fix(CLI-37,CLI-38): make status/HRESULT reply validation conformant across all five clients

One cross-client conformance pass; also closes first-cycle CLI-08.

CLI-37: an MxStatusProxy entry is a failure iff `category !=
MX_STATUS_CATEGORY_OK`. The proto contract has always said so — `success` is
the raw 16-bit COM member carried verbatim for diagnostics, not a boolean — but
four clients branched on `success` alone and .NET required both, so the same
gateway reply produced opposite verdicts per language. An absent entry stays
success; a present entry with an UNSPECIFIED category is a failure, because the
worker always maps a category and an unmapped one is not proven OK.

CLI-38: a reply fails on HRESULT iff `hresult` is present and negative, so
positive COM success codes such as S_FALSE (1) pass. .NET/Go/Java used `!= 0`,
which errored on a parity-preserving S_FALSE that Python and Rust accepted.
This makes the existing ClientLibrariesDesign.md claim true rather than
rewriting the doc to describe the divergence.

Four shared fixtures pin both rules cross-client, and each language suite also
carries a table test for the two edges a fixture cannot express (absent entry,
UNSPECIFIED category). A Java test fake that built a status with a bare
`setSuccess(1)` and no category is fixed — under the category rule that reply
was never a success.

archreview/2026-07-12/remediation/00-tracking.md

@@ -112,8 +112,8 @@ Full design + implementation for each row lives in the linked domain doc under i
 |---|---|:-:|:-:|---|---|---|
 | CLI-35 | Medium | P0 | S | GWC-25 (coord) | Done | Python CLI `stream-events` crashes on a ReplayGap |
 | CLI-36 | Medium | P0 | S | GWC-25 (coord) | Done | Go CLI `stream-events` silently destroys the ReplayGap signal |
-| CLI-37 | Medium | P1 | M | CLI-38 (co-land) | Not started | Status-array validation must branch on `category` per the proto contract (4-vs-1 divergence) |
+| CLI-37 | Medium | P1 | M | CLI-38 (co-land) | Done | Status-array validation must branch on `category` per the proto contract (4-vs-1 divergence) |
-| CLI-38 | Medium | P1 | S | — | Not started | Align .NET/Go/Java on `hresult < 0` — lands old CLI-08, cures design-doc drift |
+| CLI-38 | Medium | P1 | S | — | Done | Align .NET/Go/Java on `hresult < 0` — lands old CLI-08, cures design-doc drift |
 | CLI-39 | Medium | P1 | S | CLI-35..38, CLI-45 (land last) | Not started | Bump client versions off published 0.1.2 (converge on 0.2.0); registry-collision guard in pack-clients.ps1 |
 | CLI-40 | Low | — | M | — | Not started | Port the exact-secret credential scrub to Rust/Java/.NET |
 | CLI-41 | Low | — | M | — | Not started | Uniform malformed-reply contract for AuthenticateUser/ArchestrAUserToId/AddBufferedItem |
@@ -149,7 +149,7 @@ Sequence these together rather than piecemeal — several are one change set spa
 ## Old-tracker actions ([`../../remediation/00-tracking.md`](../../remediation/00-tracking.md))
 
 - Close **CLI-24** and **CLI-34** as `Done` (incidentally fixed; evidence in [../50-clients.md](../50-clients.md)).
-- When CLI-38 lands, close old **CLI-08** with a pointer here.
+- ~~When CLI-38 lands, close old **CLI-08** with a pointer here.~~ Done 2026-08-07: CLI-38 landed and old CLI-08 is now `Done` in the first-cycle tracker, pointing at [CLI-38](50-clients.md#cli-38--align-netgojava-on-hresult--0-lands-prior-cli-08-cures-the-doc-drift---medium--p1).
 - When WRK-26 lands, its doc section also discharges the WorkerFrameProtocol gap; when TST-25 lands, revisit old **TST-05** (scheduled live smoke) and **TST-24** (client wire tests), which it unlocks.
 
