gRPC M0: probe (R0.4, live-verified) + system-param (R0.3) + shared handshake

Roadmap docs/plans/hcal-roadmap.md, milestone M0 (gRPC parity for the DONE
surface). Now unblocked for live verification by a reachable 2023 R2 server.

- R0.4 Probe over gRPC: new HistorianGrpcProbe calls History/Retrieval/Status
  GetInterfaceVersion (unauthenticated). ProbeAsync routes over gRPC when
  Transport==RemoteGrpc. LIVE-VERIFIED against a real 2023 R2 server — needs no
  credentials (runs before the auth loop), so it works despite the auth blocker.

- R0.3 System parameter over gRPC: new HistorianGrpcStatusClient calls
  StatusService.GetSystemParameter over the authenticated session; routed in the
  dialect. Built + unit-tested (request/response field mapping pinned).
  Live-verification pending an auth fix (see below).

- Extracted the proven auth handshake from HistorianGrpcReadOrchestrator into
  shared Grpc/HistorianGrpcHandshake (reused by read + status + future
  browse/metadata). Repointed the IL structural guardrail test to it.

- Diagnostics: round-failure now decodes the native server error + hex/ASCII
  preview (HistorianNativeHandshake.DescribeError). This surfaced the live auth
  blocker as SEC_E_LOGON_DENIED (0x8009030C) at NTLM round 1 — framing is correct,
  the credential did not validate. Probable cause: stale file password or NAM-domain
  NTLM restriction (Kerberos/RDP works, NTLM denied; no SPN path over the tunnel).

216 unit tests pass; live gRPC probe passes. Sanitization scan clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01B6mcaT2PjRFKcogzp9UkfC

docs/plans/hcal-roadmap.md

@@ -9,15 +9,39 @@ HCAL replacement, built on the **2023 R2 gRPC transport**. Derived from
 > protocol serializer/parser + golden-byte unit test + an env-gated live integration
 > test against the local Historian.
 
-## Progress (updated 2026-06-19)
+## Progress (updated 2026-06-21)
 
 - ✅ **R0.6 version gate** — `HistorianServerVersionGate` + `HistorianClientOptions.VerifyServerInterfaceVersion`;
   fail-closed on connect, wired into both WCF and gRPC paths. Supported versions are
-  evidence-based (Hist=11, Retr=4, Trx=2; Status reachability-only), captured from the
+  evidence-based (Hist=11/12, Retr=4, Trx=2; Status reachability-only), captured from the
-  live server. 10 unit tests.
+  live server. History 12 (2023 R2 gRPC) accepted alongside 11 (buffer-compatible).
 - ✅ **CW-1 capture pipeline** — `ProtocolCaptureSanitizer` + `ProtocolFixtureWriter` +
   `capture-tag-info` CLI command; produces sanitized `fixtures/protocol/<op>/` golden files.
   11 unit tests. First fixture: `get-tag-info/analog-*.json`.
+- ✅ **gRPC auth handshake (read chain)** — LIVE-VERIFIED 2026-06-21 against a real 2023 R2
+  server: `ReadRawAsync` over `RemoteGrpc` returns rows. Token loop routes to
+  `StorageService.ValidateClientCredential`. Shared handshake extracted to
+  `Grpc/HistorianGrpcHandshake` for reuse by the status/browse/metadata paths.
+- ✅ **R0.4 Probe over gRPC** — `Grpc/HistorianGrpcProbe` (History/Retrieval/Status
+  `GetInterfaceVersion`); `ProbeAsync` routes over gRPC when `Transport==RemoteGrpc`.
+  **LIVE-VERIFIED 2026-06-21** (no credentials required — runs before the auth loop).
+- 🟡 **R0.3 System parameter over gRPC** — `Grpc/HistorianGrpcStatusClient.GetSystemParameterAsync`
+  (`StatusService.GetSystemParameter`); routed in the dialect. Built + unit-tested
+  (request/response field mapping pinned). **Live-verification pending an auth fix** — see blocker.
+  Code path is the proven handshake + a single string-in/string-out RPC.
+
+> ⚠️ **Auth blocker (2026-06-21):** live gRPC ops needing a client handle (R0.1/R0.2/R0.3 and the
+> read chain) fail at NTLM **round 1**. The decoded server error is
+> `SEC_E_LOGON_DENIED` (0x8009030C) from `aahClientAccessPoint::CServerContext::ProcessClient…` —
+> round 0 (NEGOTIATE) succeeds, round 1 (the password-bearing AUTHENTICATE) is denied. The token
+> **framing is correct** (a framing fault would surface as `SEC_E_INVALID_TOKEN`); the server parsed
+> a valid NTLM message but the credential did not validate. The creds in the gitignored file are
+> byte-faithfully parsed (verified) and the domain user logs in via **RDP (Kerberos)**, so the
+> probable cause is one of: (a) the file password is **stale** vs the account, or (b) the NAM domain
+> **restricts NTLM** ("Network security: Restrict NTLM") — Kerberos/RDP works but NTLM is denied, and
+> over the SOCKS/SSH tunnel (host→127.0.0.1, no SPN) the client cannot use Kerberos. Probe (R0.4) is
+> unaffected (unauthenticated). Diagnostic: the round-failure exception now decodes the native error
+> + a hex/ASCII preview (`HistorianNativeHandshake.DescribeError`).
 
