Merge remote-tracking branch 'origin/master' into test/task-assertion-return-discard

.github/workflows/v2-ci.yml

@@ -41,6 +41,8 @@ jobs:
       # #606: regenerated review summary must remain in sync with module findings.
       - name: code-reviews README drift check
         run: python3 code-reviews/regen-readme.py --check
+      - name: TRX skip guard fixtures
+        run: python3 scripts/ci/test-assert-not-all-skipped.py
       # #707: bound project workers and avoid concurrent NuGet restore work.
       - name: dotnet restore
         run: dotnet restore ZB.MOM.WW.OtOpcUa.slnx --disable-parallel -m:2

docs/drivers/S7.md

@@ -198,15 +198,53 @@ Timers are **read-only** this phase; a write attempt returns `BadNotWritable`.
 ### Counter read
 
 **Address**: `C{n}` (e.g. `C0`, `C10`). **DataType must be `Int32`**. The OPC UA node is
-a scalar `Int32` whose value is the current **count** (raw word from the PLC).
+a scalar `Int32` containing the unsigned **raw big-endian word**, widened to `Int32`:
+`(bytes[0] << 8) | bytes[1]`. `S7.Net`'s `Counter.FromByteArray` performs no BCD
+reinterpretation; for example, bytes `01 23` surface as `291`. This describes the
+current decoder, not verified agreement with a PLC's displayed count.
 Counters are **read-only** this phase; a write attempt returns `BadNotWritable`.
 
-> **Known limitation — Counter BCD encoding on S7-300/400**: `S7.Net`'s
-> `Counter.FromByteArray` returns the raw big-endian word without BCD decode.
-> On **classic S7-300/400** the C-area word is BCD-encoded (0–999), so the
-> surfaced value can differ from the actual count on that hardware. S7-1200/1500
-> use IEC/DB counters (plain integers) where the raw word is correct. BCD
-> reinterpretation for legacy C-area is a live-hardware-gated follow-up.
+The S7comm ReadVar **C-area response encoding remains unverified on hardware**.
+PLC instruction representations do not by themselves establish network encoding:
+Siemens documents a binary current value for [L: Load counter](https://docs.tia.siemens.cloud/r/en-us/v21/stl-s7-300-s7-400/stl-mnemonic-s7-300-s7-400/counter-operations-s7-300-s7-400/l-load-counter-s7-300-s7-400)
+and separate `CV` and `CV_BCD` outputs for [S_CD](https://docs.tia.siemens.cloud/r/en-us/v21/lad-s7-300-s7-400/counter-operations-s7-300-s7-400/simatic-counters-s7-300-s7-400/s_cd-assign-parameters-and-count-down-s7-300-s7-400?contentId=reR_xapFX_Ike2opHIvfzg).
+
+IEC counter values stored in DB memory use the **DB address and declared integer
+type**, a different read path from `C{n}`. CPU family alone does not select the
+counter kind or prove its wire representation. In particular, Siemens also lists
+legacy SIMATIC counters for S7-1500 in its [instruction comparison (pages 23–24)](https://cache.industry.siemens.com/dl/files/777/109986777/att_1322640/v1/s7_1500_compare_table_en.pdf?download=true).
+The driver has no counter encoding selector; hardware-faithful counter support
+requires independent raw-response evidence before any interpretation change.
+
+### Counter evidence follow-up (#616)
+
+The existing `S7_1500SpanReadTests` exercises the python-snap7 profile's synthetic
+raw words (`C0 = 4711`, `C7 = 31337`). These are outside the classic SIMATIC count
+range `0..999` documented by S_CD. These expectations describe raw-word handling;
+they do not establish classic counter count semantics. The recorded device-0 run cannot prove nonzero
+numbering. The nonzero test is environment-gated, but its options remain
+`CpuType = S71500`, rack `0`, slot `0`: setting `S7_TIMER_NUMBER_ADDRESSING=1`
+does not configure a classic CPU or make the profile a classic counter gate.
+
+Before claiming hardware validation or closing #616:
+
+- Prepare a separate target-specific semantic gate with the actual CPU type,
+  rack, slot and TSAP/connection settings. Keep the synthetic raw-word profile
+  as its own evidence of the existing decoder contract.
+- Record CPU model/order number, firmware, endpoint, connection settings and
+  driver/S7netplus plus simulator versions where applicable.
+- Observe independent PLC-side current counts and binary/BCD reference outputs
+  for valid classic counts such as `123`, a second distinguishing count (`42`
+  or `999`), and zero. Record the instruction/counter kind and DB reference
+  addresses; do not derive reference values from the driver's output.
+- Capture the actual two-byte S7comm C-area responses alongside those references.
+  Do not infer response bytes from a simulator seed or expected BCD value.
+- Verify several distinct nonzero timer/counter numbers against their independent
+  PLC values and captured requests/responses, and verify the read-only contract.
+
+The raw-byte/count and nonzero-numbering gates remain open. Password/protection
+support inherited from #303/#632 is a separate follow-up, not evidence supplied
+by these counter checks.
 
 ### Deferrals (not yet implemented)
 

scripts/ci/README.md

@@ -28,3 +28,26 @@ AKKA_TEST_TIMEFACTOR=3 dotnet test ZB.MOM.WW.OtOpcUa.slnx \
   --logger trx --results-directory artifacts/trx
 MIN_EXECUTED=12000 bash scripts/ci/assert-not-all-skipped.sh artifacts/trx/*.trx
 ```
+
+The guard uses the existing TRX `Counters/@executed` value for the aggregate
+floor. Its `skipped` diagnostic counts individual `Results/UnitTestResult`
+records whose outcome is `NotExecuted`, using the document's XML namespace.
+Some VSTest reports set summary `notExecuted` to zero even when these records
+are present. Skip records are counted per file, including repeated runs; they
+are not a count of unique test methods and do not affect the executed floor.
+For malformed XML, the diagnostic retains the old summary-counter fallback;
+this guard does not add XML validation to its existing gate policy.
+
+Run the deterministic script fixtures without building or running the solution:
+
+```bash
+python3 scripts/ci/test-assert-not-all-skipped.py
+```
+
+Verified hosted baseline: [Gitea run 975](https://gitea.dohertylan.com/dohertj2/lmxopcua/actions/runs/975)
+completed successfully on 2026-10-13 for commit
+`76bdca90e94e814e06ef10b78271e2b492b2ba32` (merged by PR #711).
+Restore, Release build, README drift check, the serialized whole-solution test
+step, the 12,000-test floor and TRX upload all passed. The floor counted
+14,630 executed tests across 62 TRX files. This baseline predates the individual
+skip-reporting correction; its printed zero skip diagnostic is not skip evidence.

scripts/ci/assert-not-all-skipped.sh

@@ -33,12 +33,31 @@ for f in "$@"; do
     exit 2
   fi
   seen=$((seen + 1))
-  # The trx <Counters .../> element in <ResultSummary> carries executed + notExecuted counts.
+  # Keep the executed-counter floor unchanged; notExecuted is only a fallback
+  # for malformed XML that this guard historically accepted.
   counters="$(grep -oE '<Counters[^>]*/?>' "$f" | head -1)"
   ex="$(printf '%s' "$counters" | grep -oE 'executed="[0-9]+"' | grep -oE '[0-9]+' || true)"
   ne="$(printf '%s' "$counters" | grep -oE 'notExecuted="[0-9]+"' | grep -oE '[0-9]+' || true)"
   ex="${ex:-0}"
   ne="${ne:-0}"
+  # VSTest can emit notExecuted="0" despite individual NotExecuted results.
+  # Count direct Results/UnitTestResult records in the document's namespace,
+  # excluding foreign elements, nested records and escaped diagnostic text.
+  ne="$(python3 - "$f" "$ne" <<'PY'
+import sys
+import xml.etree.ElementTree as ET
+
+try:
+    root = ET.parse(sys.argv[1]).getroot()
+except ET.ParseError:
+    # Skip reporting must not introduce a new malformed-XML gate failure.
+    print(sys.argv[2])
+else:
+    namespace = root.tag.split("}", 1)[0] + "}" if root.tag.startswith("{") else ""
+    results = root.findall(f"{namespace}Results/{namespace}UnitTestResult")
+    print(sum(result.get("outcome") == "NotExecuted" for result in results))
+PY
+)"
   total_executed=$((total_executed + ex))
   total_skipped=$((total_skipped + ne))
   echo "  $(basename "$f"): executed=${ex} skipped=${ne}"

scripts/ci/test-assert-not-all-skipped.py

@@ -0,0 +1,108 @@
+#!/usr/bin/env python3
+"""Deterministic subprocess checks for the TRX executed-floor guard."""
+import os
+from pathlib import Path
+import subprocess
+import tempfile
+import unittest
+
+
+SCRIPT = Path(__file__).with_name("assert-not-all-skipped.sh")
+NS = "http://microsoft.com/schemas/VisualStudio/TeamTest/2010"
+
+
+def trx(executed, outcomes, summary_skipped=0, namespace=NS, extra=""):
+    declaration = f' xmlns="{namespace}"' if namespace else ""
+    results = "".join(f'<UnitTestResult outcome="{outcome}"/>' for outcome in outcomes)
+    return (f'<TestRun{declaration}><Results>{results}{extra}</Results>'
+            f'<ResultSummary><Counters total="{len(outcomes)}" executed="{executed}" '
+            f'notExecuted="{summary_skipped}"/></ResultSummary></TestRun>')
+
+
+class SkipGuardTests(unittest.TestCase):
+    def setUp(self):
+        self.directory = tempfile.TemporaryDirectory(prefix="trx-skip-fixtures-")
+        self.addCleanup(self.directory.cleanup)
+        self.root = Path(self.directory.name)
+
+    def write(self, name, content):
+        path = self.root / name
+        path.write_text(content, encoding="utf-8")
+        return path
+
+    def run_guard(self, *paths, minimum=None):
+        env = os.environ.copy()
+        env.pop("MIN_EXECUTED", None)
+        if minimum is not None:
+            env["MIN_EXECUTED"] = str(minimum)
+        return subprocess.run(["bash", str(SCRIPT), *map(str, paths)], env=env,
+                              text=True, capture_output=True, check=False)
+
+    def assert_report(self, result, status, executed, skipped, files=1):
+        self.assertEqual(status, result.returncode, result.stdout + result.stderr)
+        self.assertIn(f"files={files} executed={executed} skipped={skipped} ", result.stdout)
+
+    def test_mixed_results_ignore_zero_summary_skip_counter(self):
+        # A summary-only skip count misses the three actual NotExecuted records.
+        path = self.write("mixed.trx", trx(827, ["Passed"] * 827 + ["NotExecuted"] * 3))
+        result = self.run_guard(path)
+        self.assert_report(result, 0, 827, 3)
+        self.assertIn("mixed.trx: executed=827 skipped=3", result.stdout)
+
+    def test_all_skipped_fails_default_floor_but_report_only_passes(self):
+        path = self.write("all-skipped.trx", trx(0, ["NotExecuted"] * 188))
+        self.assert_report(self.run_guard(path), 1, 0, 188)
+        self.assert_report(self.run_guard(path, minimum=0), 0, 0, 188)
+
+    def test_zero_tests_fails_default_floor_but_report_only_passes(self):
+        path = self.write("zero.trx", trx(0, []))
+        self.assert_report(self.run_guard(path), 1, 0, 0)
+        self.assert_report(self.run_guard(path, minimum=0), 0, 0, 0)
+
+    def test_agreeing_summary_and_outcomes_are_not_double_counted(self):
+        path = self.write("agreeing.trx", trx(1, ["Passed", "NotExecuted"], 1))
+        self.assert_report(self.run_guard(path), 0, 1, 1)
+
+    def test_outcomes_are_authoritative_when_summary_overstates_skips(self):
+        path = self.write("overstated.trx", trx(1, ["Passed", "NotExecuted"], 9))
+        self.assert_report(self.run_guard(path), 0, 1, 1)
+
+    def test_namespace_path_and_exact_outcome_exclude_decoys(self):
+        extra = ('<Other><UnitTestResult outcome="NotExecuted"/></Other>'
+                 '<foreign:UnitTestResult xmlns:foreign="urn:other" outcome="NotExecuted"/>'
+                 '<Output><Message>&lt;UnitTestResult outcome="NotExecuted"/&gt;</Message></Output>')
+        content = trx(2, ["Passed", "Failed", "NotExecuted", "notexecuted"], extra=extra)
+        # Prefixes on Results/UnitTestResult must work just like the default namespace.
+        content = content.replace('<TestRun ', f'<TestRun xmlns:t="{NS}" ')
+        content = content.replace('<Results>', '<t:Results>').replace('</Results>', '</t:Results>')
+        content = content.replace('<UnitTestResult ', '<t:UnitTestResult ')
+        path = self.write("namespaced.trx", content)
+        self.assert_report(self.run_guard(path), 0, 2, 1)
+
+    def test_unnamespaced_results_remain_supported(self):
+        path = self.write("legacy.trx", trx(1, ["Passed", "NotExecuted"], namespace=""))
+        self.assert_report(self.run_guard(path), 0, 1, 1)
+
+    def test_executed_counter_controls_aggregate_floor_at_boundary(self):
+        # Counters retain authority even when result records disagree with executed.
+        mixed = self.write("floor.trx", trx(12000, ["Passed", "NotExecuted"]))
+        skipped = self.write("skipped.trx", trx(0, ["NotExecuted"]))
+        self.assert_report(self.run_guard(mixed, skipped, minimum=12000), 0, 12000, 2, 2)
+        self.assert_report(self.run_guard(mixed, skipped, minimum=12001), 1, 12000, 2, 2)
+
+    def test_missing_arguments_and_file_keep_exit_two(self):
+        self.assertEqual(2, self.run_guard().returncode)
+        self.assertEqual(2, self.run_guard(self.root / "missing.trx").returncode)
+
+    def test_missing_counters_keeps_existing_exit_one(self):
+        path = self.write("no-counters.trx", '<TestRun><Results/></TestRun>')
+        self.assertEqual(1, self.run_guard(path, minimum=0).returncode)
+
+    def test_malformed_xml_keeps_summary_fallback_and_gate_status(self):
+        path = self.write("malformed.trx", '<TestRun><Counters executed="2" notExecuted="3"/>')
+        self.assert_report(self.run_guard(path, minimum=2), 0, 2, 3)
+        self.assert_report(self.run_guard(path, minimum=3), 1, 2, 3)
+
+
+if __name__ == "__main__":
+    unittest.main(verbosity=2)

src/Core/ZB.MOM.WW.OtOpcUa.Commons/OpcUa/DeferredServiceLevelPublisher.cs

@@ -1,21 +1,38 @@
 namespace ZB.MOM.WW.OtOpcUa.Commons.OpcUa;
 
 /// <summary>
-/// Late-binding adapter that holds an inner <see cref="IServiceLevelPublisher"/> reference
-/// swappable at runtime. Mirrors <see cref="DeferredAddressSpaceSink"/>: Akka actors resolve
-/// the publisher at DI time, but the production <c>SdkServiceLevelPublisher</c> only exists
-/// after <c>StandardServer.Start</c>. The Host's hosted service swaps the inner once the SDK
-/// is up; until then writes route through <see cref="NullServiceLevelPublisher"/>.
+/// Late-binding adapter that accepts and retains the latest requested ServiceLevel until
+/// the SDK publisher is available. Binding synchronously replays that request, including zero.
 /// </summary>
+/// <remarks>
+/// Publishing and binding are serialized through the synchronous inner call. Inner publishers
+/// must not call back into this adapter. Acceptance while unbound is not an SDK write confirmation.
+/// A failed call retains both the requested level and the installed publisher for later recovery.
