FOCAS PR 3 — ITagDiscovery + ISubscribable + IHostConnectivityProbe + IPerCallHostResolver. Completes the FOCAS driver — 7-interface capability set matching AbCip/AbLegacy/TwinCAT (minus IAlarmSource — Fanuc CNC alarms live in a different API surface, tracked as a future-phase concern). ITagDiscovery emits pre-declared tags under a FOCAS root + per-device sub-folder keyed on the canonical focas://host:port string with DeviceName fallback. Writable → Operate, non-writable → ViewOnly. No native FOCAS symbol browsing — CNCs don't expose a tag catalogue the way Logix or TwinCAT do; operators declare addresses explicitly. ISubscribable consumes the shared PollGroupEngine — 5th consumer of the engine after Modbus + AbCip + AbLegacy + TwinCAT-poll-mode. 100ms interval floor inherited. FOCAS has no native notification/subscription protocol (unlike TwinCAT ADS), so polling is the only option — every subscribed tag round-trips through cnc_rdpmcrng / cnc_rdparam / cnc_rdmacro on each tick. IHostConnectivityProbe uses the existing IFocasClient.ProbeAsync which in the real FwlibFocasClient calls cnc_statinfo (cheap handshake returning ODBST with tmmode/aut/run/motion/alarm state). Probe loop runs when Enabled=true, catches OperationCanceledException during shutdown, falls through to Stopped on exceptions, emits Running/Stopped transitions via OnHostStatusChanged with the canonical focas://host:port as the host-name key. Same-state spurious-event guard under per-device lock. IPerCallHostResolver maps tag full-ref to DeviceHostAddress for Phase 6.1 bulkhead/breaker keying per plan decision #144 — unknown refs fall back to first device, no devices → DriverInstanceId. ShutdownAsync now disposes PollGroupEngine + cancels/disposes per-device probe CTS + disposes cached clients. DeviceState gains ProbeLock / HostState / HostStateChangedUtc / ProbeCts matching the shape used by AbCip/AbLegacy/TwinCAT. 9 new unit tests in FocasCapabilityTests — discovery tag emission with correct SecurityClassification, subscription initial poll raises OnDataChange, shutdown cancels subscriptions, GetHostStatuses entry-per-device, probe Running / Stopped transitions, ResolveHost for known / unknown / no-devices paths. FocasScaffoldingTests updated with Probe.Enabled=false where the default factory would otherwise try to load Fwlib32.dll during the probe-loop spinup. Total FOCAS unit tests now 115/115 passing (+9 from PR 2's 106); full solution builds 0 errors; Modbus / AbCip / AbLegacy / TwinCAT / other drivers untouched. FOCAS driver is real-wire-capable end-to-end — read / write / discover / subscribe / probe / host-resolve for Fanuc FS 0i/16i/18i/21i/30i/31i/32i/Series 35i/Power Mate i controllers once deployment drops Fwlib32.dll beside the server. Closes task #120 subtask FOCAS.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ZB.MOM.WW.OtOpcUa.slnx

@@ -12,6 +12,8 @@
         <Project Path="src/ZB.MOM.WW.OtOpcUa.Driver.S7/ZB.MOM.WW.OtOpcUa.Driver.S7.csproj"/>
         <Project Path="src/ZB.MOM.WW.OtOpcUa.Driver.AbCip/ZB.MOM.WW.OtOpcUa.Driver.AbCip.csproj"/>
         <Project Path="src/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.csproj"/>
+        <Project Path="src/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.csproj"/>
+        <Project Path="src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.csproj"/>
         <Project Path="src/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.csproj"/>
         <Project Path="src/ZB.MOM.WW.OtOpcUa.Client.Shared/ZB.MOM.WW.OtOpcUa.Client.Shared.csproj"/>
         <Project Path="src/ZB.MOM.WW.OtOpcUa.Client.CLI/ZB.MOM.WW.OtOpcUa.Client.CLI.csproj"/>
@@ -33,6 +35,8 @@
         <Project Path="tests/ZB.MOM.WW.OtOpcUa.Driver.S7.Tests/ZB.MOM.WW.OtOpcUa.Driver.S7.Tests.csproj"/>
         <Project Path="tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests.csproj"/>
         <Project Path="tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests.csproj"/>
+        <Project Path="tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests.csproj"/>
+        <Project Path="tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests.csproj"/>
         <Project Path="tests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests/ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests.csproj"/>
         <Project Path="tests/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests.csproj"/>
         <Project Path="tests/ZB.MOM.WW.OtOpcUa.Client.Shared.Tests/ZB.MOM.WW.OtOpcUa.Client.Shared.Tests.csproj"/>

src/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/AbLegacyDriver.cs

@@ -8,18 +8,31 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.AbLegacy;
 ///     <see cref="IDriver"/> only at PR 1 time; read / write / discovery / subscribe / probe /
 ///     host-resolver capabilities ship in PRs 2 and 3.
 /// </summary>
-public sealed class AbLegacyDriver : IDriver, IDisposable, IAsyncDisposable
+public sealed class AbLegacyDriver : IDriver, IReadable, IWritable, ITagDiscovery, ISubscribable,
+    IHostConnectivityProbe, IPerCallHostResolver, IDisposable, IAsyncDisposable
 {
     private readonly AbLegacyDriverOptions _options;
     private readonly string _driverInstanceId;
+    private readonly IAbLegacyTagFactory _tagFactory;
+    private readonly PollGroupEngine _poll;
     private readonly Dictionary<string, DeviceState> _devices = new(StringComparer.OrdinalIgnoreCase);
+    private readonly Dictionary<string, AbLegacyTagDefinition> _tagsByName = new(StringComparer.OrdinalIgnoreCase);
     private DriverHealth _health = new(DriverState.Unknown, null, null);
 
-    public AbLegacyDriver(AbLegacyDriverOptions options, string driverInstanceId)
+    public event EventHandler<DataChangeEventArgs>? OnDataChange;
+    public event EventHandler<HostStatusChangedEventArgs>? OnHostStatusChanged;
+
+    public AbLegacyDriver(AbLegacyDriverOptions options, string driverInstanceId,
+        IAbLegacyTagFactory? tagFactory = null)
     {
         ArgumentNullException.ThrowIfNull(options);
         _options = options;
         _driverInstanceId = driverInstanceId;
+        _tagFactory = tagFactory ?? new LibplctagLegacyTagFactory();
+        _poll = new PollGroupEngine(
+            reader: ReadAsync,
+            onChange: (handle, tagRef, snapshot) =>
+                OnDataChange?.Invoke(this, new DataChangeEventArgs(handle, tagRef, snapshot)));
     }
 
     public string DriverInstanceId => _driverInstanceId;
@@ -38,6 +51,18 @@ public sealed class AbLegacyDriver : IDriver, IDisposable, IAsyncDisposable
                 var profile = AbLegacyPlcFamilyProfile.ForFamily(device.PlcFamily);
                 _devices[device.HostAddress] = new DeviceState(addr, device, profile);
             }
+            foreach (var tag in _options.Tags) _tagsByName[tag.Name] = tag;
+
+            // Probe loops — one per device when enabled + probe address configured.
+            if (_options.Probe.Enabled && !string.IsNullOrWhiteSpace(_options.Probe.ProbeAddress))
+            {
+                foreach (var state in _devices.Values)
+                {
+                    state.ProbeCts = new CancellationTokenSource();
+                    var ct = state.ProbeCts.Token;
+                    _ = Task.Run(() => ProbeLoopAsync(state, ct), ct);
+                }
+            }
             _health = new DriverHealth(DriverState.Healthy, DateTime.UtcNow, null);
         }
         catch (Exception ex)
@@ -54,11 +79,19 @@ public sealed class AbLegacyDriver : IDriver, IDisposable, IAsyncDisposable
         await InitializeAsync(driverConfigJson, cancellationToken).ConfigureAwait(false);
     }
 
-    public Task ShutdownAsync(CancellationToken cancellationToken)
+    public async Task ShutdownAsync(CancellationToken cancellationToken)
     {
+        await _poll.DisposeAsync().ConfigureAwait(false);
+        foreach (var state in _devices.Values)
+        {
+            try { state.ProbeCts?.Cancel(); } catch { }
+            state.ProbeCts?.Dispose();
+            state.ProbeCts = null;
+            state.DisposeRuntimes();
+        }
         _devices.Clear();
+        _tagsByName.Clear();
         _health = new DriverHealth(DriverState.Unknown, _health.LastSuccessfulRead, null);
-        return Task.CompletedTask;
     }
 
     public DriverHealth GetHealth() => _health;
@@ -69,6 +102,264 @@ public sealed class AbLegacyDriver : IDriver, IDisposable, IAsyncDisposable
     internal DeviceState? GetDeviceState(string hostAddress) =>
         _devices.TryGetValue(hostAddress, out var s) ? s : null;
 
+    // ---- IReadable ----
+
+    public async Task<IReadOnlyList<DataValueSnapshot>> ReadAsync(
+        IReadOnlyList<string> fullReferences, CancellationToken cancellationToken)
+    {
+        ArgumentNullException.ThrowIfNull(fullReferences);
+        var now = DateTime.UtcNow;
+        var results = new DataValueSnapshot[fullReferences.Count];
+
+        for (var i = 0; i < fullReferences.Count; i++)
+        {
+            var reference = fullReferences[i];
+            if (!_tagsByName.TryGetValue(reference, out var def))
+            {
+                results[i] = new DataValueSnapshot(null, AbLegacyStatusMapper.BadNodeIdUnknown, null, now);
+                continue;
+            }
+            if (!_devices.TryGetValue(def.DeviceHostAddress, out var device))
+            {
+                results[i] = new DataValueSnapshot(null, AbLegacyStatusMapper.BadNodeIdUnknown, null, now);
+                continue;
+            }
+
+            try
+            {
+                var runtime = await EnsureTagRuntimeAsync(device, def, cancellationToken).ConfigureAwait(false);
+                await runtime.ReadAsync(cancellationToken).ConfigureAwait(false);
+
+                var status = runtime.GetStatus();
+                if (status != 0)
+                {
+                    results[i] = new DataValueSnapshot(null,
+                        AbLegacyStatusMapper.MapLibplctagStatus(status), null, now);
+                    _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead,
+                        $"libplctag status {status} reading {reference}");
+                    continue;
+                }
+
+                var parsed = AbLegacyAddress.TryParse(def.Address);
+                var value = runtime.DecodeValue(def.DataType, parsed?.BitIndex);
+                results[i] = new DataValueSnapshot(value, AbLegacyStatusMapper.Good, now, now);
+                _health = new DriverHealth(DriverState.Healthy, now, null);
+            }
+            catch (OperationCanceledException) { throw; }
+            catch (Exception ex)
+            {
+                results[i] = new DataValueSnapshot(null,
+                    AbLegacyStatusMapper.BadCommunicationError, null, now);
+                _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead, ex.Message);
+            }
+        }
+
+        return results;
+    }
+
+    // ---- IWritable ----
+
+    public async Task<IReadOnlyList<WriteResult>> WriteAsync(
+        IReadOnlyList<WriteRequest> writes, CancellationToken cancellationToken)
+    {
+        ArgumentNullException.ThrowIfNull(writes);
+        var results = new WriteResult[writes.Count];
+
+        for (var i = 0; i < writes.Count; i++)
+        {
+            var w = writes[i];
+            if (!_tagsByName.TryGetValue(w.FullReference, out var def))
+            {
+                results[i] = new WriteResult(AbLegacyStatusMapper.BadNodeIdUnknown);
+                continue;
+            }
+            if (!def.Writable)
+            {
+                results[i] = new WriteResult(AbLegacyStatusMapper.BadNotWritable);
+                continue;
+            }
+            if (!_devices.TryGetValue(def.DeviceHostAddress, out var device))
+            {
+                results[i] = new WriteResult(AbLegacyStatusMapper.BadNodeIdUnknown);
+                continue;
+            }
+
+            try
+            {
+                var runtime = await EnsureTagRuntimeAsync(device, def, cancellationToken).ConfigureAwait(false);
+                var parsed = AbLegacyAddress.TryParse(def.Address);
+                runtime.EncodeValue(def.DataType, parsed?.BitIndex, w.Value);
+                await runtime.WriteAsync(cancellationToken).ConfigureAwait(false);
+
+                var status = runtime.GetStatus();
+                results[i] = new WriteResult(status == 0
+                    ? AbLegacyStatusMapper.Good
+                    : AbLegacyStatusMapper.MapLibplctagStatus(status));
+            }
+            catch (OperationCanceledException) { throw; }
+            catch (NotSupportedException nse)
+            {
+                results[i] = new WriteResult(AbLegacyStatusMapper.BadNotSupported);
+                _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead, nse.Message);
+            }
+            catch (Exception ex) when (ex is FormatException or InvalidCastException)
+            {
+                results[i] = new WriteResult(AbLegacyStatusMapper.BadTypeMismatch);
+            }
+            catch (OverflowException)
+            {
+                results[i] = new WriteResult(AbLegacyStatusMapper.BadOutOfRange);
+            }
+            catch (Exception ex)
+            {
+                results[i] = new WriteResult(AbLegacyStatusMapper.BadCommunicationError);
+                _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead, ex.Message);
+            }
+        }
+
+        return results;
+    }
+
+    // ---- ITagDiscovery ----
+
+    public Task DiscoverAsync(IAddressSpaceBuilder builder, CancellationToken cancellationToken)
+    {
+        ArgumentNullException.ThrowIfNull(builder);
+        var root = builder.Folder("AbLegacy", "AbLegacy");
+        foreach (var device in _options.Devices)
+        {
+            var label = device.DeviceName ?? device.HostAddress;
+            var deviceFolder = root.Folder(device.HostAddress, label);
+            var tagsForDevice = _options.Tags.Where(t =>
+                string.Equals(t.DeviceHostAddress, device.HostAddress, StringComparison.OrdinalIgnoreCase));
+            foreach (var tag in tagsForDevice)
+            {
+                deviceFolder.Variable(tag.Name, tag.Name, new DriverAttributeInfo(
+                    FullName: tag.Name,
+                    DriverDataType: tag.DataType.ToDriverDataType(),
+                    IsArray: false,
+                    ArrayDim: null,
+                    SecurityClass: tag.Writable
+                        ? SecurityClassification.Operate
+                        : SecurityClassification.ViewOnly,
+                    IsHistorized: false,
+                    IsAlarm: false,
+                    WriteIdempotent: tag.WriteIdempotent));
+            }
+        }
+        return Task.CompletedTask;
+    }
+
+    // ---- ISubscribable (polling overlay via shared engine) ----
+
+    public Task<ISubscriptionHandle> SubscribeAsync(
+        IReadOnlyList<string> fullReferences, TimeSpan publishingInterval, CancellationToken cancellationToken) =>
+        Task.FromResult(_poll.Subscribe(fullReferences, publishingInterval));
+
+    public Task UnsubscribeAsync(ISubscriptionHandle handle, CancellationToken cancellationToken)
+    {
+        _poll.Unsubscribe(handle);
+        return Task.CompletedTask;
+    }
+
+    // ---- IHostConnectivityProbe ----
+
+    public IReadOnlyList<HostConnectivityStatus> GetHostStatuses() =>
+        [.. _devices.Values.Select(s => new HostConnectivityStatus(s.Options.HostAddress, s.HostState, s.HostStateChangedUtc))];
+
+    private async Task ProbeLoopAsync(DeviceState state, CancellationToken ct)
+    {
+        var probeParams = new AbLegacyTagCreateParams(
+            Gateway: state.ParsedAddress.Gateway,
+            Port: state.ParsedAddress.Port,
+            CipPath: state.ParsedAddress.CipPath,
+            LibplctagPlcAttribute: state.Profile.LibplctagPlcAttribute,
+            TagName: _options.Probe.ProbeAddress!,
+            Timeout: _options.Probe.Timeout);
+
+        IAbLegacyTagRuntime? probeRuntime = null;
+        while (!ct.IsCancellationRequested)
+        {
+            var success = false;
+            try
+            {
+                probeRuntime ??= _tagFactory.Create(probeParams);
+                if (!state.ProbeInitialized)
+                {
+                    await probeRuntime.InitializeAsync(ct).ConfigureAwait(false);
+                    state.ProbeInitialized = true;
+                }
+                await probeRuntime.ReadAsync(ct).ConfigureAwait(false);
+                success = probeRuntime.GetStatus() == 0;
+            }
+            catch (OperationCanceledException) when (ct.IsCancellationRequested) { break; }
+            catch
+            {
+                try { probeRuntime?.Dispose(); } catch { }
+                probeRuntime = null;
+                state.ProbeInitialized = false;
+            }
+
+            TransitionDeviceState(state, success ? HostState.Running : HostState.Stopped);
+
+            try { await Task.Delay(_options.Probe.Interval, ct).ConfigureAwait(false); }
+            catch (OperationCanceledException) { break; }
+        }
+        try { probeRuntime?.Dispose(); } catch { }
+    }
+
+    private void TransitionDeviceState(DeviceState state, HostState newState)
+    {
+        HostState old;
+        lock (state.ProbeLock)
+        {
+            old = state.HostState;
+            if (old == newState) return;
+            state.HostState = newState;
+            state.HostStateChangedUtc = DateTime.UtcNow;
+        }
+        OnHostStatusChanged?.Invoke(this,
+            new HostStatusChangedEventArgs(state.Options.HostAddress, old, newState));
+    }
+
+    // ---- IPerCallHostResolver ----
+
+    public string ResolveHost(string fullReference)
+    {
+        if (_tagsByName.TryGetValue(fullReference, out var def))
+            return def.DeviceHostAddress;
+        return _options.Devices.FirstOrDefault()?.HostAddress ?? DriverInstanceId;
+    }
+
+    private async Task<IAbLegacyTagRuntime> EnsureTagRuntimeAsync(
+        DeviceState device, AbLegacyTagDefinition def, CancellationToken ct)
+    {
+        if (device.Runtimes.TryGetValue(def.Name, out var existing)) return existing;
+
+        var parsed = AbLegacyAddress.TryParse(def.Address)
+            ?? throw new InvalidOperationException(
+                $"AbLegacy tag '{def.Name}' has malformed Address '{def.Address}'.");
+
+        var runtime = _tagFactory.Create(new AbLegacyTagCreateParams(
+            Gateway: device.ParsedAddress.Gateway,
+            Port: device.ParsedAddress.Port,
+            CipPath: device.ParsedAddress.CipPath,
+            LibplctagPlcAttribute: device.Profile.LibplctagPlcAttribute,
+            TagName: parsed.ToLibplctagName(),
+            Timeout: _options.Timeout));
+        try
+        {
+            await runtime.InitializeAsync(ct).ConfigureAwait(false);
+        }
+        catch
+        {
+            runtime.Dispose();
+            throw;
+        }
+        device.Runtimes[def.Name] = runtime;
+        return runtime;
+    }
+
     public void Dispose() => DisposeAsync().AsTask().GetAwaiter().GetResult();
     public async ValueTask DisposeAsync() => await ShutdownAsync(CancellationToken.None).ConfigureAwait(false);
 
