src/AVEVA.Historian.Client/HistorianClientOptions.cs

@@ -64,6 +64,14 @@ public sealed class HistorianClientOptions
     /// </summary>
     public string? ConnectViaAddress { get; init; }
 
+    /// <summary>
+    /// Diagnostic override for the native OpenConnection mode the WCF event-read chain uses (default
+    /// <c>0x402</c>, read-only process). Set to e.g. <c>0x501</c> (event) or <c>0x401</c> (write-enabled)
+    /// to probe whether CM_EVENT registration / event-row retrieval needs a different connection type on a
+    /// 2023 R2 server. Null = the default read-only process mode. Intended for protocol investigation.
+    /// </summary>
+    public uint? EventReadConnectionModeOverride { get; init; }
+
     /// <summary>
     /// For <see cref="HistorianTransport.RemoteGrpc"/>: when true the channel uses TLS
     /// (<c>https://</c>); when false it uses plaintext (<c>http://</c>). Matches the stock

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

@@ -147,7 +147,7 @@ internal sealed class HistorianWcfEventOrchestrator
         EndpointAddress transactionEndpoint = HistorianWcfBindingFactory.CreateAuxiliaryEndpointAddress(_options, HistorianWcfServiceNames.Transaction);
         uint clientHandle = HistorianWcfAuthChainHelper.OpenAuthenticatedConnection(
             _options, histBinding, histEndpoint, contextKey, cancellationToken,
-            connectionMode: HistorianWcfAuthChainHelper.NativeIntegratedReadOnlyConnectionMode,
+            connectionMode: _options.EventReadConnectionModeOverride ?? HistorianWcfAuthChainHelper.NativeIntegratedReadOnlyConnectionMode,
             additionalSetup: (historyChannel, context) =>
                 AddCmEventTagViaAddT(historyChannel, context, auxBinding, statusEndpoint, transactionEndpoint, retrBinding, retrEndpoint));
         return RunEventQuery(retrBinding, retrEndpoint, clientHandle, startUtc, endUtc, filter, cancellationToken);

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

@@ -36,9 +36,14 @@ public sealed class WcfEventReadSpikeTests
     public async Task WcfEventRead_DiagnosticDump_AgainstRemoteHistorian()
     {
         string? host = Environment.GetEnvironmentVariable("HISTORIAN_WCF_EVENT_HOST");
-        if (string.IsNullOrWhiteSpace(host) || !OperatingSystem.IsWindows())
+        bool certificate = string.Equals(
+            Environment.GetEnvironmentVariable("HISTORIAN_WCF_EVENT_TRANSPORT"), "certificate", StringComparison.OrdinalIgnoreCase);
+        // The certificate (TLS) transport and NegotiateAuthentication-based app auth are cross-platform;
+        // the integrated (Windows SSPI transport-security) transport is Windows-only. Skip when the gate
+        // is unconfigured, or when an integrated run is requested off Windows.
+        if (string.IsNullOrWhiteSpace(host) || (!certificate && !OperatingSystem.IsWindows()))
         {
-            return; // inert without the dedicated gate / off Windows
+            return;
         }
 