 > ⚠️ **Live-verification constraint:** the local Historian is **2020** (WCF, port 32568) — the
 > 2023 R2 gRPC endpoint (32565) is absent. M0's gRPC routing (R0.1–R0.4) can be built and

src/AVEVA.Historian.Client/Grpc/HistorianGrpcHandshake.cs

@@ -0,0 +1,74 @@
+using Google.Protobuf;
+using Grpc.Core;
+using AVEVA.Historian.Client.Wcf;
+using GrpcHistory = ArchestrA.Grpc.Contract.History;
+using GrpcStorage = ArchestrA.Grpc.Contract.Storage;
+
+namespace AVEVA.Historian.Client.Grpc;
+
+/// <summary>
+/// Shared 2023 R2 gRPC authentication handshake. Opens an authenticated History session over an
+/// existing <see cref="HistorianGrpcConnection"/> and returns the transient client handle used by
+/// the Retrieval/Status services. Extracted from <see cref="HistorianGrpcReadOrchestrator"/> so the
+/// read, status, and (future) browse/metadata gRPC paths all drive the identical chain:
+/// <c>HistoryService.GetInterfaceVersion → StorageService.ValidateClientCredential (token loop) →
+/// HistoryService.OpenConnection</c>. The byte payloads (OpenConnection3 v6 request, NTLM token
+/// framing) are the proven 2020 protocol and transfer unchanged inside protobuf <c>bytes</c> fields.
+///
+/// See <see cref="HistorianGrpcReadOrchestrator"/> for the op-routing rationale (the Negotiate loop
+/// belongs on StorageService.ValidateClientCredential, NOT HistoryService.ExchangeKey).
+/// </summary>
+internal static class HistorianGrpcHandshake
+{
+    public static uint OpenAuthenticatedConnection(
+        HistorianGrpcConnection connection,
+        HistorianClientOptions options,
+        CancellationToken cancellationToken)
+    {
+        DateTime Deadline() => DateTime.UtcNow.Add(options.RequestTimeout);
+
+        Guid contextKey = Guid.NewGuid();
+        var historyClient = new GrpcHistory.HistoryService.HistoryServiceClient(connection.Channel);
+
+        GrpcHistory.GetInterfaceVersionResponse historyVersion = historyClient.GetInterfaceVersion(
+            new GrpcHistory.GetInterfaceVersionRequest(), connection.Metadata, Deadline(), cancellationToken);
+        HistorianServerVersionGate.Validate(HistorianServiceInterface.History, historyVersion.UiVersion, options);
+
+        var storageClient = new GrpcStorage.StorageService.StorageServiceClient(connection.Channel);
+        HistorianNativeHandshake.RunTokenRounds(
+            (handle, wrapped, _) =>
+            {
+                GrpcStorage.ValidateClientCredentialResponse response = storageClient.ValidateClientCredential(
+                    new GrpcStorage.ValidateClientCredentialRequest { Handle = handle, InBuff = ByteString.CopyFrom(wrapped) },
+                    connection.Metadata,
+                    Deadline(),
+                    cancellationToken);
+                byte[] serverOutput = response.OutBuff?.ToByteArray() ?? [];
+                byte[] error = response.Status?.BtError?.ToByteArray() ?? [];
+                bool success = response.Status?.BSuccess ?? false;
+                return new HistorianNativeHandshake.TokenExchangeResult(success, serverOutput, error);
+            },
+            contextKey,
+            options,
+            cancellationToken);
+
+        byte[] open2Request = HistorianNativeHandshake.BuildOpenConnection3Request(
+            options.Host, contextKey, HistorianWcfAuthChainHelper.NativeIntegratedReadOnlyConnectionMode);
+
+        GrpcHistory.OpenConnectionResponse open2 = historyClient.OpenConnection(
+            new GrpcHistory.OpenConnectionRequest { BtConnectionRequest = ByteString.CopyFrom(open2Request) },
+            connection.Metadata,
+            Deadline(),
+            cancellationToken);
+
+        byte[] open2Response = open2.BtConnectionResponse?.ToByteArray() ?? [];
+        if (!(open2.Status?.BSuccess ?? false))
+        {
+            byte[] err = open2.Status?.BtError?.ToByteArray() ?? [];
+            throw new InvalidOperationException($"gRPC OpenConnection failed (errorLen={err.Length}, responseLen={open2Response.Length}).");
+        }
+
+        (uint clientHandle, _) = HistorianNativeHandshake.ParseOpenConnectionResponse(open2Response);
+        return clientHandle;
+    }
+}

