAccessError) as captured:
         await session.write_secured(12, 34, secret_value, current_user_id=5, verifier_user_id=6)
 
-    # Native failure is surfaced (not "fixed") and the raw reply is preserved...
+    # Native failure is surfaced (not "fixed"): the raw reply's structure is
-    assert captured.value.raw_reply is failure
+    # preserved so callers still see the native verdict...
-    # ...but the credential-sensitive value is scrubbed from the surfaced message.
+    raw = captured.value.raw_reply
+    assert raw is not None
+    assert raw.kind == pb.MX_COMMAND_KIND_WRITE_SECURED
+    assert raw.hresult == -2147217407
+    assert raw.protocol_status.code == pb.PROTOCOL_STATUS_CODE_MXACCESS_FAILURE
+    # ...but the credential-sensitive value is scrubbed from the surfaced message
+    # AND from the reply's echoed diagnostics, so a logger dumping raw_reply's
+    # structured fields cannot reintroduce the leak.
     assert secret_value not in str(captured.value)
+    assert secret_value not in raw.protocol_status.message
+    assert "[redacted]" in raw.protocol_status.message
     command = stub.invoke.requests[0].command
     assert command.kind == pb.MX_COMMAND_KIND_WRITE_SECURED
     assert command.write_secured.current_user_id == 5

clients/rust/src/error.rs

@@ -346,10 +346,17 @@ impl From<tonic::Status> for Error {
 /// Promote a non-OK protocol status carried inside an [`MxCommandReply`]
 /// to an [`Error::Command`].
 ///
+/// [`ProtocolStatusCode::MxaccessFailure`] is deliberately **not** a
+/// command-level failure here: it signals an MXAccess-level rejection, so it
+/// falls through to [`ensure_mxaccess_success`] and surfaces as
+/// [`Error::MxAccess`] — matching the .NET, Java, Go, and Python clients. Every
+/// other non-`Ok` code stays [`Error::Command`].
+///
 /// # Errors
 ///
 /// Returns [`Error::Command`] when `reply.protocol_status` is missing or
-/// reports any code other than [`ProtocolStatusCode::Ok`].
+/// reports any code other than [`ProtocolStatusCode::Ok`] or
+/// [`ProtocolStatusCode::MxaccessFailure`].
 pub fn ensure_command_success(reply: MxCommandReply) -> Result<MxCommandReply, Error> {
     let code = reply
         .protocol_status
@@ -357,7 +364,7 @@ pub fn ensure_command_success(reply: MxCommandReply) -> Result<MxCommandReply, E
         .and_then(|status| ProtocolStatusCode::try_from(status.code).ok())
         .unwrap_or(ProtocolStatusCode::Unspecified);
 
-    if code == ProtocolStatusCode::Ok {
+    if code == ProtocolStatusCode::Ok || code == ProtocolStatusCode::MxaccessFailure {
         Ok(reply)
     } else {
         Err(Box::new(CommandError::new(reply)).into())
@@ -368,9 +375,12 @@ pub fn ensure_command_success(reply: MxCommandReply) -> Result<MxCommandReply, E
 /// [`MxCommandReply`] to an [`Error::MxAccess`].
 ///
 /// This is the second reply check applied to the typed command path, after
-/// [`ensure_command_success`] confirms the protocol envelope is `Ok`. It
+/// [`ensure_command_success`] confirms the protocol envelope is `Ok` (or a
-/// enforces MXAccess parity: a reply can carry an `Ok` protocol envelope while
+/// [`ProtocolStatusCode::MxaccessFailure`] the first check lets fall through).
-/// MXAccess itself rejected the operation. Following COM semantics, only a
+/// It enforces MXAccess parity: a reply can carry an `Ok` protocol envelope
+/// while MXAccess itself rejected the operation, and a
+/// [`ProtocolStatusCode::MxaccessFailure`] envelope is itself an MXAccess-level
+/// failure regardless of `hresult`. Following COM semantics, only a
 /// **negative** `hresult` is a failure — positive codes such as `S_FALSE = 1`
 /// are success. A `MXSTATUS_PROXY` entry is treated as a failure when its
 /// `category` is not [`MxStatusCategory::Ok`]; the `success` member mirrors the
@@ -383,17 +393,24 @@ pub fn ensure_command_success(reply: MxCommandReply) -> Result<MxCommandReply, E
 ///
 /// # Errors
 ///
-/// Returns [`Error::MxAccess`] when `reply.hresult` is negative or any
+/// Returns [`Error::MxAccess`] when the reply's protocol code is
+/// [`ProtocolStatusCode::MxaccessFailure`], `reply.hresult` is negative, or any
 /// `reply.statuses` entry reports a category other than
 /// [`MxStatusCategory::Ok`].
 pub fn ensure_mxaccess_success(reply: MxCommandReply) -> Result<MxCommandReply, Error> {
+    let protocol_code = reply
+        .protocol_status
+        .as_ref()
+        .and_then(|status| ProtocolStatusCode::try_from(status.code).ok())
+        .unwrap_or(ProtocolStatusCode::Unspecified);
+    let mxaccess_failure = protocol_code == ProtocolStatusCode::MxaccessFailure;
     let hresult_failure = reply.hresult.is_some_and(|hresult| hresult < 0);
     let status_failure = reply
         .statuses
         .iter()
         .any(|status| status.category != MxStatusCategory::Ok as i32);
 