         int port = int.TryParse(Environment.GetEnvironmentVariable("HISTORIAN_WCF_EVENT_PORT"), out int p)
@@ -50,8 +55,17 @@ public sealed class WcfEventReadSpikeTests
         string? spn = Environment.GetEnvironmentVariable("HISTORIAN_WCF_EVENT_SPN");
         string? dnsId = Environment.GetEnvironmentVariable("HISTORIAN_WCF_EVENT_DNSID");
         string? via = Environment.GetEnvironmentVariable("HISTORIAN_WCF_EVENT_VIA");
-        bool certificate = string.Equals(
-            Environment.GetEnvironmentVariable("HISTORIAN_WCF_EVENT_TRANSPORT"), "certificate", StringComparison.OrdinalIgnoreCase);
+        bool bypassVersion = string.Equals(
+            Environment.GetEnvironmentVariable("HISTORIAN_WCF_EVENT_NOVERSIONCHECK"), "1", StringComparison.Ordinal);
+        int timeoutSec = int.TryParse(Environment.GetEnvironmentVariable("HISTORIAN_WCF_EVENT_TIMEOUT_SEC"), out int ts) && ts > 0
+            ? ts : 30;
+        string? connModeRaw = Environment.GetEnvironmentVariable("HISTORIAN_WCF_EVENT_CONNMODE");
+        uint? connModeOverride = null;
+        if (!string.IsNullOrWhiteSpace(connModeRaw))
+        {
+            string hex = connModeRaw.StartsWith("0x", StringComparison.OrdinalIgnoreCase) ? connModeRaw[2..] : connModeRaw;
+            if (uint.TryParse(hex, System.Globalization.NumberStyles.HexNumber, null, out uint cm)) { connModeOverride = cm; }
+        }
         bool allowUntrusted = string.Equals(
             Environment.GetEnvironmentVariable("HISTORIAN_WCF_EVENT_ALLOW_UNTRUSTED"), "1", StringComparison.Ordinal);
         // Certificate transport carries no Windows transport credential (cert-validated TLS channel);
@@ -71,23 +85,50 @@ public sealed class WcfEventReadSpikeTests
             ServerDnsIdentity = string.IsNullOrWhiteSpace(dnsId) ? null : dnsId,
             AllowUntrustedServerCertificate = allowUntrusted,
             ConnectViaAddress = string.IsNullOrWhiteSpace(via) ? null : via,
+            VerifyServerInterfaceVersion = !bypassVersion,
+            ConnectTimeout = TimeSpan.FromSeconds(timeoutSec),
+            RequestTimeout = TimeSpan.FromSeconds(timeoutSec),
+            EventReadConnectionModeOverride = connModeOverride,
         };
 
         HistorianWcfEventOrchestrator orchestrator = new(options);
         DateTime endUtc = DateTime.UtcNow;
         DateTime startUtc = endUtc - TimeSpan.FromDays(days);
 
+        int budgetSec = int.TryParse(Environment.GetEnvironmentVariable("HISTORIAN_WCF_EVENT_BUDGET_SEC"), out int bgs) && bgs > 0
+            ? bgs : 60;
+
         int observed = 0;
         bool hasFirstEvent = false;
         string outcome = "completed";
         try
         {
-            await foreach (HistorianEvent evt in orchestrator.ReadEventsAsync(startUtc, endUtc, filter: null, CancellationToken.None))
+            // Race the read against an overall budget. The chain is synchronous WCF, so a stuck call
+            // can't be token-cancelled — but the orchestrator's static/instance diagnostics are set as it
+            // progresses, so on a budget timeout we still dump them to see which phase (auth / CM_EVENT
+            // registration / query) is hanging. The abandoned task keeps running in the background harness.
+            using var budget = new CancellationTokenSource(TimeSpan.FromSeconds(budgetSec));
+            Task<int> readTask = Task.Run(async () =>
             {
-                observed++;
-                hasFirstEvent = true;
+                int n = 0;
+                await foreach (HistorianEvent evt in orchestrator.ReadEventsAsync(startUtc, endUtc, filter: null, budget.Token))
+                {
+                    n++;
                     _ = evt; // event identity intentionally NOT logged (sanitized)
                 }
+                return n;
+            });
+
+            Task finished = await Task.WhenAny(readTask, Task.Delay(TimeSpan.FromSeconds(budgetSec + 5)));
+            if (finished == readTask)
+            {
+                observed = await readTask;
+                hasFirstEvent = observed > 0;
+            }
+            else
+            {
+                outcome = $"TIMED OUT after {budgetSec}s (chain still running — see return codes for phase reached)";
+            }
         }
         catch (Exception ex)
         {
@@ -100,7 +141,7 @@ public sealed class WcfEventReadSpikeTests
         }
 
         // Sanitized diagnostic dump — counts, native return codes, buffer lengths, sha256 ONLY.
-        _output.WriteLine($"[C2 WCF spike] transport:                {options.Transport} (integratedSec={integrated}, allowUntrusted={allowUntrusted})");
+        _output.WriteLine($"[C2 WCF spike] transport:                {options.Transport} (integratedSec={integrated}, allowUntrusted={allowUntrusted}, connMode={(connModeOverride.HasValue ? "0x" + connModeOverride.Value.ToString("X") : "default-0x402")})");
         _output.WriteLine($"[C2 WCF spike] outcome:                  {outcome}");
         _output.WriteLine($"[C2 WCF spike] events observed:          {observed}");
         _output.WriteLine($"[C2 WCF spike] hasFirstEvent:            {hasFirstEvent}");