@@ -80,5 +371,19 @@ public sealed class AbLegacyDriver : IDriver, IDisposable, IAsyncDisposable
         public AbLegacyHostAddress ParsedAddress { get; } = parsedAddress;
         public AbLegacyDeviceOptions Options { get; } = options;
         public AbLegacyPlcFamilyProfile Profile { get; } = profile;
+        public Dictionary<string, IAbLegacyTagRuntime> Runtimes { get; } =
+            new(StringComparer.OrdinalIgnoreCase);
+
+        public object ProbeLock { get; } = new();
+        public HostState HostState { get; set; } = HostState.Unknown;
+        public DateTime HostStateChangedUtc { get; set; } = DateTime.UtcNow;
+        public CancellationTokenSource? ProbeCts { get; set; }
+        public bool ProbeInitialized { get; set; }
+
+        public void DisposeRuntimes()
+        {
+            foreach (var r in Runtimes.Values) r.Dispose();
+            Runtimes.Clear();
+        }
     }
 }

src/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/IAbLegacyTagRuntime.cs

@@ -0,0 +1,29 @@
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbLegacy;
+
+/// <summary>
+///     Wire-layer abstraction over a single PCCC tag. Mirrors <c>IAbCipTagRuntime</c>'s shape so
+///     the same test-fake pattern applies; the only meaningful difference is the protocol layer
+///     underneath (<c>ab_pccc</c> vs <c>ab_eip</c>).
+/// </summary>
+public interface IAbLegacyTagRuntime : IDisposable
+{
+    Task InitializeAsync(CancellationToken cancellationToken);
+    Task ReadAsync(CancellationToken cancellationToken);
+    Task WriteAsync(CancellationToken cancellationToken);
+    int GetStatus();
+    object? DecodeValue(AbLegacyDataType type, int? bitIndex);
+    void EncodeValue(AbLegacyDataType type, int? bitIndex, object? value);
+}
+
+public interface IAbLegacyTagFactory
+{
+    IAbLegacyTagRuntime Create(AbLegacyTagCreateParams createParams);
+}
+
+public sealed record AbLegacyTagCreateParams(
+    string Gateway,
+    int Port,
+    string CipPath,
+    string LibplctagPlcAttribute,
+    string TagName,
+    TimeSpan Timeout);

src/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/LibplctagLegacyTagRuntime.cs

@@ -0,0 +1,97 @@
+using libplctag;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbLegacy;
+
+/// <summary>
+///     Default libplctag-backed <see cref="IAbLegacyTagRuntime"/>. Uses <c>ab_pccc</c> protocol
+///     on top of EtherNet/IP — libplctag's PCCC layer handles the file-letter + word + bit +
+///     sub-element decoding internally, so our wrapper just has to forward the atomic type to
+///     the right Get/Set call.
+/// </summary>
+internal sealed class LibplctagLegacyTagRuntime : IAbLegacyTagRuntime
+{
+    private readonly Tag _tag;
+
+    public LibplctagLegacyTagRuntime(AbLegacyTagCreateParams p)
+    {
+        _tag = new Tag
+        {
+            Gateway = p.Gateway,
+            Path = p.CipPath,
+            PlcType = MapPlcType(p.LibplctagPlcAttribute),
+            Protocol = Protocol.ab_eip, // PCCC-over-EIP; libplctag routes via the PlcType-specific PCCC layer
+            Name = p.TagName,
+            Timeout = p.Timeout,
+        };
+    }
+
+    public Task InitializeAsync(CancellationToken cancellationToken) => _tag.InitializeAsync(cancellationToken);
+    public Task ReadAsync(CancellationToken cancellationToken) => _tag.ReadAsync(cancellationToken);
+    public Task WriteAsync(CancellationToken cancellationToken) => _tag.WriteAsync(cancellationToken);
+
+    public int GetStatus() => (int)_tag.GetStatus();
+
+    public object? DecodeValue(AbLegacyDataType type, int? bitIndex) => type switch
+    {
+        AbLegacyDataType.Bit => bitIndex is int bit
+            ? _tag.GetBit(bit)
+            : _tag.GetInt8(0) != 0,
+        AbLegacyDataType.Int or AbLegacyDataType.AnalogInt => (int)_tag.GetInt16(0),
+        AbLegacyDataType.Long => _tag.GetInt32(0),
+        AbLegacyDataType.Float => _tag.GetFloat32(0),
+        AbLegacyDataType.String => _tag.GetString(0),
+        AbLegacyDataType.TimerElement or AbLegacyDataType.CounterElement
+            or AbLegacyDataType.ControlElement => _tag.GetInt32(0),
+        _ => null,
+    };
+
+    public void EncodeValue(AbLegacyDataType type, int? bitIndex, object? value)
+    {
+        switch (type)
+        {
+            case AbLegacyDataType.Bit:
+                if (bitIndex is int)
+                    throw new NotSupportedException(
+                        "Bit-within-word writes require read-modify-write; tracked in task #181.");
+                _tag.SetInt8(0, Convert.ToBoolean(value) ? (sbyte)1 : (sbyte)0);
+                break;
+            case AbLegacyDataType.Int:
+            case AbLegacyDataType.AnalogInt:
+                _tag.SetInt16(0, Convert.ToInt16(value));
+                break;
+            case AbLegacyDataType.Long:
+                _tag.SetInt32(0, Convert.ToInt32(value));
+                break;
+            case AbLegacyDataType.Float:
+                _tag.SetFloat32(0, Convert.ToSingle(value));
+                break;
+            case AbLegacyDataType.String:
+                _tag.SetString(0, Convert.ToString(value) ?? string.Empty);
+                break;
+            case AbLegacyDataType.TimerElement:
+            case AbLegacyDataType.CounterElement:
+            case AbLegacyDataType.ControlElement:
+                _tag.SetInt32(0, Convert.ToInt32(value));
+                break;
+            default:
+                throw new NotSupportedException($"AbLegacyDataType {type} not writable.");
+        }
+    }
+
+    public void Dispose() => _tag.Dispose();
+
+    private static PlcType MapPlcType(string attribute) => attribute switch
+    {
+        "slc500" => PlcType.Slc500,
+        "micrologix" => PlcType.MicroLogix,
+        "plc5" => PlcType.Plc5,
+        "logixpccc" => PlcType.LogixPccc,
+        _ => PlcType.Slc500,
+    };
+}
+
+internal sealed class LibplctagLegacyTagFactory : IAbLegacyTagFactory
+{
+    public IAbLegacyTagRuntime Create(AbLegacyTagCreateParams createParams) =>
+        new LibplctagLegacyTagRuntime(createParams);
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasAddress.cs

@@ -0,0 +1,95 @@
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
+
+/// <summary>
+///     Parsed FOCAS address covering the three addressing spaces a driver touches:
+///     <see cref="FocasAreaKind.Pmc"/> (letter + byte + optional bit — <c>X0.0</c>, <c>R100</c>,
+///     <c>F20.3</c>), <see cref="FocasAreaKind.Parameter"/> (CNC parameter number —
+///     <c>PARAM:1020</c>, <c>PARAM:1815/0</c> for bit 0), and <see cref="FocasAreaKind.Macro"/>
+///     (macro variable number — <c>MACRO:100</c>, <c>MACRO:500</c>).
+/// </summary>
+/// <remarks>
+///     PMC letters: <c>X/Y</c> (IO), <c>F/G</c> (signals between PMC + CNC), <c>R</c> (internal
+///     relay), <c>D</c> (data table), <c>C</c> (counter), <c>K</c> (keep relay), <c>A</c>
+///     (message display), <c>E</c> (extended relay), <c>T</c> (timer). Byte numbering is 0-based;
+///     bit index when present is 0–7 and uses <c>.N</c> for PMC or <c>/N</c> for parameters.
+/// </remarks>
+public sealed record FocasAddress(
+    FocasAreaKind Kind,
+    string? PmcLetter,
+    int Number,
+    int? BitIndex)
+{
+    public string Canonical => Kind switch
+    {
+        FocasAreaKind.Pmc => BitIndex is null
+            ? $"{PmcLetter}{Number}"
+            : $"{PmcLetter}{Number}.{BitIndex}",
+        FocasAreaKind.Parameter => BitIndex is null
+            ? $"PARAM:{Number}"
+            : $"PARAM:{Number}/{BitIndex}",
+        FocasAreaKind.Macro => $"MACRO:{Number}",
+        _ => $"?{Number}",
+    };
+
+    public static FocasAddress? TryParse(string? value)
+    {
+        if (string.IsNullOrWhiteSpace(value)) return null;
+        var src = value.Trim();
+
+        if (src.StartsWith("PARAM:", StringComparison.OrdinalIgnoreCase))
+            return ParseScoped(src["PARAM:".Length..], FocasAreaKind.Parameter, bitSeparator: '/');
+
+        if (src.StartsWith("MACRO:", StringComparison.OrdinalIgnoreCase))
+            return ParseScoped(src["MACRO:".Length..], FocasAreaKind.Macro, bitSeparator: null);
+
+        // PMC path: letter + digits + optional .bit
+        if (src.Length < 2 || !char.IsLetter(src[0])) return null;
+        var letter = src[0..1].ToUpperInvariant();
+        if (!IsValidPmcLetter(letter)) return null;
+
+        var remainder = src[1..];
+        int? bit = null;
+        var dotIdx = remainder.IndexOf('.');
+        if (dotIdx >= 0)
+        {
+            if (!int.TryParse(remainder[(dotIdx + 1)..], out var bitValue) || bitValue is < 0 or > 7)
+                return null;
+            bit = bitValue;
+            remainder = remainder[..dotIdx];
+        }
+        if (!int.TryParse(remainder, out var number) || number < 0) return null;
+        return new FocasAddress(FocasAreaKind.Pmc, letter, number, bit);
+    }
+
+    private static FocasAddress? ParseScoped(string body, FocasAreaKind kind, char? bitSeparator)
+    {
+        int? bit = null;
+        if (bitSeparator is char sep)
+        {
+            var slashIdx = body.IndexOf(sep);
+            if (slashIdx >= 0)
+            {
+                if (!int.TryParse(body[(slashIdx + 1)..], out var bitValue) || bitValue is < 0 or > 31)
+                    return null;
+                bit = bitValue;
+                body = body[..slashIdx];
+            }
+        }
+        if (!int.TryParse(body, out var number) || number < 0) return null;
+        return new FocasAddress(kind, PmcLetter: null, number, bit);
+    }
+
+    private static bool IsValidPmcLetter(string letter) => letter switch
+    {
+        "X" or "Y" or "F" or "G" or "R" or "D" or "C" or "K" or "A" or "E" or "T" => true,
+        _ => false,
+    };
+}
+
+/// <summary>Addressing-space kinds the driver understands.</summary>
+public enum FocasAreaKind
+{
+    Pmc,
+    Parameter,
+    Macro,
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasDataType.cs

@@ -0,0 +1,39 @@
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
+
+/// <summary>
+///     FOCAS atomic data types. Narrower than Logix/IEC — FANUC CNCs expose mostly integer +
+///     floating-point data with no UDT concept; macro variables are double-precision floats
+///     and PMC reads return byte / signed word / signed dword.
+/// </summary>
+public enum FocasDataType
+{
+    /// <summary>Single bit (PMC bit, or bit within a CNC parameter).</summary>
+    Bit,
+    /// <summary>8-bit signed byte (PMC 1-byte read).</summary>
+    Byte,
+    /// <summary>16-bit signed word (PMC 2-byte read, or CNC parameter as short).</summary>
+    Int16,
+    /// <summary>32-bit signed int (PMC 4-byte read, or CNC parameter as int).</summary>
+    Int32,
+    /// <summary>32-bit IEEE-754 float (rare; some CNC macro variables).</summary>
+    Float32,
+    /// <summary>64-bit IEEE-754 double (most macro variables are double-precision).</summary>
+    Float64,
+    /// <summary>ASCII string (alarm text, parameter names, some PMC string areas).</summary>
+    String,
+}
+
+public static class FocasDataTypeExtensions
+{
+    public static DriverDataType ToDriverDataType(this FocasDataType t) => t switch
+    {
+        FocasDataType.Bit => DriverDataType.Boolean,
+        FocasDataType.Byte or FocasDataType.Int16 or FocasDataType.Int32 => DriverDataType.Int32,
+        FocasDataType.Float32 => DriverDataType.Float32,
+        FocasDataType.Float64 => DriverDataType.Float64,
+        FocasDataType.String => DriverDataType.String,
+        _ => DriverDataType.Int32,
+    };
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasDriver.cs