-    if hresult_failure || status_failure {
+    if mxaccess_failure || hresult_failure || status_failure {
         Err(Box::new(MxAccessError::new(reply)).into())
     } else {
         Ok(reply)

clients/rust/src/session.rs

@@ -11,7 +11,7 @@
 use std::sync::atomic::{AtomicU64, Ordering};
 
 use crate::client::{EventStream, GatewayClient};
-use crate::error::{ensure_protocol_success, Error};
+use crate::error::{ensure_protocol_success, Error, MxAccessError};
 use crate::generated::mxaccess_gateway::v1::mx_command::Payload;
 use crate::generated::mxaccess_gateway::v1::mx_command_reply;
 use crate::generated::mxaccess_gateway::v1::{
@@ -1117,16 +1117,46 @@ fn string_secret(value: &MxValue) -> Vec<String> {
 }
 
 /// Attach caller-supplied exact secrets to an [`Error::MxAccess`] before it
-/// propagates, so its `Display` scrubs any occurrence of the credential (e.g. a
+/// propagates. This both scrubs the stored reply's caller-readable string
-/// password MXAccess echoed back verbatim). Any other error variant is returned
+/// fields (so `reply()`/`into_reply()` cannot recover a credential MXAccess
-/// unchanged.
+/// echoed back verbatim) and keeps the secrets on the error as a
+/// belt-and-suspenders for `Display`/`Debug`. Any other error variant is
+/// returned unchanged.
 fn attach_secrets(error: Error, secrets: Vec<String>) -> Error {
     match error {
-        Error::MxAccess(boxed) => Error::MxAccess(Box::new(boxed.with_secrets(secrets))),
+        Error::MxAccess(boxed) => {
+            let mut reply = boxed.into_reply();
+            scrub_reply_strings(&mut reply, &secrets);
+            Error::MxAccess(Box::new(MxAccessError::new(reply).with_secrets(secrets)))
+        }
         other => other,
     }
 }
 
+/// Replace every non-empty secret occurrence with `<redacted>` in the reply's
+/// caller-readable string fields — `protocol_status.message`,
+/// `diagnostic_message`, and each `statuses[i].diagnostic_text`. A caller
+/// reading the structured reply back off an [`Error::MxAccess`] would otherwise
+/// reintroduce the leak that `Display`/`Debug` already close.
+fn scrub_reply_strings(reply: &mut MxCommandReply, secrets: &[String]) {
+    for secret in secrets {
+        if secret.is_empty() {
+            continue;
+        }
+        if let Some(status) = reply.protocol_status.as_mut() {
+            status.message = status.message.replace(secret.as_str(), "<redacted>");
+        }
+        reply.diagnostic_message = reply
+            .diagnostic_message
+            .replace(secret.as_str(), "<redacted>");
+        for status in &mut reply.statuses {
+            status.diagnostic_text = status
+                .diagnostic_text
+                .replace(secret.as_str(), "<redacted>");
+        }
+    }
+}
+
 fn suspend_status(reply: MxCommandReply) -> Result<MxStatus, Error> {
     match reply.payload {
         Some(mx_command_reply::Payload::Suspend(suspend)) => suspend

clients/rust/tests/client_behavior.rs

@@ -84,8 +84,10 @@ async fn session_helpers_build_commands_and_preserve_command_errors() {
         .write(12, 34, ClientMxValue::int32(123), 0)
         .await
         .unwrap_err();
-    let Error::Command(error) = error else {
+    // A MXACCESS_FAILURE-coded reply is an MXAccess-level failure, routed to
-        panic!("write failure should preserve the raw command reply: {error:?}");
+    // Error::MxAccess (matching .NET/Java/Go/Python) rather than Error::Command.
+    let Error::MxAccess(error) = error else {
+        panic!("MXACCESS_FAILURE reply should route to Error::MxAccess: {error:?}");
     };
     assert_eq!(
         error.reply().protocol_status.as_ref().unwrap().code,
@@ -841,6 +843,92 @@ async fn authenticate_user_scrubs_exact_caller_credential_echoed_in_diagnostic()
     );
 }
 