 ## Change log
@@ -164,3 +164,4 @@ Sequence these together rather than piecemeal — several are one change set spa
 | 2026-08-07 | **TST-29 → `Done`:** migrated the Phase-5 (orphan-worker reattach) deferred-not-planned governance record and the settled Phase-4 Viewer-default decision from `oldtasks.md` into a new "Session-Resilience Epic Scope" entry in `docs/DesignDecisions.md`; repointed CLAUDE.md and `stillpending.md:7,165` from `oldtasks.md` to `docs/DesignDecisions.md` / `docs/plans/2026-06-15-session-resilience.md.tasks.json`; `git rm oldtasks.md`. The five untracked root docs-review artifacts (`MxAccessGateway-docs-{issues,fixed,final}.md`, `MxGatewayClient-docs-{issues,fixed}.md`) were absent from this worktree — delete from the main working tree separately. |
 | 2026-08-07 | **GWC-24 → `Done`** (branch `fix/gwc-24-staging-bound`). `WorkerClient._eventStaging` is now `Channel.CreateBounded` at `2 × EventChannelCapacity` (`Wait`, single reader/writer, no sync continuations); a rejected staging `TryWrite` faults the client `ProtocolViolation` with `QueueOverflow("worker-event-staging")` unless `IsTerminalState()` (shutdown stays a silent drop), so a consumer draining slower than its worker produces dies at a fixed ceiling instead of growing gateway memory. Queue-depth accounting moved from `EnqueueWorkerEventAsync` to `StageWorkerEvent`, so the single gauge reports staged + queued; the timed-write fault (`EventChannelFullModeTimeout` / `QueueOverflow("worker-events")`) is unchanged and still catches the full-stall case first. No new config key — total gateway-side buffering is `3 × MxGateway:Events:QueueCapacity`, derived; coordination with still-open old **GWC-21** (`EventChannelFullModeTimeout` configurability) remains open and was not blocked on. Docs same commit: `GatewayProcessDesign.md` (two overflow faults), `MxAccessWorkerInstanceDesign.md`, `GatewayConfiguration.md`, `Metrics.md`. Tests: `WorkerClientTests.StagingChannelOverflowFaultsWorkerWithoutWaitingForFullModeTimeout` and `.WorkerEventQueueDepthGaugeCountsStagedEvents`; `WorkerClientTests` 22/22 green, `NonWindows.slnx` builds with 0 warnings. |
 | 2026-08-07 | **ReplayGap end-to-end cluster (GWC-25 + CLI-35 + CLI-36) → `Done`** on `fix/gwc-25-replaygap-trio`. GWC-25: `SessionEventDistributor.RegisterWithReplay`'s empty-ring branch now reports `oldestAvailableSequence = _highestSequenceSeen + 1` when `gap == true` (still `0` when no gap), so the universal `oldest - 1` resume formula no longer wraps to `ulong.MaxValue` and dead-stream the subscriber; `docs/Sessions.md` documents the empty-ring value. CLI-35: the Python CLI renders a `ReplayGap` as a `{"replayGap": {...}}` row via a new `_event_row` helper instead of crashing in `MessageToDict`. CLI-36: the Go CLI branches on `result.IsReplayGap()` and prints the typed `REPLAY_GAP requested_after=<n> oldest_available=<n>` line / `replayGap` JSON row instead of formatting the library's cleared `Event`. `docs/CrossLanguageSmokeMatrix.md` gained a per-CLI gap-rendering table (one edit covering both client findings). Four new tests as designed (3 × `SessionEventDistributorTests`, `GatewayEndToEndReconnectReplayTests.ReconnectAfterFullAgeEvictionResumesWithSentinelFormula`) plus `test_stream_events_renders_replay_gap` (Python) and `TestRunStreamEventsPrintsReplayGap` (Go); all written red first and each reproducing its defect verbatim. **Deferred:** GWC-25's `ReplayGap.oldest_available_sequence` proto-comment amendment is **not** in this change — it is comment-only but triggers the full five-client regen fan-out, so it lands with the later codegen wave (alongside IPC-23's proto-comment edits) rather than forcing a regen for one sentence. Note for that wave: the fake-worker gateway e2e suite cannot run on the macOS worktree without `TMPDIR` shortened (macOS caps the Unix-domain-socket path backing .NET named pipes at 104 chars; `TMPDIR=/tmp dotnet test …` works and was used here). |
+| 2026-08-07 | **CLI-37 + CLI-38 -> `Done`** (branch `fix/cli-37-38-conformance`), one cross-client conformance commit; **closes old-tracker CLI-08**. Canonical rules landed everywhere: an `MxStatusProxy` entry fails iff `category != MX_STATUS_CATEGORY_OK` (`success` is the raw COM member, diagnostics only; absent entry = success, present entry with `UNSPECIFIED` = failure), and a reply fails on HRESULT iff `hresult` is present and `< 0` (so `S_FALSE = 1` passes). Edits: .NET `MxStatusProxyExtensions.IsSuccess` (drop the `Success != 0` conjunct) + `MxCommandReplyExtensions` (`!= 0` -> `< 0`); Go `StatusSucceeded` (category) + `errors.go` (`< 0`); Java `MxStatuses.succeeded` (category, Javadoc corrected) + `MxGatewayErrors` (`< 0`); Python `errors.py` (category); Rust `ensure_mxaccess_success` (category, doc comment corrected). Four shared fixtures added under `clients/proto/fixtures/behavior/command-replies/` (`write.status-category-{error-success-set,ok-success-zero}.reply.json`, `write.hresult-{s-false,e-fail}.reply.json`) + manifest + `docs/ClientBehaviorFixtures.md`; each of the five suites now runs all four fixture-driven, plus a per-language table test for the two edges fixtures cannot express (nil/null entry, `UNSPECIFIED` category). Docs same commit: `ClientLibrariesDesign.md` per-item rule sentence (its existing HRESULT `< 0` claim is now true), .NET/Go/Java README error sections. Also fixed a Java test fake that built a status with a bare `setSuccess(1)` and no category. Verification: dotnet build 0 warnings + 110 passed/1 skipped; `gofmt -l` clean, `go build ./...`, `go test ./...` all ok; `gradle test` BUILD SUCCESSFUL with **no** generated-file churn to revert this time (no `.proto` changed and `generateProto` stayed up to date); `python -m pytest` 155 passed/1 skipped; `cargo fmt` (no unrelated reformat), `cargo check`, `cargo test --workspace` 100 passed, `cargo clippy --all-targets -- -D warnings` clean. Gateway-side `ClientBehaviorFixtureTests` 8/8 re-run because the new fixtures are validated there. |

archreview/2026-07-12/remediation/50-clients.md

@@ -18,8 +18,8 @@ Operating constraints carried from prior work:
 |----|-----|------|-----|-----|--------|-------|
 | CLI-35 | Medium | P0 | S | — | Done | Python CLI `stream-events` crashes on a ReplayGap |
 | CLI-36 | Medium | P0 | S | — | Done | Go CLI `stream-events` silently destroys the ReplayGap signal |
-| CLI-37 | Medium | P1 | M | CLI-38 | Not started | Status-array validation must branch on `category` per the proto contract (4-vs-1 divergence) |
+| CLI-37 | Medium | P1 | M | CLI-38 | Done | Status-array validation must branch on `category` per the proto contract (4-vs-1 divergence) |
-| CLI-38 | Medium | P1 | S | — | Not started | Align .NET/Go/Java on `hresult < 0` — lands prior CLI-08 and cures the design-doc drift |
+| CLI-38 | Medium | P1 | S | — | Done | Align .NET/Go/Java on `hresult < 0` — lands prior CLI-08 and cures the design-doc drift |
 | CLI-39 | Medium | P1 | S | CLI-35..38, CLI-45 | Not started | Bump client versions off the already-published 0.1.2 before the next publish; add registry-collision guard |
 | CLI-40 | Low | — | M | — | Not started | Port the exact-secret credential scrub to Rust/Java/.NET |
 | CLI-41 | Low | — | M | — | Not started | Uniform malformed-reply contract for AuthenticateUser/ArchestrAUserToId/AddBufferedItem |

archreview/remediation/00-tracking.md

@@ -181,7 +181,7 @@ Full design + implementation for each row lives in the linked domain doc under i
 | CLI-05 | Medium | — | S | — | Not started | .NET session cannot be re-attached to an existing session id |
 | CLI-06 | Medium | — | S | — | Not started | .NET `DisposeAsync` blocks/throws on unreachable gateway |
 | CLI-07 | Medium | — | S | — | Not started | .NET retry budget self-defeats on `DeadlineExceeded` |
-| CLI-08 | Medium | — | S | CLI-03 | Not started | .NET/Go/Java treat any nonzero HRESULT as failure (should be `< 0`) |
+| CLI-08 | Medium | — | S | CLI-03 | Done | .NET/Go/Java treat any nonzero HRESULT as failure (should be `< 0`) — landed via 2026-07-12 [CLI-38](../2026-07-12/remediation/50-clients.md#cli-38--align-netgojava-on-hresult--0-lands-prior-cli-08-cures-the-doc-drift---medium--p1) |
 | CLI-09 | Medium | — | M | — | Not started | Go has no typed auth-error mapping (Unauthenticated vs PermissionDenied) |
 | CLI-10 | Medium | — | M | — | Not started | Go uses deprecated `grpc.DialContext` + `grpc.WithBlock()` |
 | CLI-11 | Medium | — | S | — | Not started | Go CLI cannot opt into strict TLS validation |

clients/dotnet/README.md

@@ -163,6 +163,12 @@ can keep the full `MxCommandReply`, HRESULT, and status array when MXAccess
 itself rejects a command. `MxAccessException.Reply` contains the raw generated
 reply.
 