@@ -0,0 +1,344 @@
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
+
+/// <summary>
+///     FOCAS driver for Fanuc CNC controllers (FS 0i / 16i / 18i / 21i / 30i / 31i / 32i / Series
+///     35i / Power Mate i). Talks to the CNC via the Fanuc FOCAS/2 FWLIB protocol through an
+///     <see cref="IFocasClient"/> the deployment supplies — FWLIB itself is Fanuc-proprietary
+///     and cannot be redistributed.
+/// </summary>
+/// <remarks>
+///     PR 1 ships <see cref="IDriver"/> only; read / write / discover / subscribe / probe / host-
+///     resolver capabilities land in PRs 2 and 3. The <see cref="IFocasClient"/> abstraction
+///     shipped here lets PR 2 onward stay license-clean — all tests run against a fake client
+///     + the default <see cref="UnimplementedFocasClientFactory"/> makes misconfigured servers
+///     fail fast.
+/// </remarks>
+public sealed class FocasDriver : IDriver, IReadable, IWritable, ITagDiscovery, ISubscribable,
+    IHostConnectivityProbe, IPerCallHostResolver, IDisposable, IAsyncDisposable
+{
+    private readonly FocasDriverOptions _options;
+    private readonly string _driverInstanceId;
+    private readonly IFocasClientFactory _clientFactory;
+    private readonly PollGroupEngine _poll;
+    private readonly Dictionary<string, DeviceState> _devices = new(StringComparer.OrdinalIgnoreCase);
+    private readonly Dictionary<string, FocasTagDefinition> _tagsByName = new(StringComparer.OrdinalIgnoreCase);
+    private DriverHealth _health = new(DriverState.Unknown, null, null);
+
+    public event EventHandler<DataChangeEventArgs>? OnDataChange;
+    public event EventHandler<HostStatusChangedEventArgs>? OnHostStatusChanged;
+
+    public FocasDriver(FocasDriverOptions options, string driverInstanceId,
+        IFocasClientFactory? clientFactory = null)
+    {
+        ArgumentNullException.ThrowIfNull(options);
+        _options = options;
+        _driverInstanceId = driverInstanceId;
+        _clientFactory = clientFactory ?? new FwlibFocasClientFactory();
+        _poll = new PollGroupEngine(
+            reader: ReadAsync,
+            onChange: (handle, tagRef, snapshot) =>
+                OnDataChange?.Invoke(this, new DataChangeEventArgs(handle, tagRef, snapshot)));
+    }
+
+    public string DriverInstanceId => _driverInstanceId;
+    public string DriverType => "FOCAS";
+
+    public Task InitializeAsync(string driverConfigJson, CancellationToken cancellationToken)
+    {
+        _health = new DriverHealth(DriverState.Initializing, null, null);
+        try
+        {
+            foreach (var device in _options.Devices)
+            {
+                var addr = FocasHostAddress.TryParse(device.HostAddress)
+                    ?? throw new InvalidOperationException(
+                        $"FOCAS device has invalid HostAddress '{device.HostAddress}' — expected 'focas://{{ip}}[:{{port}}]'.");
+                _devices[device.HostAddress] = new DeviceState(addr, device);
+            }
+            foreach (var tag in _options.Tags) _tagsByName[tag.Name] = tag;
+
+            if (_options.Probe.Enabled)
+            {
+                foreach (var state in _devices.Values)
+                {
+                    state.ProbeCts = new CancellationTokenSource();
+                    var ct = state.ProbeCts.Token;
+                    _ = Task.Run(() => ProbeLoopAsync(state, ct), ct);
+                }
+            }
+            _health = new DriverHealth(DriverState.Healthy, DateTime.UtcNow, null);
+        }
+        catch (Exception ex)
+        {
+            _health = new DriverHealth(DriverState.Faulted, null, ex.Message);
+            throw;
+        }
+        return Task.CompletedTask;
+    }
+
+    public async Task ReinitializeAsync(string driverConfigJson, CancellationToken cancellationToken)
+    {
+        await ShutdownAsync(cancellationToken).ConfigureAwait(false);
+        await InitializeAsync(driverConfigJson, cancellationToken).ConfigureAwait(false);
+    }
+
+    public async Task ShutdownAsync(CancellationToken cancellationToken)
+    {
+        await _poll.DisposeAsync().ConfigureAwait(false);
+        foreach (var state in _devices.Values)
+        {
+            try { state.ProbeCts?.Cancel(); } catch { }
+            state.ProbeCts?.Dispose();
+            state.ProbeCts = null;
+            state.DisposeClient();
+        }
+        _devices.Clear();
+        _tagsByName.Clear();
+        _health = new DriverHealth(DriverState.Unknown, _health.LastSuccessfulRead, null);
+    }
+
+    public DriverHealth GetHealth() => _health;
+    public long GetMemoryFootprint() => 0;
+    public Task FlushOptionalCachesAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+
+    internal int DeviceCount => _devices.Count;
+    internal DeviceState? GetDeviceState(string hostAddress) =>
+        _devices.TryGetValue(hostAddress, out var s) ? s : null;
+
+    // ---- IReadable ----
+
+    public async Task<IReadOnlyList<DataValueSnapshot>> ReadAsync(
+        IReadOnlyList<string> fullReferences, CancellationToken cancellationToken)
+    {
+        ArgumentNullException.ThrowIfNull(fullReferences);
+        var now = DateTime.UtcNow;
+        var results = new DataValueSnapshot[fullReferences.Count];
+
+        for (var i = 0; i < fullReferences.Count; i++)
+        {
+            var reference = fullReferences[i];
+            if (!_tagsByName.TryGetValue(reference, out var def))
+            {
+                results[i] = new DataValueSnapshot(null, FocasStatusMapper.BadNodeIdUnknown, null, now);
+                continue;
+            }
+            if (!_devices.TryGetValue(def.DeviceHostAddress, out var device))
+            {
+                results[i] = new DataValueSnapshot(null, FocasStatusMapper.BadNodeIdUnknown, null, now);
+                continue;
+            }
+
+            try
+            {
+                var client = await EnsureConnectedAsync(device, cancellationToken).ConfigureAwait(false);
+                var parsed = FocasAddress.TryParse(def.Address)
+                    ?? throw new InvalidOperationException($"FOCAS tag '{def.Name}' has malformed Address '{def.Address}'.");
+                var (value, status) = await client.ReadAsync(parsed, def.DataType, cancellationToken).ConfigureAwait(false);
+
+                results[i] = new DataValueSnapshot(value, status, now, now);
+                if (status == FocasStatusMapper.Good)
+                    _health = new DriverHealth(DriverState.Healthy, now, null);
+                else
+                    _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead,
+                        $"FOCAS status 0x{status:X8} reading {reference}");
+            }
+            catch (OperationCanceledException) { throw; }
+            catch (Exception ex)
+            {
+                results[i] = new DataValueSnapshot(null, FocasStatusMapper.BadCommunicationError, null, now);
+                _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead, ex.Message);
+            }
+        }
+
+        return results;
+    }
+
+    // ---- IWritable ----
+
+    public async Task<IReadOnlyList<WriteResult>> WriteAsync(
+        IReadOnlyList<WriteRequest> writes, CancellationToken cancellationToken)
+    {
+        ArgumentNullException.ThrowIfNull(writes);
+        var results = new WriteResult[writes.Count];
+
+        for (var i = 0; i < writes.Count; i++)
+        {
+            var w = writes[i];
+            if (!_tagsByName.TryGetValue(w.FullReference, out var def))
+            {
+                results[i] = new WriteResult(FocasStatusMapper.BadNodeIdUnknown);
+                continue;
+            }
+            if (!def.Writable)
+            {
+                results[i] = new WriteResult(FocasStatusMapper.BadNotWritable);
+                continue;
+            }
+            if (!_devices.TryGetValue(def.DeviceHostAddress, out var device))
+            {
+                results[i] = new WriteResult(FocasStatusMapper.BadNodeIdUnknown);
+                continue;
+            }
+
+            try
+            {
+                var client = await EnsureConnectedAsync(device, cancellationToken).ConfigureAwait(false);
+                var parsed = FocasAddress.TryParse(def.Address)
+                    ?? throw new InvalidOperationException($"FOCAS tag '{def.Name}' has malformed Address '{def.Address}'.");
+                var status = await client.WriteAsync(parsed, def.DataType, w.Value, cancellationToken).ConfigureAwait(false);
+                results[i] = new WriteResult(status);
+            }
+            catch (OperationCanceledException) { throw; }
+            catch (NotSupportedException nse)
+            {
+                results[i] = new WriteResult(FocasStatusMapper.BadNotSupported);
+                _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead, nse.Message);
+            }
+            catch (Exception ex) when (ex is FormatException or InvalidCastException)
+            {
+                results[i] = new WriteResult(FocasStatusMapper.BadTypeMismatch);
+            }
+            catch (OverflowException)
+            {
+                results[i] = new WriteResult(FocasStatusMapper.BadOutOfRange);
+            }
+            catch (Exception ex)
+            {
+                results[i] = new WriteResult(FocasStatusMapper.BadCommunicationError);
+                _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead, ex.Message);
+            }
+        }
+
+        return results;
+    }
+
+    // ---- ITagDiscovery ----
+
+    public Task DiscoverAsync(IAddressSpaceBuilder builder, CancellationToken cancellationToken)
+    {
+        ArgumentNullException.ThrowIfNull(builder);
+        var root = builder.Folder("FOCAS", "FOCAS");
+        foreach (var device in _options.Devices)
+        {
+            var label = device.DeviceName ?? device.HostAddress;
+            var deviceFolder = root.Folder(device.HostAddress, label);
+            var tagsForDevice = _options.Tags.Where(t =>
+                string.Equals(t.DeviceHostAddress, device.HostAddress, StringComparison.OrdinalIgnoreCase));
+            foreach (var tag in tagsForDevice)
+            {
+                deviceFolder.Variable(tag.Name, tag.Name, new DriverAttributeInfo(
+                    FullName: tag.Name,
+                    DriverDataType: tag.DataType.ToDriverDataType(),
+                    IsArray: false,
+                    ArrayDim: null,
+                    SecurityClass: tag.Writable
+                        ? SecurityClassification.Operate
+                        : SecurityClassification.ViewOnly,
+                    IsHistorized: false,
+                    IsAlarm: false,
+                    WriteIdempotent: tag.WriteIdempotent));
+            }
+        }
+        return Task.CompletedTask;
+    }
+
+    // ---- ISubscribable (polling overlay via shared engine) ----
+
+    public Task<ISubscriptionHandle> SubscribeAsync(
+        IReadOnlyList<string> fullReferences, TimeSpan publishingInterval, CancellationToken cancellationToken) =>
+        Task.FromResult(_poll.Subscribe(fullReferences, publishingInterval));
+
+    public Task UnsubscribeAsync(ISubscriptionHandle handle, CancellationToken cancellationToken)
+    {
+        _poll.Unsubscribe(handle);
+        return Task.CompletedTask;
+    }
+
+    // ---- IHostConnectivityProbe ----
+
+    public IReadOnlyList<HostConnectivityStatus> GetHostStatuses() =>
+        [.. _devices.Values.Select(s => new HostConnectivityStatus(s.Options.HostAddress, s.HostState, s.HostStateChangedUtc))];
+
+    private async Task ProbeLoopAsync(DeviceState state, CancellationToken ct)
+    {
+        while (!ct.IsCancellationRequested)
+        {
+            var success = false;
+            try
+            {
+                var client = await EnsureConnectedAsync(state, ct).ConfigureAwait(false);
+                success = await client.ProbeAsync(ct).ConfigureAwait(false);
+            }
+            catch (OperationCanceledException) when (ct.IsCancellationRequested) { break; }
+            catch { /* connect-failure path already disposed + cleared the client */ }
+
+            TransitionDeviceState(state, success ? HostState.Running : HostState.Stopped);
+
+            try { await Task.Delay(_options.Probe.Interval, ct).ConfigureAwait(false); }
+            catch (OperationCanceledException) { break; }
+        }
+    }
+
+    private void TransitionDeviceState(DeviceState state, HostState newState)
+    {
+        HostState old;
+        lock (state.ProbeLock)
+        {
+            old = state.HostState;
+            if (old == newState) return;
+            state.HostState = newState;
+            state.HostStateChangedUtc = DateTime.UtcNow;
+        }
+        OnHostStatusChanged?.Invoke(this,
+            new HostStatusChangedEventArgs(state.Options.HostAddress, old, newState));
+    }
+
+    // ---- IPerCallHostResolver ----
+
+    public string ResolveHost(string fullReference)
+    {
+        if (_tagsByName.TryGetValue(fullReference, out var def))
+            return def.DeviceHostAddress;
+        return _options.Devices.FirstOrDefault()?.HostAddress ?? DriverInstanceId;
+    }
+
+    private async Task<IFocasClient> EnsureConnectedAsync(DeviceState device, CancellationToken ct)
+    {
+        if (device.Client is { IsConnected: true } c) return c;
+        device.Client ??= _clientFactory.Create();
+        try
+        {
+            await device.Client.ConnectAsync(device.ParsedAddress, _options.Timeout, ct).ConfigureAwait(false);
+        }
+        catch
+        {
+            device.Client.Dispose();
+            device.Client = null;
+            throw;
+        }
+        return device.Client;
+    }
+
+    public void Dispose() => DisposeAsync().AsTask().GetAwaiter().GetResult();
+    public async ValueTask DisposeAsync() => await ShutdownAsync(CancellationToken.None).ConfigureAwait(false);
+
+    internal sealed class DeviceState(FocasHostAddress parsedAddress, FocasDeviceOptions options)
+    {
+        public FocasHostAddress ParsedAddress { get; } = parsedAddress;
+        public FocasDeviceOptions Options { get; } = options;
+        public IFocasClient? Client { get; set; }
+
+        public object ProbeLock { get; } = new();
+        public HostState HostState { get; set; } = HostState.Unknown;
+        public DateTime HostStateChangedUtc { get; set; } = DateTime.UtcNow;
+        public CancellationTokenSource? ProbeCts { get; set; }
+
+        public void DisposeClient()
+        {
+            Client?.Dispose();
+            Client = null;
+        }
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasDriverOptions.cs

@@ -0,0 +1,38 @@
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
+
+/// <summary>
+///     FOCAS driver configuration. One instance supports N CNC devices. Per plan decision #144
+///     each device gets its own <c>(DriverInstanceId, HostAddress)</c> bulkhead key at the
+///     Phase 6.1 resilience layer.
+/// </summary>
+public sealed class FocasDriverOptions
+{
+    public IReadOnlyList<FocasDeviceOptions> Devices { get; init; } = [];
+    public IReadOnlyList<FocasTagDefinition> Tags { get; init; } = [];
+    public FocasProbeOptions Probe { get; init; } = new();
+    public TimeSpan Timeout { get; init; } = TimeSpan.FromSeconds(2);
+}
+
+public sealed record FocasDeviceOptions(
+    string HostAddress,
+    string? DeviceName = null);
+
+/// <summary>
+///     One FOCAS-backed OPC UA variable. <paramref name="Address"/> is the canonical FOCAS
+///     address string that parses via <see cref="FocasAddress.TryParse"/> —
+///     <c>X0.0</c> / <c>R100</c> / <c>PARAM:1815/0</c> / <c>MACRO:500</c>.
+/// </summary>
+public sealed record FocasTagDefinition(
+    string Name,
+    string DeviceHostAddress,
+    string Address,
+    FocasDataType DataType,
+    bool Writable = true,
+    bool WriteIdempotent = false);
+
+public sealed class FocasProbeOptions
+{
+    public bool Enabled { get; init; } = true;
+    public TimeSpan Interval { get; init; } = TimeSpan.FromSeconds(5);
+    public TimeSpan Timeout { get; init; } = TimeSpan.FromSeconds(2);
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasHostAddress.cs