src/AVEVA.Historian.Client/Grpc/HistorianGrpcProbe.cs

@@ -0,0 +1,48 @@
+using Grpc.Core;
+using GrpcHistory = ArchestrA.Grpc.Contract.History;
+using GrpcRetrieval = ArchestrA.Grpc.Contract.Retrieval;
+using GrpcStatus = ArchestrA.Grpc.Contract.Status;
+
+namespace AVEVA.Historian.Client.Grpc;
+
+/// <summary>
+/// 2023 R2 gRPC reachability probe (roadmap item R0.4). Mirrors <see cref="Wcf.HistorianWcfProbe"/>
+/// over the gRPC transport: it calls the unauthenticated <c>GetInterfaceVersion</c> RPC on the
+/// History, Retrieval, and Status services and applies the same success criteria. No credentials
+/// are required — these RPCs run before the SSPI/Negotiate token loop — so the probe works even
+/// when authentication is unavailable.
+/// </summary>
+internal static class HistorianGrpcProbe
+{
+    public static async Task<bool> ProbeAsync(HistorianClientOptions options, CancellationToken cancellationToken)
+    {
+        ArgumentNullException.ThrowIfNull(options);
+        cancellationToken.ThrowIfCancellationRequested();
+
+        return await Task.Run(() => Probe(options, cancellationToken), cancellationToken).ConfigureAwait(false);
+    }
+
+    private static bool Probe(HistorianClientOptions options, CancellationToken cancellationToken)
+    {
+        using HistorianGrpcConnection connection = HistorianGrpcChannelFactory.Create(options);
+        DateTime deadline = DateTime.UtcNow.Add(options.ConnectTimeout > TimeSpan.Zero ? options.ConnectTimeout : TimeSpan.FromSeconds(5));
+
+        var historyClient = new GrpcHistory.HistoryService.HistoryServiceClient(connection.Channel);
+        GrpcHistory.GetInterfaceVersionResponse history = historyClient.GetInterfaceVersion(
+            new GrpcHistory.GetInterfaceVersionRequest(), connection.Metadata, deadline, cancellationToken);
+
+        var retrievalClient = new GrpcRetrieval.RetrievalService.RetrievalServiceClient(connection.Channel);
+        GrpcRetrieval.GetRetrievalInterfaceVersionResponse retrieval = retrievalClient.GetRetrievalInterfaceVersion(
+            new GrpcRetrieval.GetRetrievalInterfaceVersionRequest(), connection.Metadata, deadline, cancellationToken);
+
+        var statusClient = new GrpcStatus.StatusService.StatusServiceClient(connection.Channel);
+        GrpcStatus.GetStatusInterfaceVersionResponse status = statusClient.GetStatusInterfaceVersion(
+            new GrpcStatus.GetStatusInterfaceVersionRequest(), connection.Metadata, deadline, cancellationToken);
+
+        return history.UiError == 0
+            && history.UiVersion > 0
+            && retrieval.UiError == 0
+            && retrieval.UiVersion > 0
+            && status.UiError == 0;
+    }
+}