+`EnsureMxAccessSuccess()` follows COM semantics: only a **negative** HRESULT is
+a failure, so positive success codes such as `S_FALSE` (1) pass. A status entry
+fails only when `Category` is not `MxStatusCategory.Ok` — `MxStatusProxy.Success`
+mirrors the raw COM member for diagnostics and never decides the verdict, which
+is why `IsSuccess()` branches on the category alone.
+
 ## Write Semantics And Common Pitfalls
 
 These are MXAccess parity behaviors that surprise new callers. The gateway

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

@@ -32,6 +32,57 @@ public sealed class MxCommandReplyExtensionsTests
         Assert.Contains("0x80040200", exception.Message);
     }
 
+    /// <summary>Verifies that a non-OK status category fails even when the raw success member is set.</summary>
+    [Fact]
+    public void EnsureMxAccessSuccess_WithNonOkCategoryAndSuccessSet_Throws()
+    {
+        MxCommandReply reply = ReadReplyFixture(
+            "write.status-category-error-success-set.reply.json");
+
+        reply.EnsureProtocolSuccess();
+        MxAccessException exception = Assert.Throws<MxAccessException>(
+            reply.EnsureMxAccessSuccess);
+
+        Assert.Equal(1, Assert.Single(exception.Statuses).Success);
+        Assert.Contains("CommunicationError", exception.Message, StringComparison.Ordinal);
+    }
+
+    /// <summary>Verifies that an Ok status category succeeds even when the raw success member is zero.</summary>
+    [Fact]
+    public void EnsureMxAccessSuccess_WithOkCategoryAndZeroSuccess_ReturnsReply()
+    {
+        MxCommandReply reply = ReadReplyFixture(
+            "write.status-category-ok-success-zero.reply.json");
+
+        Assert.Equal(0, Assert.Single(reply.Statuses).Success);
+        Assert.Same(reply, reply.EnsureProtocolSuccess());
+        Assert.Same(reply, reply.EnsureMxAccessSuccess());
+    }
+
+    /// <summary>Verifies that a positive HResult (S_FALSE) is a COM success code, not a failure.</summary>
+    [Fact]
+    public void EnsureMxAccessSuccess_WithPositiveHResult_ReturnsReply()
+    {
+        MxCommandReply reply = ReadReplyFixture("write.hresult-s-false.reply.json");
+
+        Assert.Equal(1, reply.Hresult);
+        Assert.Same(reply, reply.EnsureProtocolSuccess());
+        Assert.Same(reply, reply.EnsureMxAccessSuccess());
+    }
+
+    /// <summary>Verifies that a negative HResult fails even when every status entry is Ok.</summary>
+    [Fact]
+    public void EnsureMxAccessSuccess_WithNegativeHResult_Throws()
+    {
+        MxCommandReply reply = ReadReplyFixture("write.hresult-e-fail.reply.json");
+
+        reply.EnsureProtocolSuccess();
+        MxAccessException exception = Assert.Throws<MxAccessException>(
+            reply.EnsureMxAccessSuccess);
+
+        Assert.Equal(-2147467259, exception.HResultCode);
+    }
+
     /// <summary>Verifies that session-not-found protocol failures throw the correct gateway exception.</summary>
     [Fact]
     public void EnsureProtocolSuccess_WithSessionFailure_ThrowsSessionException()

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

@@ -19,9 +19,8 @@ public sealed class MxStatusProxyExtensionsTests
         {
             MxStatusProxy status = JsonParser.Default.Parse<MxStatusProxy>(
                 testCase.GetProperty("status").GetRawText());
-            int success = testCase.GetProperty("status").GetProperty("success").GetInt32();
 
-            Assert.Equal(success != 0 && status.Category is MxStatusCategory.Ok, status.IsSuccess());
+            Assert.Equal(status.Category is MxStatusCategory.Ok, status.IsSuccess());
             Assert.Equal(
                 testCase.GetProperty("status").GetProperty("rawCategory").GetInt32(),
                 status.RawCategory);
@@ -31,6 +30,22 @@ public sealed class MxStatusProxyExtensionsTests
         }
     }
 
+    /// <summary>Verifies that the raw success member never overrides the authoritative category.</summary>
+    [Theory]
+    [InlineData(MxStatusCategory.Ok, 0, true)]
+    [InlineData(MxStatusCategory.Ok, 1, true)]
+    [InlineData(MxStatusCategory.CommunicationError, 1, false)]
+    [InlineData(MxStatusCategory.Unspecified, 1, false)]
+    public void IsSuccess_BranchesOnCategoryOnly(
+        MxStatusCategory category,
+        int success,
+        bool expected)
+    {
+        MxStatusProxy status = new() { Category = category, Success = success };
+
+        Assert.Equal(expected, status.IsSuccess());
+    }
+
     private static string ReadFixture(string category, string fileName)
     {
         DirectoryInfo directory = new(AppContext.BaseDirectory);

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

@@ -23,7 +23,11 @@ public static class MxCommandReplyExtensions
         throw CreateProtocolException(reply, code);
     }
 
-    /// <summary>Validates that the reply indicates MXAccess success (no HResult or status failures), throwing MxAccessException if not.</summary>
+    /// <summary>
+    /// Validates that the reply indicates MXAccess success, throwing MxAccessException if not.
+    /// Following COM semantics, only a negative HResult is a failure — positive success codes
+    /// such as <c>S_FALSE</c> pass — and a status entry fails only when its category is not Ok.
+    /// </summary>
     /// <param name="reply">The command reply to check.</param>
     /// <returns>The same reply, for chaining.</returns>
     public static MxCommandReply EnsureMxAccessSuccess(this MxCommandReply reply)
@@ -31,7 +35,7 @@ public static class MxCommandReplyExtensions
         ArgumentNullException.ThrowIfNull(reply);
 
         bool mxAccessFailure = reply.ProtocolStatus?.Code is ProtocolStatusCode.MxaccessFailure;
-        bool hResultFailure = reply.HasHresult && reply.Hresult != 0;
+        bool hResultFailure = reply.HasHresult && reply.Hresult < 0;
         bool statusFailure = reply.Statuses.Any(status => !status.IsSuccess());
 
         if (!mxAccessFailure && !hResultFailure && !statusFailure)

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

@@ -5,15 +5,18 @@ namespace ZB.MOM.WW.MxGateway.Client;
 /// <summary>Extension methods for MxStatusProxy values.</summary>
 public static class MxStatusProxyExtensions
 {
-    /// <summary>Returns whether the status indicates success (success flag set and category is Ok).</summary>
+    /// <summary>
+    /// Returns whether the status indicates success, which the wire contract defines as
+    /// <see cref="MxStatusCategory.Ok"/>. The raw <c>Success</c> member is a verbatim COM
+    /// diagnostic, not a boolean, so it never participates in the verdict.
+    /// </summary>
     /// <param name="status">The status to check.</param>
     /// <returns><see langword="true"/> if the status indicates success; otherwise <see langword="false"/>.</returns>
     public static bool IsSuccess(this MxStatusProxy status)
     {
         ArgumentNullException.ThrowIfNull(status);
 
-        return status.Success != 0
+        return status.Category is MxStatusCategory.Ok;
-            && status.Category is MxStatusCategory.Ok;
     }
 
     /// <summary>Returns a formatted summary of the status for diagnostic output.</summary>

clients/go/README.md

@@ -94,6 +94,12 @@ goroutine cleanup. Raw protobuf messages remain available through the
 `errors.As` for `GatewayError`, `CommandError`, and `MxAccessError`; command
 errors preserve the raw reply.
 