+/// Drive `authenticate_user` against a canned reply that echoes the caller's
+/// credential in every string field, then assert the surfaced
+/// [`Error::MxAccess`] leaks it nowhere — neither through the structured reply a
+/// caller can read back (`reply().protocol_status.message`,
+/// `reply().diagnostic_message`, `reply().statuses[i].diagnostic_text`) nor
+/// through `Display`/`Debug`.
+async fn assert_authenticate_user_scrubs_structured_reply(fixture: &str) {
+    let credential = "sup3rSecretVerify9f3a2b";
+    let state = Arc::new(FakeState::default());
+    *state.invoke_override.lock().await = Some(InvokeOverride::CannedReply(Box::new(
+        command_reply_fixture(fixture),
+    )));
+    let endpoint = spawn_fake_gateway(state.clone()).await;
+    let client = GatewayClient::connect(ClientOptions::new(endpoint))
+        .await
+        .unwrap();
+    let session = client.session("session-fixture");
+
+    let error = session
+        .authenticate_user(7, "verifier", credential)
+        .await
+        .unwrap_err();
+
+    let Error::MxAccess(mx_access) = &error else {
+        panic!("{fixture}: credential-echoed reply must route to Error::MxAccess, got {error:?}");
+    };
+
+    // The structured reply a caller can read back must be scrubbed too — the raw
+    // MxCommandReply otherwise reintroduces the leak Display/Debug already close.
+    let reply = mx_access.reply();
+    if let Some(status) = reply.protocol_status.as_ref() {
+        assert!(
+            !status.message.contains(credential),
+            "{fixture}: credential leaked via reply().protocol_status.message: {}",
+            status.message
+        );
+    }
+    assert!(
+        !reply.diagnostic_message.contains(credential),
+        "{fixture}: credential leaked via reply().diagnostic_message: {}",
+        reply.diagnostic_message
+    );
+    for (index, status) in reply.statuses.iter().enumerate() {
+        assert!(
+            !status.diagnostic_text.contains(credential),
+            "{fixture}: credential leaked via reply().statuses[{index}].diagnostic_text: {}",
+            status.diagnostic_text
+        );
+    }
+
+    let display = error.to_string();
+    let debug = format!("{error:?}");
+    assert!(
+        !display.contains(credential),
+        "{fixture}: credential leaked into Display: {display}"
+    );
+    assert!(
+        !debug.contains(credential),
+        "{fixture}: credential leaked into Debug: {debug}"
+    );
+    assert!(
+        display.contains("<redacted>"),
+        "{fixture}: Display must mark the redaction: {display}"
+    );
+}
+
+#[tokio::test]
+async fn authenticate_user_scrubs_credential_from_structured_reply_ok_protocol_variant() {
+    // OK protocol envelope + negative hresult: already Error::MxAccess before
+    // ISSUE 2, but the stored reply's string fields still leaked the credential.
+    assert_authenticate_user_scrubs_structured_reply(
+        "authenticate-user.echoed-credential.reply.json",
+    )
+    .await;
+}
+
+#[tokio::test]
+async fn authenticate_user_scrubs_credential_from_structured_reply_mxaccess_failure_variant() {
+    // PROTOCOL_STATUS_CODE_MXACCESS_FAILURE: before ISSUE 2 this landed in
+    // Error::Command (unscrubbed, raw Display/Debug) — the red-first case.
+    assert_authenticate_user_scrubs_structured_reply(
+        "authenticate-user.echoed-credential-mxaccess-failure.reply.json",
+    )
+    .await;
+}
+
 #[tokio::test]
 async fn authenticate_user_maps_missing_payload_reply_to_malformed_reply() {
     // CLI-41: an OK reply with neither a typed AuthenticateUser payload nor a
@@ -1548,15 +1636,35 @@ fn command_reply_fixture(file_name: &str) -> MxCommandReply {
         })
     });
 
+    // Honor the fixture's real protocol status (code + message) so a canned
+    // reply can drive the MXACCESS_FAILURE routing path, not just an OK
+    // envelope. Falls back to an OK envelope when the fixture omits it.
+    let protocol_status = fixture.get("protocolStatus").map_or_else(
+        || ok_status("command ok"),
+        |status| {
+            let code_name = status["code"].as_str().unwrap_or("PROTOCOL_STATUS_CODE_OK");
+            ProtocolStatus {
+                code: ProtocolStatusCode::from_str_name(code_name)
+                    .unwrap_or_else(|| panic!("unknown protocol status code {code_name}"))
+                    as i32,
+                message: status["message"].as_str().unwrap_or_default().to_owned(),
+            }
+        },
+    );
+
     MxCommandReply {
         session_id: fixture["sessionId"].as_str().unwrap_or_default().to_owned(),
         correlation_id: fixture["correlationId"]
             .as_str()
             .unwrap_or_default()
             .to_owned(),
-        protocol_status: Some(ok_status("command ok")),
+        protocol_status: Some(protocol_status),
         hresult: fixture["hresult"].as_i64().map(|hresult| hresult as i32),
         statuses,
+        diagnostic_message: fixture["diagnosticMessage"]
+            .as_str()
+            .unwrap_or_default()
+            .to_owned(),
         return_value,
         ..MxCommandReply::default()
     }