+/// </remarks>
 public sealed class DeferredServiceLevelPublisher : IServiceLevelPublisher
 {
-    private volatile IServiceLevelPublisher _inner = NullServiceLevelPublisher.Instance;
+    private readonly object _gate = new();
+    private IServiceLevelPublisher? _inner;
+    private byte? _latest;
 
-    /// <summary>Swap the underlying publisher. Pass null to revert to the Null no-op.</summary>
-    /// <param name="inner">The publisher implementation to use, or null to use the null publisher.</param>
-    public void SetInner(IServiceLevelPublisher? inner) =>
-        _inner = inner ?? NullServiceLevelPublisher.Instance;
+    /// <summary>Bind and replay the latest request, or unbind while retaining that request.</summary>
+    /// <param name="inner">The publisher implementation to use, or null to unbind.</param>
+    public void SetInner(IServiceLevelPublisher? inner)
+    {
+        lock (_gate)
+        {
+            _inner = inner;
+            if (_latest is { } latest) _inner?.Publish(latest);
+        }
+    }
 
     /// <inheritdoc />
-    public void Publish(byte serviceLevel) => _inner.Publish(serviceLevel);
+    public void Publish(byte serviceLevel)
+    {
+        lock (_gate)
+        {
+            _latest = serviceLevel;
+            _inner?.Publish(serviceLevel);
+        }
+    }
 }

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7/S7Driver.cs

@@ -1465,7 +1465,7 @@ public sealed class S7Driver
     {
         // AREA precedence first (before the DataType switch): a Timer (T{n}) decodes its 2-byte
         // S5TIME word to a duration in SECONDS via S7.Net's Timer.FromByteArray (returns double);
-        // a Counter (C{n}) decodes its 2-byte word to a COUNT via Counter.FromByteArray (returns
+        // a Counter (C{n}) exposes its 2-byte RAW WORD via Counter.FromByteArray (returns
         // ushort, surfaced as a non-negative int to match the tag's Int32 type). Routing on Area
         // here is essential: a Timer tag is typed Float64, so letting it fall to the Float64 arm
         // below would ReadDoubleBigEndian over a 2-byte block = garbage/throw. Boxed explicitly so
@@ -1474,11 +1474,12 @@ public sealed class S7Driver
             return (object)global::S7.Net.Types.Timer.FromByteArray(block);
         if (addr.Area is S7Area.Counter)
         {
-            // NOTE: S7.Net Counter.FromByteArray returns the RAW big-endian word ((bytes[0]<<8)|bytes[1]),
-            // NOT a BCD decode. On classic S7-300/400 the C-area word is BCD (0-999), so on that hardware
-            // this raw value can differ from the displayed count; S7-1200/1500 use IEC/DB counters (plain
-            // ints), where it is correct. Surfacing S7.Net's value verbatim is the faithful choice; BCD
-            // reinterpretation for legacy C-area counters is a live-hardware-gated follow-up.
+            // S7.Net Counter.FromByteArray returns the raw big-endian word ((bytes[0]<<8)|bytes[1]),
+            // without BCD reinterpretation. This preserves the raw value, not a verified PLC count:
+            // S7comm C-area response encoding still needs independent raw bytes and PLC-side
+            // count/binary/BCD references (#616). CPU family alone does not prove that encoding.
+            // IEC counter integers in DB memory take the DB type codec, not this C-area path;
+            // S7-1500 also has legacy SIMATIC counters. See docs/drivers/S7.md for the evidence gate.
             return (object)(int)global::S7.Net.Types.Counter.FromByteArray(block);
         }
 

src/Server/ZB.MOM.WW.OtOpcUa.Host/OpcUa/FailedServiceLevelBindingCleanup.cs

@@ -0,0 +1,38 @@
+using Microsoft.Extensions.Logging;
+
+namespace ZB.MOM.WW.OtOpcUa.Host.OpcUa;
+
+/// <summary>Coordinates endpoint cleanup after ServiceLevel binding fails during startup.</summary>
+internal static class FailedServiceLevelBindingCleanup
+{
+    /// <summary>Stops and disposes the endpoint, returning whether ownership can be released.</summary>
+    /// <param name="stop">The SDK stop operation.</param>
+    /// <param name="dispose">The application-host disposal operation.</param>
+    /// <param name="logger">The cleanup logger.</param>
+    /// <returns>Whether cleanup completed successfully.</returns>
+    internal static async Task<bool> StopAndDisposeAsync(
+        Func<Task> stop, Func<ValueTask> dispose, ILogger logger)
+    {
+        var completed = true;
+        try
+        {
+            await stop().ConfigureAwait(false);
+        }
+        catch (Exception ex)
+        {
+            completed = false;
+            logger.LogError(ex, "OtOpcUaServerHostedService: SDK stop failed after binding failure; retaining endpoint ownership for shutdown retry");
+        }
+        // Attempt application cleanup even when stopping faults; keep ownership on either failure.
+        try
+        {
+            await dispose().ConfigureAwait(false);
+        }
+        catch (Exception ex)
+        {
+            completed = false;
+            logger.LogError(ex, "OtOpcUaServerHostedService: endpoint disposal failed after binding failure; retaining endpoint ownership for shutdown retry");
+        }
+        return completed;
+    }
+}

src/Server/ZB.MOM.WW.OtOpcUa.Host/OpcUa/OtOpcUaServerHostedService.cs

@@ -339,11 +339,36 @@ public sealed class OtOpcUaServerHostedService : IHostedService, IAsyncDisposabl
         _server.NodeManager.Clock = historyUpdate.Clock;
 
         // ServiceLevel publisher needs IServerInternal — only available after Start.
-        if (_server.CurrentInstance is { } serverInternal)
+        try
         {
-            _deferredServiceLevel.SetInner(new SdkServiceLevelPublisher(
-                serverInternal,
-                _loggerFactory.CreateLogger<SdkServiceLevelPublisher>()));
+            if (_server.CurrentInstance is { } serverInternal)
+            {
+                _deferredServiceLevel.SetInner(new SdkServiceLevelPublisher(
+                    serverInternal,
+                    _loggerFactory.CreateLogger<SdkServiceLevelPublisher>()));
+            }
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex,
+                "OtOpcUaServerHostedService: ServiceLevel binding failed; stopping the OPC UA endpoint while the admin host continues");
+            try
+            {
+                await StopAsync(cancellationToken).ConfigureAwait(false);
+            }
+            catch (Exception cleanupError)
+            {
+                _logger.LogError(cleanupError, "OtOpcUaServerHostedService: failed to detach OPC UA bindings after startup failure");
+            }
+            var released = await FailedServiceLevelBindingCleanup.StopAndDisposeAsync(
+                async () => await _server.StopAsync(CancellationToken.None).ConfigureAwait(false),
+                () => _appHost.DisposeAsync(), _logger).ConfigureAwait(false);
+            if (released)
+            {
+                _appHost = null;
+                _server = null;
+            }
+            return;
         }
 
         // arch-review 03/S19 — LAST, after the node manager is known non-null and after the ACL gate is

src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/OpcUaApplicationHost.cs

@@ -69,8 +69,10 @@ public sealed class OpcUaApplicationHostOptions
     ///         Note this controls <i>admission</i>, not authority. An admitted anonymous session is a
     ///         normal principal (<c>anonymous</c>) whose grants come from <c>NodeAcl</c> rows naming it,
     ///         exactly like a key's principal — there is no anonymous bypass branch in the evaluator.
-    ///         Until per-node enforcement lands, an admitted session of ANY kind can still read the whole
-    ///         address space, because reads carry no authorization check yet.
+    ///         When a wired data-plane authorizer is enabled, per-node ACL checks apply to anonymous
+    ///         sessions, including reads. Reads denied by the node manager return <c>BadUserAccessDenied</c>.
+    ///         With the authorizer disabled or not wired, reads retain the legacy behaviour without
+    ///         per-node ACL enforcement.
     ///     </para>
     /// </remarks>
     public bool AllowAnonymous { get; set; } = true;
@@ -558,10 +560,15 @@ public sealed class OpcUaApplicationHost : IAsyncDisposable
     /// <returns>A task that represents the asynchronous operation.</returns>
     public async ValueTask DisposeAsync()
     {
-        if (_impersonateHandler is not null && _server?.CurrentInstance?.SessionManager is { } sessionManager)
+        try
         {
-            try { sessionManager.ImpersonateUser -= _impersonateHandler; }
-            catch (Exception ex) { _logger.LogWarning(ex, "OpcUaApplicationHost: detaching ImpersonateUser threw"); }
+            // An explicit SDK stop may already have halted CurrentInstance; still continue disposal.
+            if (_impersonateHandler is not null && _server?.CurrentInstance?.SessionManager is { } sessionManager)
+                sessionManager.ImpersonateUser -= _impersonateHandler;
+        }
+        catch (Exception ex)
+        {
+            _logger.LogWarning(ex, "OpcUaApplicationHost: detaching ImpersonateUser threw");
         }
         _impersonateHandler = null;
 

src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/SdkServiceLevelPublisher.cs

@@ -38,8 +38,8 @@ public sealed class SdkServiceLevelPublisher : IServiceLevelPublisher
         var node = _serverInternal.ServerObject?.ServiceLevel;
         if (node is null)
         {
-            _logger.LogWarning("SdkServiceLevelPublisher: ServerObject.ServiceLevel unavailable; skipping write");
-            return;
+            _logger.LogWarning("SdkServiceLevelPublisher: ServerObject.ServiceLevel unavailable");
+            throw new InvalidOperationException("Server.ServiceLevel is unavailable.");
         }
 
         try
@@ -55,6 +55,7 @@ public sealed class SdkServiceLevelPublisher : IServiceLevelPublisher
         catch (Exception ex)
         {
             _logger.LogWarning(ex, "SdkServiceLevelPublisher: write to Server.ServiceLevel threw");
+            throw;
         }
     }
 }

src/Server/ZB.MOM.WW.OtOpcUa.Runtime/OpcUa/OpcUaPublishActor.cs

@@ -147,6 +147,7 @@ public sealed class OpcUaPublishActor : ReceiveActor, IWithTimers
     private readonly TimeSpan _staleWindow;
     private readonly TimeSpan _probeFreshnessWindow;
     private readonly TimeSpan _healthTickInterval;
+    private readonly Func<DateTime> _utcNow;
     private readonly Akka.Cluster.Cluster _cluster = Akka.Cluster.Cluster.Get(Context.System);
     private readonly ILoggingAdapter _log = Context.GetLogger();
 
@@ -200,9 +201,10 @@ public sealed class OpcUaPublishActor : ReceiveActor, IWithTimers
     /// <param name="probeFreshnessWindow">The window beyond which a peer's OPC UA probe verdict about
     /// this node is considered stale (and thus given the benefit of the doubt rather than demoting);
     /// defaults to 30 seconds.</param>
-    /// <param name="healthTickInterval">The period between self-driven DB-health refresh ticks (each
-    /// Asks <paramref name="dbHealthProbe"/> for its cached status); defaults to 5 seconds. No timer is
-    /// started when <paramref name="dbHealthProbe"/> is null.</param>
+    /// <param name="healthTickInterval">The period between freshness ticks; defaults to 5 seconds.
+    /// DB-backed nodes Ask the probe for cached status; DB-less nodes recompute snapshot freshness.
+    /// Legacy nodes without a probe do not start a timer.</param>
+    /// <param name="utcNow">The UTC clock used for freshness; defaults to <see cref="DateTime.UtcNow"/>.</param>
     /// <param name="dbLess">Per-cluster mesh Phase 4: this is a driver-only node with no ConfigDb, so the
     /// ServiceLevel DB-reachability input is retired (<c>DbReachable</c> treated constant-true, only
     /// staleness demotes). No <paramref name="dbHealthProbe"/> is wired on such a node.</param>
@@ -219,7 +221,8 @@ public sealed class OpcUaPublishActor : ReceiveActor, IWithTimers
         TimeSpan? probeFreshnessWindow = null,
         TimeSpan? healthTickInterval = null,
         bool dbLess = false,
-        IDataPlaneAuthoritySink? dataPlaneAuthority = null) =>
+        IDataPlaneAuthoritySink? dataPlaneAuthority = null,
+        Func<DateTime>? utcNow = null) =>
         Akka.Actor.Props.Create(() => new OpcUaPublishActor(
             sink ?? NullOpcUaAddressSpaceSink.Instance,
             serviceLevel ?? NullServiceLevelPublisher.Instance,
@@ -232,7 +235,8 @@ public sealed class OpcUaPublishActor : ReceiveActor, IWithTimers
             probeFreshnessWindow,
             healthTickInterval,
             dbLess,
-            dataPlaneAuthority)).WithDispatcher(DispatcherId);
+            dataPlaneAuthority,
+            utcNow)).WithDispatcher(DispatcherId);
 
     /// <summary>Test-only Props that omits the pinned-dispatcher requirement and skips the
     /// DPS subscribe so unit tests can spin up the actor on a vanilla TestKit cluster.</summary>
@@ -249,9 +253,10 @@ public sealed class OpcUaPublishActor : ReceiveActor, IWithTimers
     /// <param name="probeFreshnessWindow">The window beyond which a peer's OPC UA probe verdict about
     /// this node is considered stale (and thus given the benefit of the doubt rather than demoting);
     /// defaults to 30 seconds.</param>
-    /// <param name="healthTickInterval">The period between self-driven DB-health refresh ticks (each
-    /// Asks <paramref name="dbHealthProbe"/> for its cached status); defaults to 5 seconds. No timer is
-    /// started when <paramref name="dbHealthProbe"/> is null.</param>
+    /// <param name="healthTickInterval">The period between freshness ticks; defaults to 5 seconds.
+    /// DB-backed nodes Ask the probe for cached status; DB-less nodes recompute snapshot freshness.
+    /// Legacy nodes without a probe do not start a timer.</param>
+    /// <param name="utcNow">The UTC clock used for freshness; defaults to <see cref="DateTime.UtcNow"/>.</param>
     /// <param name="dbLess">Per-cluster mesh Phase 4: this is a driver-only node with no ConfigDb, so the
     /// ServiceLevel DB-reachability input is retired (<c>DbReachable</c> treated constant-true, only
     /// staleness demotes). No <paramref name="dbHealthProbe"/> is wired on such a node.</param>
@@ -269,7 +274,8 @@ public sealed class OpcUaPublishActor : ReceiveActor, IWithTimers
         TimeSpan? probeFreshnessWindow = null,
         TimeSpan? healthTickInterval = null,
         bool dbLess = false,
-        IDataPlaneAuthoritySink? dataPlaneAuthority = null) =>
+        IDataPlaneAuthoritySink? dataPlaneAuthority = null,
+        Func<DateTime>? utcNow = null) =>
         Akka.Actor.Props.Create(() => new OpcUaPublishActor(
             sink ?? NullOpcUaAddressSpaceSink.Instance,
             serviceLevel ?? NullServiceLevelPublisher.Instance,
@@ -282,7 +288,8 @@ public sealed class OpcUaPublishActor : ReceiveActor, IWithTimers
             probeFreshnessWindow,
             healthTickInterval,
             dbLess,
-            dataPlaneAuthority));
+            dataPlaneAuthority,
+            utcNow));
 
     /// <summary>Initializes a new instance of the <see cref="OpcUaPublishActor"/> class.</summary>
     /// <param name="sink">The OPC UA address space sink.</param>
@@ -298,9 +305,10 @@ public sealed class OpcUaPublishActor : ReceiveActor, IWithTimers
     /// <param name="probeFreshnessWindow">The window beyond which a peer's OPC UA probe verdict about
     /// this node is considered stale (and thus given the benefit of the doubt rather than demoting);
     /// defaults to 30 seconds.</param>
-    /// <param name="healthTickInterval">The period between self-driven DB-health refresh ticks (each
-    /// Asks <paramref name="dbHealthProbe"/> for its cached status); defaults to 5 seconds. No timer is
-    /// started when <paramref name="dbHealthProbe"/> is null.</param>
+    /// <param name="healthTickInterval">The period between freshness ticks; defaults to 5 seconds.
+    /// DB-backed nodes Ask the probe for cached status; DB-less nodes recompute snapshot freshness.