+`EnsureMxAccessSuccess` follows COM semantics: only a **negative** HRESULT is a
+failure, so positive success codes such as `S_FALSE` (1) pass. `StatusSucceeded`
+judges each `MXSTATUS_PROXY` entry by its category — an entry fails when
+`Category` is not `MX_STATUS_CATEGORY_OK`, and the raw `Success` member is a
+diagnostic that never decides the verdict. A nil entry is success.
+
 ### Reconnect-replay gap
 
 Each `EventResult` carries exactly one of `Event`, `ReplayGap`, or `Err`. When

clients/go/mxgateway/conversion_test.go

@@ -65,7 +65,8 @@ func TestStatusConversionFixtures(t *testing.T) {
 			if err := protojson.Unmarshal(tc.Status, &status); err != nil {
 				t.Fatalf("parse status: %v", err)
 			}
-			if got, want := StatusSucceeded(&status), status.GetSuccess() != 0; got != want {
+			want := status.GetCategory() == pb.MxStatusCategory_MX_STATUS_CATEGORY_OK
+			if got := StatusSucceeded(&status); got != want {
 				t.Fatalf("StatusSucceeded() = %v, want %v", got, want)
 			}
 		})

clients/go/mxgateway/errors.go

@@ -180,11 +180,15 @@ func EnsureProtocolSuccess(op string, status *ProtocolStatus, reply *MxCommandRe
 
 // EnsureMxAccessSuccess returns a typed MxAccessError for failing HRESULTs or
 // MXSTATUS_PROXY entries.
+//
+// Following COM semantics, only a negative HRESULT is a failure — positive
+// success codes such as S_FALSE (1) pass. Status entries are judged by
+// StatusSucceeded, which branches on the authoritative category.
 func EnsureMxAccessSuccess(op string, reply *MxCommandReply) error {
 	if reply == nil {
 		return nil
 	}
-	if reply.Hresult != nil && reply.GetHresult() != 0 {
+	if reply.Hresult != nil && reply.GetHresult() < 0 {
 		return &MxAccessError{Reply: reply}
 	}
 	for _, status := range reply.GetStatuses() {

clients/go/mxgateway/protofixtures_test.go

@@ -48,6 +48,89 @@ func TestGeneratedGoldenFixturesParse(t *testing.T) {
 	}
 }
 
+// TestCommandReplyValidationFixtures locks the shared reply-validation rules to
+// the behavior fixtures: a status entry fails iff its category is not OK (the
+// raw success member is diagnostics only), and an HRESULT fails iff it is
+// present and negative (S_FALSE and other positive COM success codes pass).
+func TestCommandReplyValidationFixtures(t *testing.T) {
+	tests := []struct {
+		fixture     string
+		wantFailure bool
+	}{
+		{fixture: "register.ok.reply.json", wantFailure: false},
+		{fixture: "write.mxaccess-failure.reply.json", wantFailure: true},
+		{fixture: "write.status-category-error-success-set.reply.json", wantFailure: true},
+		{fixture: "write.status-category-ok-success-zero.reply.json", wantFailure: false},
+		{fixture: "write.hresult-s-false.reply.json", wantFailure: false},
+		{fixture: "write.hresult-e-fail.reply.json", wantFailure: true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.fixture, func(t *testing.T) {
+			data, err := os.ReadFile(filepath.Join(
+				"..", "..", "proto", "fixtures", "behavior", "command-replies", tt.fixture))
+			if err != nil {
+				t.Fatalf("read fixture: %v", err)
+			}
+
+			var reply pb.MxCommandReply
+			if err := protojson.Unmarshal(data, &reply); err != nil {
+				t.Fatalf("parse fixture: %v", err)
+			}
+
+			err = EnsureMxAccessSuccess("invoke", &reply)
+			if got := err != nil; got != tt.wantFailure {
+				t.Fatalf("EnsureMxAccessSuccess() failed = %v (err %v), want %v", got, err, tt.wantFailure)
+			}
+		})
+	}
+}
+
+// TestStatusSucceededBranchesOnCategory pins the per-entry rule directly,
+// including the two edges the fixtures cannot express: a nil entry is success
+// and a present entry with an unspecified category is a failure.
+func TestStatusSucceededBranchesOnCategory(t *testing.T) {
+	tests := []struct {
+		name   string
+		status *MxStatusProxy
+		want   bool
+	}{
+		{name: "nil entry", status: nil, want: true},
+		{
+			name: "ok category with zero success",
+			status: &pb.MxStatusProxy{
+				Success:  0,
+				Category: pb.MxStatusCategory_MX_STATUS_CATEGORY_OK,
+			},
+			want: true,
+		},
+		{
+			name: "error category with success set",
+			status: &pb.MxStatusProxy{
+				Success:  1,
+				Category: pb.MxStatusCategory_MX_STATUS_CATEGORY_COMMUNICATION_ERROR,
+			},
+			want: false,
+		},
+		{
+			name: "unspecified category with success set",
+			status: &pb.MxStatusProxy{
+				Success:  1,
+				Category: pb.MxStatusCategory_MX_STATUS_CATEGORY_UNSPECIFIED,
+			},
+			want: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := StatusSucceeded(tt.status); got != tt.want {
+				t.Fatalf("StatusSucceeded() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
 func TestOpenSessionFixtureProtocolVersions(t *testing.T) {
 	data, err := os.ReadFile(filepath.Join("..", "..", "proto", "fixtures", "golden", "open-session-reply.ok.json"))
 	if err != nil {

clients/go/mxgateway/status.go

@@ -1,6 +1,17 @@
 package mxgateway
 
+import (
+	pb "gitea.dohertylan.com/dohertj2/mxaccessgw/clients/go/internal/generated"
+)
+
 // StatusSucceeded reports whether an MXSTATUS_PROXY entry represents success.
+//
+// The wire contract makes Category authoritative: an entry succeeds only when
+// its category is MX_STATUS_CATEGORY_OK. The Success member mirrors the raw
+// 16-bit COM value verbatim for diagnostics and is not a boolean, so it takes
+// no part in the verdict. A nil entry is success (nothing was reported); a
+// present entry with an unspecified category is a failure, because the worker
+// always maps a category and an unmapped one is not proven OK.
 func StatusSucceeded(status *MxStatusProxy) bool {
-	return status == nil || status.GetSuccess() != 0
+	return status == nil || status.GetCategory() == pb.MxStatusCategory_MX_STATUS_CATEGORY_OK
 }

clients/java/README.md

@@ -139,7 +139,12 @@ commands, so you do not need to build raw `MxCommand` messages:
 
 All of them run the same MXAccess reply validation as the bulk helpers (protocol
 status plus HRESULT/`MxStatusProxy` check) via the shared `invoke` path, so an
-MXAccess COM-side failure surfaces as `MxAccessException`.
+MXAccess COM-side failure surfaces as `MxAccessException`. That validation
+follows COM semantics: only a **negative** HRESULT is a failure, so positive
+success codes such as `S_FALSE` (1) pass. `MxStatuses.succeeded` judges each
+entry by its category — an entry fails when its category is not
+`MX_STATUS_CATEGORY_OK`, and the raw `success` member is a diagnostic that never
+decides the verdict. A `null` entry is success.
 