@@ -0,0 +1,41 @@
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
+
+/// <summary>
+///     Parsed FOCAS target address — IP + TCP port. Canonical <c>focas://{ip}[:{port}]</c>.
+///     Default port 8193 (Fanuc-reserved FOCAS Ethernet port).
+/// </summary>
+public sealed record FocasHostAddress(string Host, int Port)
+{
+    /// <summary>Fanuc-reserved TCP port for FOCAS Ethernet.</summary>
+    public const int DefaultPort = 8193;
+
+    public override string ToString() => Port == DefaultPort
+        ? $"focas://{Host}"
+        : $"focas://{Host}:{Port}";
+
+    public static FocasHostAddress? TryParse(string? value)
+    {
+        if (string.IsNullOrWhiteSpace(value)) return null;
+        const string prefix = "focas://";
+        if (!value.StartsWith(prefix, StringComparison.OrdinalIgnoreCase)) return null;
+
+        var body = value[prefix.Length..];
+        if (string.IsNullOrEmpty(body)) return null;
+
+        var colonIdx = body.LastIndexOf(':');
+        string host;
+        var port = DefaultPort;
+        if (colonIdx >= 0)
+        {
+            host = body[..colonIdx];
+            if (!int.TryParse(body[(colonIdx + 1)..], out port) || port is <= 0 or > 65535)
+                return null;
+        }
+        else
+        {
+            host = body;
+        }
+        if (string.IsNullOrEmpty(host)) return null;
+        return new FocasHostAddress(host, port);
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasStatusMapper.cs

@@ -0,0 +1,48 @@
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
+
+/// <summary>
+///     Maps FOCAS / FWLIB return codes to OPC UA StatusCodes. The FWLIB C API uses an
+///     <c>EW_*</c> constant family per the Fanuc FOCAS/1 and FOCAS/2 documentation
+///     (<c>EW_OK = 0</c>, <c>EW_NUMBER</c>, <c>EW_SOCKET</c>, etc.). Mirrors the shape of the
+///     AbCip / TwinCAT mappers so Admin UI status displays stay uniform across drivers.
+/// </summary>
+public static class FocasStatusMapper
+{
+    public const uint Good = 0u;
+    public const uint BadInternalError = 0x80020000u;
+    public const uint BadNodeIdUnknown = 0x80340000u;
+    public const uint BadNotWritable = 0x803B0000u;
+    public const uint BadOutOfRange = 0x803C0000u;
+    public const uint BadNotSupported = 0x803D0000u;
+    public const uint BadDeviceFailure = 0x80550000u;
+    public const uint BadCommunicationError = 0x80050000u;
+    public const uint BadTimeout = 0x800A0000u;
+    public const uint BadTypeMismatch = 0x80730000u;
+
+    /// <summary>
+    ///     Map common FWLIB <c>EW_*</c> return codes. The values below match Fanuc's published
+    ///     numeric conventions (EW_OK=0, EW_FUNC=1, EW_NUMBER=3, EW_LENGTH=4, EW_ATTRIB=7,
+    ///     EW_DATA=8, EW_NOOPT=6, EW_PROT=5, EW_OVRFLOW=2, EW_PARITY=9, EW_PASSWD=11,
+    ///     EW_BUSY=-1, EW_HANDLE=-8, EW_VERSION=-9, EW_UNEXP=-10, EW_SOCKET=-16).
+    /// </summary>
+    public static uint MapFocasReturn(int ret) => ret switch
+    {
+        0 => Good,
+        1 => BadNotSupported,          // EW_FUNC — CNC does not support this function
+        2 => BadOutOfRange,            // EW_OVRFLOW
+        3 => BadOutOfRange,            // EW_NUMBER
+        4 => BadOutOfRange,            // EW_LENGTH
+        5 => BadNotWritable,           // EW_PROT
+        6 => BadNotSupported,          // EW_NOOPT — optional CNC feature missing
+        7 => BadTypeMismatch,          // EW_ATTRIB
+        8 => BadNodeIdUnknown,         // EW_DATA — invalid data address
+        9 => BadCommunicationError,    // EW_PARITY
+        11 => BadNotWritable,          // EW_PASSWD
+        -1 => BadDeviceFailure,        // EW_BUSY
+        -8 => BadInternalError,        // EW_HANDLE — CNC handle not available
+        -9 => BadNotSupported,         // EW_VERSION — FWLIB vs CNC version mismatch
+        -10 => BadCommunicationError,  // EW_UNEXP
+        -16 => BadCommunicationError,  // EW_SOCKET
+        _ => BadCommunicationError,
+    };
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FwlibFocasClient.cs

@@ -0,0 +1,269 @@
+using System.Buffers.Binary;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
+
+/// <summary>
+///     <see cref="IFocasClient"/> implementation backed by Fanuc's licensed
+///     <c>Fwlib32.dll</c> via <see cref="FwlibNative"/> P/Invoke. The DLL is NOT shipped with
+///     OtOpcUa; the deployment places it next to the server executable or on <c>PATH</c>
+///     (per Fanuc licensing — see <c>docs/v2/focas-deployment.md</c>).
+/// </summary>
+/// <remarks>
+///     <para>Construction is licence-safe — .NET P/Invoke is lazy, so instantiating this class
+///     does NOT load <c>Fwlib32.dll</c>. The DLL only loads on the first wire call (Connect /
+///     Read / Write / Probe). When missing, those calls throw <see cref="DllNotFoundException"/>
+///     which the driver surfaces as <c>BadCommunicationError</c> through the normal exception
+///     mapping.</para>
+///
+///     <para>Session-scoped handle — <c>cnc_allclibhndl3</c> opens one FWLIB handle per CNC;
+///     all PMC / parameter / macro reads on that device go through the same handle. Dispose
+///     calls <c>cnc_freelibhndl</c>.</para>
+/// </remarks>
+internal sealed class FwlibFocasClient : IFocasClient
+{
+    private ushort _handle;
+    private bool _connected;
+
+    public bool IsConnected => _connected;
+
+    public Task ConnectAsync(FocasHostAddress address, TimeSpan timeout, CancellationToken cancellationToken)
+    {
+        if (_connected) return Task.CompletedTask;
+
+        var timeoutMs = (int)Math.Max(1, timeout.TotalMilliseconds);
+        var ret = FwlibNative.AllcLibHndl3(address.Host, (ushort)address.Port, timeoutMs, out var handle);
+        if (ret != 0)
+            throw new InvalidOperationException(
+                $"FWLIB cnc_allclibhndl3 failed with EW_{ret} connecting to {address}.");
+        _handle = handle;
+        _connected = true;
+        return Task.CompletedTask;
+    }
+
+    public Task<(object? value, uint status)> ReadAsync(
+        FocasAddress address, FocasDataType type, CancellationToken cancellationToken)
+    {
+        if (!_connected) return Task.FromResult<(object?, uint)>((null, FocasStatusMapper.BadCommunicationError));
+        cancellationToken.ThrowIfCancellationRequested();
+
+        return address.Kind switch
+        {
+            FocasAreaKind.Pmc => Task.FromResult(ReadPmc(address, type)),
+            FocasAreaKind.Parameter => Task.FromResult(ReadParameter(address, type)),
+            FocasAreaKind.Macro => Task.FromResult(ReadMacro(address)),
+            _ => Task.FromResult<(object?, uint)>((null, FocasStatusMapper.BadNotSupported)),
+        };
+    }
+
+    public Task<uint> WriteAsync(
+        FocasAddress address, FocasDataType type, object? value, CancellationToken cancellationToken)
+    {
+        if (!_connected) return Task.FromResult(FocasStatusMapper.BadCommunicationError);
+        cancellationToken.ThrowIfCancellationRequested();
+
+        return address.Kind switch
+        {
+            FocasAreaKind.Pmc => Task.FromResult(WritePmc(address, type, value)),
+            FocasAreaKind.Parameter => Task.FromResult(WriteParameter(address, type, value)),
+            FocasAreaKind.Macro => Task.FromResult(WriteMacro(address, value)),
+            _ => Task.FromResult(FocasStatusMapper.BadNotSupported),
+        };
+    }
+
+    public Task<bool> ProbeAsync(CancellationToken cancellationToken)
+    {
+        if (!_connected) return Task.FromResult(false);
+        var buf = new FwlibNative.ODBST();
+        var ret = FwlibNative.StatInfo(_handle, ref buf);
+        return Task.FromResult(ret == 0);
+    }
+
+    // ---- PMC ----
+
+    private (object? value, uint status) ReadPmc(FocasAddress address, FocasDataType type)
+    {
+        var addrType = FocasPmcAddrType.FromLetter(address.PmcLetter ?? "")
+            ?? throw new InvalidOperationException($"Unknown PMC letter '{address.PmcLetter}'.");
+        var dataType = FocasPmcDataType.FromFocasDataType(type);
+        var length = PmcReadLength(type);
+
+        var buf = new FwlibNative.IODBPMC { Data = new byte[40] };
+        var ret = FwlibNative.PmcRdPmcRng(
+            _handle, addrType, dataType,
+            (ushort)address.Number, (ushort)address.Number, (ushort)length, ref buf);
+        if (ret != 0) return (null, FocasStatusMapper.MapFocasReturn(ret));
+
+        var value = type switch
+        {
+            FocasDataType.Bit => ExtractBit(buf.Data[0], address.BitIndex ?? 0),
+            FocasDataType.Byte => (object)(sbyte)buf.Data[0],
+            FocasDataType.Int16 => (object)BinaryPrimitives.ReadInt16LittleEndian(buf.Data),
+            FocasDataType.Int32 => (object)BinaryPrimitives.ReadInt32LittleEndian(buf.Data),
+            FocasDataType.Float32 => (object)BinaryPrimitives.ReadSingleLittleEndian(buf.Data),
+            FocasDataType.Float64 => (object)BinaryPrimitives.ReadDoubleLittleEndian(buf.Data),
+            _ => (object)buf.Data[0],
+        };
+        return (value, FocasStatusMapper.Good);
+    }
+
+    private uint WritePmc(FocasAddress address, FocasDataType type, object? value)
+    {
+        var addrType = FocasPmcAddrType.FromLetter(address.PmcLetter ?? "") ?? (short)0;
+        var dataType = FocasPmcDataType.FromFocasDataType(type);
+        var length = PmcWriteLength(type);
+
+        var buf = new FwlibNative.IODBPMC
+        {
+            TypeA = addrType,
+            TypeD = dataType,
+            DatanoS = (ushort)address.Number,
+            DatanoE = (ushort)address.Number,
+            Data = new byte[40],
+        };
+        EncodePmcValue(buf.Data, type, value, address.BitIndex);
+
+        var ret = FwlibNative.PmcWrPmcRng(_handle, (ushort)length, ref buf);
+        return ret == 0 ? FocasStatusMapper.Good : FocasStatusMapper.MapFocasReturn(ret);
+    }
+
+    private (object? value, uint status) ReadParameter(FocasAddress address, FocasDataType type)
+    {
+        var buf = new FwlibNative.IODBPSD { Data = new byte[32] };
+        var length = ParamReadLength(type);
+        var ret = FwlibNative.RdParam(_handle, (ushort)address.Number, axis: 0, (short)length, ref buf);
+        if (ret != 0) return (null, FocasStatusMapper.MapFocasReturn(ret));
+
+        var value = type switch
+        {
+            FocasDataType.Bit when address.BitIndex is int bit => ExtractBit(buf.Data[0], bit),
+            FocasDataType.Byte => (object)(sbyte)buf.Data[0],
+            FocasDataType.Int16 => (object)BinaryPrimitives.ReadInt16LittleEndian(buf.Data),
+            FocasDataType.Int32 => (object)BinaryPrimitives.ReadInt32LittleEndian(buf.Data),
+            _ => (object)BinaryPrimitives.ReadInt32LittleEndian(buf.Data),
+        };
+        return (value, FocasStatusMapper.Good);
+    }
+
+    private uint WriteParameter(FocasAddress address, FocasDataType type, object? value)
+    {
+        var buf = new FwlibNative.IODBPSD
+        {
+            Datano = (short)address.Number,
+            Type = 0,
+            Data = new byte[32],
+        };
+        var length = ParamReadLength(type);
+        EncodeParamValue(buf.Data, type, value);
+        var ret = FwlibNative.WrParam(_handle, (short)length, ref buf);
+        return ret == 0 ? FocasStatusMapper.Good : FocasStatusMapper.MapFocasReturn(ret);
+    }
+
+    private (object? value, uint status) ReadMacro(FocasAddress address)
+    {
+        var buf = new FwlibNative.ODBM();
+        var ret = FwlibNative.RdMacro(_handle, (short)address.Number, length: 8, ref buf);
+        if (ret != 0) return (null, FocasStatusMapper.MapFocasReturn(ret));
+
+        // Macro value = mcr_val / 10^dec_val. Convert to double so callers get the correct
+        // scaled value regardless of the decimal-point count the CNC reports.
+        var scaled = buf.McrVal / Math.Pow(10.0, buf.DecVal);
+        return (scaled, FocasStatusMapper.Good);
+    }
+
+    private uint WriteMacro(FocasAddress address, object? value)
+    {
+        // Write as integer + 0 decimal places — callers that need decimal precision can extend
+        // this via a future WriteMacroScaled overload. Consistent with what most HMIs do today.
+        var intValue = Convert.ToInt32(value);
+        var ret = FwlibNative.WrMacro(_handle, (short)address.Number, length: 8, intValue, decimalPointCount: 0);
+        return ret == 0 ? FocasStatusMapper.Good : FocasStatusMapper.MapFocasReturn(ret);
+    }
+
+    public void Dispose()
+    {
+        if (_connected)
+        {
+            try { FwlibNative.FreeLibHndl(_handle); } catch { }
+            _connected = false;
+        }
+    }
+
+    // ---- helpers ----
+
+    private static int PmcReadLength(FocasDataType type) => type switch
+    {
+        FocasDataType.Bit or FocasDataType.Byte => 8 + 1,    // 8-byte header + 1 byte payload
+        FocasDataType.Int16 => 8 + 2,
+        FocasDataType.Int32 => 8 + 4,
+        FocasDataType.Float32 => 8 + 4,
+        FocasDataType.Float64 => 8 + 8,
+        _ => 8 + 1,
+    };
+
+    private static int PmcWriteLength(FocasDataType type) => PmcReadLength(type);
+    private static int ParamReadLength(FocasDataType type) => type switch
+    {
+        FocasDataType.Bit or FocasDataType.Byte => 4 + 1,
+        FocasDataType.Int16 => 4 + 2,
+        FocasDataType.Int32 => 4 + 4,
+        _ => 4 + 4,
+    };
+
+    private static bool ExtractBit(byte word, int bit) => (word & (1 << bit)) != 0;
+
+    internal static void EncodePmcValue(byte[] data, FocasDataType type, object? value, int? bitIndex)
+    {
+        switch (type)
+        {
+            case FocasDataType.Bit:
+                // Bit-in-byte write is a read-modify-write at the PMC level — the underlying
+                // pmc_wrpmcrng takes a byte payload, so caller must set the bit on a byte they
+                // just read. This path is flagged for the follow-up RMW work in task #181.
+                throw new NotSupportedException(
+                    "FOCAS Bit writes require read-modify-write; tracked in task #181.");
+            case FocasDataType.Byte:
+                data[0] = (byte)(sbyte)Convert.ToSByte(value);
+                break;
+            case FocasDataType.Int16:
+                BinaryPrimitives.WriteInt16LittleEndian(data, Convert.ToInt16(value));
+                break;
+            case FocasDataType.Int32:
+                BinaryPrimitives.WriteInt32LittleEndian(data, Convert.ToInt32(value));
+                break;
+            case FocasDataType.Float32:
+                BinaryPrimitives.WriteSingleLittleEndian(data, Convert.ToSingle(value));
+                break;
+            case FocasDataType.Float64:
+                BinaryPrimitives.WriteDoubleLittleEndian(data, Convert.ToDouble(value));
+                break;
+            default:
+                throw new NotSupportedException($"FocasDataType {type} not writable via PMC.");
+        }
+        _ = bitIndex; // bit-in-byte handled above
+    }
+
+    internal static void EncodeParamValue(byte[] data, FocasDataType type, object? value)
+    {
+        switch (type)
+        {
+            case FocasDataType.Byte:
+                data[0] = (byte)(sbyte)Convert.ToSByte(value);
+                break;
+            case FocasDataType.Int16:
+                BinaryPrimitives.WriteInt16LittleEndian(data, Convert.ToInt16(value));
+                break;
+            case FocasDataType.Int32:
+                BinaryPrimitives.WriteInt32LittleEndian(data, Convert.ToInt32(value));
+                break;
+            default:
+                BinaryPrimitives.WriteInt32LittleEndian(data, Convert.ToInt32(value));
+                break;
+        }
+    }
+}
+
+/// <summary>Default <see cref="IFocasClientFactory"/> — produces a fresh <see cref="FwlibFocasClient"/> per device.</summary>
+public sealed class FwlibFocasClientFactory : IFocasClientFactory
+{
+    public IFocasClient Create() => new FwlibFocasClient();
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FwlibNative.cs