+    /// Legacy nodes without a probe do not start a timer.</param>
+    /// <param name="utcNow">The UTC clock used for freshness; defaults to <see cref="DateTime.UtcNow"/>.</param>
     /// <param name="dbLess">Per-cluster mesh Phase 4: this is a driver-only node with no ConfigDb, so the
     /// ServiceLevel DB-reachability input is retired (<c>DbReachable</c> treated constant-true, only
     /// staleness demotes). No <paramref name="dbHealthProbe"/> is wired on such a node.</param>
@@ -316,7 +324,8 @@ public sealed class OpcUaPublishActor : ReceiveActor, IWithTimers
         TimeSpan? probeFreshnessWindow = null,
         TimeSpan? healthTickInterval = null,
         bool dbLess = false,
-        IDataPlaneAuthoritySink? dataPlaneAuthority = null)
+        IDataPlaneAuthoritySink? dataPlaneAuthority = null,
+        Func<DateTime>? utcNow = null)
     {
         _sink = sink;
         _dataPlaneAuthority = dataPlaneAuthority;
@@ -330,6 +339,7 @@ public sealed class OpcUaPublishActor : ReceiveActor, IWithTimers
         _staleWindow = staleWindow ?? TimeSpan.FromSeconds(30);
         _probeFreshnessWindow = probeFreshnessWindow ?? TimeSpan.FromSeconds(30);
         _healthTickInterval = healthTickInterval ?? TimeSpan.FromSeconds(5);
+        _utcNow = utcNow ?? (() => DateTime.UtcNow);
 
         Receive<AttributeValueUpdate>(HandleAttributeUpdate);
         Receive<AttributeValueBatchUpdate>(HandleAttributeBatchUpdate);
@@ -353,11 +363,10 @@ public sealed class OpcUaPublishActor : ReceiveActor, IWithTimers
             DistributedPubSub.Get(Context.System).Mediator.Tell(new Subscribe(RedundancyStateTopic, Self));
         }
 
-        // Production delivery of DB-health: when a probe is wired, kick an immediate refresh + start the
-        // periodic tick so _lastDbHealth gets populated and kept fresh without any external pump. Gated
-        // ONLY on the probe being present (independent of the DPS subscribe) so the calculator path works
-        // in tests too. No probe → stay on the legacy role-only seam (no timer).
-        if (_dbHealthProbe is not null)
+        // DB-backed nodes refresh their cached probe status; DB-less nodes still need periodic
+        // snapshot/probe-verdict age checks even when no new messages arrive. Legacy nodes keep
+        // their role-only behavior without a timer.
+        if (_dbLess || _dbHealthProbe is not null)
         {
             Self.Tell(HealthTick.Instance);                                        // immediate first refresh
             Timers.StartPeriodicTimer("db-health", HealthTick.Instance, _healthTickInterval);
@@ -970,10 +979,10 @@ public sealed class OpcUaPublishActor : ReceiveActor, IWithTimers
         // node starting Detached/role-less (first level = 0) would be dedup'd away, leaving the SDK's
         // built-in default (255 = full service) standing — a degraded node wrongly advertising 255.
         if (_publishedAtLeastOnce && msg.ServiceLevel == _lastServiceLevel) return;
-        _lastServiceLevel = msg.ServiceLevel;
         try
         {
             _serviceLevel.Publish(msg.ServiceLevel);
+            _lastServiceLevel = msg.ServiceLevel;
             _publishedAtLeastOnce = true;
             OtOpcUaTelemetry.ServiceLevelChange.Add(1,
                 new KeyValuePair<string, object?>("level", msg.ServiceLevel));
@@ -981,6 +990,8 @@ public sealed class OpcUaPublishActor : ReceiveActor, IWithTimers
         }
         catch (Exception ex)
         {
+            // A failed write may be partially applied; even a previous successful value must retry.
+            _publishedAtLeastOnce = false;
             _log.Warning(ex, "OpcUaPublish: ServiceLevel publisher threw at level {Level}", msg.ServiceLevel);
         }
     }
@@ -1004,7 +1015,8 @@ public sealed class OpcUaPublishActor : ReceiveActor, IWithTimers
         RecomputeServiceLevel();
     }
 
-    /// <summary>Periodic self-tick: Asks the local <see cref="DbHealthProbeActor"/> for its cached
+    /// <summary>Periodic self-tick: recomputes freshness directly when no DB probe exists; otherwise
+    /// Asks the local <see cref="DbHealthProbeActor"/> for its cached
     /// status and pipes the reply back to <see cref="Self"/>, where <see cref="HandleDbHealthStatus"/>
     /// caches it + recomputes. A hung/late probe (Ask timeout) pipes a <c>Reachable=false</c> status so
     /// the node FAIL-SAFE-DEMOTES rather than freezing the last-known-good. The continuation only
@@ -1013,11 +1025,17 @@ public sealed class OpcUaPublishActor : ReceiveActor, IWithTimers
     /// touched here.</summary>
     private void OnHealthTick()
     {
-        _dbHealthProbe!.Ask<DbHealthProbeActor.DbHealthStatus>(
+        if (_dbHealthProbe is null)
+        {
+            RecomputeServiceLevel();
+            return;
+        }
+
+        _dbHealthProbe.Ask<DbHealthProbeActor.DbHealthStatus>(
                 DbHealthProbeActor.GetStatus.Instance, TimeSpan.FromSeconds(1))
             .ContinueWith(t => t.IsCompletedSuccessfully
                 ? t.Result
-                : new DbHealthProbeActor.DbHealthStatus(false, DateTime.UtcNow, "db-health ask timeout"))
+                : new DbHealthProbeActor.DbHealthStatus(false, _utcNow(), "db-health ask timeout"))
             .PipeTo(Self);
     }
 
@@ -1030,7 +1048,7 @@ public sealed class OpcUaPublishActor : ReceiveActor, IWithTimers
     {
         // The result targets the probed node. If it isn't me, it's about a peer — ignore it.
         if (_localNode is null || r.NodeId != _localNode.Value) return;
-        _probeAboutMe = (r.Ok, DateTime.UtcNow);
+        _probeAboutMe = (r.Ok, _utcNow());
         RecomputeServiceLevel();
     }
 
@@ -1042,7 +1060,7 @@ public sealed class OpcUaPublishActor : ReceiveActor, IWithTimers
     private bool OpcUaProbeOk()
     {
         if (_probeAboutMe is not { } verdict) return true;
-        if (DateTime.UtcNow - verdict.At > _probeFreshnessWindow) return true;
+        if (_utcNow() - verdict.At > _probeFreshnessWindow) return true;
         return verdict.Ok;
     }
 
@@ -1079,7 +1097,7 @@ public sealed class OpcUaPublishActor : ReceiveActor, IWithTimers
         // wins, so a DB-less Detached node stays 0.
         if (_dbLess)
         {
-            var utcNow = DateTime.UtcNow;
+            var utcNow = _utcNow();
             var dbLessInputs = new NodeHealthInputs(
                 MemberState: SafeSelfStatus(),
                 DbReachable: true,
@@ -1099,7 +1117,7 @@ public sealed class OpcUaPublishActor : ReceiveActor, IWithTimers
             return;
         }
 
-        var now = DateTime.UtcNow;
+        var now = _utcNow();
         var inputs = new NodeHealthInputs(
             MemberState: SafeSelfStatus(),
             DbReachable: _lastDbHealth.Reachable,

tests/Core/ZB.MOM.WW.OtOpcUa.Commons.Tests/OpcUa/DeferredServiceLevelPublisherTests.cs

@@ -10,10 +10,10 @@ namespace ZB.MOM.WW.OtOpcUa.Commons.Tests.OpcUa;
 public class DeferredServiceLevelPublisherTests
 {
     [Fact]
-    public void Before_SetInner_Publish_is_a_noop()
+    public void Before_SetInner_Publish_accepts_a_cached_request()
     {
         var publisher = new DeferredServiceLevelPublisher();
-        // Must not throw; the NullServiceLevelPublisher absorbs it.
+        // Accept the request before an SDK publisher exists.
         publisher.Publish(200);
     }
 
@@ -30,7 +30,7 @@ public class DeferredServiceLevelPublisherTests
     }
 
     [Fact]
-    public void SetInner_null_reverts_to_null_publisher()
+    public void SetInner_null_detaches_the_previous_publisher()
     {
         var spy = new SpyPublisher();
         var publisher = new DeferredServiceLevelPublisher();
@@ -39,8 +39,139 @@ public class DeferredServiceLevelPublisherTests
 
         publisher.Publish(100);
 
-        // The spy should NOT have received the publish after revert.
-        spy.LastPublished.ShouldBe((byte)0, "spy should not have been updated after revert to null");
+        // The previous publisher must not receive an unbound request.
+        spy.LastPublished.ShouldBe((byte)0, "the previous publisher should not be updated after unbinding");
+    }
+
+    [Fact]
+    public void Binding_without_a_request_does_not_invent_a_level()
+    {
+        var received = new List<byte>();
+        new DeferredServiceLevelPublisher().SetInner(new CallbackPublisher(received.Add));
+        received.ShouldBeEmpty();
+    }
+
+    [Theory]
+    [InlineData((byte)100)]
+    [InlineData((byte)0)]
+    public void Binding_replays_the_latest_request_including_zero(byte latest)
+    {
+        var publisher = new DeferredServiceLevelPublisher();
+        publisher.Publish(240);
+        publisher.Publish(latest);
+        var received = new List<byte>();
+        publisher.SetInner(new CallbackPublisher(received.Add));
+        received.ShouldBe(new[] { latest });
+    }
+
+    [Fact]
+    public void Unbinding_retains_latest_for_rebinding()
+    {
+        var publisher = new DeferredServiceLevelPublisher();
+        var old = new List<byte>();
+        publisher.SetInner(new CallbackPublisher(old.Add));
+        publisher.Publish(240);
+        publisher.SetInner(null);
+        publisher.Publish(0);
+        var replacement = new List<byte>();
+        publisher.SetInner(new CallbackPublisher(replacement.Add));
+        old.ShouldBe(new byte[] { 240 });
+        replacement.ShouldBe(new byte[] { 0 });
+    }
+
+    [Fact]
+    public void Failed_publish_retains_the_requested_value_for_replay()
+    {
+        var publisher = new DeferredServiceLevelPublisher();
+        publisher.SetInner(new CallbackPublisher(_ => throw new InvalidOperationException()));
+        Should.Throw<InvalidOperationException>(() => publisher.Publish(0));
+        var received = new List<byte>();
+        publisher.SetInner(new CallbackPublisher(received.Add));
+        received.ShouldBe(new byte[] { 0 });
+    }
+
+    [Fact]
+    public void Failed_replay_keeps_candidate_bound_for_later_publish()
+    {
+        var publisher = new DeferredServiceLevelPublisher();
+        publisher.Publish(100);
+        var fail = true;
+        var received = new List<byte>();
+        var candidate = new CallbackPublisher(value =>
+        {
+            if (fail) throw new InvalidOperationException();
+            received.Add(value);
+        });
+        Should.Throw<InvalidOperationException>(() => publisher.SetInner(candidate));
+        fail = false;
+        publisher.Publish(0);
+        publisher.SetInner(null);
+        publisher.SetInner(candidate);
+        received.ShouldBe(new byte[] { 0, 0 });
+    }
+
+    [Fact]
+    public void Failed_replay_retains_latest_for_a_replacement_publisher()
+    {
+        var publisher = new DeferredServiceLevelPublisher();
+        publisher.Publish(100);
+        Should.Throw<InvalidOperationException>(() => publisher.SetInner(
+            new CallbackPublisher(_ => throw new InvalidOperationException())));
+        var received = new List<byte>();
+        publisher.SetInner(new CallbackPublisher(received.Add));
+        received.ShouldBe(new byte[] { 100 });
+    }
+
+    [Fact]
+    public async Task Binding_waits_for_inflight_publish_then_replays_latest()
+    {
+        var publisher = new DeferredServiceLevelPublisher();
+        using var entered = new ManualResetEventSlim();
+        using var release = new ManualResetEventSlim();
+        publisher.SetInner(new CallbackPublisher(_ =>
+        {
+            entered.Set();
+            release.Wait(TimeSpan.FromSeconds(5), TestContext.Current.CancellationToken).ShouldBeTrue();
+        }));
+        var publish = Task.Run(() => publisher.Publish(100), TestContext.Current.CancellationToken);
+        var received = new List<byte>();
+        using var bindingStarted = new ManualResetEventSlim();
+        Exception? bindingError = null;
+        var binding = new Thread(() =>
+        {
+            bindingStarted.Set();
+            try { publisher.SetInner(new CallbackPublisher(received.Add)); }
+            catch (Exception ex) { bindingError = ex; }
+        });
+        var bindingWasStarted = false;
+        try
+        {
+            entered.Wait(TimeSpan.FromSeconds(5), TestContext.Current.CancellationToken).ShouldBeTrue();
+            binding.Start();
+            bindingWasStarted = true;
+            bindingStarted.Wait(TimeSpan.FromSeconds(5), TestContext.Current.CancellationToken).ShouldBeTrue();
+            // Past the marker, SetInner is the thread's only potentially blocking operation.
+            // Observe actual contention rather than assuming Task.Run has entered the adapter.
+            SpinWait.SpinUntil(() => !binding.IsAlive ||
+                (binding.ThreadState & System.Threading.ThreadState.WaitSleepJoin) != 0,
+                TimeSpan.FromSeconds(3)).ShouldBeTrue();
+            (binding.ThreadState & System.Threading.ThreadState.WaitSleepJoin).ShouldNotBe(
+                (System.Threading.ThreadState)0, "binding must wait for the in-flight delivery");
+        }
+        finally
+        {
+            release.Set();
+            if (bindingWasStarted) binding.Join(TimeSpan.FromSeconds(5)).ShouldBeTrue();
+            await publish.WaitAsync(TimeSpan.FromSeconds(5), TestContext.Current.CancellationToken);
+        }
+        bindingError.ShouldBeNull();
+        publisher.Publish(0);
+        received.ShouldBe(new byte[] { 100, 0 });
+    }
+
+    private sealed class CallbackPublisher(Action<byte> publish) : IServiceLevelPublisher
+    {
+        public void Publish(byte serviceLevel) => publish(serviceLevel);
     }
 
     // ---- test double ----

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/AbCipReinitializeReleasesStateTests.cs

@@ -1,4 +1,5 @@
 using Shouldly;
+using ZB.MOM.WW.OtOpcUa.Tests;
 using Xunit;
 
 namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests;
@@ -8,7 +9,7 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests;
 ///     orphaned the previous state's probe loop + handles. It now releases them first.
 /// </summary>
 [Trait("Category", "Unit")]
-public sealed class AbCipReinitializeReleasesStateTests
+public sealed class AbCipReinitializeReleasesStateTests(ITestOutputHelper output)
 {
     /// <summary>Initialize twice: the first state's probe loop has stopped and its probe handle is disposed.</summary>
     [Fact]
@@ -27,28 +28,94 @@ public sealed class AbCipReinitializeReleasesStateTests
                 ProbeTagPath = "@raw_cpu_type",
             },
         }, "drv-reinit", factory);
-        await drv.InitializeAsync("{}", CancellationToken.None);
+        await FixtureCleanup.RunAsync(async () =>
+        {
+            await drv.InitializeAsync("{}", CancellationToken.None);
 
-        var first = drv.GetDeviceState(host)!;
-        // Positive control: the first probe loop is running and has initialised its runtime.
+            var first = drv.GetDeviceState(host)!;
+            // Positive control: the first probe loop is running and has initialised its runtime.