 **Secret redaction.** Credentials passed to `authenticateUser` (and the
 credential-sensitive values passed to `writeSecured`/`writeSecured2`) travel

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

@@ -47,7 +47,9 @@ final class MxGatewayErrors {
         if (reply == null) {
             return;
         }
-        if (reply.hasHresult() && reply.getHresult() != 0) {
+        // COM semantics: only a negative HRESULT is a failure. Positive success
+        // codes such as S_FALSE (1) pass.
+        if (reply.hasHresult() && reply.getHresult() < 0) {
             throw new MxAccessException(operation, reply);
         }
         for (var status : reply.getStatusesList()) {

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

@@ -8,8 +8,11 @@ import mxaccess_gateway.v1.MxaccessGateway.MxStatusSource;
  * Helpers for inspecting {@link MxStatusProxy} values returned by the gateway.
  *
  * <p>An {@code MxStatusProxy} mirrors the MXAccess COM {@code MXSTATUS_PROXY}
- * struct. The success flag uses the MXAccess convention where any non-zero
+ * struct. Per the wire contract, {@code category} is the authoritative verdict:
- * value indicates success.
+ * an entry succeeds only when its category is
+ * {@code MX_STATUS_CATEGORY_OK}. The {@code success} member carries the raw
+ * 16-bit COM value verbatim for diagnostics and is not a boolean, so it never
+ * decides success or failure.
  */
 public final class MxStatuses {
     private MxStatuses() {
@@ -18,12 +21,17 @@ public final class MxStatuses {
     /**
      * Returns whether the supplied status proxy reports success.
      *
+     * <p>A {@code null} status is success because nothing was reported. A
+     * present entry whose category is {@code MX_STATUS_CATEGORY_UNSPECIFIED}
+     * is a failure: the worker always maps a category, so an unmapped one is
+     * not proven OK.
+     *
      * @param status the status proxy, may be {@code null}
-     * @return {@code true} if {@code status} is {@code null} or its success
+     * @return {@code true} if {@code status} is {@code null} or its category is
-     *         flag is non-zero, {@code false} otherwise
+     *         {@code MX_STATUS_CATEGORY_OK}, {@code false} otherwise
      */
     public static boolean succeeded(MxStatusProxy status) {
-        return status == null || status.getSuccess() != 0;
+        return status == null || status.getCategory() == MxStatusCategory.MX_STATUS_CATEGORY_OK;
     }
 
     /**
@@ -44,9 +52,11 @@ public final class MxStatuses {
      */
     public record MxStatusView(MxStatusProxy raw) {
         /**
-         * Returns the raw success flag (non-zero indicates success).
+         * Returns the raw {@code success} member exactly as MXAccess reported
+         * it. This is a diagnostic value, not a verdict — use
+         * {@link MxStatuses#succeeded(MxStatusProxy)} to decide success.
          *
-         * @return the success flag value
+         * @return the raw success member
          */
         public int success() {
             return raw.getSuccess();

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

@@ -701,14 +701,17 @@ final class MxGatewayClientSessionTests {
                         .setSessionId(request.getSessionId())
                         .setKind(request.getCommand().getKind())
                         .setProtocolStatus(ok());
+                // `category` is the authoritative success indicator, so the fake
+                // must set it — a bare non-zero `success` is not a success.
+                var okStatus = mxaccess_gateway.v1.MxaccessGateway.MxStatusProxy.newBuilder()
+                        .setSuccess(1)
+                        .setCategory(mxaccess_gateway.v1.MxaccessGateway.MxStatusCategory.MX_STATUS_CATEGORY_OK);
                 if (request.getCommand().getKind() == MxCommandKind.MX_COMMAND_KIND_SUSPEND) {
                     reply.setSuspend(mxaccess_gateway.v1.MxaccessGateway.SuspendReply.newBuilder()
-                            .setStatus(mxaccess_gateway.v1.MxaccessGateway.MxStatusProxy.newBuilder()
+                            .setStatus(okStatus));
-                                    .setSuccess(1)));
                 } else if (request.getCommand().getKind() == MxCommandKind.MX_COMMAND_KIND_ACTIVATE) {
                     reply.setActivate(mxaccess_gateway.v1.MxaccessGateway.ActivateReply.newBuilder()
-                            .setStatus(mxaccess_gateway.v1.MxaccessGateway.MxStatusProxy.newBuilder()
+                            .setStatus(okStatus));
-                                    .setSuccess(1)));
                 }
                 responseObserver.onNext(reply.build());
                 responseObserver.onCompleted();

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

@@ -4,6 +4,7 @@ import static org.junit.jupiter.api.Assertions.assertArrayEquals;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import com.google.gson.JsonArray;
@@ -20,6 +21,8 @@ import mxaccess_gateway.v1.MxaccessGateway.MxStatusProxy;
 import mxaccess_gateway.v1.MxaccessGateway.MxValue;
 import mxaccess_gateway.v1.MxaccessGateway.ProtocolStatusCode;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
 
 final class MxGatewayFixtureTests {
     @Test
@@ -89,6 +92,50 @@ final class MxGatewayFixtureTests {
         throw new AssertionError("expected MxAccessException");
     }
 
+    @ParameterizedTest
+    @CsvSource({
+        "register.ok.reply.json,false",
+        "write.status-category-error-success-set.reply.json,true",
+        "write.status-category-ok-success-zero.reply.json,false",
+        "write.hresult-s-false.reply.json,false",
+        "write.hresult-e-fail.reply.json,true",
+    })
+    void replyValidationFixturesBranchOnCategoryAndNegativeHresult(String fixture, boolean expectFailure)
+            throws Exception {
+        MxCommandReply.Builder builder = MxCommandReply.newBuilder();
+        JsonFormat.parser().merge(
+                Files.readString(fixtureRoot().resolve("command-replies/" + fixture)),
+                builder);
+        MxCommandReply reply = builder.build();
+
+        if (expectFailure) {
+            assertThrows(MxAccessException.class, () -> MxGatewayErrors.ensureMxAccessSuccess("write", reply));
+        } else {
+            MxGatewayErrors.ensureMxAccessSuccess("write", reply);
+        }
+    }
+
+    @ParameterizedTest
+    @CsvSource({
+        "MX_STATUS_CATEGORY_OK,0,true",
+        "MX_STATUS_CATEGORY_OK,1,true",
+        "MX_STATUS_CATEGORY_COMMUNICATION_ERROR,1,false",
+        "MX_STATUS_CATEGORY_UNSPECIFIED,1,false",
+    })
+    void statusEntryVerdictIgnoresTheRawSuccessMember(String category, int success, boolean expectSucceeded) {
+        MxStatusProxy status = MxStatusProxy.newBuilder()
+                .setCategory(MxStatusCategory.valueOf(category))
+                .setSuccess(success)
+                .build();
+
+        assertEquals(expectSucceeded, MxStatuses.succeeded(status));
+    }
+
+    @Test
+    void absentStatusEntryIsSuccess() {
+        assertTrue(MxStatuses.succeeded(null));
+    }
+
     @Test
     void grpcAuthErrorsAreClassifiedAndRedacted() {
         RuntimeException authError = MxGatewayErrors.fromGrpc(