@@ -0,0 +1,190 @@
+using System.Runtime.InteropServices;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
+
+/// <summary>
+///     P/Invoke surface for Fanuc FWLIB (<c>Fwlib32.dll</c>). Declarations extracted from
+///     <c>fwlib32.h</c> in the strangesast/fwlib repo; the licensed DLL itself is NOT shipped
+///     with OtOpcUa — the deployment places <c>Fwlib32.dll</c> next to the server executable
+///     or on <c>PATH</c>.
+/// </summary>
+/// <remarks>
+///     Deliberately narrow — only the calls <see cref="FwlibFocasClient"/> actually makes.
+///     FOCAS has 800+ functions in <c>fwlib32.h</c>; pulling in every one would bloat the
+///     P/Invoke surface + signal more coverage than this driver provides. Expand as capabilities
+///     are added.
+/// </remarks>
+internal static class FwlibNative
+{
+    private const string Library = "Fwlib32.dll";
+
+    // ---- Handle lifetime ----
+
+    /// <summary>Open an Ethernet FWLIB handle. Returns EW_OK (0) on success; handle written out.</summary>
+    [DllImport(Library, EntryPoint = "cnc_allclibhndl3", CharSet = CharSet.Ansi, ExactSpelling = true)]
+    public static extern short AllcLibHndl3(
+        [MarshalAs(UnmanagedType.LPStr)] string ipaddr,
+        ushort port,
+        int timeout,
+        out ushort handle);
+
+    [DllImport(Library, EntryPoint = "cnc_freelibhndl", ExactSpelling = true)]
+    public static extern short FreeLibHndl(ushort handle);
+
+    // ---- PMC ----
+
+    /// <summary>PMC range read. <paramref name="addrType"/> is the ADR_* enum; <paramref name="dataType"/> is 0 byte / 1 word / 2 long.</summary>
+    [DllImport(Library, EntryPoint = "pmc_rdpmcrng", ExactSpelling = true)]
+    public static extern short PmcRdPmcRng(
+        ushort handle,
+        short addrType,
+        short dataType,
+        ushort startNumber,
+        ushort endNumber,
+        ushort length,
+        ref IODBPMC buffer);
+
+    [DllImport(Library, EntryPoint = "pmc_wrpmcrng", ExactSpelling = true)]
+    public static extern short PmcWrPmcRng(
+        ushort handle,
+        ushort length,
+        ref IODBPMC buffer);
+
+    // ---- Parameters ----
+
+    [DllImport(Library, EntryPoint = "cnc_rdparam", ExactSpelling = true)]
+    public static extern short RdParam(
+        ushort handle,
+        ushort number,
+        short axis,
+        short length,
+        ref IODBPSD buffer);
+
+    [DllImport(Library, EntryPoint = "cnc_wrparam", ExactSpelling = true)]
+    public static extern short WrParam(
+        ushort handle,
+        short length,
+        ref IODBPSD buffer);
+
+    // ---- Macro variables ----
+
+    [DllImport(Library, EntryPoint = "cnc_rdmacro", ExactSpelling = true)]
+    public static extern short RdMacro(
+        ushort handle,
+        short number,
+        short length,
+        ref ODBM buffer);
+
+    [DllImport(Library, EntryPoint = "cnc_wrmacro", ExactSpelling = true)]
+    public static extern short WrMacro(
+        ushort handle,
+        short number,
+        short length,
+        int macroValue,
+        short decimalPointCount);
+
+    // ---- Status ----
+
+    [DllImport(Library, EntryPoint = "cnc_statinfo", ExactSpelling = true)]
+    public static extern short StatInfo(ushort handle, ref ODBST buffer);
+
+    // ---- Structs ----
+
+    /// <summary>
+    ///     IODBPMC — PMC range I/O buffer. 8-byte header + 40-byte union. We marshal the union
+    ///     as a fixed byte buffer + interpret per <see cref="FocasDataType"/> on the managed side.
+    /// </summary>
+    [StructLayout(LayoutKind.Sequential, Pack = 1)]
+    public struct IODBPMC
+    {
+        public short TypeA;
+        public short TypeD;
+        public ushort DatanoS;
+        public ushort DatanoE;
+        // 40-byte union: cdata[5] / idata[5] / ldata[5] / fdata[5] / dbdata[5] — dbdata is the widest.
+        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 40)]
+        public byte[] Data;
+    }
+
+    /// <summary>
+    ///     IODBPSD — CNC parameter I/O buffer. Axis-aware; for non-axis parameters pass axis=0.
+    ///     Union payload is bytes / shorts / longs — we marshal 32 bytes as the widest slot.
+    /// </summary>
+    [StructLayout(LayoutKind.Sequential, Pack = 1)]
+    public struct IODBPSD
+    {
+        public short Datano;
+        public short Type; // axis index (0 for non-axis)
+        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 32)]
+        public byte[] Data;
+    }
+
+    /// <summary>ODBM — macro variable read buffer. Value = <c>McrVal / 10^DecVal</c>.</summary>
+    [StructLayout(LayoutKind.Sequential, Pack = 1)]
+    public struct ODBM
+    {
+        public short Datano;
+        public short Dummy;
+        public int McrVal;      // long in C; 32-bit signed
+        public short DecVal;    // decimal-point count
+    }
+
+    /// <summary>ODBST — CNC status info. Machine state, alarm flags, automatic / edit mode.</summary>
+    [StructLayout(LayoutKind.Sequential, Pack = 1)]
+    public struct ODBST
+    {
+        public short Dummy;
+        public short TmMode;
+        public short Aut;
+        public short Run;
+        public short Motion;
+        public short Mstb;
+        public short Emergency;
+        public short Alarm;
+        public short Edit;
+    }
+}
+
+/// <summary>
+///     PMC address-letter → FOCAS <c>ADR_*</c> numeric code. Per Fanuc FOCAS/2 spec the codes
+///     are: G=0, F=1, Y=2, X=3, A=4, R=5, T=6, K=7, C=8, D=9, E=10. Exposed internally +
+///     tested so the FwlibFocasClient translation is verifiable without the DLL loaded.
+/// </summary>
+internal static class FocasPmcAddrType
+{
+    public static short? FromLetter(string letter) => letter.ToUpperInvariant() switch
+    {
+        "G" => 0,
+        "F" => 1,
+        "Y" => 2,
+        "X" => 3,
+        "A" => 4,
+        "R" => 5,
+        "T" => 6,
+        "K" => 7,
+        "C" => 8,
+        "D" => 9,
+        "E" => 10,
+        _ => null,
+    };
+}
+
+/// <summary>PMC data-type numeric codes per FOCAS/2: 0 = byte, 1 = word, 2 = long, 4 = float, 5 = double.</summary>
+internal static class FocasPmcDataType
+{
+    public const short Byte = 0;
+    public const short Word = 1;
+    public const short Long = 2;
+    public const short Float = 4;
+    public const short Double = 5;
+
+    public static short FromFocasDataType(FocasDataType t) => t switch
+    {
+        FocasDataType.Bit or FocasDataType.Byte => Byte,
+        FocasDataType.Int16 => Word,
+        FocasDataType.Int32 => Long,
+        FocasDataType.Float32 => Float,
+        FocasDataType.Float64 => Double,
+        _ => Byte,
+    };
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/IFocasClient.cs

@@ -0,0 +1,70 @@
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
+
+/// <summary>
+///     Wire-layer abstraction over one FOCAS session to a CNC. The driver holds one per
+///     configured device; lifetime matches the device.
+/// </summary>
+/// <remarks>
+///     <para><b>No default wire implementation ships with this assembly.</b> FWLIB
+///     (<c>Fwlib32.dll</c>) is Fanuc-proprietary and requires a valid customer license — it
+///     cannot legally be redistributed. The deployment team supplies an
+///     <see cref="IFocasClientFactory"/> that wraps the licensed <c>Fwlib32.dll</c> via
+///     P/Invoke and registers it at server startup.</para>
+///
+///     <para>The default <see cref="UnimplementedFocasClientFactory"/> throws with a pointer at
+///     the deployment docs so misconfigured servers fail fast with a clear error rather than
+///     mysteriously hanging.</para>
+/// </remarks>
+public interface IFocasClient : IDisposable
+{
+    /// <summary>Open the FWLIB handle + TCP session. Idempotent.</summary>
+    Task ConnectAsync(FocasHostAddress address, TimeSpan timeout, CancellationToken cancellationToken);
+
+    /// <summary>True when the FWLIB handle is valid + the socket is up.</summary>
+    bool IsConnected { get; }
+
+    /// <summary>
+    ///     Read the value at <paramref name="address"/> in the requested
+    ///     <paramref name="type"/>. Returns a boxed .NET value + the OPC UA status mapped
+    ///     through <see cref="FocasStatusMapper"/>.
+    /// </summary>
+    Task<(object? value, uint status)> ReadAsync(
+        FocasAddress address,
+        FocasDataType type,
+        CancellationToken cancellationToken);
+
+    /// <summary>
+    ///     Write <paramref name="value"/> to <paramref name="address"/>. Returns the mapped
+    ///     OPC UA status (0 = Good).
+    /// </summary>
+    Task<uint> WriteAsync(
+        FocasAddress address,
+        FocasDataType type,
+        object? value,
+        CancellationToken cancellationToken);
+
+    /// <summary>
+    ///     Cheap health probe — e.g. <c>cnc_rdcncstat</c>. Returns <c>true</c> when the CNC
+    ///     responds with any valid status.
+    /// </summary>
+    Task<bool> ProbeAsync(CancellationToken cancellationToken);
+}
+
+/// <summary>Factory for <see cref="IFocasClient"/>s. One client per configured device.</summary>
+public interface IFocasClientFactory
+{
+    IFocasClient Create();
+}
+
+/// <summary>
+///     Default factory that throws at construction time — the deployment must register a real
+///     factory. Keeps the driver assembly licence-clean while still allowing the skeleton to
+///     compile + the abstraction tests to run.
+/// </summary>
+public sealed class UnimplementedFocasClientFactory : IFocasClientFactory
+{
+    public IFocasClient Create() => throw new NotSupportedException(
+        "FOCAS driver has no wire client configured. Register a real IFocasClientFactory at " +
+        "server startup wrapping the licensed Fwlib32.dll — see docs/v2/focas-deployment.md. " +
+        "Fanuc licensing forbids shipping Fwlib32.dll in the OtOpcUa package.");
+}

src/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.csproj

@@ -0,0 +1,32 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <TargetFramework>net10.0</TargetFramework>
+        <Nullable>enable</Nullable>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <LangVersion>latest</LangVersion>
+        <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+        <GenerateDocumentationFile>true</GenerateDocumentationFile>
+        <NoWarn>$(NoWarn);CS1591</NoWarn>
+        <RootNamespace>ZB.MOM.WW.OtOpcUa.Driver.FOCAS</RootNamespace>
+        <AssemblyName>ZB.MOM.WW.OtOpcUa.Driver.FOCAS</AssemblyName>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <ProjectReference Include="..\ZB.MOM.WW.OtOpcUa.Core.Abstractions\ZB.MOM.WW.OtOpcUa.Core.Abstractions.csproj"/>
+    </ItemGroup>
+
+    <!--
+        No NuGet reference to a FOCAS library — FWLIB is Fanuc-proprietary and the licensed
+        Fwlib32.dll cannot be redistributed. The deployment side supplies an IFocasClient
+        implementation that P/Invokes against whatever Fwlib32.dll the customer has licensed.
+        Driver.FOCAS.IntegrationTests in a separate repo can wire in the real binary.
+        Follow-up task #193 tracks the real-client reference implementation that customers may
+        drop in privately.
+    -->
+
+    <ItemGroup>
+        <InternalsVisibleTo Include="ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests"/>
+    </ItemGroup>
+
+</Project>