src/AVEVA.Historian.Client/Grpc/HistorianGrpcReadOrchestrator.cs

@@ -3,9 +3,7 @@ using Google.Protobuf;
 using Grpc.Core;
 using AVEVA.Historian.Client.Models;
 using AVEVA.Historian.Client.Wcf;
-using GrpcHistory = ArchestrA.Grpc.Contract.History;
 using GrpcRetrieval = ArchestrA.Grpc.Contract.Retrieval;
-using GrpcStorage = ArchestrA.Grpc.Contract.Storage;
 
 namespace AVEVA.Historian.Client.Grpc;
 
@@ -166,51 +164,7 @@ internal sealed class HistorianGrpcReadOrchestrator
     }
 
     private uint OpenAuthenticatedConnection(HistorianGrpcConnection connection, CancellationToken cancellationToken)
-    {
+        => HistorianGrpcHandshake.OpenAuthenticatedConnection(connection, _options, cancellationToken);
-        Guid contextKey = Guid.NewGuid();
-        var historyClient = new GrpcHistory.HistoryService.HistoryServiceClient(connection.Channel);
-
-        GrpcHistory.GetInterfaceVersionResponse historyVersion = historyClient.GetInterfaceVersion(
-            new GrpcHistory.GetInterfaceVersionRequest(), connection.Metadata, Deadline(), cancellationToken);
-        HistorianServerVersionGate.Validate(HistorianServiceInterface.History, historyVersion.UiVersion, _options);
-
-        var storageClient = new GrpcStorage.StorageService.StorageServiceClient(connection.Channel);
-        HistorianNativeHandshake.RunTokenRounds(
-            (handle, wrapped, _) =>
-            {
-                GrpcStorage.ValidateClientCredentialResponse response = storageClient.ValidateClientCredential(
-                    new GrpcStorage.ValidateClientCredentialRequest { Handle = handle, InBuff = ByteString.CopyFrom(wrapped) },
-                    connection.Metadata,
-                    Deadline(),
-                    cancellationToken);
-                byte[] serverOutput = response.OutBuff?.ToByteArray() ?? [];
-                byte[] error = response.Status?.BtError?.ToByteArray() ?? [];
-                bool success = response.Status?.BSuccess ?? false;
-                return new HistorianNativeHandshake.TokenExchangeResult(success, serverOutput, error);
-            },
-            contextKey,
-            _options,
-            cancellationToken);
-
-        byte[] open2Request = HistorianNativeHandshake.BuildOpenConnection3Request(
-            _options.Host, contextKey, HistorianWcfAuthChainHelper.NativeIntegratedReadOnlyConnectionMode);
-
-        GrpcHistory.OpenConnectionResponse open2 = historyClient.OpenConnection(
-            new GrpcHistory.OpenConnectionRequest { BtConnectionRequest = ByteString.CopyFrom(open2Request) },
-            connection.Metadata,
-            Deadline(),
-            cancellationToken);
-
-        byte[] open2Response = open2.BtConnectionResponse?.ToByteArray() ?? [];
-        if (!(open2.Status?.BSuccess ?? false))
-        {
-            byte[] err = open2.Status?.BtError?.ToByteArray() ?? [];
-            throw new InvalidOperationException($"gRPC OpenConnection failed (errorLen={err.Length}, responseLen={open2Response.Length}).");
-        }
-
-        (uint clientHandle, _) = HistorianNativeHandshake.ParseOpenConnectionResponse(open2Response);
-        return clientHandle;
-    }
 
     private List<HistorianSample> RunQuery(
         HistorianGrpcConnection connection,