clients/proto/fixtures/behavior/command-replies/write.hresult-e-fail.reply.json

@@ -0,0 +1,29 @@
+{
+  "sessionId": "session-fixture",
+  "correlationId": "gateway-correlation-write-e-fail",
+  "kind": "MX_COMMAND_KIND_WRITE",
+  "protocolStatus": {
+    "code": "PROTOCOL_STATUS_CODE_OK",
+    "message": "Write reached MXAccess."
+  },
+  "hresult": -2147467259,
+  "returnValue": {
+    "dataType": "MX_DATA_TYPE_NO_DATA",
+    "variantType": "VT_EMPTY",
+    "isNull": true,
+    "rawDiagnostic": "MXAccess returned no value for the failed write.",
+    "rawDataType": 2
+  },
+  "statuses": [
+    {
+      "success": 1,
+      "category": "MX_STATUS_CATEGORY_OK",
+      "detectedBy": "MX_STATUS_SOURCE_RESPONDING_LMX",
+      "detail": 0,
+      "rawCategory": 0,
+      "rawDetectedBy": 3,
+      "diagnosticText": "OK"
+    }
+  ],
+  "diagnosticMessage": "COM semantics: a negative HRESULT (E_FAIL, 0x80004005) is a failure even when every status entry is OK."
+}

clients/proto/fixtures/behavior/command-replies/write.hresult-s-false.reply.json

@@ -0,0 +1,29 @@
+{
+  "sessionId": "session-fixture",
+  "correlationId": "gateway-correlation-write-s-false",
+  "kind": "MX_COMMAND_KIND_WRITE",
+  "protocolStatus": {
+    "code": "PROTOCOL_STATUS_CODE_OK",
+    "message": "Write completed with S_FALSE."
+  },
+  "hresult": 1,
+  "returnValue": {
+    "dataType": "MX_DATA_TYPE_NO_DATA",
+    "variantType": "VT_EMPTY",
+    "isNull": true,
+    "rawDiagnostic": "MXAccess returned no value for the write.",
+    "rawDataType": 2
+  },
+  "statuses": [
+    {
+      "success": 1,
+      "category": "MX_STATUS_CATEGORY_OK",
+      "detectedBy": "MX_STATUS_SOURCE_RESPONDING_LMX",
+      "detail": 0,
+      "rawCategory": 0,
+      "rawDetectedBy": 3,
+      "diagnosticText": "OK"
+    }
+  ],
+  "diagnosticMessage": "COM semantics: a positive HRESULT such as S_FALSE (1) is a success code, not a failure."
+}

clients/proto/fixtures/behavior/command-replies/write.status-category-error-success-set.reply.json

@@ -0,0 +1,29 @@
+{
+  "sessionId": "session-fixture",
+  "correlationId": "gateway-correlation-write-category-error",
+  "kind": "MX_COMMAND_KIND_WRITE",
+  "protocolStatus": {
+    "code": "PROTOCOL_STATUS_CODE_OK",
+    "message": "Write reached MXAccess."
+  },
+  "hresult": 0,
+  "returnValue": {
+    "dataType": "MX_DATA_TYPE_NO_DATA",
+    "variantType": "VT_EMPTY",
+    "isNull": true,
+    "rawDiagnostic": "MXAccess returned no value for the write.",
+    "rawDataType": 2
+  },
+  "statuses": [
+    {
+      "success": 1,
+      "category": "MX_STATUS_CATEGORY_COMMUNICATION_ERROR",
+      "detectedBy": "MX_STATUS_SOURCE_RESPONDING_LMX",
+      "detail": 77,
+      "rawCategory": 5,
+      "rawDetectedBy": 3,
+      "diagnosticText": "Responding LMX lost communication mid-write."
+    }
+  ],
+  "diagnosticMessage": "Category is authoritative: a non-OK category is a failure even when the raw success member is non-zero."
+}

clients/proto/fixtures/behavior/command-replies/write.status-category-ok-success-zero.reply.json

@@ -0,0 +1,29 @@
+{
+  "sessionId": "session-fixture",
+  "correlationId": "gateway-correlation-write-category-ok",
+  "kind": "MX_COMMAND_KIND_WRITE",
+  "protocolStatus": {
+    "code": "PROTOCOL_STATUS_CODE_OK",
+    "message": "Write completed."
+  },
+  "hresult": 0,
+  "returnValue": {
+    "dataType": "MX_DATA_TYPE_NO_DATA",
+    "variantType": "VT_EMPTY",
+    "isNull": true,
+    "rawDiagnostic": "MXAccess returned no value for the write.",
+    "rawDataType": 2
+  },
+  "statuses": [
+    {
+      "success": 0,
+      "category": "MX_STATUS_CATEGORY_OK",
+      "detectedBy": "MX_STATUS_SOURCE_RESPONDING_LMX",
+      "detail": 0,
+      "rawCategory": 0,
+      "rawDetectedBy": 3,
+      "diagnosticText": "OK, reported with a zero raw success member."
+    }
+  ],
+  "diagnosticMessage": "Category is authoritative: MX_STATUS_CATEGORY_OK is success even when the raw success member is zero."
+}

clients/proto/fixtures/behavior/manifest.json

@@ -20,6 +20,34 @@
       "path": "command-replies/write.mxaccess-failure.reply.json",
       "expectation": "MXAccess failures are data-bearing replies with HRESULT and status details, not transport failures."
     },
+    {
+      "id": "command-reply.write.status-category-error-success-set",
+      "category": "command_replies",
+      "messageType": "mxaccess_gateway.v1.MxCommandReply",
+      "path": "command-replies/write.status-category-error-success-set.reply.json",
+      "expectation": "A status entry fails when its category is not MX_STATUS_CATEGORY_OK, even though the raw success member is non-zero."
+    },
+    {
+      "id": "command-reply.write.status-category-ok-success-zero",
+      "category": "command_replies",
+      "messageType": "mxaccess_gateway.v1.MxCommandReply",
+      "path": "command-replies/write.status-category-ok-success-zero.reply.json",
+      "expectation": "A status entry succeeds when its category is MX_STATUS_CATEGORY_OK, even though the raw success member is zero."
+    },
+    {
+      "id": "command-reply.write.hresult-s-false",
+      "category": "command_replies",
+      "messageType": "mxaccess_gateway.v1.MxCommandReply",
+      "path": "command-replies/write.hresult-s-false.reply.json",
+      "expectation": "A positive HRESULT such as S_FALSE (1) is a COM success code and does not fail the reply."
+    },
+    {
+      "id": "command-reply.write.hresult-e-fail",
+      "category": "command_replies",
+      "messageType": "mxaccess_gateway.v1.MxCommandReply",
+      "path": "command-replies/write.hresult-e-fail.reply.json",
+      "expectation": "A negative HRESULT fails the reply even when every status entry reports MX_STATUS_CATEGORY_OK."
+    },
     {
       "id": "event-stream.session-ordered",
       "category": "event_streams",

clients/python/src/zb_mom_ww_mxgateway/errors.py

@@ -137,8 +137,10 @@ def ensure_mxaccess_success(operation: str, reply: pb.MxCommandReply) -> pb.MxCo
             raw_reply=reply,
         )
 