src/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT/AdsTwinCATClient.cs

@@ -0,0 +1,233 @@
+using System.Collections.Concurrent;
+using TwinCAT.Ads;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.TwinCAT;
+
+/// <summary>
+///     Default <see cref="ITwinCATClient"/> backed by Beckhoff's <see cref="AdsClient"/>.
+///     One instance per AMS target; reused across reads / writes / probes.
+/// </summary>
+/// <remarks>
+///     <para>Wire behavior depends on a reachable AMS router — on Windows the router comes
+///     from TwinCAT XAR; elsewhere from the <c>Beckhoff.TwinCAT.Ads.TcpRouter</c> package
+///     hosted by the server process. Neither is built-in here; deployment wires one in.</para>
+///
+///     <para>Error mapping — ADS error codes surface through <see cref="AdsErrorException"/>
+///     and get translated to OPC UA status codes via <see cref="TwinCATStatusMapper.MapAdsError"/>.</para>
+/// </remarks>
+internal sealed class AdsTwinCATClient : ITwinCATClient
+{
+    private readonly AdsClient _client = new();
+    private readonly ConcurrentDictionary<uint, NotificationRegistration> _notifications = new();
+
+    public AdsTwinCATClient()
+    {
+        _client.AdsNotificationEx += OnAdsNotificationEx;
+    }
+
+    public bool IsConnected => _client.IsConnected;
+
+    public Task ConnectAsync(TwinCATAmsAddress address, TimeSpan timeout, CancellationToken cancellationToken)
+    {
+        if (_client.IsConnected) return Task.CompletedTask;
+        _client.Timeout = (int)Math.Max(1_000, timeout.TotalMilliseconds);
+        var netId = AmsNetId.Parse(address.NetId);
+        _client.Connect(netId, address.Port);
+        return Task.CompletedTask;
+    }
+
+    public async Task<(object? value, uint status)> ReadValueAsync(
+        string symbolPath,
+        TwinCATDataType type,
+        int? bitIndex,
+        CancellationToken cancellationToken)
+    {
+        try
+        {
+            var clrType = MapToClrType(type);
+            var result = await _client.ReadValueAsync(symbolPath, clrType, cancellationToken)
+                .ConfigureAwait(false);
+
+            if (result.ErrorCode != AdsErrorCode.NoError)
+                return (null, TwinCATStatusMapper.MapAdsError((uint)result.ErrorCode));
+
+            var value = result.Value;
+            if (bitIndex is int bit && type == TwinCATDataType.Bool && value is not bool)
+                value = ExtractBit(value, bit);
+
+            return (value, TwinCATStatusMapper.Good);
+        }
+        catch (AdsErrorException ex)
+        {
+            return (null, TwinCATStatusMapper.MapAdsError((uint)ex.ErrorCode));
+        }
+    }
+
+    public async Task<uint> WriteValueAsync(
+        string symbolPath,
+        TwinCATDataType type,
+        int? bitIndex,
+        object? value,
+        CancellationToken cancellationToken)
+    {
+        if (bitIndex is int && type == TwinCATDataType.Bool)
+            throw new NotSupportedException(
+                "BOOL-within-word writes require read-modify-write; tracked in task #181.");
+
+        try
+        {
+            var converted = ConvertForWrite(type, value);
+            var result = await _client.WriteValueAsync(symbolPath, converted, cancellationToken)
+                .ConfigureAwait(false);
+            return result.ErrorCode == AdsErrorCode.NoError
+                ? TwinCATStatusMapper.Good
+                : TwinCATStatusMapper.MapAdsError((uint)result.ErrorCode);
+        }
+        catch (AdsErrorException ex)
+        {
+            return TwinCATStatusMapper.MapAdsError((uint)ex.ErrorCode);
+        }
+    }
+
+    public async Task<bool> ProbeAsync(CancellationToken cancellationToken)
+    {
+        try
+        {
+            var state = await _client.ReadStateAsync(cancellationToken).ConfigureAwait(false);
+            return state.ErrorCode == AdsErrorCode.NoError;
+        }
+        catch
+        {
+            return false;
+        }
+    }
+
+    public async Task<ITwinCATNotificationHandle> AddNotificationAsync(
+        string symbolPath,
+        TwinCATDataType type,
+        int? bitIndex,
+        TimeSpan cycleTime,
+        Action<string, object?> onChange,
+        CancellationToken cancellationToken)
+    {
+        var clrType = MapToClrType(type);
+        // NotificationSettings takes cycle + max-delay in 100ns units. AdsTransMode.OnChange
+        // fires when the value differs; OnCycle fires every cycle. OnChange is the right default
+        // for OPC UA data-change semantics — the PLC already has the best view of "has this
+        // changed" so we let it decide.
+        var cycleTicks = (uint)Math.Max(1, cycleTime.Ticks / TimeSpan.TicksPerMillisecond * 10_000);
+        var settings = new NotificationSettings(AdsTransMode.OnChange, (int)cycleTicks, 0);
+
+        // AddDeviceNotificationExAsync returns Task<ResultHandle>; AdsNotificationEx fires
+        // with the handle as part of the event args so we use the handle as the correlation
+        // key into _notifications.
+        var result = await _client.AddDeviceNotificationExAsync(
+            symbolPath, settings, userData: null, clrType, args: null, cancellationToken)
+            .ConfigureAwait(false);
+        if (result.ErrorCode != AdsErrorCode.NoError)
+            throw new InvalidOperationException(
+                $"AddDeviceNotificationExAsync failed with ADS error {result.ErrorCode} for {symbolPath}");
+
+        var reg = new NotificationRegistration(symbolPath, type, bitIndex, onChange, this, result.Handle);
+        _notifications[result.Handle] = reg;
+        return reg;
+    }
+
+    private void OnAdsNotificationEx(object? sender, AdsNotificationExEventArgs args)
+    {
+        if (!_notifications.TryGetValue(args.Handle, out var reg)) return;
+        var value = args.Value;
+        if (reg.BitIndex is int bit && reg.Type == TwinCATDataType.Bool && value is not bool)
+            value = ExtractBit(value, bit);
+        try { reg.OnChange(reg.SymbolPath, value); } catch { /* consumer-side errors don't crash the ADS thread */ }
+    }
+
+    internal async Task DeleteNotificationAsync(uint handle, CancellationToken cancellationToken)
+    {
+        _notifications.TryRemove(handle, out _);
+        try { await _client.DeleteDeviceNotificationAsync(handle, cancellationToken).ConfigureAwait(false); }
+        catch { /* best-effort tear-down; target may already be gone */ }
+    }
+
+    public void Dispose()
+    {
+        _client.AdsNotificationEx -= OnAdsNotificationEx;
+        _notifications.Clear();
+        _client.Dispose();
+    }
+
+    private sealed class NotificationRegistration(
+        string symbolPath,
+        TwinCATDataType type,
+        int? bitIndex,
+        Action<string, object?> onChange,
+        AdsTwinCATClient owner,
+        uint handle) : ITwinCATNotificationHandle
+    {
+        public string SymbolPath { get; } = symbolPath;
+        public TwinCATDataType Type { get; } = type;
+        public int? BitIndex { get; } = bitIndex;
+        public Action<string, object?> OnChange { get; } = onChange;
+
+        public void Dispose()
+        {
+            // Fire-and-forget AMS call — caller has already committed to the tear-down.
+            _ = owner.DeleteNotificationAsync(handle, CancellationToken.None);
+        }
+    }
+
+    private static Type MapToClrType(TwinCATDataType type) => type switch
+    {
+        TwinCATDataType.Bool => typeof(bool),
+        TwinCATDataType.SInt => typeof(sbyte),
+        TwinCATDataType.USInt => typeof(byte),
+        TwinCATDataType.Int => typeof(short),
+        TwinCATDataType.UInt => typeof(ushort),
+        TwinCATDataType.DInt => typeof(int),
+        TwinCATDataType.UDInt => typeof(uint),
+        TwinCATDataType.LInt => typeof(long),
+        TwinCATDataType.ULInt => typeof(ulong),
+        TwinCATDataType.Real => typeof(float),
+        TwinCATDataType.LReal => typeof(double),
+        TwinCATDataType.String or TwinCATDataType.WString => typeof(string),
+        TwinCATDataType.Time or TwinCATDataType.Date
+            or TwinCATDataType.DateTime or TwinCATDataType.TimeOfDay => typeof(uint),
+        _ => typeof(int),
+    };
+
+    private static object ConvertForWrite(TwinCATDataType type, object? value) => type switch
+    {
+        TwinCATDataType.Bool => Convert.ToBoolean(value),
+        TwinCATDataType.SInt => Convert.ToSByte(value),
+        TwinCATDataType.USInt => Convert.ToByte(value),
+        TwinCATDataType.Int => Convert.ToInt16(value),
+        TwinCATDataType.UInt => Convert.ToUInt16(value),
+        TwinCATDataType.DInt => Convert.ToInt32(value),
+        TwinCATDataType.UDInt => Convert.ToUInt32(value),
+        TwinCATDataType.LInt => Convert.ToInt64(value),
+        TwinCATDataType.ULInt => Convert.ToUInt64(value),
+        TwinCATDataType.Real => Convert.ToSingle(value),
+        TwinCATDataType.LReal => Convert.ToDouble(value),
+        TwinCATDataType.String or TwinCATDataType.WString => Convert.ToString(value) ?? string.Empty,
+        TwinCATDataType.Time or TwinCATDataType.Date
+            or TwinCATDataType.DateTime or TwinCATDataType.TimeOfDay => Convert.ToUInt32(value),
+        _ => throw new NotSupportedException($"TwinCATDataType {type} not writable."),
+    };
+
+    private static bool ExtractBit(object? rawWord, int bit) => rawWord switch
+    {
+        short s => (s & (1 << bit)) != 0,
+        ushort us => (us & (1 << bit)) != 0,
+        int i => (i & (1 << bit)) != 0,
+        uint ui => (ui & (1u << bit)) != 0,
+        long l => (l & (1L << bit)) != 0,
+        ulong ul => (ul & (1UL << bit)) != 0,
+        _ => false,
+    };
+}
+
+/// <summary>Default <see cref="ITwinCATClientFactory"/> — one <see cref="AdsTwinCATClient"/> per call.</summary>
+internal sealed class AdsTwinCATClientFactory : ITwinCATClientFactory
+{
+    public ITwinCATClient Create() => new AdsTwinCATClient();
+}

src/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT/ITwinCATClient.cs

@@ -0,0 +1,78 @@
+namespace ZB.MOM.WW.OtOpcUa.Driver.TwinCAT;
+
+/// <summary>
+///     Wire-layer abstraction over one connection to a TwinCAT AMS target. One instance per
+///     <see cref="TwinCATAmsAddress"/>; reused across reads / writes / probes for the device.
+///     Tests swap in a fake via <see cref="ITwinCATClientFactory"/>.
+/// </summary>
+/// <remarks>
+///     Unlike libplctag-backed drivers where one native handle exists per tag, TwinCAT's
+///     AdsClient is one connection per target with symbolic reads / writes issued against it.
+///     The abstraction reflects that — single <see cref="ConnectAsync"/>, many
+///     <see cref="ReadValueAsync"/> / <see cref="WriteValueAsync"/> calls.
+/// </remarks>
+public interface ITwinCATClient : IDisposable
+{
+    /// <summary>Establish the AMS connection. Idempotent — subsequent calls are no-ops when already connected.</summary>
+    Task ConnectAsync(TwinCATAmsAddress address, TimeSpan timeout, CancellationToken cancellationToken);
+
+    /// <summary>True when the AMS router + target both accept commands.</summary>
+    bool IsConnected { get; }
+
+    /// <summary>
+    ///     Read a symbolic value. Returns a boxed .NET value matching the requested
+    ///     <paramref name="type"/>, or <c>null</c> when the read produced no data; the
+    ///     <c>status</c> tuple member carries the mapped OPC UA status (0 = Good).
+    /// </summary>
+    Task<(object? value, uint status)> ReadValueAsync(
+        string symbolPath,
+        TwinCATDataType type,
+        int? bitIndex,
+        CancellationToken cancellationToken);
+
+    /// <summary>
+    ///     Write a symbolic value. Returns the mapped OPC UA status for the operation
+    ///     (0 = Good, non-zero = error mapped via <see cref="TwinCATStatusMapper"/>).
+    /// </summary>
+    Task<uint> WriteValueAsync(
+        string symbolPath,
+        TwinCATDataType type,
+        int? bitIndex,
+        object? value,
+        CancellationToken cancellationToken);
+
+    /// <summary>
+    ///     Cheap health probe — returns <c>true</c> when the target's AMS state is reachable.
+    ///     Used by <see cref="Core.Abstractions.IHostConnectivityProbe"/>'s probe loop.
+    /// </summary>
+    Task<bool> ProbeAsync(CancellationToken cancellationToken);
+
+    /// <summary>
+    ///     Register a cyclic / on-change ADS notification for a symbol. Returns a handle whose
+    ///     <see cref="IDisposable.Dispose"/> tears the notification down. Callback fires on the
+    ///     thread libplctag / AdsClient uses for notifications — consumers should marshal to
+    ///     their own scheduler before doing work of any size.
+    /// </summary>
+    /// <param name="symbolPath">ADS symbol path (e.g. <c>MAIN.bStart</c>).</param>
+    /// <param name="type">Declared type; drives the native layout + callback value boxing.</param>
+    /// <param name="bitIndex">For BOOL-within-word tags — the bit to extract from the parent word.</param>
+    /// <param name="cycleTime">Minimum interval between change notifications (native-floor depends on target).</param>
+    /// <param name="onChange">Invoked with <c>(symbolPath, boxedValue)</c> per notification.</param>
+    /// <param name="cancellationToken">Cancels the initial registration; does not tear down an established notification.</param>
+    Task<ITwinCATNotificationHandle> AddNotificationAsync(
+        string symbolPath,
+        TwinCATDataType type,
+        int? bitIndex,
+        TimeSpan cycleTime,
+        Action<string, object?> onChange,
+        CancellationToken cancellationToken);
+}
+
+/// <summary>Opaque handle for a registered ADS notification. <see cref="IDisposable.Dispose"/> tears it down.</summary>
+public interface ITwinCATNotificationHandle : IDisposable { }
+
+/// <summary>Factory for <see cref="ITwinCATClient"/>s. One client per device.</summary>
+public interface ITwinCATClientFactory
+{
+    ITwinCATClient Create();
+}

src/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT/TwinCATAmsAddress.cs

@@ -0,0 +1,64 @@
+namespace ZB.MOM.WW.OtOpcUa.Driver.TwinCAT;
+
+/// <summary>
+///     Parsed TwinCAT AMS address — six-octet AMS Net ID + port. Canonical form
+///     <c>ads://{netId}:{port}</c> where <c>netId</c> is five-dot-separated octets (six of them)
+///     and <c>port</c> is the AMS service port (851 = TC3 PLC runtime 1, 852 = runtime 2, 801 /
+///     811 / 821 = TC2 PLC runtimes, 10000 = system service, etc.).
+/// </summary>
+/// <remarks>
+///     Format examples:
+///     <list type="bullet">
+///         <item><c>ads://5.23.91.23.1.1:851</c> — remote TC3 runtime</item>
+///         <item><c>ads://5.23.91.23.1.1</c> — defaults to port 851 (TC3 PLC runtime 1)</item>
+///         <item><c>ads://127.0.0.1.1.1:851</c> — local loopback (when the router is local)</item>
+///     </list>
+///     <para>AMS Net ID is NOT an IP — it's a Beckhoff-specific identifier that the router
+///     translates to an IP route. Typically the first four octets match the host's IPv4 and
+///     the last two are <c>.1.1</c>, but the router can be configured otherwise.</para>
+/// </remarks>
+public sealed record TwinCATAmsAddress(string NetId, int Port)
+{
+    /// <summary>Default AMS port — TC3 PLC runtime 1.</summary>
+    public const int DefaultPlcPort = 851;
+
+    public override string ToString() => Port == DefaultPlcPort
+        ? $"ads://{NetId}"
+        : $"ads://{NetId}:{Port}";
+
+    public static TwinCATAmsAddress? TryParse(string? value)
+    {
+        if (string.IsNullOrWhiteSpace(value)) return null;
+        const string prefix = "ads://";
+        if (!value.StartsWith(prefix, StringComparison.OrdinalIgnoreCase)) return null;
+
+        var body = value[prefix.Length..];
+        if (string.IsNullOrEmpty(body)) return null;
+
+        var colonIdx = body.LastIndexOf(':');
+        string netId;
+        var port = DefaultPlcPort;
+        if (colonIdx >= 0)
+        {
+            netId = body[..colonIdx];
+            if (!int.TryParse(body[(colonIdx + 1)..], out port) || port is <= 0 or > 65535)
+                return null;
+        }
+        else
+        {
+            netId = body;
+        }
+
+        if (!IsValidNetId(netId)) return null;
+        return new TwinCATAmsAddress(netId, port);
+    }
+
+    private static bool IsValidNetId(string netId)
+    {
+        var parts = netId.Split('.');
+        if (parts.Length != 6) return false;
+        foreach (var p in parts)
+            if (!byte.TryParse(p, out _)) return false;
+        return true;
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT/TwinCATDataType.cs