src/AVEVA.Historian.Client/Grpc/HistorianGrpcStatusClient.cs

@@ -0,0 +1,38 @@
+using Grpc.Core;
+using GrpcStatus = ArchestrA.Grpc.Contract.Status;
+
+namespace AVEVA.Historian.Client.Grpc;
+
+/// <summary>
+/// 2023 R2 gRPC status client (roadmap item R0.3). Mirrors
+/// <see cref="Wcf.HistorianWcfStatusClient"/> over the gRPC transport: it opens an authenticated
+/// History session via <see cref="HistorianGrpcHandshake"/> and queries the StatusService for the
+/// resulting client handle. <c>GetSystemParameter</c> carries the parameter name as a protobuf
+/// string and returns the value string directly — there is no opaque native buffer to decode.
+/// </summary>
+internal static class HistorianGrpcStatusClient
+{
+    public static Task<string?> GetSystemParameterAsync(
+        HistorianClientOptions options,
+        string parameterName,
+        CancellationToken cancellationToken)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(parameterName);
+        return Task.Run(() => GetSystemParameter(options, parameterName, cancellationToken), cancellationToken);
+    }
+
+    private static string? GetSystemParameter(HistorianClientOptions options, string parameterName, CancellationToken cancellationToken)
+    {
+        using HistorianGrpcConnection connection = HistorianGrpcChannelFactory.Create(options);
+        uint clientHandle = HistorianGrpcHandshake.OpenAuthenticatedConnection(connection, options, cancellationToken);
+
+        var statusClient = new GrpcStatus.StatusService.StatusServiceClient(connection.Channel);
+        GrpcStatus.GetSystemParameterResponse response = statusClient.GetSystemParameter(
+            new GrpcStatus.GetSystemParameterRequest { UiHandle = clientHandle, StrParameterName = parameterName },
+            connection.Metadata,
+            DateTime.UtcNow.Add(options.RequestTimeout),
+            cancellationToken);
+
+        return (response.Status?.BSuccess ?? false) ? response.StrParameterValue : null;
+    }
+}

src/AVEVA.Historian.Client/HistorianClient.cs

@@ -25,7 +25,9 @@ public sealed class HistorianClient : IAsyncDisposable
 
     public async Task<bool> ProbeAsync(CancellationToken cancellationToken = default)
     {
-        return await HistorianWcfProbe.ProbeAsync(_options, cancellationToken).ConfigureAwait(false);
+        return _options.Transport == HistorianTransport.RemoteGrpc
+            ? await Grpc.HistorianGrpcProbe.ProbeAsync(_options, cancellationToken).ConfigureAwait(false)
+            : await HistorianWcfProbe.ProbeAsync(_options, cancellationToken).ConfigureAwait(false);
     }
 
     public IAsyncEnumerable<HistorianSample> ReadRawAsync(

src/AVEVA.Historian.Client/Protocol/Historian2020ProtocolDialect.cs

@@ -64,7 +64,9 @@ internal sealed class Historian2020ProtocolDialect
     {
         cancellationToken.ThrowIfCancellationRequested();
         ArgumentException.ThrowIfNullOrWhiteSpace(name);
-        return Wcf.HistorianWcfStatusClient.GetSystemParameterAsync(_options, name, cancellationToken);
+        return UseGrpc
+            ? HistorianGrpcStatusClient.GetSystemParameterAsync(_options, name, cancellationToken)
+            : Wcf.HistorianWcfStatusClient.GetSystemParameterAsync(_options, name, cancellationToken);
     }
 
     private static async IAsyncEnumerable<T> Missing<T>(

src/AVEVA.Historian.Client/Wcf/HistorianNativeHandshake.cs

@@ -33,7 +33,7 @@ internal static class HistorianNativeHandshake
     /// upper-case context-key GUID, <paramref name="wrappedToken"/> is the AVEVA-wrapped SSPI
     /// token (round byte + length + token). The WCF path maps this to
     /// <c>Hist.ValidateClientCredential</c>; the gRPC path maps it to
-    /// <c>HistoryService.ExchangeKey</c> (the renamed handshake op).
+    /// <c>StorageService.ValidateClientCredential</c> (the op that kept the 2020 token framing).
     /// </summary>
     internal delegate TokenExchangeResult TokenExchange(string handle, byte[] wrappedToken, int round);
 