+    # `category` is the authoritative verdict per the wire contract; `success`
+    # is the raw COM member carried verbatim for diagnostics only.
     for mx_status in reply.statuses:
-        if mx_status.success == 0:
+        if mx_status.category != pb.MX_STATUS_CATEGORY_OK:
             raise MxAccessError(
                 _mxaccess_message(operation, reply),
                 protocol_status=status,

clients/python/tests/test_errors.py

@@ -32,6 +32,55 @@ def test_write_failure_fixture_preserves_raw_reply() -> None:
     assert len(captured.value.raw_reply.statuses) == 2
 
 
+@pytest.mark.parametrize(
+    ("fixture", "expect_failure"),
+    [
+        ("command-replies/register.ok.reply.json", False),
+        ("command-replies/write.status-category-error-success-set.reply.json", True),
+        ("command-replies/write.status-category-ok-success-zero.reply.json", False),
+        ("command-replies/write.hresult-s-false.reply.json", False),
+        ("command-replies/write.hresult-e-fail.reply.json", True),
+    ],
+)
+def test_reply_validation_fixtures_branch_on_category_and_negative_hresult(
+    fixture: str,
+    expect_failure: bool,
+) -> None:
+    reply = _load_reply(fixture)
+
+    if expect_failure:
+        with pytest.raises(MxAccessError):
+            ensure_mxaccess_success("write", reply)
+    else:
+        assert ensure_mxaccess_success("write", reply) is reply
+
+
+@pytest.mark.parametrize(
+    ("category", "success", "expect_failure"),
+    [
+        (pb.MX_STATUS_CATEGORY_OK, 0, False),
+        (pb.MX_STATUS_CATEGORY_OK, 1, False),
+        (pb.MX_STATUS_CATEGORY_COMMUNICATION_ERROR, 1, True),
+        (pb.MX_STATUS_CATEGORY_UNSPECIFIED, 1, True),
+    ],
+)
+def test_status_entry_verdict_ignores_the_raw_success_member(
+    category: int,
+    success: int,
+    expect_failure: bool,
+) -> None:
+    reply = pb.MxCommandReply(
+        protocol_status=pb.ProtocolStatus(code=pb.PROTOCOL_STATUS_CODE_OK),
+        statuses=[pb.MxStatusProxy(success=success, category=category)],
+    )
+
+    if expect_failure:
+        with pytest.raises(MxAccessError):
+            ensure_mxaccess_success("write", reply)
+    else:
+        assert ensure_mxaccess_success("write", reply) is reply
+
+
 def test_session_status_maps_to_session_error() -> None:
     status = pb.ProtocolStatus(
         code=pb.PROTOCOL_STATUS_CODE_SESSION_NOT_FOUND,

clients/rust/src/error.rs

@@ -308,10 +308,12 @@ pub fn ensure_command_success(reply: MxCommandReply) -> Result<MxCommandReply, E
 /// This is the second reply check applied to the typed command path, after
 /// [`ensure_command_success`] confirms the protocol envelope is `Ok`. It
 /// enforces MXAccess parity: a reply can carry an `Ok` protocol envelope while
-/// MXAccess itself rejected the operation. Following COM semantics (and the
+/// MXAccess itself rejected the operation. Following COM semantics, only a
-/// Python client), only a **negative** `hresult` is a failure — positive codes
+/// **negative** `hresult` is a failure — positive codes such as `S_FALSE = 1`
-/// such as `S_FALSE = 1` are success. A `MXSTATUS_PROXY` entry is treated as a
+/// are success. A `MXSTATUS_PROXY` entry is treated as a failure when its
-/// failure when its `success` member is `0`.
+/// `category` is not [`MxStatusCategory::Ok`]; the `success` member mirrors the
+/// raw COM value verbatim for diagnostics and never enters the verdict, so an
+/// entry with an unspecified category fails even when `success` is non-zero.
 ///
 /// Per-item bulk failures are reported inside each result entry
 /// (`was_successful = false`) rather than in the top-level `hresult`/`statuses`
@@ -320,10 +322,14 @@ pub fn ensure_command_success(reply: MxCommandReply) -> Result<MxCommandReply, E
 /// # Errors
 ///
 /// Returns [`Error::MxAccess`] when `reply.hresult` is negative or any
-/// `reply.statuses` entry reports a non-success `success` member.
+/// `reply.statuses` entry reports a category other than
+/// [`MxStatusCategory::Ok`].
 pub fn ensure_mxaccess_success(reply: MxCommandReply) -> Result<MxCommandReply, Error> {
     let hresult_failure = reply.hresult.is_some_and(|hresult| hresult < 0);
-    let status_failure = reply.statuses.iter().any(|status| status.success == 0);
+    let status_failure = reply
+        .statuses
+        .iter()
+        .any(|status| status.category != MxStatusCategory::Ok as i32);
 
     if hresult_failure || status_failure {
         Err(Box::new(MxAccessError::new(reply)).into())
@@ -412,8 +418,10 @@ mod tests {
         let mut reply = ok_reply();
         // Positive hresult (e.g. S_FALSE = 1) is a success, not a failure.
         reply.hresult = Some(1);
+        // A zero `success` member with an OK category is still a success: the
+        // category is authoritative and `success` is diagnostics only.
         reply.statuses = vec![MxStatusProxy {
-            success: 1,
+            success: 0,
             category: MxStatusCategory::Ok as i32,
             ..MxStatusProxy::default()
         }];
@@ -424,8 +432,9 @@ mod tests {
     #[test]
     fn ensure_mxaccess_success_flags_failing_status_entry() {
         let mut reply = ok_reply();
+        // A non-OK category fails even though the raw `success` member is set.
         reply.statuses = vec![MxStatusProxy {
-            success: 0,
+            success: 1,
             category: MxStatusCategory::CommunicationError as i32,
             detail: 42,
             diagnostic_text: "write rejected for mxgw_visible_secret".to_owned(),

clients/rust/src/value.rs

@@ -282,7 +282,11 @@ impl MxStatus {
         &self.raw
     }
 
-    /// `MXSTATUS_PROXY.Success` flag (0 = error, non-zero = good/warning).
+    /// Raw `MXSTATUS_PROXY.Success` member, carried verbatim from COM.
+    ///
+    /// This is a diagnostic value, not a verdict: the wire contract makes
+    /// [`Self::category`] authoritative, and `ensure_mxaccess_success` branches
+    /// on the category alone.
     pub fn success(&self) -> i32 {
         self.raw.success
     }

clients/rust/tests/client_behavior.rs

@@ -14,6 +14,7 @@ use tokio::sync::{mpsc, Mutex};
 use tokio_stream::wrappers::{ReceiverStream, TcpListenerStream};
 use tonic::transport::Server;
 use tonic::{Request, Response, Status};
+use zb_mom_ww_mxgateway_client::error::ensure_mxaccess_success;
 use zb_mom_ww_mxgateway_client::generated::mxaccess_gateway::v1::mx_access_gateway_server::{
     MxAccessGateway, MxAccessGatewayServer,
 };
@@ -337,6 +338,57 @@ fn authentication_and_authorization_statuses_are_distinct_and_redacted() {
     assert!(!auth.to_string().contains("visible_secret"));
 }
 