+            var deadline = DateTime.UtcNow.AddSeconds(5);
+            while (!(factory.Tags.TryGetValue("@raw_cpu_type", out var t) && t.InitializeCount > 0))
+            {
+                if (DateTime.UtcNow > deadline) throw new TimeoutException("probe never started");
+                await Task.Delay(10);
+            }
+            var firstTag = factory.Tags["@raw_cpu_type"];
+            var firstLoop = first.ProbeTask;
+            _ = firstLoop.ShouldNotBeNull();
+            firstLoop!.IsCompleted.ShouldBeFalse();
+            firstTag.Disposed.ShouldBeFalse();
+
+            await drv.InitializeAsync("{}", CancellationToken.None);
+
+            firstLoop.IsCompleted.ShouldBeTrue(); // joined
+            firstTag.Disposed.ShouldBeTrue();
+            drv.GetDeviceState(host).ShouldNotBeSameAs(first);
+        }, () => drv.ShutdownAsync(CancellationToken.None),
+            failure => output.WriteLine($"AbCip SecondInitialize cleanup failed: {failure}"));
+    }
+
+    /// <summary>Failure after a live first or replacement state must release both owned resources.</summary>
+    [Theory]
+    [InlineData(false)]
+    [InlineData(true)]
+    public async Task Body_failure_releases_live_probe_resources(bool afterReplacement)
+    {
+        const string host = "ab://10.0.0.5/1,0";
+        var factory = new FakeAbCipTagFactory();
+        var drv = new AbCipDriver(new AbCipDriverOptions
+        {
+            Devices = [new AbCipDeviceOptions(host)],
+            Probe = new AbCipProbeOptions
+            {
+                Enabled = true,
+                Interval = TimeSpan.FromMilliseconds(20),
+                Timeout = TimeSpan.FromMilliseconds(200),
+                ProbeTagPath = "@raw_cpu_type",
+            },
+        }, "drv-reinit", factory);
+        Task? firstLoop = null, secondLoop = null;
+        FakeAbCipTag? firstTag = null, secondTag = null;
+        var sentinel = new InvalidOperationException("body sentinel");
+        var actual = await Should.ThrowAsync<InvalidOperationException>(() => FixtureCleanup.RunAsync(async () =>
+        {
+            await drv.InitializeAsync("{}", CancellationToken.None);
+            await WaitForProbeAsync(() => factory.Tags.TryGetValue("@raw_cpu_type", out var tag) && tag.InitializeCount > 0);
+            firstTag = factory.Tags["@raw_cpu_type"];
+            firstLoop = drv.GetDeviceState(host)!.ProbeTask;
+            _ = firstLoop.ShouldNotBeNull();
+            firstLoop!.IsCompleted.ShouldBeFalse();
+            firstTag.Disposed.ShouldBeFalse();
+            if (afterReplacement)
+            {
+                await drv.InitializeAsync("{}", CancellationToken.None);
+                await WaitForProbeAsync(() => factory.Tags.TryGetValue("@raw_cpu_type", out var tag) && !ReferenceEquals(tag, firstTag) && tag.InitializeCount > 0);
+                secondTag = factory.Tags["@raw_cpu_type"];
+                secondLoop = drv.GetDeviceState(host)!.ProbeTask;
+                _ = secondLoop.ShouldNotBeNull();
+                secondLoop!.IsCompleted.ShouldBeFalse();
+            }
+            throw sentinel;
+        }, () => drv.ShutdownAsync(CancellationToken.None),
+            failure => output.WriteLine($"AbCip failure fixture cleanup failed: {failure}")));
+        actual.ShouldBeSameAs(sentinel);
+        firstLoop!.IsCompleted.ShouldBeTrue();
+        firstTag!.Disposed.ShouldBeTrue();
+        if (afterReplacement)
+        {
+            secondLoop!.IsCompleted.ShouldBeTrue();
+            secondTag!.Disposed.ShouldBeTrue();
+        }
+    }
+
+    private static async Task WaitForProbeAsync(Func<bool> condition)
+    {
         var deadline = DateTime.UtcNow.AddSeconds(5);
-        while (!(factory.Tags.TryGetValue("@raw_cpu_type", out var t) && t.InitializeCount > 0))
+        while (!condition())
         {
             if (DateTime.UtcNow > deadline) throw new TimeoutException("probe never started");
             await Task.Delay(10);
         }
-        var firstTag = factory.Tags["@raw_cpu_type"];
-        var firstLoop = first.ProbeTask;
-        firstLoop.ShouldNotBeNull();
-        firstLoop!.IsCompleted.ShouldBeFalse();
-        firstTag.Disposed.ShouldBeFalse();
-
-        await drv.InitializeAsync("{}", CancellationToken.None);
-
-        firstLoop.IsCompleted.ShouldBeTrue(); // joined
-        firstTag.Disposed.ShouldBeTrue();
-        drv.GetDeviceState(host).ShouldNotBeSameAs(first);
-
-        await drv.ShutdownAsync(CancellationToken.None);
     }
+
 }

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/FixtureCleanupTests.cs

@@ -0,0 +1,92 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Tests;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests;
+
+[Trait("Category", "Unit")]
+public sealed class FixtureCleanupTests
+{
+    [Fact]
+    public async Task Successful_body_runs_one_awaited_cleanup()
+    {
+        var calls = 0;
+        var release = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
+        var run = FixtureCleanup.RunAsync(() => Task.CompletedTask, async () =>
+        {
+            calls++;
+            await release.Task;
+        }, _ => throw new Exception("unexpected report"));
+
+        run.IsCompleted.ShouldBeFalse();
+        release.SetResult();
+        await run;
+        calls.ShouldBe(1);
+    }
+
+    [Fact]
+    public async Task Body_fault_remains_same_exception_and_original_throwing_stack()
+    {
+        var primary = new InvalidOperationException("body");
+        var cleanupCalls = 0;
+        var actual = await Should.ThrowAsync<InvalidOperationException>(() => FixtureCleanup.RunAsync(
+            () => ThrowFromBody(primary),
+            () => { cleanupCalls++; return Task.CompletedTask; },
+            _ => throw new Exception("unexpected report")));
+
+        actual.ShouldBeSameAs(primary);
+        actual.StackTrace.ShouldNotBeNull().ShouldContain(nameof(ThrowFromBody));
+        cleanupCalls.ShouldBe(1);
+    }
+
+    [Fact]
+    public async Task Cleanup_only_fault_is_thrown_exactly()
+    {
+        var cleanup = new ApplicationException("cleanup");
+        var actual = await Should.ThrowAsync<ApplicationException>(() => FixtureCleanup.RunAsync(
+            () => Task.CompletedTask,
+            () => Task.FromException(cleanup),
+            _ => throw new Exception("unexpected report")));
+        actual.ShouldBeSameAs(cleanup);
+    }
+
+    [Fact]
+    public async Task Both_faults_preserve_primary_and_record_secondary_once()
+    {
+        var primary = new InvalidOperationException("body");
+        var cleanup = new ApplicationException("cleanup");
+        var reported = new List<Exception>();
+        var actual = await Should.ThrowAsync<InvalidOperationException>(() => FixtureCleanup.RunAsync(
+            () => ThrowFromBody(primary),
+            () => Task.FromException(cleanup),
+            reported.Add));
+
+        actual.ShouldBeSameAs(primary);
+        actual.StackTrace.ShouldNotBeNull().ShouldContain(nameof(ThrowFromBody));
+        actual.Data[FixtureCleanup.SecondaryExceptionKey].ShouldBeSameAs(cleanup);
+        reported.Count.ShouldBe(1);
+        reported[0].ShouldBeSameAs(cleanup);
+    }
+
+    [Fact]
+    public async Task Reporting_fault_does_not_replace_primary()
+    {
+        var primary = new InvalidOperationException("body");
+        var cleanup = new ApplicationException("cleanup");
+        var reportCalls = 0;
+        var actual = await Should.ThrowAsync<InvalidOperationException>(() => FixtureCleanup.RunAsync(
+            () => ThrowFromBody(primary),
+            () => Task.FromException(cleanup),
+            _ => { reportCalls++; throw new Exception("report"); }));
+
+        actual.ShouldBeSameAs(primary);
+        actual.Data[FixtureCleanup.SecondaryExceptionKey].ShouldBeSameAs(cleanup);
+        reportCalls.ShouldBe(1);
+    }
+
+    private static async Task ThrowFromBody(Exception failure)
+    {
+        await Task.Yield();
+        throw failure;
+    }
+}

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests.csproj

@@ -38,4 +38,7 @@
         <Compile Include="..\ZB.MOM.WW.OtOpcUa.Driver.Ab.Transport.Tests\Fakes\FakeCipTarget.cs" Link="Fakes\FakeCipTarget.cs" />
     </ItemGroup>
 
+    <ItemGroup>
+        <Compile Include="..\..\TestSupport\FixtureCleanup.cs" Link="TestSupport\FixtureCleanup.cs" />
+    </ItemGroup>
 </Project>

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/AbLegacyReinitializeReleasesStateTests.cs

@@ -1,4 +1,5 @@
 using Shouldly;
+using ZB.MOM.WW.OtOpcUa.Tests;
 using Xunit;
 using ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.PlcFamilies;
 
@@ -10,7 +11,7 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests;
 ///     probe loop + runtime. It now releases them first.
 /// </summary>
 [Trait("Category", "Unit")]
-public sealed class AbLegacyReinitializeReleasesStateTests
+public sealed class AbLegacyReinitializeReleasesStateTests(ITestOutputHelper output)
 {
     /// <summary>Initialize twice: the first state's probe loop has stopped and its probe runtime is disposed.</summary>
     [Fact]
@@ -23,28 +24,88 @@ public sealed class AbLegacyReinitializeReleasesStateTests
             Devices = [new AbLegacyDeviceOptions(host, AbLegacyPlcFamily.Slc500)],
             Probe = new AbLegacyProbeOptions { Enabled = true, Interval = TimeSpan.FromMilliseconds(20), ProbeAddress = "S:0" },
         }, "drv-reinit", factory);
-        await drv.InitializeAsync("{}", CancellationToken.None);
+        await FixtureCleanup.RunAsync(async () =>
+        {
+            await drv.InitializeAsync("{}", CancellationToken.None);
 
-        var first = drv.GetDeviceState(host)!;
-        // Positive control: the first state's probe loop is running and has created + initialised its runtime.
+            var first = drv.GetDeviceState(host)!;
+            // Positive control: the first state's probe loop is running and has created + initialised its runtime.
+            var deadline = DateTime.UtcNow.AddSeconds(5);
+            while (!(factory.Tags.TryGetValue("S:0", out var t) && t.InitializeCount > 0))
+            {
+                if (DateTime.UtcNow > deadline) throw new TimeoutException("probe never started");
+                await Task.Delay(10);
+            }
+            var firstTag = factory.Tags["S:0"];
+            var firstLoop = first.ProbeTask;
+            _ = firstLoop.ShouldNotBeNull();
+            firstLoop!.IsCompleted.ShouldBeFalse();
+            firstTag.Disposed.ShouldBeFalse();
+
+            await drv.InitializeAsync("{}", CancellationToken.None);
+
+            firstLoop.IsCompleted.ShouldBeTrue(); // joined
+            firstTag.Disposed.ShouldBeTrue();
+            drv.GetDeviceState(host).ShouldNotBeSameAs(first);
+        }, () => drv.ShutdownAsync(CancellationToken.None),
+            failure => output.WriteLine($"AbLegacy SecondInitialize cleanup failed: {failure}"));
+    }
+
+    /// <summary>Failure after a live first or replacement state must release both owned resources.</summary>
+    [Theory]
+    [InlineData(false)]
+    [InlineData(true)]
+    public async Task Body_failure_releases_live_probe_resources(bool afterReplacement)
+    {
+        const string host = "ab://10.0.0.5/1,0";
+        var factory = new FakeAbLegacyTagFactory();
+        var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            Devices = [new AbLegacyDeviceOptions(host, AbLegacyPlcFamily.Slc500)],
+            Probe = new AbLegacyProbeOptions { Enabled = true, Interval = TimeSpan.FromMilliseconds(20), ProbeAddress = "S:0" },
+        }, "drv-reinit", factory);
+        Task? firstLoop = null, secondLoop = null;
+        FakeAbLegacyTag? firstTag = null, secondTag = null;
+        var sentinel = new InvalidOperationException("body sentinel");
+        var actual = await Should.ThrowAsync<InvalidOperationException>(() => FixtureCleanup.RunAsync(async () =>
+        {
+            await drv.InitializeAsync("{}", CancellationToken.None);
+            await WaitForProbeAsync(() => factory.Tags.TryGetValue("S:0", out var tag) && tag.InitializeCount > 0);
+            firstTag = factory.Tags["S:0"];
+            firstLoop = drv.GetDeviceState(host)!.ProbeTask;
+            _ = firstLoop.ShouldNotBeNull();
+            firstLoop!.IsCompleted.ShouldBeFalse();
+            firstTag.Disposed.ShouldBeFalse();
+            if (afterReplacement)
+            {
+                await drv.InitializeAsync("{}", CancellationToken.None);
+                await WaitForProbeAsync(() => factory.Tags.TryGetValue("S:0", out var tag) && !ReferenceEquals(tag, firstTag) && tag.InitializeCount > 0);
+                secondTag = factory.Tags["S:0"];
+                secondLoop = drv.GetDeviceState(host)!.ProbeTask;
+                _ = secondLoop.ShouldNotBeNull();
+                secondLoop!.IsCompleted.ShouldBeFalse();
+            }
+            throw sentinel;
+        }, () => drv.ShutdownAsync(CancellationToken.None),
+            failure => output.WriteLine($"AbLegacy failure fixture cleanup failed: {failure}")));
+        actual.ShouldBeSameAs(sentinel);
+        firstLoop!.IsCompleted.ShouldBeTrue();
+        firstTag!.Disposed.ShouldBeTrue();
+        if (afterReplacement)
+        {
+            secondLoop!.IsCompleted.ShouldBeTrue();
+            secondTag!.Disposed.ShouldBeTrue();
+        }
+    }
+
+    private static async Task WaitForProbeAsync(Func<bool> condition)
+    {
         var deadline = DateTime.UtcNow.AddSeconds(5);
-        while (!(factory.Tags.TryGetValue("S:0", out var t) && t.InitializeCount > 0))
+        while (!condition())
         {
             if (DateTime.UtcNow > deadline) throw new TimeoutException("probe never started");
             await Task.Delay(10);
         }
-        var firstTag = factory.Tags["S:0"];
-        var firstLoop = first.ProbeTask;
-        firstLoop.ShouldNotBeNull();
-        firstLoop!.IsCompleted.ShouldBeFalse();
-        firstTag.Disposed.ShouldBeFalse();
-
-        await drv.InitializeAsync("{}", CancellationToken.None);
-
-        firstLoop.IsCompleted.ShouldBeTrue(); // joined
-        firstTag.Disposed.ShouldBeTrue();
-        drv.GetDeviceState(host).ShouldNotBeSameAs(first);
-
-        await drv.ShutdownAsync(CancellationToken.None);
     }
+
 }

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests.csproj

@@ -38,4 +38,7 @@
         <None Include="..\ZB.MOM.WW.OtOpcUa.Driver.Ab.Transport.Tests\Captures\*.hex" Link="Captures\%(Filename)%(Extension)" CopyToOutputDirectory="PreserveNewest"/>
     </ItemGroup>
 
+    <ItemGroup>
+        <Compile Include="..\..\TestSupport\FixtureCleanup.cs" Link="TestSupport\FixtureCleanup.cs" />
+    </ItemGroup>
 </Project>

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FocasReinitializeReleasesStateTests.cs

@@ -1,4 +1,5 @@
 using Shouldly;
+using ZB.MOM.WW.OtOpcUa.Tests;
 using Xunit;
 using ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
 
@@ -10,7 +11,7 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests;
 ///     probe loop + client. It now releases them first.