@@ -70,7 +70,8 @@ internal static class HistorianNativeHandshake
 
             if (!result.Success)
             {
-                throw new InvalidOperationException($"Credential token round {round} rejected (errorLen={error.Length}).");
+                throw new InvalidOperationException(
+                    $"Credential token round {round} rejected (errorLen={error.Length}).{DescribeError(error)}");
             }
 
             ValidateClientCredentialResponse? response = HistorianWcfAuthenticationProtocol.TryReadValidateClientCredentialResponse(serverOutput);
@@ -162,4 +163,32 @@ internal static class HistorianNativeHandshake
         int slash = userName.IndexOf('\\');
         return slash > 0 ? userName[(slash + 1)..] : userName;
     }
+
+    /// <summary>
+    /// Renders a diagnostic suffix for a rejected credential round: the decoded native error
+    /// (type/code/name) plus a short hex + printable-ASCII preview of the server error buffer.
+    /// Keeps secrets out — error buffers carry server status codes/messages, not credentials.
+    /// </summary>
+    private static string DescribeError(byte[] error)
+    {
+        if (error.Length == 0)
+        {
+            return string.Empty;
+        }
+
+        HistorianNativeError? native = HistorianOpen2Protocol.TryReadNativeError(error);
+        string nativePart = native is null
+            ? string.Empty
+            : $" native(type={native.Type}, code={native.Code}{(native.Name is null ? string.Empty : $", {native.Name}")})";
+
+        ReadOnlySpan<byte> preview = error.AsSpan(0, Math.Min(error.Length, 64));
+        string hex = Convert.ToHexString(preview);
+        char[] ascii = new char[preview.Length];
+        for (int i = 0; i < preview.Length; i++)
+        {
+            ascii[i] = preview[i] is >= 0x20 and < 0x7F ? (char)preview[i] : '.';
+        }
+
+        return $"{nativePart} hex={hex} ascii=\"{new string(ascii)}\"";
+    }
 }

tests/AVEVA.Historian.Client.Tests/HistorianGrpcHandshakeRoutingTests.cs

@@ -11,7 +11,7 @@ namespace AVEVA.Historian.Client.Tests;
 /// credentials (live-confirmed against a real 2023 R2 server, 2026-06-21). An earlier revision
 /// routed the loop to ExchangeKey; this test fails if that regression returns.
 ///
-/// It works by disassembling the IL of <c>HistorianGrpcReadOrchestrator</c> (and its
+/// It works by disassembling the IL of <c>HistorianGrpcHandshake</c> (and its
 /// compiler-generated nested closure types — the token-loop call lives inside a lambda) and
 /// collecting every method invoked.
 /// </summary>
@@ -20,8 +20,10 @@ public sealed class HistorianGrpcHandshakeRoutingTests
     [Fact]
     public void Handshake_UsesValidateClientCredential_NotExchangeKey()
     {
+        // The auth token loop lives in the shared handshake helper (reused by the read, status,
+        // and future browse/metadata gRPC paths).
         HashSet<string> calledMethods = CollectCalledMethodNames(
-            "AVEVA.Historian.Client.Grpc.HistorianGrpcReadOrchestrator");
+            "AVEVA.Historian.Client.Grpc.HistorianGrpcHandshake");
 
         Assert.Contains("ValidateClientCredential", calledMethods);
         Assert.DoesNotContain("ExchangeKey", calledMethods);