@@ -0,0 +1,49 @@
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.TwinCAT;
+
+/// <summary>
+///     TwinCAT / IEC 61131-3 atomic data types. Wider type surface than Logix because IEC adds
+///     <c>WSTRING</c> (UTF-16) and <c>TIME</c>/<c>DATE</c>/<c>DT</c>/<c>TOD</c> variants.
+/// </summary>
+public enum TwinCATDataType
+{
+    Bool,
+    SInt,   // signed 8-bit
+    USInt,  // unsigned 8-bit
+    Int,    // signed 16-bit
+    UInt,   // unsigned 16-bit
+    DInt,   // signed 32-bit
+    UDInt,  // unsigned 32-bit
+    LInt,   // signed 64-bit
+    ULInt,  // unsigned 64-bit
+    Real,   // 32-bit IEEE-754
+    LReal,  // 64-bit IEEE-754
+    String, // ASCII string
+    WString,// UTF-16 string
+    Time,   // TIME — ms since epoch of day, stored as UDINT
+    Date,   // DATE — days since 1970-01-01, stored as UDINT
+    DateTime, // DT — seconds since 1970-01-01, stored as UDINT
+    TimeOfDay,// TOD — ms since midnight, stored as UDINT
+    /// <summary>UDT / FB instance. Resolved per member at discovery time.</summary>
+    Structure,
+}
+
+public static class TwinCATDataTypeExtensions
+{
+    public static DriverDataType ToDriverDataType(this TwinCATDataType t) => t switch
+    {
+        TwinCATDataType.Bool => DriverDataType.Boolean,
+        TwinCATDataType.SInt or TwinCATDataType.USInt
+            or TwinCATDataType.Int or TwinCATDataType.UInt
+            or TwinCATDataType.DInt or TwinCATDataType.UDInt => DriverDataType.Int32,
+        TwinCATDataType.LInt or TwinCATDataType.ULInt => DriverDataType.Int32, // matches Int64 gap
+        TwinCATDataType.Real => DriverDataType.Float32,
+        TwinCATDataType.LReal => DriverDataType.Float64,
+        TwinCATDataType.String or TwinCATDataType.WString => DriverDataType.String,
+        TwinCATDataType.Time or TwinCATDataType.Date
+            or TwinCATDataType.DateTime or TwinCATDataType.TimeOfDay => DriverDataType.Int32,
+        TwinCATDataType.Structure => DriverDataType.String,
+        _ => DriverDataType.Int32,
+    };
+}

src/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT/TwinCATDriver.cs

@@ -0,0 +1,415 @@
+using System.Collections.Concurrent;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.TwinCAT;
+
+/// <summary>
+///     TwinCAT ADS driver — talks to Beckhoff PLC runtimes (TC2 + TC3) via AMS / ADS. PR 1 ships
+///     the <see cref="IDriver"/> skeleton; read / write / discover / subscribe / probe / host-
+///     resolver land in PRs 2 and 3.
+/// </summary>
+public sealed class TwinCATDriver : IDriver, IReadable, IWritable, ITagDiscovery, ISubscribable,
+    IHostConnectivityProbe, IPerCallHostResolver, IDisposable, IAsyncDisposable
+{
+    private readonly TwinCATDriverOptions _options;
+    private readonly string _driverInstanceId;
+    private readonly ITwinCATClientFactory _clientFactory;
+    private readonly PollGroupEngine _poll;
+    private readonly Dictionary<string, DeviceState> _devices = new(StringComparer.OrdinalIgnoreCase);
+    private readonly Dictionary<string, TwinCATTagDefinition> _tagsByName = new(StringComparer.OrdinalIgnoreCase);
+    private DriverHealth _health = new(DriverState.Unknown, null, null);
+
+    public event EventHandler<DataChangeEventArgs>? OnDataChange;
+    public event EventHandler<HostStatusChangedEventArgs>? OnHostStatusChanged;
+
+    public TwinCATDriver(TwinCATDriverOptions options, string driverInstanceId,
+        ITwinCATClientFactory? clientFactory = null)
+    {
+        ArgumentNullException.ThrowIfNull(options);
+        _options = options;
+        _driverInstanceId = driverInstanceId;
+        _clientFactory = clientFactory ?? new AdsTwinCATClientFactory();
+        _poll = new PollGroupEngine(
+            reader: ReadAsync,
+            onChange: (handle, tagRef, snapshot) =>
+                OnDataChange?.Invoke(this, new DataChangeEventArgs(handle, tagRef, snapshot)));
+    }
+
+    public string DriverInstanceId => _driverInstanceId;
+    public string DriverType => "TwinCAT";
+
+    public Task InitializeAsync(string driverConfigJson, CancellationToken cancellationToken)
+    {
+        _health = new DriverHealth(DriverState.Initializing, null, null);
+        try
+        {
+            foreach (var device in _options.Devices)
+            {
+                var addr = TwinCATAmsAddress.TryParse(device.HostAddress)
+                    ?? throw new InvalidOperationException(
+                        $"TwinCAT device has invalid HostAddress '{device.HostAddress}' — expected 'ads://{{netId}}:{{port}}'.");
+                _devices[device.HostAddress] = new DeviceState(addr, device);
+            }
+            foreach (var tag in _options.Tags) _tagsByName[tag.Name] = tag;
+
+            if (_options.Probe.Enabled)
+            {
+                foreach (var state in _devices.Values)
+                {
+                    state.ProbeCts = new CancellationTokenSource();
+                    var ct = state.ProbeCts.Token;
+                    _ = Task.Run(() => ProbeLoopAsync(state, ct), ct);
+                }
+            }
+            _health = new DriverHealth(DriverState.Healthy, DateTime.UtcNow, null);
+        }
+        catch (Exception ex)
+        {
+            _health = new DriverHealth(DriverState.Faulted, null, ex.Message);
+            throw;
+        }
+        return Task.CompletedTask;
+    }
+
+    public async Task ReinitializeAsync(string driverConfigJson, CancellationToken cancellationToken)
+    {
+        await ShutdownAsync(cancellationToken).ConfigureAwait(false);
+        await InitializeAsync(driverConfigJson, cancellationToken).ConfigureAwait(false);
+    }
+
+    public async Task ShutdownAsync(CancellationToken cancellationToken)
+    {
+        // Native subs first — disposing the handles is cheap + lets the client close its
+        // notifications before the AdsClient itself goes away.
+        foreach (var sub in _nativeSubs.Values)
+            foreach (var r in sub.Registrations) { try { r.Dispose(); } catch { } }
+        _nativeSubs.Clear();
+
+        await _poll.DisposeAsync().ConfigureAwait(false);
+        foreach (var state in _devices.Values)
+        {
+            try { state.ProbeCts?.Cancel(); } catch { }
+            state.ProbeCts?.Dispose();
+            state.ProbeCts = null;
+            state.DisposeClient();
+        }
+        _devices.Clear();
+        _tagsByName.Clear();
+        _health = new DriverHealth(DriverState.Unknown, _health.LastSuccessfulRead, null);
+    }
+
+    public DriverHealth GetHealth() => _health;
+    public long GetMemoryFootprint() => 0;
+    public Task FlushOptionalCachesAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+
+    internal int DeviceCount => _devices.Count;
+    internal DeviceState? GetDeviceState(string hostAddress) =>
+        _devices.TryGetValue(hostAddress, out var s) ? s : null;
+
+    // ---- IReadable ----
+
+    public async Task<IReadOnlyList<DataValueSnapshot>> ReadAsync(
+        IReadOnlyList<string> fullReferences, CancellationToken cancellationToken)
+    {
+        ArgumentNullException.ThrowIfNull(fullReferences);
+        var now = DateTime.UtcNow;
+        var results = new DataValueSnapshot[fullReferences.Count];
+
+        for (var i = 0; i < fullReferences.Count; i++)
+        {
+            var reference = fullReferences[i];
+            if (!_tagsByName.TryGetValue(reference, out var def))
+            {
+                results[i] = new DataValueSnapshot(null, TwinCATStatusMapper.BadNodeIdUnknown, null, now);
+                continue;
+            }
+            if (!_devices.TryGetValue(def.DeviceHostAddress, out var device))
+            {
+                results[i] = new DataValueSnapshot(null, TwinCATStatusMapper.BadNodeIdUnknown, null, now);
+                continue;
+            }
+
+            try
+            {
+                var client = await EnsureConnectedAsync(device, cancellationToken).ConfigureAwait(false);
+                var parsed = TwinCATSymbolPath.TryParse(def.SymbolPath);
+                var symbolName = parsed?.ToAdsSymbolName() ?? def.SymbolPath;
+                var (value, status) = await client.ReadValueAsync(
+                    symbolName, def.DataType, parsed?.BitIndex, cancellationToken).ConfigureAwait(false);
+
+                results[i] = new DataValueSnapshot(value, status, now, now);
+                if (status == TwinCATStatusMapper.Good)
+                    _health = new DriverHealth(DriverState.Healthy, now, null);
+                else
+                    _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead,
+                        $"ADS status {status:X8} reading {reference}");
+            }
+            catch (OperationCanceledException) { throw; }
+            catch (Exception ex)
+            {
+                results[i] = new DataValueSnapshot(null, TwinCATStatusMapper.BadCommunicationError, null, now);
+                _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead, ex.Message);
+            }
+        }
+
+        return results;
+    }
+
+    // ---- IWritable ----
+
+    public async Task<IReadOnlyList<WriteResult>> WriteAsync(
+        IReadOnlyList<WriteRequest> writes, CancellationToken cancellationToken)
+    {
+        ArgumentNullException.ThrowIfNull(writes);
+        var results = new WriteResult[writes.Count];
+
+        for (var i = 0; i < writes.Count; i++)
+        {
+            var w = writes[i];
+            if (!_tagsByName.TryGetValue(w.FullReference, out var def))
+            {
+                results[i] = new WriteResult(TwinCATStatusMapper.BadNodeIdUnknown);
+                continue;
+            }
+            if (!def.Writable)
+            {
+                results[i] = new WriteResult(TwinCATStatusMapper.BadNotWritable);
+                continue;
+            }
+            if (!_devices.TryGetValue(def.DeviceHostAddress, out var device))
+            {
+                results[i] = new WriteResult(TwinCATStatusMapper.BadNodeIdUnknown);
+                continue;
+            }
+
+            try
+            {
+                var client = await EnsureConnectedAsync(device, cancellationToken).ConfigureAwait(false);
+                var parsed = TwinCATSymbolPath.TryParse(def.SymbolPath);
+                var symbolName = parsed?.ToAdsSymbolName() ?? def.SymbolPath;
+                var status = await client.WriteValueAsync(
+                    symbolName, def.DataType, parsed?.BitIndex, w.Value, cancellationToken).ConfigureAwait(false);
+                results[i] = new WriteResult(status);
+            }
+            catch (OperationCanceledException) { throw; }
+            catch (NotSupportedException nse)
+            {
+                results[i] = new WriteResult(TwinCATStatusMapper.BadNotSupported);
+                _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead, nse.Message);
+            }
+            catch (Exception ex) when (ex is FormatException or InvalidCastException)
+            {
+                results[i] = new WriteResult(TwinCATStatusMapper.BadTypeMismatch);
+            }
+            catch (OverflowException)
+            {
+                results[i] = new WriteResult(TwinCATStatusMapper.BadOutOfRange);
+            }
+            catch (Exception ex)
+            {
+                results[i] = new WriteResult(TwinCATStatusMapper.BadCommunicationError);
+                _health = new DriverHealth(DriverState.Degraded, _health.LastSuccessfulRead, ex.Message);
+            }
+        }
+
+        return results;
+    }
+
+    // ---- ITagDiscovery ----
+
+    public Task DiscoverAsync(IAddressSpaceBuilder builder, CancellationToken cancellationToken)
+    {
+        ArgumentNullException.ThrowIfNull(builder);
+        var root = builder.Folder("TwinCAT", "TwinCAT");
+        foreach (var device in _options.Devices)
+        {
+            var label = device.DeviceName ?? device.HostAddress;
+            var deviceFolder = root.Folder(device.HostAddress, label);
+            var tagsForDevice = _options.Tags.Where(t =>
+                string.Equals(t.DeviceHostAddress, device.HostAddress, StringComparison.OrdinalIgnoreCase));
+            foreach (var tag in tagsForDevice)
+            {
+                deviceFolder.Variable(tag.Name, tag.Name, new DriverAttributeInfo(
+                    FullName: tag.Name,
+                    DriverDataType: tag.DataType.ToDriverDataType(),
+                    IsArray: false,
+                    ArrayDim: null,
+                    SecurityClass: tag.Writable
+                        ? SecurityClassification.Operate
+                        : SecurityClassification.ViewOnly,
+                    IsHistorized: false,
+                    IsAlarm: false,
+                    WriteIdempotent: tag.WriteIdempotent));
+            }
+        }
+        return Task.CompletedTask;
+    }
+
+    // ---- ISubscribable (native ADS notifications with poll fallback) ----
+
+    private readonly ConcurrentDictionary<long, NativeSubscription> _nativeSubs = new();
+    private long _nextNativeSubId;
+
+    /// <summary>
+    ///     Subscribe via native ADS notifications when <see cref="TwinCATDriverOptions.UseNativeNotifications"/>
+    ///     is <c>true</c>, otherwise fall through to the shared <see cref="PollGroupEngine"/>.
+    ///     Native path registers one <see cref="ITwinCATNotificationHandle"/> per tag against the
+    ///     target's PLC runtime — the PLC pushes changes on its own cycle so we skip the poll
+    ///     loop entirely. Unsub path disposes the handles.
+    /// </summary>
+    public async Task<ISubscriptionHandle> SubscribeAsync(
+        IReadOnlyList<string> fullReferences, TimeSpan publishingInterval, CancellationToken cancellationToken)
+    {
+        if (!_options.UseNativeNotifications)
+            return _poll.Subscribe(fullReferences, publishingInterval);
+
+        var id = Interlocked.Increment(ref _nextNativeSubId);
+        var handle = new NativeSubscriptionHandle(id);
+        var registrations = new List<ITwinCATNotificationHandle>(fullReferences.Count);
+        var now = DateTime.UtcNow;
+
+        try
+        {
+            foreach (var reference in fullReferences)
+            {
+                if (!_tagsByName.TryGetValue(reference, out var def)) continue;
+                if (!_devices.TryGetValue(def.DeviceHostAddress, out var device)) continue;
+
+                var client = await EnsureConnectedAsync(device, cancellationToken).ConfigureAwait(false);
+                var parsed = TwinCATSymbolPath.TryParse(def.SymbolPath);
+                var symbolName = parsed?.ToAdsSymbolName() ?? def.SymbolPath;
+                var bitIndex = parsed?.BitIndex;
+
+                var reg = await client.AddNotificationAsync(
+                    symbolName, def.DataType, bitIndex, publishingInterval,
+                    (_, value) => OnDataChange?.Invoke(this,
+                        new DataChangeEventArgs(handle, reference, new DataValueSnapshot(
+                            value, TwinCATStatusMapper.Good, DateTime.UtcNow, DateTime.UtcNow))),
+                    cancellationToken).ConfigureAwait(false);
+                registrations.Add(reg);
+            }
+        }
+        catch
+        {
+            // On any registration failure, tear down everything we got so far + rethrow. Leaves
+            // the subscription in a clean "never existed" state rather than a half-registered
+            // state the caller has to clean up.
+            foreach (var r in registrations) { try { r.Dispose(); } catch { } }
+            throw;
+        }
+
+        _nativeSubs[id] = new NativeSubscription(handle, registrations);
+        return handle;
+    }
+
+    public Task UnsubscribeAsync(ISubscriptionHandle handle, CancellationToken cancellationToken)
+    {
+        if (handle is NativeSubscriptionHandle native && _nativeSubs.TryRemove(native.Id, out var sub))
+        {
+            foreach (var r in sub.Registrations) { try { r.Dispose(); } catch { } }
+            return Task.CompletedTask;
+        }
+        _poll.Unsubscribe(handle);
+        return Task.CompletedTask;
+    }
+
+    private sealed record NativeSubscriptionHandle(long Id) : ISubscriptionHandle
+    {
+        public string DiagnosticId => $"twincat-native-sub-{Id}";
+    }
+
+    private sealed record NativeSubscription(
+        NativeSubscriptionHandle Handle,
+        IReadOnlyList<ITwinCATNotificationHandle> Registrations);
+
+    // ---- IHostConnectivityProbe ----
+
+    public IReadOnlyList<HostConnectivityStatus> GetHostStatuses() =>
+        [.. _devices.Values.Select(s => new HostConnectivityStatus(s.Options.HostAddress, s.HostState, s.HostStateChangedUtc))];
+
+    private async Task ProbeLoopAsync(DeviceState state, CancellationToken ct)
+    {
+        while (!ct.IsCancellationRequested)
+        {
+            var success = false;
+            try
+            {
+                var client = await EnsureConnectedAsync(state, ct).ConfigureAwait(false);
+                success = await client.ProbeAsync(ct).ConfigureAwait(false);
+            }
+            catch (OperationCanceledException) when (ct.IsCancellationRequested) { break; }
+            catch
+            {
+                // Probe failure — EnsureConnectedAsync's connect-failure path already disposed
+                // + cleared the client, so next tick will reconnect.
+            }
+
+            TransitionDeviceState(state, success ? HostState.Running : HostState.Stopped);
+
+            try { await Task.Delay(_options.Probe.Interval, ct).ConfigureAwait(false); }
+            catch (OperationCanceledException) { break; }
+        }
+    }
+
+    private void TransitionDeviceState(DeviceState state, HostState newState)
+    {
+        HostState old;
+        lock (state.ProbeLock)
+        {
+            old = state.HostState;
+            if (old == newState) return;
+            state.HostState = newState;
+            state.HostStateChangedUtc = DateTime.UtcNow;
+        }
+        OnHostStatusChanged?.Invoke(this,
+            new HostStatusChangedEventArgs(state.Options.HostAddress, old, newState));
+    }
+
+    // ---- IPerCallHostResolver ----
+
+    public string ResolveHost(string fullReference)
+    {
+        if (_tagsByName.TryGetValue(fullReference, out var def))
+            return def.DeviceHostAddress;
+        return _options.Devices.FirstOrDefault()?.HostAddress ?? DriverInstanceId;
+    }
+
+    private async Task<ITwinCATClient> EnsureConnectedAsync(DeviceState device, CancellationToken ct)
+    {
+        if (device.Client is { IsConnected: true } c) return c;
+        device.Client ??= _clientFactory.Create();
+        try
+        {
+            await device.Client.ConnectAsync(device.ParsedAddress, _options.Timeout, ct)
+                .ConfigureAwait(false);
+        }
+        catch
+        {
+            device.Client.Dispose();
+            device.Client = null;
+            throw;
+        }
+        return device.Client;
+    }
+
+    public void Dispose() => DisposeAsync().AsTask().GetAwaiter().GetResult();
+    public async ValueTask DisposeAsync() => await ShutdownAsync(CancellationToken.None).ConfigureAwait(false);
+
+    internal sealed class DeviceState(TwinCATAmsAddress parsedAddress, TwinCATDeviceOptions options)
+    {
+        public TwinCATAmsAddress ParsedAddress { get; } = parsedAddress;
+        public TwinCATDeviceOptions Options { get; } = options;
+        public ITwinCATClient? Client { get; set; }
+
+        public object ProbeLock { get; } = new();
+        public HostState HostState { get; set; } = HostState.Unknown;
+        public DateTime HostStateChangedUtc { get; set; } = DateTime.UtcNow;
+        public CancellationTokenSource? ProbeCts { get; set; }
+
+        public void DisposeClient()
+        {
+            Client?.Dispose();
+            Client = null;
+        }
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT/TwinCATDriverOptions.cs