 /// </summary>
 [Trait("Category", "Unit")]
-public sealed class FocasReinitializeReleasesStateTests
+public sealed class FocasReinitializeReleasesStateTests(ITestOutputHelper output)
 {
     /// <summary>Initialize twice: the first state's probe loop has finished and its client is disposed.</summary>
     [Fact]
@@ -25,25 +26,78 @@ public sealed class FocasReinitializeReleasesStateTests
             Probe = new FocasProbeOptions { Enabled = true, Interval = TimeSpan.FromMilliseconds(20), Timeout = TimeSpan.FromSeconds(2) },
         };
         var drv = new FocasDriver(options, "focas-reinit", factory);
-        await drv.InitializeAsync("{}", CancellationToken.None);
+        await FixtureCleanup.RunAsync(async () =>
+        {
+            await drv.InitializeAsync("{}", CancellationToken.None);
 
-        var first = drv.GetDeviceState(host)!;
-        // Positive control: the first state's probe loop is demonstrably running and holds a live client.
-        await WaitUntilAsync(() => factory.Clients.Count > 0 && factory.Clients[0].IsConnected);
-        var firstLoop = first.ProbeTask;
-        firstLoop.ShouldNotBeNull();
-        firstLoop!.IsCompleted.ShouldBeFalse();
-        var firstClient = factory.Clients[0];
+            var first = drv.GetDeviceState(host)!;
+            // Positive control: the first state's probe loop is demonstrably running and holds a live client.
+            await WaitUntilAsync(() => factory.Clients.Count > 0 && factory.Clients[0].IsConnected);
+            var firstLoop = first.ProbeTask;
+            _ = firstLoop.ShouldNotBeNull();
+            firstLoop!.IsCompleted.ShouldBeFalse();
+            var firstClient = factory.Clients[0];
 
-        await drv.InitializeAsync("{}", CancellationToken.None);
+            await drv.InitializeAsync("{}", CancellationToken.None);
 
-        firstLoop.IsCompleted.ShouldBeTrue(); // joined
-        firstClient.DisposeCount.ShouldBeGreaterThanOrEqualTo(1);
+            firstLoop.IsCompleted.ShouldBeTrue(); // joined
+            firstClient.DisposeCount.ShouldBeGreaterThanOrEqualTo(1);
+            firstClient.IsConnected.ShouldBeFalse();
+            drv.GetDeviceState(host).ShouldNotBeSameAs(first);
+            _ = drv.GetDeviceState(host)!.ProbeTask.ShouldNotBeNull(); // the new state is running
+        }, () => drv.ShutdownAsync(CancellationToken.None),
+            failure => output.WriteLine($"FOCAS SecondInitialize cleanup failed: {failure}"));
+    }
+
+
+    /// <summary>Failure after a live first or replacement state must release both owned resources.</summary>
+    [Theory]
+    [InlineData(false)]
+    [InlineData(true)]
+    public async Task Body_failure_releases_live_probe_resources(bool afterReplacement)
+    {
+        const string host = "focas://10.0.0.5:8193";
+        var factory = new FakeFocasClientFactory();
+        var options = new FocasDriverOptions
+        {
+            Devices = [new FocasDeviceOptions(host)],
+            RawTags = [FocasRawTags.Entry(new FocasTagDefinition("R", host, "R100", FocasDataType.Byte))],
+            Probe = new FocasProbeOptions { Enabled = true, Interval = TimeSpan.FromMilliseconds(20), Timeout = TimeSpan.FromSeconds(2) },
+        };
+        var drv = new FocasDriver(options, "focas-reinit", factory);
+        Task? firstLoop = null, secondLoop = null;
+        FakeFocasClient? firstClient = null, secondClient = null;
+        var sentinel = new InvalidOperationException("body sentinel");
+        var actual = await Should.ThrowAsync<InvalidOperationException>(() => FixtureCleanup.RunAsync(async () =>
+        {
+            await drv.InitializeAsync("{}", CancellationToken.None);
+            await WaitUntilAsync(() => factory.Clients.Count > 0 && factory.Clients[0].IsConnected);
+            firstClient = factory.Clients[0];
+            firstLoop = drv.GetDeviceState(host)!.ProbeTask;
+            _ = firstLoop.ShouldNotBeNull();
+            firstLoop!.IsCompleted.ShouldBeFalse();
+            if (afterReplacement)
+            {
+                await drv.InitializeAsync("{}", CancellationToken.None);
+                await WaitUntilAsync(() => factory.Clients.Count > 1 && factory.Clients[1].IsConnected);
+                secondClient = factory.Clients[1];
+                secondLoop = drv.GetDeviceState(host)!.ProbeTask;
+                _ = secondLoop.ShouldNotBeNull();
+                secondLoop!.IsCompleted.ShouldBeFalse();
+            }
+            throw sentinel;
+        }, () => drv.ShutdownAsync(CancellationToken.None),
+            failure => output.WriteLine($"FOCAS failure fixture cleanup failed: {failure}")));
+        actual.ShouldBeSameAs(sentinel);
+        firstLoop!.IsCompleted.ShouldBeTrue();
+        firstClient!.DisposeCount.ShouldBeGreaterThanOrEqualTo(1);
         firstClient.IsConnected.ShouldBeFalse();
-        drv.GetDeviceState(host).ShouldNotBeSameAs(first);
-        drv.GetDeviceState(host)!.ProbeTask.ShouldNotBeNull(); // the new state is running
-
-        await drv.ShutdownAsync(CancellationToken.None);
+        if (afterReplacement)
+        {
+            secondLoop!.IsCompleted.ShouldBeTrue();
+            secondClient!.DisposeCount.ShouldBeGreaterThanOrEqualTo(1);
+            secondClient.IsConnected.ShouldBeFalse();
+        }
     }
 
     private static async Task WaitUntilAsync(Func<bool> cond)

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests.csproj

@@ -34,4 +34,7 @@
         <ProjectReference Include="..\..\..\src\Drivers\ZB.MOM.WW.OtOpcUa.Driver.FOCAS\ZB.MOM.WW.OtOpcUa.Driver.FOCAS.csproj"/>
     </ItemGroup>
 
+    <ItemGroup>
+        <Compile Include="..\..\TestSupport\FixtureCleanup.cs" Link="TestSupport\FixtureCleanup.cs" />
+    </ItemGroup>
 </Project>

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests/MTConnectDriverLifecycleTests.cs

@@ -1,4 +1,5 @@
 using Shouldly;
+using ZB.MOM.WW.OtOpcUa.Tests;
 using Xunit;
 using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
 
@@ -16,7 +17,7 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests;
 ///     keeps talking to the old Agent, and a cache flush that wedges browse. Each of those is a
 ///     defect the happy-path assertions alone would pass straight over.
 /// </remarks>
-public sealed class MTConnectDriverLifecycleTests
+public sealed class MTConnectDriverLifecycleTests(ITestOutputHelper output)
 {
     private const string AgentUri = "http://fixture-agent:5000";
 
@@ -598,18 +599,79 @@ public sealed class MTConnectDriverLifecycleTests
     // same "browse must not be left permanently empty" obligation.
 
     [Fact]
-    public void Dropping_the_probe_cache_keeps_the_observation_index()
+    public async Task Dropping_the_probe_cache_keeps_the_observation_index()
     {
-        var (driver, _) = InitializedDriverAsync().GetAwaiter().GetResult();
+        var (driver, _) = NewDriver();
+        await FixtureCleanup.RunAsync(async () =>
+        {
+            await driver.InitializeAsync("{}", CancellationToken.None);
 
-        driver.InvalidateProbeModel();
+            driver.InvalidateProbeModel();
 
-        driver.CachedProbeModel.ShouldBeNull();
+            driver.CachedProbeModel.ShouldBeNull();
 
-        // The index is required for correctness (it IS the read surface) — never flushable.
-        driver.ObservationIndex.Count.ShouldBe(FixtureDataItemCount);
-        driver.ObservationIndex.Get("dev1_pos").StatusCode.ShouldBe(0u);
-        driver.GetHealth().State.ShouldBe(DriverState.Healthy);
+            // The index is required for correctness (it IS the read surface) — never flushable.
+            driver.ObservationIndex.Count.ShouldBe(FixtureDataItemCount);
+            driver.ObservationIndex.Get("dev1_pos").StatusCode.ShouldBe(0u);
+            driver.GetHealth().State.ShouldBe(DriverState.Healthy);
+        }, () => driver.ShutdownAsync(CancellationToken.None),
+            failure => output.WriteLine($"MTConnect cache drop cleanup failed: {failure}"));
+    }
+
+    [Fact]
+    public async Task Body_failure_after_probe_scheduler_enters_stops_probe_and_disposes_client()
+    {
+        var client = CannedAgentClient.FromFixtures();
+        var entered = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
+        var released = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
+        var cancelled = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
+        var driver = new MTConnectDriver(Opts(), "mt1", _ => client,
+            probeScheduler: async (_, ct) =>
+            {
+                entered.TrySetResult();
+                try { await released.Task.WaitAsync(ct); }
+                catch (OperationCanceledException) when (ct.IsCancellationRequested)
+                {
+                    cancelled.TrySetResult();
+                    throw;
+                }
+            });
+        Task? probe = null;
+        var sentinel = new InvalidOperationException("body sentinel");
+        try
+        {
+            var actual = await Should.ThrowAsync<InvalidOperationException>(() => FixtureCleanup.RunAsync(async () =>
+            {
+                await driver.InitializeAsync("{}", CancellationToken.None);
+                await entered.Task.WaitAsync(TimeSpan.FromSeconds(5), TestContext.Current.CancellationToken);
+                probe = driver.ProbeLoopTask;
+                _ = probe.ShouldNotBeNull();
+                probe!.IsCompleted.ShouldBeFalse();
+                client.IsDisposed.ShouldBeFalse();
+                throw sentinel;
+            }, () => driver.ShutdownAsync(CancellationToken.None),
+                failure => output.WriteLine($"MTConnect probe fixture cleanup failed: {failure}")));
+            actual.ShouldBeSameAs(sentinel);
+            await cancelled.Task.WaitAsync(TimeSpan.FromSeconds(5), TestContext.Current.CancellationToken);
+            probe!.IsCompleted.ShouldBeTrue();
+            client.DisposeCount.ShouldBe(1);
+        }
+        finally { released.TrySetResult(); }
+    }
+
+    [Fact]
+    public async Task Initialization_failure_disposes_the_client_inside_fixture_boundary()
+    {
+        var client = CannedAgentClient.FromFixtures();
+        var failure = new HttpRequestException("current unavailable");
+        client.CurrentFailure = failure;
+        var driver = new MTConnectDriver(Opts(), "mt1", _ => client);
+        var actual = await Should.ThrowAsync<HttpRequestException>(() => FixtureCleanup.RunAsync(
+            () => driver.InitializeAsync("{}", CancellationToken.None),
+            () => driver.ShutdownAsync(CancellationToken.None),
+            secondary => output.WriteLine($"MTConnect init fixture cleanup failed: {secondary}")));
+        actual.ShouldBeSameAs(failure);
+        client.DisposeCount.ShouldBe(1);
     }
 
     [Fact]

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests.csproj

@@ -39,4 +39,7 @@
         </Content>
     </ItemGroup>
 
+    <ItemGroup>
+        <Compile Include="..\..\TestSupport\FixtureCleanup.cs" Link="TestSupport\FixtureCleanup.cs" />
+    </ItemGroup>
 </Project>

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests/ModbusLifecycleHygieneTests.cs

@@ -1,6 +1,7 @@
 using System.Collections.Concurrent;
 using System.Reflection;
 using Shouldly;
+using ZB.MOM.WW.OtOpcUa.Tests;
 using Xunit;
 using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
 using ZB.MOM.WW.OtOpcUa.Driver.Modbus;
@@ -14,7 +15,7 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests;
 ///     unit test alongside them per Driver.Modbus-012.
 /// </summary>
 [Trait("Category", "Unit")]
-public sealed class ModbusLifecycleHygieneTests
+public sealed class ModbusLifecycleHygieneTests(ITestOutputHelper output)
 {
     private sealed class FakeTransport : IModbusTransport
     {
@@ -528,7 +529,7 @@ public sealed class ModbusLifecycleHygieneTests
 
     /// <summary>Verifies that DecodeBitArray rejects an empty bitmap with InvalidDataException.</summary>
     [Fact]
-    public void DecodeBitArray_rejects_an_empty_bitmap_with_InvalidDataException()
+    public async Task DecodeBitArray_rejects_an_empty_bitmap_with_InvalidDataException()
     {
         var decode = typeof(ModbusDriver).GetMethod(
             "DecodeBitArray", BindingFlags.NonPublic | BindingFlags.Static)!;
@@ -542,11 +543,49 @@ public sealed class ModbusLifecycleHygieneTests
             RawTags = ModbusRawTags.Entries([new ModbusTagDefinition("Coil", ModbusRegion.Coils, 0, ModbusDataType.Bool)]),
         };
         var drv = new ModbusDriver(opts, "modbus-1", _ => fake);
-        drv.InitializeAsync("{}", CancellationToken.None).GetAwaiter().GetResult();
+        await FixtureCleanup.RunAsync(async () =>
+        {
+            await drv.InitializeAsync("{}", CancellationToken.None);
 
-        var r = drv.ReadAsync(["Coil"], CancellationToken.None).GetAwaiter().GetResult();
-        // The empty-bitmap guard surfaces via the BadCommunicationError catch-all.
-        r[0].StatusCode.ShouldBe(0x80050000u);
+            var r = await drv.ReadAsync(["Coil"], CancellationToken.None);
+            // The empty-bitmap guard surfaces via the BadCommunicationError catch-all.