docs/ClientBehaviorFixtures.md

@@ -77,7 +77,8 @@ credential-redaction contracts for the credential-bearing helpers:
 
 | Fixture | Reply | Expected behavior |
 |---|---|---|
-| `authenticate-user.echoed-credential.reply.json` | OK envelope, negative `hresult`, and the caller's credential echoed into `protocolStatus.message`, `statuses[0].diagnosticText`, and `diagnosticMessage` | the surfaced error redacts the exact secret (never leaks the verbatim value) |
+| `authenticate-user.echoed-credential.reply.json` | OK envelope, negative `hresult`, and the caller's credential echoed into `protocolStatus.message`, `statuses[0].diagnosticText`, and `diagnosticMessage` | the surfaced error redacts the exact secret from **both** the rendered message and the structured reply accessors (never leaks the verbatim value) |
+| `authenticate-user.echoed-credential-mxaccess-failure.reply.json` | the same echo, but coded `PROTOCOL_STATUS_CODE_MXACCESS_FAILURE` | identical redaction; confirms every client routes the MXAccess-failure protocol code to its MXAccess error type and scrubs it |
 | `authenticate-user.missing-payload.reply.json` | OK envelope, no `AuthenticateUser` payload, no `return_value` | a typed malformed-reply error, never a proto3 default `0` and never an NRE |
 | `authenticate-user.return-value-only.reply.json` | OK envelope, `return_value.int32_value = 7`, no typed payload | the id resolves to `7` via the legacy `return_value` compatibility path |
 
@@ -91,13 +92,17 @@ The rules those fixtures lock in are:
   It never surfaces a proto3 default `0` and never throws a null-reference.
 - **Credential redaction (CLI-40).** The credential-bearing helpers
   (`AuthenticateUser`, `WriteSecured`/`WriteSecured2`) scrub the exact secret
-  values they were called with from any surfaced error text, replacing each
+  values they were called with from any surfaced error — both the rendered
-  occurrence with the client's redaction marker. This is defense-in-depth on top
+  message text **and** the structured reply the error still exposes (a
-  of the by-construction guarantee that exceptions carry reply-derived text, not
+  server-echoed credential lives in `protocolStatus.message` and
-  the request. The marker is `<redacted>` in the Go, Rust, and Java clients and
+  `statuses[].diagnosticText`, which the error's raw-reply accessor would
-  `[redacted]` in the Python client and the .NET CLI; the assertion each suite
+  otherwise re-expose to a logger dumping structured fields). The redacted error
-  makes is that the surfaced message no longer contains the credential and does
+  therefore carries a scrubbed clone of the reply. This is defense-in-depth on
-  contain the client's marker.
+  top of the by-construction guarantee that exceptions carry reply-derived text,
+  not the request. The marker is `<redacted>` in the Go, Rust, and Java clients
+  and `[redacted]` in the Python client and the .NET CLI; each suite asserts that
+  neither the surfaced message nor the exposed reply still contains the
+  credential, and that the message contains the client's marker.
 
 ## Event Streams
 

docs/ClientLibrariesDesign.md

@@ -138,10 +138,16 @@ secured payloads route through each client's secret-redaction seam so they never
 reach logs, exception text, or `ToString`/`Debug`/`Display` — the value is carried
 only on the wire. In addition to that by-construction guarantee (exceptions carry
 reply-derived text, not the request), every client scrubs the **exact** secret
-values it was called with from any surfaced error text as defense-in-depth, so a
+values it was called with from any surfaced error as defense-in-depth, so a
 gateway or MXAccess diagnostic that echoes a credential back cannot leak it
-(CLI-40). Each client's test suite asserts a distinctive credential is absent
+(CLI-40). The scrub covers **both** the rendered message and the structured reply
-from any surfaced error and that the redaction marker is present.
+the error still exposes (`protocolStatus.message`, `statuses[].diagnosticText`,
+`diagnosticMessage`): the redacted error carries a scrubbed clone of the reply so
+a logger dumping the exception's structured fields cannot reintroduce the leak.
+This holds regardless of whether the reply is coded `OK` (with a failing HRESULT)
+or `MXACCESS_FAILURE` — every client routes both to its MXAccess error type. Each
+client's test suite asserts the distinctive credential is absent from both the
+surfaced message and the exposed reply, and that the redaction marker is present.
 
 Shipped in all five clients (.NET / Go / Rust / Python / Java).