+#[test]
+fn command_reply_validation_fixtures_branch_on_category_and_negative_hresult() {
+    // The shared behavior fixtures pin both reply-validation rules: a status
+    // entry fails iff its category is not OK (the raw `success` member is
+    // diagnostics only) and an HRESULT fails iff it is present and negative.
+    for (fixture, expect_failure) in [
+        ("register.ok.reply.json", false),
+        ("write.status-category-error-success-set.reply.json", true),
+        ("write.status-category-ok-success-zero.reply.json", false),
+        ("write.hresult-s-false.reply.json", false),
+        ("write.hresult-e-fail.reply.json", true),
+    ] {
+        let reply = command_reply_fixture(fixture);
+        let result = ensure_mxaccess_success(reply);
+
+        assert_eq!(
+            result.is_err(),
+            expect_failure,
+            "fixture {fixture} expected failure = {expect_failure}, got {result:?}"
+        );
+    }
+}
+
+#[test]
+fn status_entry_verdict_ignores_the_raw_success_member() {
+    // Edges the fixtures cannot express: an OK category always passes and an
+    // unspecified category always fails, whatever `success` carries.
+    for (category, success, expect_failure) in [
+        (MxStatusCategory::Ok, 0, false),
+        (MxStatusCategory::Ok, 1, false),
+        (MxStatusCategory::CommunicationError, 1, true),
+        (MxStatusCategory::Unspecified, 1, true),
+    ] {
+        let reply = MxCommandReply {
+            protocol_status: Some(ok_status("command ok")),
+            statuses: vec![MxStatusProxy {
+                success,
+                category: category as i32,
+                ..MxStatusProxy::default()
+            }],
+            ..MxCommandReply::default()
+        };
+
+        assert_eq!(
+            ensure_mxaccess_success(reply).is_err(),
+            expect_failure,
+            "category {category:?} with success {success} expected failure = {expect_failure}"
+        );
+    }
+}
+
 #[test]
 fn command_error_display_keeps_raw_reply_accessible() {
     let reply = mxaccess_failure_reply();
@@ -1358,6 +1410,52 @@ fn event(sequence: u64) -> MxEvent {
     }
 }
 
+/// Load a shared command-reply fixture into an [`MxCommandReply`].
+///
+/// The fixtures are protobuf JSON, which prost cannot parse directly, so this
+/// reads the fields the reply-validation rules actually consume (`hresult` and
+/// the status `success`/`category` pair) and rebuilds the message. Enum names
+/// resolve through the generated `from_str_name`, so a fixture naming a
+/// category the contract does not define fails the test rather than silently
+/// degrading to `Unspecified`.
+fn command_reply_fixture(file_name: &str) -> MxCommandReply {
+    let fixture = behavior_fixture(&format!("command-replies/{file_name}"));
+
+    let statuses = fixture["statuses"]
+        .as_array()
+        .map(Vec::as_slice)
+        .unwrap_or_default()
+        .iter()
+        .map(|status| {
+            let category_name = status["category"].as_str().unwrap();
+            MxStatusProxy {
+                success: status["success"].as_i64().unwrap() as i32,
+                category: MxStatusCategory::from_str_name(category_name)
+                    .unwrap_or_else(|| panic!("unknown status category {category_name}"))
+                    as i32,
+                detail: status["detail"].as_i64().unwrap_or_default() as i32,
+                diagnostic_text: status["diagnosticText"]
+                    .as_str()
+                    .unwrap_or_default()
+                    .to_owned(),
+                ..MxStatusProxy::default()
+            }
+        })
+        .collect();
+
+    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")),
+        hresult: fixture["hresult"].as_i64().map(|hresult| hresult as i32),
+        statuses,
+        ..MxCommandReply::default()
+    }
+}
+
 fn behavior_fixture(path: &str) -> Value {
     let path = std::path::Path::new(env!("CARGO_MANIFEST_DIR"))
         .join("../proto/fixtures/behavior")

docs/ClientBehaviorFixtures.md

@@ -44,6 +44,32 @@ MXAccess failures remain command replies when the gateway reached the worker and
 the worker captured HRESULT or `MXSTATUS_PROXY` details. Client wrappers should
 map those replies to rich command errors without discarding the raw reply.
 
+### Reply Validation Conformance
+
+Four command reply fixtures pin the two reply-validation rules every client
+applies, because both rules have edges where a naive reading disagrees with the
+wire contract:
+
+| Fixture | Reply | Expected verdict |
+|---|---|---|
+| `write.status-category-error-success-set.reply.json` | one status with `success = 1`, `category = MX_STATUS_CATEGORY_COMMUNICATION_ERROR` | failure |
+| `write.status-category-ok-success-zero.reply.json` | one status with `success = 0`, `category = MX_STATUS_CATEGORY_OK` | success |
+| `write.hresult-s-false.reply.json` | `hresult = 1` (`S_FALSE`), statuses OK | success |
+| `write.hresult-e-fail.reply.json` | `hresult = -2147467259` (`E_FAIL`), statuses OK | failure |
+
+The rules those fixtures lock in are:
+
+- **Status entries.** An `MxStatusProxy` entry is a failure exactly when
+  `category != MX_STATUS_CATEGORY_OK`. `success` mirrors the raw 16-bit COM
+  member and is diagnostics only, so it never participates in the verdict — the
+  proto contract makes `category` authoritative. An absent entry is success
+  (nothing was reported); a present entry with
+  `MX_STATUS_CATEGORY_UNSPECIFIED` is a failure, because the worker always maps
+  a category and an unmapped one is not proven OK.
+- **HRESULT.** A reply fails on HRESULT exactly when `hresult` is present and
+  negative. Positive COM success codes such as `S_FALSE` pass, matching COM
+  semantics.
+
 ## Event Streams
 
 Event stream fixtures live in

docs/ClientLibrariesDesign.md

@@ -115,7 +115,14 @@ remove/write family, the parity-critical single-item helpers are:
 `Activate`, and `Unregister`. Each is a thin wrapper over the same raw-command
 machinery the bulk helpers use — it adds no wire surface — and runs the same
 MXAccess-level reply validation (HRESULT `< 0` + per-item `MxStatusProxy`) as the
-rest of the client. **MXAccess parity is preserved exactly**: e.g. `WriteSecured`
+rest of the client. The per-item rule is **`MxStatusProxy` failure iff
+`category != MX_STATUS_CATEGORY_OK`**; `success` is the raw COM member carried
+for diagnostics only and never decides the verdict, so an absent entry is
+success while a present entry with an unspecified category is a failure. The
+shared fixtures in `clients/proto/fixtures/behavior/command-replies/` pin both
+rules across all five clients (see
+[Client Behavior Fixtures](./ClientBehaviorFixtures.md)).
+**MXAccess parity is preserved exactly**: e.g. `WriteSecured`
 failing before a prior `AuthenticateUser` + `AdviseSupervisory` surfaces the
 native failure unchanged — the helper does not pre-validate or reorder it.