+            r[0].StatusCode.ShouldBe(0x80050000u);
+        }, () => drv.ShutdownAsync(CancellationToken.None),
+            failure => output.WriteLine($"Modbus empty bitmap cleanup failed: {failure}"));
+    }
+
+    [Fact]
+    public async Task Body_failure_after_probe_request_cancels_it_and_disposes_transport()
+    {
+        var fake = new EmptyBitTransport();
+        var opts = new ModbusDriverOptions
+        {
+            Host = "fake",
+            RawTags = ModbusRawTags.Entries([new ModbusTagDefinition("Coil", ModbusRegion.Coils, 0, ModbusDataType.Bool)]),
+        };
+        var drv = new ModbusDriver(opts, "modbus-1", _ => fake);
+        var sentinel = new InvalidOperationException("body sentinel");
+        try
+        {
+            var actual = await Should.ThrowAsync<InvalidOperationException>(() => FixtureCleanup.RunAsync(async () =>
+            {
+                await drv.InitializeAsync("{}", CancellationToken.None);
+                var result = await drv.ReadAsync(["Coil"], CancellationToken.None);
+                result[0].StatusCode.ShouldBe(0x80050000u);
+                fake.CoilRequestCount.ShouldBe(1);
+                await fake.ProbeEntered.Task.WaitAsync(TimeSpan.FromSeconds(5), TestContext.Current.CancellationToken);
+                fake.ProbeToken.IsCancellationRequested.ShouldBeFalse();
+                fake.DisposeCount.ShouldBe(0);
+                throw sentinel;
+            }, () => drv.ShutdownAsync(CancellationToken.None),
+                failure => output.WriteLine($"Modbus probe fixture cleanup failed: {failure}")));
+            actual.ShouldBeSameAs(sentinel);
+            fake.ProbeToken.IsCancellationRequested.ShouldBeTrue();
+            await fake.ProbeCancelled.Task.WaitAsync(TimeSpan.FromSeconds(5), TestContext.Current.CancellationToken);
+            await fake.ProbeRequestCompleted.Task.WaitAsync(TimeSpan.FromSeconds(5), TestContext.Current.CancellationToken);
+            fake.DisposeCount.ShouldBe(1);
+        }
+        finally { fake.ReleaseProbe.TrySetResult(); }
     }
 
     /// <summary>
@@ -556,6 +595,14 @@ public sealed class ModbusLifecycleHygieneTests
     /// </summary>
     private sealed class EmptyBitTransport : IModbusTransport
     {
+        public TaskCompletionSource ProbeEntered { get; } = new(TaskCreationOptions.RunContinuationsAsynchronously);
+        public TaskCompletionSource ProbeCancelled { get; } = new(TaskCreationOptions.RunContinuationsAsynchronously);
+        public TaskCompletionSource ProbeRequestCompleted { get; } = new(TaskCreationOptions.RunContinuationsAsynchronously);
+        public TaskCompletionSource ReleaseProbe { get; } = new(TaskCreationOptions.RunContinuationsAsynchronously);
+        public CancellationToken ProbeToken { get; private set; }
+        public int DisposeCount { get; private set; }
+        public int CoilRequestCount { get; private set; }
+
         /// <summary>Returns a completed task without performing any connection.</summary>
         /// <param name="ct">The cancellation token for the operation.</param>
         public Task ConnectAsync(CancellationToken ct) => Task.CompletedTask;
@@ -563,10 +610,29 @@ public sealed class ModbusLifecycleHygieneTests
         /// <param name="unitId">The Modbus unit ID.</param>
         /// <param name="pdu">The protocol data unit being sent.</param>
         /// <param name="ct">The cancellation token for the operation.</param>
-        public Task<byte[]> SendAsync(byte unitId, byte[] pdu, CancellationToken ct)
-            => Task.FromResult(new byte[] { pdu[0], 0 });
-        /// <summary>Completes the disposal without doing any work.</summary>
-        public ValueTask DisposeAsync() => ValueTask.CompletedTask;
+        public async Task<byte[]> SendAsync(byte unitId, byte[] pdu, CancellationToken ct)
+        {
+            if (pdu[0] == 0x03)
+            {
+                ProbeToken = ct;
+                ProbeEntered.TrySetResult();
+                try { await ReleaseProbe.Task.WaitAsync(ct); }
+                catch (OperationCanceledException) when (ct.IsCancellationRequested)
+                {
+                    ProbeCancelled.TrySetResult();
+                    throw;
+                }
+                finally { ProbeRequestCompleted.TrySetResult(); }
+            }
+            if (pdu[0] == 0x01) CoilRequestCount++;
+            return new byte[] { pdu[0], 0 };
+        }
+        /// <summary>Records transport disposal.</summary>
+        public ValueTask DisposeAsync()
+        {
+            DisposeCount++;
+            return ValueTask.CompletedTask;
+        }
     }
 
     // -------------------- Finding -003 (volatile _health) --------------------

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.Tests.csproj

@@ -29,4 +29,7 @@
         <ProjectReference Include="..\..\..\src\Drivers\ZB.MOM.WW.OtOpcUa.Driver.Modbus\ZB.MOM.WW.OtOpcUa.Driver.Modbus.csproj"/>
     </ItemGroup>
 
+    <ItemGroup>
+        <Compile Include="..\..\TestSupport\FixtureCleanup.cs" Link="TestSupport\FixtureCleanup.cs" />
+    </ItemGroup>
 </Project>

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7.IntegrationTests/S7_1500/S7_1500SpanReadTests.cs

@@ -27,7 +27,15 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.S7.IntegrationTests.S7_1500;
 ///         areas: <b>PASSED</b> — 4 passed, 0 failed, 1 skipped (the device number-addressing test,
 ///         see below). The Timer/Counter batch was served by 4 requests for 7 tags: one DB1 span,
 ///         one 3-item multi-var carrying only the scalars, and one 2-byte area read apiece for
-///         <c>T0</c> (decoded 456.0 s from S5TIME <c>0x2456</c>) and <c>C0</c> (decoded count 4711).
+///         <c>T0</c> (decoded 456.0 s from S5TIME <c>0x2456</c>) and <c>C0</c> (surfaced raw word 4711).
+///     </para>
+///     <para>
+///         <b>Counter evidence limit.</b> The profile's C0=4711 and C7=31337 are synthetic raw
+///         words, outside classic SIMATIC counts 0..999. The device-0 record proves the fixture's
+///         raw-word decode and batching exclusion, not classic count semantics or nonzero
+///         addressing. BuildOptions retains S71500/rack 0/slot 0; a target-specific semantic gate
+///         still needs independent PLC counts and binary/BCD references paired with captured
+///         C-area bytes, CPU model/firmware and connection settings (docs/drivers/S7.md, #616).
 ///     </para>
 ///     <para>
 ///         <b>What the layout buys.</b> The ten tags are positioned so the planner's rules produce a
@@ -73,11 +81,12 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.S7.IntegrationTests.S7_1500;
 ///         returns TM bytes 0..1, and it takes <c>start 80</c> (= 10 × 8) to reach the timer seeded
 ///         at TM byte 10. Device <b>0</b> is the single fixed point of the two conventions
 ///         (<c>0 &gt;&gt; 3 == 2 × 0 == 0</c>), so it is the only device this fixture can pin a
-///         VALUE for, and that is what the mixed batch uses. The spec-correct <c>2 × N</c> cells
+///         VALUE for, and that is what the mixed batch uses. The profile's <c>2 × N</c> cells
 ///         are seeded too and
 ///         <see cref="Timer_and_counter_decode_the_seeded_values_at_their_device_numbers"/> asserts
 ///         them — skipped unless <c>S7_TIMER_NUMBER_ADDRESSING=1</c> declares the endpoint a real
-///         CPU. The device-number offset arithmetic itself stays unit-covered
+///         CPU. This flag is an operator declaration, not hardware evidence.
+///         The device-number offset arithmetic itself stays unit-covered
 ///         (<c>S7ScalarBlockTests</c>, <c>S7SpanReadParityTests</c>).
 ///     </para>
 ///     <para>
@@ -240,7 +249,7 @@ public sealed class S7_1500SpanReadTests(Snap7ServerFixture sim)
             snapshot.StatusCode.ShouldBe(0u, $"'{name}' must be Good");
 
         // (a) Correct decode off real wire. A Timer surfaces as the S5TIME word's duration in
-        // seconds (double) and a Counter as the raw count (int) — two different areas, two
+        // seconds (double) and a Counter as the raw word (int) — two different areas, two
         // different values, two different CLR types, so a read that reached the wrong area or
         // decoded through the wrong arm cannot pass.
         byName["TC_Timer"].Value.ShouldBe(TimerCounterLayout.Device0TimerSeconds);
@@ -280,15 +289,19 @@ public sealed class S7_1500SpanReadTests(Snap7ServerFixture sim)
 
     /// <summary>
     ///     Verifies a Timer and a Counter at NON-zero device numbers decode their seeded values —
-    ///     the assertion the shared fixture cannot serve.
+    ///     the raw-word assertion the shared fixture cannot serve.
     /// </summary>
     /// <remarks>
     ///     Skipped unless <c>S7_TIMER_NUMBER_ADDRESSING=1</c> declares the endpoint a device
     ///     number-addressing CPU, because python-snap7's server is not one: it resolves the TM/CT
     ///     request address as a bit address, so <c>T5</c> reads TM byte 0 rather than TM byte 10
-    ///     (measured 2026-08-17 — see the type remarks). Set the variable alongside
-    ///     <c>S7_SIM_ENDPOINT</c> when pointing this suite at a real S7 CPU seeded to match
-    ///     <c>Docker/profiles/s7_1500.json</c>'s TM/CT areas.
+    ///     (measured 2026-08-17 — see the type remarks). The flag only enables this test;
+    ///     BuildOptions still selects S71500, rack 0, slot 0 and the profile's raw C7 word 31337.
+    ///     It does not configure a classic CPU or prove classic 0..999 count semantics. A separate
+    ///     target-specific gate needs valid counts, independent PLC binary/BCD references and
+    ///     captured C-area bytes, plus CPU model/firmware and connection settings (#616).
+    ///     See docs/drivers/S7.md for the evidence checklist. The skip message below retains the
+    ///     historical fixture instructions; enabling the flag alone does not satisfy this gate.
     /// </remarks>
     [Fact]
     public async Task Timer_and_counter_decode_the_seeded_values_at_their_device_numbers()
@@ -408,12 +421,13 @@ public sealed class S7_1500SpanReadTests(Snap7ServerFixture sim)
     /// <summary>
     ///     The Timer/Counter layouts. Two sets: a mixed batch that provokes all three read shapes at
     ///     once (block span, multi-var, per-tag Timer/Counter), and a device-numbered pair only a
-    ///     real CPU can serve. Addresses map 1:1 to the TM0 / CT0 seeds in
+    ///     device number-addressing endpoint can serve. These synthetic raw-word expectations
+    ///     do not prove classic counter semantics. Addresses map 1:1 to the TM0 / CT0 seeds in
     ///     <c>Docker/profiles/s7_1500.json</c>.
     /// </summary>
     private static class TimerCounterLayout
     {
-        /// <summary>Declares the endpoint a real S7 CPU, which addresses TM/CT by device number.</summary>
+        /// <summary>Operator opt-in for nonzero TM/CT addressing; does not change CPU options or prove encoding.</summary>
         public const string RealCpuEnvVar = "S7_TIMER_NUMBER_ADDRESSING";
 
         /// <summary>
@@ -425,7 +439,7 @@ public sealed class S7_1500SpanReadTests(Snap7ServerFixture sim)
         /// <summary>T0's seed 0x2456 — S5TIME base 2 (×1 s) over BCD 456.</summary>
         public const double Device0TimerSeconds = 456.0d;
 
-        /// <summary>C0's seed — the raw big-endian count word.</summary>
+        /// <summary>C0's synthetic raw big-endian word 4711; not a classic 0..999 count reference.</summary>
         public const int Device0CounterCount = 4711;
 
         /// <summary>
@@ -441,7 +455,7 @@ public sealed class S7_1500SpanReadTests(Snap7ServerFixture sim)
             new("TC_Lone_I16",   "DB1.DBW600", S7DataType.Int16),
             new("TC_Lone_Mk",    "MW10",       S7DataType.UInt16),
             // Timer tags are typed Float64 (decoded to seconds) and Counter tags Int32 (decoded to
-            // a count) — the init guard rejects any other typing. Writable:false is mandatory, not
+            // a raw word) — the init guard rejects any other typing. Writable:false is mandatory, not
             // stylistic: S7TagDefinition defaults Writable to TRUE and the same guard rejects a
             // writable Timer/Counter outright (they are read-only this phase).
             new("TC_Timer",      "T0",         S7DataType.Float64, Writable: false),

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests/TwinCATReinitializeReleasesStateTests.cs

@@ -1,4 +1,5 @@
 using Shouldly;
+using ZB.MOM.WW.OtOpcUa.Tests;
 using Xunit;
 
 namespace ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests;
@@ -8,7 +9,7 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests;
 ///     orphaned the previous state's probe loop + client. It now releases them first.
 /// </summary>
 [Trait("Category", "Unit")]
-public sealed class TwinCATReinitializeReleasesStateTests
+public sealed class TwinCATReinitializeReleasesStateTests(ITestOutputHelper output)
 {
     /// <summary>Initialize twice: the first state's probe loop has finished and its client is disposed.</summary>
     [Fact]
@@ -21,28 +22,88 @@ public sealed class TwinCATReinitializeReleasesStateTests
             Devices = [new TwinCATDeviceOptions(host)],
             Probe = new TwinCATProbeOptions { Enabled = true, Interval = TimeSpan.FromMilliseconds(20), Timeout = TimeSpan.FromSeconds(1) },
         }, "drv-reinit", factory);
-        await drv.InitializeAsync("{}", CancellationToken.None);
+        await FixtureCleanup.RunAsync(async () =>
+        {
+            await drv.InitializeAsync("{}", CancellationToken.None);
 
-        var first = drv.GetDeviceState(host)!;
-        // Positive control: the first probe loop is running and holds a connected client.
+            var first = drv.GetDeviceState(host)!;
+            // Positive control: the first probe loop is running and holds a connected client.