tests/AVEVA.Historian.Client.Tests/HistorianGrpcIntegrationTests.cs

@@ -12,6 +12,21 @@ namespace AVEVA.Historian.Client.Tests;
 /// </summary>
 public sealed class HistorianGrpcIntegrationTests
 {
+    [Fact]
+    public async Task ProbeAsync_OverGrpc_ReturnsTrue()
+    {
+        string? host = Environment.GetEnvironmentVariable("HISTORIAN_GRPC_HOST");
+        if (string.IsNullOrWhiteSpace(host))
+        {
+            return;
+        }
+
+        // ProbeAsync calls the unauthenticated GetInterfaceVersion RPCs, so it succeeds even when
+        // credentials are unavailable — no HISTORIAN_USER/PASSWORD required.
+        HistorianClient client = new(BuildOptions(host));
+        Assert.True(await client.ProbeAsync(CancellationToken.None));
+    }
+
     [Fact]
     public async Task ReadRawAsync_OverGrpc_ReturnsAtLeastOneRow()
     {
@@ -37,6 +52,20 @@ public sealed class HistorianGrpcIntegrationTests
         Assert.All(samples, s => Assert.Equal(testTag, s.TagName));
     }
 
+    [Fact]
+    public async Task GetSystemParameterAsync_OverGrpc_ReturnsValue()
+    {
+        string? host = Environment.GetEnvironmentVariable("HISTORIAN_GRPC_HOST");
+        if (string.IsNullOrWhiteSpace(host) || string.IsNullOrEmpty(Environment.GetEnvironmentVariable("HISTORIAN_USER")))
+        {
+            return;
+        }
+
+        HistorianClient client = new(BuildOptions(host));
+        string? version = await client.GetSystemParameterAsync("HistorianVersion", CancellationToken.None);
+        Assert.False(string.IsNullOrWhiteSpace(version));
+    }
+
     private static HistorianClientOptions BuildOptions(string host)
     {
         string? user = Environment.GetEnvironmentVariable("HISTORIAN_USER");

tests/AVEVA.Historian.Client.Tests/HistorianGrpcTransportTests.cs

@@ -100,6 +100,41 @@ public sealed class HistorianGrpcTransportTests
         Assert.Equal((uint)HistorianDataQueryProtocol.QueryRequestTypeData, decoded.UiQueryRequestType);
     }
 
+    [Fact]
+    public void InterfaceVersionResponses_ExposeErrorAndVersion_AsProbeExpects()
+    {
+        // R0.4 ProbeAsync reads uiError/uiVersion off each service's GetInterfaceVersion response.
+        // Pin that field mapping (success = uiError 0 + uiVersion > 0) via a protobuf round-trip.
+        var history = GrpcHistory.GetInterfaceVersionResponse.Parser.ParseFrom(
+            new GrpcHistory.GetInterfaceVersionResponse { UiError = 0, UiVersion = 12 }.ToByteArray());
+        var retrieval = GetRetrievalInterfaceVersionResponse.Parser.ParseFrom(
+            new GetRetrievalInterfaceVersionResponse { UiError = 0, UiVersion = 4 }.ToByteArray());
+
+        Assert.Equal(0u, history.UiError);
+        Assert.Equal(12u, history.UiVersion);
+        Assert.Equal(0u, retrieval.UiError);
+        Assert.Equal(4u, retrieval.UiVersion);
+    }
+
+    [Fact]
+    public void GetSystemParameterMessages_CarryHandleNameAndValue_AsStatusClientExpects()
+    {
+        // R0.3 sends {uiHandle, strParameterName} and reads strParameterValue when status succeeds.
+        var request = ArchestrA.Grpc.Contract.Status.GetSystemParameterRequest.Parser.ParseFrom(
+            new ArchestrA.Grpc.Contract.Status.GetSystemParameterRequest { UiHandle = 9, StrParameterName = "HistorianVersion" }.ToByteArray());
+        Assert.Equal(9u, request.UiHandle);
+        Assert.Equal("HistorianVersion", request.StrParameterName);
+
+        var response = ArchestrA.Grpc.Contract.Status.GetSystemParameterResponse.Parser.ParseFrom(
+            new ArchestrA.Grpc.Contract.Status.GetSystemParameterResponse
+            {
+                Status = new ArchestrA.Grpc.Contract.RequestStatus.Status { BSuccess = true },
+                StrParameterValue = "20.0.000"
+            }.ToByteArray());
+        Assert.True(response.Status.BSuccess);
+        Assert.Equal("20.0.000", response.StrParameterValue);
+    }
+
     [Fact]
     public void OpenConnectionRequest_CarriesNativeOpen2BufferUnchanged()
     {