+            var deadline = DateTime.UtcNow.AddSeconds(5);
+            while (!(factory.Clients.Count > 0 && factory.Clients[0].IsConnected))
+            {
+                if (DateTime.UtcNow > deadline) throw new TimeoutException("probe never connected");
+                await Task.Delay(10);
+            }
+            var firstClient = factory.Clients[0];
+            var firstLoop = first.ProbeTask;
+            _ = firstLoop.ShouldNotBeNull();
+            firstLoop!.IsCompleted.ShouldBeFalse();
+
+            await drv.InitializeAsync("{}", CancellationToken.None);
+
+            firstLoop.IsCompleted.ShouldBeTrue(); // joined
+            firstClient.DisposeCount.ShouldBeGreaterThanOrEqualTo(1);
+            firstClient.IsConnected.ShouldBeFalse();
+            drv.GetDeviceState(host).ShouldNotBeSameAs(first);
+        }, () => drv.ShutdownAsync(CancellationToken.None),
+            failure => output.WriteLine($"TwinCAT SecondInitialize cleanup failed: {failure}"));
+    }
+
+    /// <summary>Failure after a live first or replacement state must release both owned resources.</summary>
+    [Theory]
+    [InlineData(false)]
+    [InlineData(true)]
+    public async Task Body_failure_releases_live_probe_resources(bool afterReplacement)
+    {
+        const string host = "ads://5.23.91.23.1.1:851";
+        var factory = new FakeTwinCATClientFactory();
+        var drv = new TwinCATDriver(new TwinCATDriverOptions
+        {
+            Devices = [new TwinCATDeviceOptions(host)],
+            Probe = new TwinCATProbeOptions { Enabled = true, Interval = TimeSpan.FromMilliseconds(20), Timeout = TimeSpan.FromSeconds(1) },
+        }, "drv-reinit", factory);
+        Task? firstLoop = null, secondLoop = null;
+        FakeTwinCATClient? firstClient = null, secondClient = null;
+        var sentinel = new InvalidOperationException("body sentinel");
+        var actual = await Should.ThrowAsync<InvalidOperationException>(() => FixtureCleanup.RunAsync(async () =>
+        {
+            await drv.InitializeAsync("{}", CancellationToken.None);
+            await WaitUntilAsync(() => factory.Clients.Count > 0 && factory.Clients[0].IsConnected);
+            firstClient = factory.Clients[0];
+            firstLoop = drv.GetDeviceState(host)!.ProbeTask;
+            _ = firstLoop.ShouldNotBeNull();
+            firstLoop!.IsCompleted.ShouldBeFalse();
+            if (afterReplacement)
+            {
+                await drv.InitializeAsync("{}", CancellationToken.None);
+                await WaitUntilAsync(() => factory.Clients.Count > 1 && factory.Clients[1].IsConnected);
+                secondClient = factory.Clients[1];
+                secondLoop = drv.GetDeviceState(host)!.ProbeTask;
+                _ = secondLoop.ShouldNotBeNull();
+                secondLoop!.IsCompleted.ShouldBeFalse();
+            }
+            throw sentinel;
+        }, () => drv.ShutdownAsync(CancellationToken.None),
+            failure => output.WriteLine($"TwinCAT failure fixture cleanup failed: {failure}")));
+        actual.ShouldBeSameAs(sentinel);
+        firstLoop!.IsCompleted.ShouldBeTrue();
+        firstClient!.DisposeCount.ShouldBeGreaterThanOrEqualTo(1);
+        firstClient.IsConnected.ShouldBeFalse();
+        if (afterReplacement)
+        {
+            secondLoop!.IsCompleted.ShouldBeTrue();
+            secondClient!.DisposeCount.ShouldBeGreaterThanOrEqualTo(1);
+            secondClient.IsConnected.ShouldBeFalse();
+        }
+    }
+
+    private static async Task WaitUntilAsync(Func<bool> condition)
+    {
         var deadline = DateTime.UtcNow.AddSeconds(5);
-        while (!(factory.Clients.Count > 0 && factory.Clients[0].IsConnected))
+        while (!condition())
         {
             if (DateTime.UtcNow > deadline) throw new TimeoutException("probe never connected");
             await Task.Delay(10);
         }
-        var firstClient = factory.Clients[0];
-        var firstLoop = first.ProbeTask;
-        firstLoop.ShouldNotBeNull();
-        firstLoop!.IsCompleted.ShouldBeFalse();
-
-        await drv.InitializeAsync("{}", CancellationToken.None);
-
-        firstLoop.IsCompleted.ShouldBeTrue(); // joined
-        firstClient.DisposeCount.ShouldBeGreaterThanOrEqualTo(1);
-        firstClient.IsConnected.ShouldBeFalse();
-        drv.GetDeviceState(host).ShouldNotBeSameAs(first);
-
-        await drv.ShutdownAsync(CancellationToken.None);
     }
 }

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests.csproj

@@ -29,4 +29,7 @@
         <ProjectReference Include="..\..\..\src\Drivers\ZB.MOM.WW.OtOpcUa.Driver.TwinCAT\ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.csproj"/>
     </ItemGroup>
 
+    <ItemGroup>
+        <Compile Include="..\..\TestSupport\FixtureCleanup.cs" Link="TestSupport\FixtureCleanup.cs" />
+    </ItemGroup>
 </Project>

tests/Server/ZB.MOM.WW.OtOpcUa.Host.Tests/OpcUa/FailedServiceLevelBindingCleanupTests.cs

@@ -0,0 +1,45 @@
+using Microsoft.Extensions.Logging.Abstractions;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Host.OpcUa;
+
+namespace ZB.MOM.WW.OtOpcUa.Host.Tests.OpcUa;
+
+public sealed class FailedServiceLevelBindingCleanupTests
+{
+    [Fact]
+    public async Task Successful_cleanup_observes_stop_before_disposal_and_releases_ownership()
+    {
+        var events = new List<string>();
+        var released = await FailedServiceLevelBindingCleanup.StopAndDisposeAsync(
+            () => { events.Add("stop"); return Task.CompletedTask; },
+            () => { events.Add("dispose"); return ValueTask.CompletedTask; },
+            NullLogger.Instance);
+        events.ShouldBe(new[] { "stop", "dispose" });
+        released.ShouldBeTrue();
+    }
+
+    [Fact]
+    public async Task Failed_stop_still_disposes_and_retains_ownership_for_retry()
+    {
+        var events = new List<string>();
+        var released = await FailedServiceLevelBindingCleanup.StopAndDisposeAsync(
+            () => { events.Add("stop"); throw new InvalidOperationException("controlled stop failure"); },
+            () => { events.Add("dispose"); return ValueTask.CompletedTask; },
+            NullLogger.Instance);
+        events.ShouldBe(new[] { "stop", "dispose" });
+        released.ShouldBeFalse();
+    }
+
+    [Fact]
+    public async Task Failed_disposal_retains_ownership_without_escaping_the_binding_failure_handler()
+    {
+        var events = new List<string>();
+        var released = await FailedServiceLevelBindingCleanup.StopAndDisposeAsync(
+            () => { events.Add("stop"); return Task.CompletedTask; },
+            () => { events.Add("dispose"); throw new InvalidOperationException("controlled disposal failure"); },
+            NullLogger.Instance);
+        events.ShouldBe(new[] { "stop", "dispose" });
+        released.ShouldBeFalse();
+    }
+}

tests/Server/ZB.MOM.WW.OtOpcUa.Host.Tests/OpcUa/OtOpcUaServerHostedServiceBindingFailureTests.cs

@@ -0,0 +1,103 @@
+using System.Net;
+using System.Net.Sockets;
+using Akka.Hosting;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Logging.Abstractions;
+using Microsoft.Extensions.Options;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Commons.OpcUa;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Core.Authorization;
+using ZB.MOM.WW.OtOpcUa.Host.OpcUa;
+using ZB.MOM.WW.OtOpcUa.OpcUaServer;
+using ZB.MOM.WW.OtOpcUa.OpcUaServer.Security;
+
+namespace ZB.MOM.WW.OtOpcUa.Host.Tests.OpcUa;
+
+public sealed class OtOpcUaServerHostedServiceBindingFailureTests
+{
+    [Fact]
+    public async Task Binding_failure_closes_started_endpoint_and_allows_other_host_services_to_start()
+    {
+        using var deadline = new CancellationTokenSource(TimeSpan.FromSeconds(15));
+        using var probe = new TcpListener(IPAddress.Loopback, 0);
+        probe.Start();
+        var port = ((IPEndPoint)probe.LocalEndpoint).Port;
+        probe.Stop();
+        var pki = Path.Combine(Path.GetTempPath(), $"otopcua-binding-{Guid.NewGuid():N}");
+        var deferred = new DeferredServiceLevelPublisher();
+        deferred.Publish(0);
+        var bindingReached = false;
+        var listenerObserved = false;
+        OtOpcUaServerHostedService? service = null;
+        var factory = new FaultInjectingLoggerFactory(() =>
+        {
+            using var connected = new TcpClient();
+            connected.Connect(IPAddress.Loopback, port);
+            listenerObserved = connected.Connected;
+            bindingReached = true;
+            throw new InvalidOperationException("controlled binding factory failure");
+        });
+        service = new OtOpcUaServerHostedService(
+            Options.Create(new OpcUaApplicationHostOptions
+            {
+                ApplicationName = "OtOpcUa.BindingFailure",
+                ApplicationUri = $"urn:OtOpcUa.BindingFailure:{Guid.NewGuid():N}",
+                OpcUaPort = port, PublicHostname = "localhost", PkiStoreRoot = pki,
+            }), new DeferredAddressSpaceSink(), deferred,
+            NullOpcUaUserAuthenticator.Instance, NullHistorianDataSource.Instance,
+            EmptyDataPlaneAuthoritySource.Instance, new ConfigurationBuilder().Build(),
+            () => throw new NotSupportedException("no actor system required"), new ActorRegistry(),
+            null, Options.Create(new AclOptions()), TimeProvider.System, factory);
+        var admin = new AdminBootSentinel();
+        using var host = new HostBuilder().ConfigureServices(services =>
+        {
+            services.AddSingleton<IHostedService>(service);
+            services.AddSingleton<IHostedService>(admin);
+        }).Build();
+        try
+        {
+            await host.StartAsync(deadline.Token);
+            listenerObserved.ShouldBeTrue("the SDK endpoint was actually listening before replay");
+            bindingReached.ShouldBeTrue();
+            admin.Started.ShouldBeTrue();
+            using var client = new TcpClient();
+            await Should.ThrowAsync<SocketException>(async () =>
+                await client.ConnectAsync(IPAddress.Loopback, port, deadline.Token));
+            // After construction failure, subsequent requests are accepted into the unbound cache.
+            deferred.Publish(100);
+            await host.StopAsync(deadline.Token);
+        }
+        finally
+        {
+            await service.DisposeAsync();
+            if (Directory.Exists(pki)) Directory.Delete(pki, recursive: true);
+        }
+    }
+
+    private sealed class FaultInjectingLoggerFactory(Action installFault) : ILoggerFactory
+    {
+        public ILogger CreateLogger(string categoryName)
+        {
+            if (categoryName == typeof(SdkServiceLevelPublisher).FullName) installFault();
+            return NullLogger.Instance;
+        }
+        public void AddProvider(ILoggerProvider provider) { }
+        public void Dispose() { }
+    }
+
+    private sealed class AdminBootSentinel : IHostedService
+    {
+        public bool Started { get; private set; }
+        public Task StartAsync(CancellationToken cancellationToken)
+        {
+            Started = true;
+            return Task.CompletedTask;
+        }
+        public Task StopAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+    }
+}

tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.IntegrationTests/ServiceLevelBindingReplayTests.cs

@@ -0,0 +1,71 @@
+using Microsoft.Extensions.Logging.Abstractions;
+using Opc.Ua;
+using Opc.Ua.Client;
+using Opc.Ua.Server;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Commons.OpcUa;
+
+namespace ZB.MOM.WW.OtOpcUa.OpcUaServer.IntegrationTests;
+
+/// <summary>Local loopback evidence that late binding replaces the SDK default on the wire.</summary>
+public sealed class ServiceLevelBindingReplayTests
+{
+    [Theory]
+    [InlineData((byte)100)]
+    [InlineData((byte)0)]
+    public async Task Late_binding_replays_latest_request_to_standard_ServiceLevel_read(byte latest)
+    {
+        using var deadline = CancellationTokenSource.CreateLinkedTokenSource(TestContext.Current.CancellationToken);
+        deadline.CancelAfter(TimeSpan.FromSeconds(15));
+        var ct = deadline.Token;
+        var pki = Path.Combine(Path.GetTempPath(), $"otopcua-replay-{Guid.NewGuid():N}");
+        var clientPki = TestClientSecurity.AllocatePkiRoot();
+        var port = 0;
+        try
+        {
+            var deferred = new DeferredServiceLevelPublisher();
+            deferred.Publish(240);
+            deferred.Publish(latest);
+            var started = await OpcUaHostStart.StartAsync(p =>
+            {
+                port = p;
+                return new OpcUaApplicationHost(new OpcUaApplicationHostOptions
+                {
+                    ApplicationName = "OtOpcUa.Replay",
+                    ApplicationUri = $"urn:OtOpcUa.Replay:{Path.GetFileName(pki)}",
+                    OpcUaPort = p, PublicHostname = "localhost", PkiStoreRoot = pki,
+                }, NullLogger<OpcUaApplicationHost>.Instance);
+            }, () => new StandardServer(), ct);
+            await using var host = started.Host;
+            deferred.SetInner(new SdkServiceLevelPublisher(started.Server.CurrentInstance,
+                NullLogger<SdkServiceLevelPublisher>.Instance));
+            var config = new ApplicationConfiguration
+            {
+                ApplicationName = "OtOpcUa.ReplayClient",
+                ApplicationUri = $"urn:OtOpcUa.ReplayClient:{Guid.NewGuid():N}",
+                ApplicationType = ApplicationType.Client,
+                SecurityConfiguration = TestClientSecurity.Build(clientPki),
+                ClientConfiguration = new ClientConfiguration { DefaultSessionTimeout = 10_000 },
+                TransportQuotas = new TransportQuotas { OperationTimeout = 5_000 },
+            };
+            await config.ValidateAsync(ApplicationType.Client, ct);
+            config.CertificateValidator.CertificateValidation += (_, e) => e.Accept = true;
+            var endpoint = await CoreClientUtils.SelectEndpointAsync(config,
+                $"opc.tcp://localhost:{port}/OtOpcUa", false, DefaultTelemetry.Create(_ => { }), ct);
+            using var session = await new DefaultSessionFactory(DefaultTelemetry.Create(_ => { })).CreateAsync(
+                config, new ConfiguredEndpoint(null, endpoint, EndpointConfiguration.Create(config)),
+                updateBeforeConnect: false, checkDomain: false, sessionName: "ServiceLevelReplay",
+                sessionTimeout: 10_000, identity: new UserIdentity(new AnonymousIdentityToken()),
+                preferredLocales: null, ct: ct);
+            var read = await session.ReadValueAsync(new Opc.Ua.NodeId(2267u), ct);
+            read.StatusCode.ShouldBe(StatusCodes.Good);
+            read.Value.ShouldBe(latest);
+        }
+        finally
+        {
+            if (Directory.Exists(pki)) Directory.Delete(pki, recursive: true);
+            if (Directory.Exists(clientPki)) Directory.Delete(clientPki, recursive: true);
+        }
+    }
+}

tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/DeferredServiceLevelPublisherTests.cs

@@ -6,9 +6,9 @@ namespace ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests;
 
 public sealed class DeferredServiceLevelPublisherTests
 {
-    /// <summary>Verifies that publish before SetInner is a safe no-op.</summary>
+    /// <summary>Verifies that publish before SetInner safely accepts a cached request.</summary>
     [Fact]
-    public void Publish_before_SetInner_is_a_safe_noop()
+    public void Publish_before_SetInner_accepts_a_cached_request()
     {
         var deferred = new DeferredServiceLevelPublisher();
 
@@ -28,9 +28,9 @@ public sealed class DeferredServiceLevelPublisherTests
         recording.LastValue.ShouldBe((byte)200);
     }
 
-    /// <summary>Verifies that SetInner with null reverts to the null publisher.</summary>
+    /// <summary>Verifies that SetInner with null detaches the previous publisher.</summary>
     [Fact]
-    public void SetInner_null_reverts_to_Null_publisher()
+    public void SetInner_null_detaches_the_previous_publisher()
     {
         var recording = new RecordingPublisher();
         var deferred = new DeferredServiceLevelPublisher();

tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/SdkServiceLevelPublisherTests.cs

@@ -19,6 +19,40 @@ public sealed class SdkServiceLevelPublisherTests : IDisposable
         Path.GetTempPath(),
         $"otopcua-pki-{Guid.NewGuid():N}");
 
+    [Fact]
+    public void Missing_ServiceLevel_is_reported_as_failure()
+    {
+        var server = System.Reflection.DispatchProxy.Create<IServerInternal, FaultingServer>();
+        var publisher = new SdkServiceLevelPublisher(server, NullLogger<SdkServiceLevelPublisher>.Instance);
+        Should.Throw<InvalidOperationException>(() => publisher.Publish(0));
+    }
+
+    [Fact]
+    public void Sdk_write_failure_propagates_the_original_exception()
+    {
+        var server = System.Reflection.DispatchProxy.Create<IServerInternal, FaultingServer>();
+        var proxy = (FaultingServer)(object)server;
+        proxy.Node = new Opc.Ua.ServerObjectState(null)
+        {
+            ServiceLevel = new Opc.Ua.PropertyState<byte>(null),
+        };
+        proxy.Fault = new InvalidOperationException("controlled diagnostics failure");
+        var publisher = new SdkServiceLevelPublisher(server, NullLogger<SdkServiceLevelPublisher>.Instance);
+        Should.Throw<InvalidOperationException>(() => publisher.Publish(0)).ShouldBeSameAs(proxy.Fault);
+    }
+
+    public class FaultingServer : System.Reflection.DispatchProxy
+    {
+        public Opc.Ua.ServerObjectState? Node { get; set; }
+        public Exception? Fault { get; set; }
+        protected override object? Invoke(System.Reflection.MethodInfo? method, object?[]? args)
+        {
+            if (method?.Name == "get_ServerObject") return Node;
+            if (method?.Name == "get_DiagnosticsLock") throw Fault!;
+            throw new NotSupportedException(method?.Name);
+        }
+    }
+
     /// <summary>Verifies that the publisher writes values to the standard Server.ServiceLevel variable.</summary>
     [Fact]
     public async Task Publish_writes_value_to_Server_ServiceLevel_variable()

tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/OpcUa/OpcUaPublishActorFreshnessTests.cs

@@ -0,0 +1,240 @@
+using System.Collections.Concurrent;
+using Akka.Actor;
+using Akka.TestKit;
+using Akka.TestKit.Xunit2;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Commons.Messages.Redundancy;
+using ZB.MOM.WW.OtOpcUa.Commons.Types;
+using ZB.MOM.WW.OtOpcUa.Commons.OpcUa;
+using ZB.MOM.WW.OtOpcUa.OpcUaServer;
+using ZB.MOM.WW.OtOpcUa.Runtime.OpcUa;
+using ZB.MOM.WW.OtOpcUa.Runtime.Health;
+using ZB.MOM.WW.OtOpcUa.Runtime.Tests.Harness;
+
+namespace ZB.MOM.WW.OtOpcUa.Runtime.Tests.OpcUa;
+
+public sealed class OpcUaPublishActorFreshnessTests : RuntimeActorTestBase
+{
+    [Theory]
+    [InlineData(false, 240, 200)]
+    [InlineData(true, 250, 210)]
+    public void DbLess_timer_demotes_without_incoming_messages(bool primary, byte fresh, byte stale)
+    {
+        var publisher = new RecordingPublisher();
+        var clock = new ControlledClock();
+        var local = NodeId.Parse("freshness-node");
+        var actor = Sys.ActorOf(OpcUaPublishActor.PropsForTests(
+            serviceLevel: publisher, localNode: local, dbLess: true,
+            staleWindow: TimeSpan.FromSeconds(1), healthTickInterval: TimeSpan.FromMilliseconds(25),
+            utcNow: clock.Read));
+        actor.Tell(Snapshot(local, primary, clock.Now));
+        AwaitAssert(() => publisher.Levels.ShouldBe(new[] { fresh }), PresenceBudget);
+        // Equality remains fresh. Observe several real ticks with a fixed clock; no actor Tell.
+        clock.Advance(TimeSpan.FromSeconds(1));
+        var reads = clock.Reads;
+        AwaitCondition(() => clock.Reads >= reads + 4, PresenceBudget);
+        // Drain earlier self-enqueued publications without triggering a health recomputation.
+        actor.Tell(new Identify("freshness-barrier"), TestActor);
+        ExpectMsg<ActorIdentity>().Subject.ShouldBe(actor);
+        publisher.Levels.ShouldBe(new[] { fresh });
+        clock.Advance(TimeSpan.FromTicks(1));
+        // No further Tell: only the production timer can notice age crossing the window.
+        AwaitAssert(() => publisher.Levels.ShouldBe(new[] { fresh, stale }), PresenceBudget);
+        // A new fresh snapshot restores service, after which ticks continue to age that snapshot.
+        actor.Tell(Snapshot(local, primary, clock.Now));
+        AwaitAssert(() => publisher.Levels.ShouldBe(new[] { fresh, stale, fresh }), PresenceBudget);
+        clock.Advance(TimeSpan.FromSeconds(1) + TimeSpan.FromTicks(1));
+        AwaitAssert(() => publisher.Levels.ShouldBe(new[] { fresh, stale, fresh, stale }), PresenceBudget);
+    }
+
+    [Fact]
+    public void DbLess_timer_expires_negative_peer_verdict_only_after_exact_boundary()
+    {
+        var publisher = new RecordingPublisher();
+        var clock = new ControlledClock();
+        var local = NodeId.Parse("peer-verdict-node");
+        var actor = Sys.ActorOf(OpcUaPublishActor.PropsForTests(
+            serviceLevel: publisher, localNode: local, dbLess: true,
+            staleWindow: TimeSpan.FromSeconds(10), probeFreshnessWindow: TimeSpan.FromSeconds(2),
+            healthTickInterval: TimeSpan.FromMilliseconds(25), utcNow: clock.Read));
+        actor.Tell(Snapshot(local, false, clock.Now));
+        AwaitAssert(() => publisher.Levels.ShouldBe(new byte[] { 240 }), PresenceBudget);
+        actor.Tell(new PeerOpcUaProbeActor.OpcUaProbeResult(local, Ok: false));
+        AwaitAssert(() => publisher.Levels.ShouldBe(new byte[] { 240, 0 }), PresenceBudget);
+        clock.Advance(TimeSpan.FromSeconds(2));
+        var reads = clock.Reads;
+        AwaitCondition(() => clock.Reads >= reads + 4, PresenceBudget);
+        // Drain earlier self-enqueued publications without triggering a health recomputation.
+        actor.Tell(new Identify("freshness-barrier"), TestActor);
+        ExpectMsg<ActorIdentity>().Subject.ShouldBe(actor);
+        publisher.Levels.ShouldBe(new byte[] { 240, 0 });
+        clock.Advance(TimeSpan.FromTicks(1));
+        AwaitAssert(() => publisher.Levels.ShouldBe(new byte[] { 240, 0, 240 }), PresenceBudget);
+    }
+
+    [Fact]
+    public void Stopping_DbLess_actor_cancels_freshness_timer_and_publications()
+    {
+        var publisher = new RecordingPublisher();
+        var clock = new ControlledClock();
+        var local = NodeId.Parse("stopped-node");
+        var actor = Sys.ActorOf(OpcUaPublishActor.PropsForTests(
+            serviceLevel: publisher, localNode: local, dbLess: true,
+            staleWindow: TimeSpan.FromSeconds(1), healthTickInterval: TimeSpan.FromMilliseconds(25),
+            utcNow: clock.Read));
+        actor.Tell(Snapshot(local, false, clock.Now));
+        AwaitAssert(() => publisher.Levels.ShouldBe(new byte[] { 240 }), PresenceBudget);
+        var reads = clock.Reads;
+        AwaitCondition(() => clock.Reads >= reads + 4, PresenceBudget);
+        Watch(actor);
+        Sys.Stop(actor);
+        ExpectTerminated(actor);
+        reads = clock.Reads;
+        clock.Advance(TimeSpan.FromSeconds(2));
+        ExpectNoMsg(TimeSpan.FromMilliseconds(150)); // Six timer periods after confirmed termination.
+        clock.Reads.ShouldBe(reads);
+        publisher.Levels.ShouldBe(new byte[] { 240 });
+    }
+
+    [Fact]
+    public void DbBacked_timer_refreshes_probe_status_periodically()
+    {
+        var publisher = new RecordingPublisher();
+        var clock = new ControlledClock();
+        var local = NodeId.Parse("db-backed-periodic-node");
+        var db = CreateTestProbe();
+        var actor = Sys.ActorOf(OpcUaPublishActor.PropsForTests(
+            serviceLevel: publisher, localNode: local, dbHealthProbe: db.Ref,
+            healthTickInterval: TimeSpan.FromMilliseconds(100), utcNow: clock.Read));
+        actor.Tell(Snapshot(local, false, clock.Now));
+        db.ExpectMsg<DbHealthProbeActor.GetStatus>();
+        db.Reply(new DbHealthProbeActor.DbHealthStatus(true, clock.Now, null));
+        AwaitAssert(() => publisher.Levels.ShouldContain((byte)240), PresenceBudget);
+        // A second request comes from the periodic timer, not the immediate startup tick.
+        db.ExpectMsg<DbHealthProbeActor.GetStatus>();
+        db.Reply(new DbHealthProbeActor.DbHealthStatus(false, clock.Now, "unreachable"));
+        AwaitAssert(() => publisher.Levels.Last().ShouldBe((byte)100), PresenceBudget);
+    }
+
+    [Fact]
+    public void DbBacked_timer_ask_timeout_demotes_last_known_healthy_node()
+    {
+        var publisher = new RecordingPublisher();
+        var clock = new ControlledClock();
+        var local = NodeId.Parse("db-backed-timeout-node");
+        var db = CreateTestProbe();
+        var actor = Sys.ActorOf(OpcUaPublishActor.PropsForTests(
+            serviceLevel: publisher, localNode: local, dbHealthProbe: db.Ref,
+            healthTickInterval: TimeSpan.FromMilliseconds(100), utcNow: clock.Read));
+        actor.Tell(Snapshot(local, true, clock.Now));
+        db.ExpectMsg<DbHealthProbeActor.GetStatus>();
+        db.Reply(new DbHealthProbeActor.DbHealthStatus(true, clock.Now, null));
+        AwaitAssert(() => publisher.Levels.ShouldContain((byte)250), PresenceBudget);
+        // Leave subsequent real Ask requests unanswered: the timeout status must reach the actor.
+        db.ExpectMsg<DbHealthProbeActor.GetStatus>();
+        AwaitAssert(() => publisher.Levels.Last().ShouldBe((byte)110), PresenceBudget);
+    }
+
+    [Fact]
+    public void Missing_local_snapshot_entry_retries_zero_on_timer_and_recovers()
+    {
+        var publisher = new RetryZeroPublisher();
+        var clock = new ControlledClock();
+        var local = NodeId.Parse("missing-entry-node");
+        var actor = Sys.ActorOf(OpcUaPublishActor.PropsForTests(
+            serviceLevel: publisher, localNode: local, dbLess: true,
+            healthTickInterval: TimeSpan.FromMilliseconds(25), utcNow: clock.Read));
+        actor.Tell(Snapshot(local, false, clock.Now));
+        AwaitAssert(() => publisher.Levels.ShouldBe(new byte[] { 240 }), PresenceBudget);
+
+        // Only this snapshot Tell requests the first zero. Fail it and the next attempt so
+        // subsequent zero attempts must come from the periodic timer, exercising the null-entry
+        // branch repeatedly rather than mistaking the Detached branch for missing-node coverage.
+        actor.Tell(Snapshot(NodeId.Parse("other-node"), false, clock.Now));
+        AwaitAssert(() => publisher.Levels.ShouldBe(new byte[] { 240, 0 }), PresenceBudget);
+        publisher.ZeroAttempts.ShouldBeGreaterThanOrEqualTo(3);
+
+        actor.Tell(Snapshot(local, false, clock.Now));
+        AwaitAssert(() => publisher.Levels.ShouldBe(new byte[] { 240, 0, 240 }), PresenceBudget);
+        clock.Advance(TimeSpan.FromSeconds(30) + TimeSpan.FromTicks(1));
+        AwaitAssert(() => publisher.Levels.ShouldBe(new byte[] { 240, 0, 240, 200 }), PresenceBudget);
+    }
+
+    [Fact]
+    public void No_snapshot_startup_does_not_publish_across_virtual_timer_periods()
+    {
+        // This actor requires the Cluster extension, but the absent/missing-entry guards do
+        // not inspect membership. Do not self-join: the ordinary harness waits for Up in its
+        // constructor, which cannot progress with a frozen scheduler.
+        using var local = new TestKit(AkkaTestHocon + @"
+            akka.scheduler.implementation = ""Akka.TestKit.TestScheduler, Akka.TestKit""");
+        var scheduler = (TestScheduler)local.Sys.Scheduler;
+        var publisher = new RetryZeroPublisher();
+        var clock = new ControlledClock();
+        var actor = local.ActorOfAsTestActorRef<OpcUaPublishActor>(OpcUaPublishActor.PropsForTests(
+            serviceLevel: publisher, localNode: NodeId.Parse("no-snapshot-node"), dbLess: true,
+            healthTickInterval: TimeSpan.FromSeconds(1), utcNow: clock.Read));
+
+        // TestActorRef uses the calling-thread dispatcher: Advance completes delivery before
+        // these assertions, including the immediate startup tick and three periodic ticks.
+        for (var period = 0; period < 3; period++)
+            scheduler.Advance(TimeSpan.FromSeconds(1));
+        publisher.Levels.ShouldBeEmpty();
+        publisher.ZeroAttempts.ShouldBe(0);
+        clock.Reads.ShouldBe(0);
+
+        // Positive control: the same registered timer must subsequently retry a failed zero.
+        // No whole snapshot at startup means no publication; a received snapshot missing the
+        // local entry means zero. Keep these two policies explicitly distinct.
+        actor.Tell(Snapshot(NodeId.Parse("other-node"), false, clock.Now));
+        publisher.ZeroAttempts.ShouldBe(1);
+        scheduler.Advance(TimeSpan.FromSeconds(1));
+        publisher.ZeroAttempts.ShouldBe(2);
+        publisher.Levels.ShouldBeEmpty();
+        scheduler.Advance(TimeSpan.FromSeconds(1));
+        publisher.ZeroAttempts.ShouldBe(3);
+        publisher.Levels.ShouldBe(new byte[] { 0 });
+        clock.Reads.ShouldBe(0);
+    }
+
+    private sealed class RetryZeroPublisher : IServiceLevelPublisher
+    {
+        private readonly ConcurrentQueue<byte> _levels = new();
+        private int _zeroAttempts;
+        public byte[] Levels => _levels.ToArray();
+        public int ZeroAttempts => Volatile.Read(ref _zeroAttempts);
+        public void Publish(byte serviceLevel)
+        {
+            if (serviceLevel == 0 && Interlocked.Increment(ref _zeroAttempts) <= 2)
+                throw new InvalidOperationException("test zero-publication failure");
+            _levels.Enqueue(serviceLevel);
+        }
+    }
+
+    private sealed class ControlledClock
+    {
+        private long _ticks = new DateTime(2026, 1, 1, 0, 0, 0, DateTimeKind.Utc).Ticks;
+        private int _reads;
+        public DateTime Now => new(Interlocked.Read(ref _ticks), DateTimeKind.Utc);
+        public int Reads => Volatile.Read(ref _reads);
+        public DateTime Read()
+        {
+            Interlocked.Increment(ref _reads);
+            return Now;
+        }
+        public void Advance(TimeSpan age) => Interlocked.Add(ref _ticks, age.Ticks);
+    }
+
+    private static RedundancyStateChanged Snapshot(NodeId local, bool primary, DateTime asOf) =>
+        new(new[] { new NodeRedundancyState(local,
+            primary ? RedundancyRole.Primary : RedundancyRole.Secondary,
+            IsClusterLeader: primary, IsDriverPrimary: primary, asOf) }, CorrelationId.NewId());
+
+    private sealed class RecordingPublisher : IServiceLevelPublisher
+    {
+        private readonly ConcurrentQueue<byte> _levels = new();
+        public byte[] Levels => _levels.ToArray();
+        public void Publish(byte serviceLevel) => _levels.Enqueue(serviceLevel);
+    }
+}

tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/OpcUa/OpcUaPublishActorTests.cs

@@ -15,6 +15,49 @@ namespace ZB.MOM.WW.OtOpcUa.Runtime.Tests.OpcUa;
 
 public sealed class OpcUaPublishActorTests : RuntimeActorTestBase
 {
+    [Fact]
+    public void Failed_value_is_retried_and_last_level_only_tracks_success()
+    {
+        var sink = new RecoveringPublisher { Fail = false };
+        var actor = ActorOfAsTestActorRef<OpcUaPublishActor>(OpcUaPublishActor.PropsForTests(serviceLevel: sink));
+        actor.Tell(new OpcUaPublishActor.ServiceLevelChanged(100));
+        sink.Fail = true;
+        actor.Tell(new OpcUaPublishActor.ServiceLevelChanged(0));
+        actor.UnderlyingActor.LastServiceLevel.ShouldBe((byte)100);
+        sink.Fail = false;
+        actor.Tell(new OpcUaPublishActor.ServiceLevelChanged(0));
+        sink.Delivered.ShouldBe(new byte[] { 100, 0 });
+    }
+
+    [Fact]
+    public void Requesting_prior_success_after_failure_updates_delivery_and_replay()
+    {
+        var sink = new RecoveringPublisher();
+        var deferred = new DeferredServiceLevelPublisher();
+        deferred.SetInner(sink);
+        var actor = ActorOfAsTestActorRef<OpcUaPublishActor>(OpcUaPublishActor.PropsForTests(serviceLevel: deferred));
+        actor.Tell(new OpcUaPublishActor.ServiceLevelChanged(100));
+        sink.Fail = true;
+        actor.Tell(new OpcUaPublishActor.ServiceLevelChanged(0));
+        sink.Fail = false;
+        actor.Tell(new OpcUaPublishActor.ServiceLevelChanged(100));
+        sink.Delivered.ShouldBe(new byte[] { 100, 100 });
+        var rebound = new RecoveringPublisher();
+        deferred.SetInner(rebound);
+        rebound.Delivered.ShouldBe(new byte[] { 100 });
+    }
+
+    private sealed class RecoveringPublisher : IServiceLevelPublisher
+    {
+        public bool Fail { get; set; }
+        public List<byte> Delivered { get; } = new();
+        public void Publish(byte level)
+        {
+            if (Fail) throw new InvalidOperationException("controlled failure");
+            Delivered.Add(level);
+        }
+    }
+
     /// <summary>Verifies that message contracts are accepted without a pinned dispatcher in tests.</summary>
     [Fact]
     public void Accepts_message_contracts_without_pinned_dispatcher_in_tests()

tests/TestSupport/FixtureCleanup.cs

@@ -0,0 +1,32 @@
+namespace ZB.MOM.WW.OtOpcUa.Tests;
+
+internal static class FixtureCleanup
+{
+    internal const string SecondaryExceptionKey = "FixtureCleanup.SecondaryException";
+
+    internal static async Task RunAsync(Func<Task> body, Func<Task> cleanup, Action<Exception> report)
+    {
+        Exception? primary = null;
+        try
+        {
+            await body();
+        }
+        catch (Exception failure)
+        {
+            primary = failure;
+            throw;
+        }
+        finally
+        {
+            try
+            {
+                await cleanup();
+            }
+            catch (Exception secondary) when (primary is not null)
+            {
+                try { primary.Data[SecondaryExceptionKey] = secondary; } catch { }
+                try { report(secondary); } catch { }
+            }
+        }
+    }
+}