@@ -0,0 +1,53 @@
+namespace ZB.MOM.WW.OtOpcUa.Driver.TwinCAT;
+
+/// <summary>
+///     TwinCAT ADS driver configuration. One instance supports N targets (each identified by
+///     an AMS Net ID + port). Compiles + runs without a local AMS router but every wire call
+///     fails with <c>BadCommunicationError</c> until a router is reachable.
+/// </summary>
+public sealed class TwinCATDriverOptions
+{
+    public IReadOnlyList<TwinCATDeviceOptions> Devices { get; init; } = [];
+    public IReadOnlyList<TwinCATTagDefinition> Tags { get; init; } = [];
+    public TwinCATProbeOptions Probe { get; init; } = new();
+    public TimeSpan Timeout { get; init; } = TimeSpan.FromSeconds(2);
+
+    /// <summary>
+    ///     When <c>true</c> (default), <c>SubscribeAsync</c> registers native ADS notifications
+    ///     via <c>AddDeviceNotificationExAsync</c> — the PLC pushes changes on its own cycle
+    ///     rather than the driver polling. Strictly better for latency + CPU when the target
+    ///     supports it (TC2 + TC3 PLC runtimes always do; some soft-PLC / third-party ADS
+    ///     implementations may not). When <c>false</c>, the driver falls through to the shared
+    ///     <see cref="Core.Abstractions.PollGroupEngine"/> — same semantics as the other
+    ///     libplctag-backed drivers. Set <c>false</c> for deployments where the AMS router has
+    ///     notification limits you can't raise.
+    /// </summary>
+    public bool UseNativeNotifications { get; init; } = true;
+}
+
+/// <summary>
+///     One TwinCAT target. <paramref name="HostAddress"/> must parse via
+///     <see cref="TwinCATAmsAddress.TryParse"/>; misconfigured devices fail driver initialisation.
+/// </summary>
+public sealed record TwinCATDeviceOptions(
+    string HostAddress,
+    string? DeviceName = null);
+
+/// <summary>
+///     One TwinCAT-backed OPC UA variable. <paramref name="SymbolPath"/> is the full TwinCAT
+///     symbolic name (e.g. <c>MAIN.bStart</c>, <c>GVL.Counter</c>, <c>Motor1.Status.Running</c>).
+/// </summary>
+public sealed record TwinCATTagDefinition(
+    string Name,
+    string DeviceHostAddress,
+    string SymbolPath,
+    TwinCATDataType DataType,
+    bool Writable = true,
+    bool WriteIdempotent = false);
+
+public sealed class TwinCATProbeOptions
+{
+    public bool Enabled { get; init; } = true;
+    public TimeSpan Interval { get; init; } = TimeSpan.FromSeconds(5);
+    public TimeSpan Timeout { get; init; } = TimeSpan.FromSeconds(2);
+}

src/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT/TwinCATStatusMapper.cs

@@ -0,0 +1,43 @@
+namespace ZB.MOM.WW.OtOpcUa.Driver.TwinCAT;
+
+/// <summary>
+///     Maps AMS / ADS error codes to OPC UA StatusCodes. ADS error codes are defined in
+///     <c>AdsErrorCode</c> from <c>Beckhoff.TwinCAT.Ads</c> — this mapper covers the ones a
+///     driver actually encounters during normal operation (symbol-not-found, access-denied,
+///     timeout, router-not-initialized, invalid-group/offset, etc.).
+/// </summary>
+public static class TwinCATStatusMapper
+{
+    public const uint Good = 0u;
+    public const uint BadInternalError = 0x80020000u;
+    public const uint BadNodeIdUnknown = 0x80340000u;
+    public const uint BadNotWritable = 0x803B0000u;
+    public const uint BadOutOfRange = 0x803C0000u;
+    public const uint BadNotSupported = 0x803D0000u;
+    public const uint BadDeviceFailure = 0x80550000u;
+    public const uint BadCommunicationError = 0x80050000u;
+    public const uint BadTimeout = 0x800A0000u;
+    public const uint BadTypeMismatch = 0x80730000u;
+
+    /// <summary>
+    ///     Map an AMS / ADS error code (uint from AdsErrorCode enum). 0 = success; non-zero
+    ///     codes follow Beckhoff's AMS error table (7 = target port not found, 1792 =
+    ///     ADSERR_DEVICE_SRVNOTSUPP, 1793 = ADSERR_DEVICE_INVALIDGRP, 1794 =
+    ///     ADSERR_DEVICE_INVALIDOFFSET, 1798 = ADSERR_DEVICE_SYMBOLNOTFOUND, 1808 =
+    ///     ADSERR_DEVICE_ACCESSDENIED, 1861 = ADSERR_CLIENT_SYNCTIMEOUT).
+    /// </summary>
+    public static uint MapAdsError(uint adsError) => adsError switch
+    {
+        0 => Good,
+        6 or 7 => BadCommunicationError,           // target port unreachable
+        1792 => BadNotSupported,                    // service not supported
+        1793 => BadOutOfRange,                      // invalid index group
+        1794 => BadOutOfRange,                      // invalid index offset
+        1798 => BadNodeIdUnknown,                   // symbol not found
+        1807 => BadDeviceFailure,                   // device in invalid state
+        1808 => BadNotWritable,                     // access denied
+        1811 or 1812 => BadOutOfRange,              // size mismatch
+        1861 => BadTimeout,                          // sync timeout
+        _ => BadCommunicationError,
+    };
+}

src/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT/TwinCATSymbolPath.cs

@@ -0,0 +1,103 @@
+namespace ZB.MOM.WW.OtOpcUa.Driver.TwinCAT;
+
+/// <summary>
+///     Parsed TwinCAT symbolic tag path. Handles global-variable-list (<c>GVL.Counter</c>),
+///     program-variable (<c>MAIN.bStart</c>), structured member access
+///     (<c>Motor1.Status.Running</c>), array subscripts (<c>Data[5]</c>), multi-dim arrays
+///     (<c>Matrix[1,2]</c>), and bit-access (<c>Flags.0</c>).
+/// </summary>
+/// <remarks>
+///     <para>TwinCAT's symbolic syntax mirrors IEC 61131-3 structured-text identifiers — so the
+///     grammar maps cleanly onto the AbCip Logix path parser, but without Logix's
+///     <c>Program:</c> scope prefix. The leading segment is the namespace (POU name /
+///     GVL name) and subsequent segments walk into struct/array members.</para>
+/// </remarks>
+public sealed record TwinCATSymbolPath(
+    IReadOnlyList<TwinCATSymbolSegment> Segments,
+    int? BitIndex)
+{
+    public string ToAdsSymbolName()
+    {
+        var buf = new System.Text.StringBuilder();
+        for (var i = 0; i < Segments.Count; i++)
+        {
+            if (i > 0) buf.Append('.');
+            var seg = Segments[i];
+            buf.Append(seg.Name);
+            if (seg.Subscripts.Count > 0)
+                buf.Append('[').Append(string.Join(",", seg.Subscripts)).Append(']');
+        }
+        if (BitIndex is not null) buf.Append('.').Append(BitIndex.Value);
+        return buf.ToString();
+    }
+
+    public static TwinCATSymbolPath? TryParse(string? value)
+    {
+        if (string.IsNullOrWhiteSpace(value)) return null;
+        var src = value.Trim();
+
+        var parts = new List<string>();
+        var depth = 0;
+        var start = 0;
+        for (var i = 0; i < src.Length; i++)
+        {
+            var c = src[i];
+            if (c == '[') depth++;
+            else if (c == ']') depth--;
+            else if (c == '.' && depth == 0)
+            {
+                parts.Add(src[start..i]);
+                start = i + 1;
+            }
+        }
+        parts.Add(src[start..]);
+        if (depth != 0 || parts.Any(string.IsNullOrEmpty)) return null;
+
+        int? bitIndex = null;
+        if (parts.Count >= 2 && int.TryParse(parts[^1], out var maybeBit)
+            && maybeBit is >= 0 and <= 31
+            && !parts[^1].Contains('['))
+        {
+            bitIndex = maybeBit;
+            parts.RemoveAt(parts.Count - 1);
+        }
+
+        var segments = new List<TwinCATSymbolSegment>(parts.Count);
+        foreach (var part in parts)
+        {
+            var bracketIdx = part.IndexOf('[');
+            if (bracketIdx < 0)
+            {
+                if (!IsValidIdent(part)) return null;
+                segments.Add(new TwinCATSymbolSegment(part, []));
+                continue;
+            }
+            if (!part.EndsWith(']')) return null;
+            var name = part[..bracketIdx];
+            if (!IsValidIdent(name)) return null;
+            var inner = part[(bracketIdx + 1)..^1];
+            var subs = new List<int>();
+            foreach (var tok in inner.Split(','))
+            {
+                if (!int.TryParse(tok, out var n) || n < 0) return null;
+                subs.Add(n);
+            }
+            if (subs.Count == 0) return null;
+            segments.Add(new TwinCATSymbolSegment(name, subs));
+        }
+        if (segments.Count == 0) return null;
+
+        return new TwinCATSymbolPath(segments, bitIndex);
+    }
+
+    private static bool IsValidIdent(string s)
+    {
+        if (string.IsNullOrEmpty(s)) return false;
+        if (!char.IsLetter(s[0]) && s[0] != '_') return false;
+        for (var i = 1; i < s.Length; i++)
+            if (!char.IsLetterOrDigit(s[i]) && s[i] != '_') return false;
+        return true;
+    }
+}
+
+public sealed record TwinCATSymbolSegment(string Name, IReadOnlyList<int> Subscripts);

src/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.csproj

@@ -0,0 +1,31 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <TargetFramework>net10.0</TargetFramework>
+        <Nullable>enable</Nullable>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <LangVersion>latest</LangVersion>
+        <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
+        <GenerateDocumentationFile>true</GenerateDocumentationFile>
+        <NoWarn>$(NoWarn);CS1591</NoWarn>
+        <RootNamespace>ZB.MOM.WW.OtOpcUa.Driver.TwinCAT</RootNamespace>
+        <AssemblyName>ZB.MOM.WW.OtOpcUa.Driver.TwinCAT</AssemblyName>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <ProjectReference Include="..\ZB.MOM.WW.OtOpcUa.Core.Abstractions\ZB.MOM.WW.OtOpcUa.Core.Abstractions.csproj"/>
+    </ItemGroup>
+
+    <ItemGroup>
+        <!-- Official Beckhoff ADS client. Requires a running AMS router (TwinCAT XAR, TwinCAT HMI
+             Server, or the standalone Beckhoff.TwinCAT.Ads.TcpRouter package) to reach remote
+             systems. The router is a runtime concern, not a build concern — the library compiles
+             + runs fine without one; ADS calls just fail with transport errors. -->
+        <PackageReference Include="Beckhoff.TwinCAT.Ads" Version="7.0.172"/>
+    </ItemGroup>
+
+    <ItemGroup>
+        <InternalsVisibleTo Include="ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests"/>
+    </ItemGroup>
+
+</Project>

tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/AbLegacyCapabilityTests.cs

@@ -0,0 +1,249 @@
+using System.Collections.Concurrent;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Driver.AbLegacy;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests;
+
+[Trait("Category", "Unit")]
+public sealed class AbLegacyCapabilityTests
+{
+    // ---- ITagDiscovery ----
+
+    [Fact]
+    public async Task DiscoverAsync_emits_pre_declared_tags_under_device_folder()
+    {
+        var builder = new RecordingBuilder();
+        var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            Devices = [new AbLegacyDeviceOptions("ab://10.0.0.5/1,0", DeviceName: "Press-SLC-1")],
+            Tags =
+            [
+                new AbLegacyTagDefinition("Speed", "ab://10.0.0.5/1,0", "N7:0", AbLegacyDataType.Int),
+                new AbLegacyTagDefinition("Temperature", "ab://10.0.0.5/1,0", "F8:0", AbLegacyDataType.Float, Writable: false),
+            ],
+            Probe = new AbLegacyProbeOptions { Enabled = false },
+        }, "drv-1");
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        await drv.DiscoverAsync(builder, CancellationToken.None);
+
+        builder.Folders.ShouldContain(f => f.BrowseName == "AbLegacy");
+        builder.Folders.ShouldContain(f => f.BrowseName == "ab://10.0.0.5/1,0" && f.DisplayName == "Press-SLC-1");
+        builder.Variables.Count.ShouldBe(2);
+        builder.Variables.Single(v => v.BrowseName == "Speed").Info.SecurityClass.ShouldBe(SecurityClassification.Operate);
+        builder.Variables.Single(v => v.BrowseName == "Temperature").Info.SecurityClass.ShouldBe(SecurityClassification.ViewOnly);
+    }
+
+    // ---- ISubscribable ----
+
+    [Fact]
+    public async Task Subscribe_initial_poll_raises_OnDataChange()
+    {
+        var factory = new FakeAbLegacyTagFactory
+        {
+            Customise = p => new FakeAbLegacyTag(p) { Value = 42 },
+        };
+        var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            Devices = [new AbLegacyDeviceOptions("ab://10.0.0.5/1,0")],
+            Tags = [new AbLegacyTagDefinition("X", "ab://10.0.0.5/1,0", "N7:0", AbLegacyDataType.Int)],
+            Probe = new AbLegacyProbeOptions { Enabled = false },
+        }, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var events = new ConcurrentQueue<DataChangeEventArgs>();
+        drv.OnDataChange += (_, e) => events.Enqueue(e);
+
+        var handle = await drv.SubscribeAsync(["X"], TimeSpan.FromMilliseconds(200), CancellationToken.None);
+        await WaitForAsync(() => events.Count >= 1, TimeSpan.FromSeconds(2));
+
+        events.First().Snapshot.Value.ShouldBe(42);
+        await drv.UnsubscribeAsync(handle, CancellationToken.None);
+    }
+
+    [Fact]
+    public async Task Unsubscribe_halts_polling()
+    {
+        var tagRef = new FakeAbLegacyTag(
+            new AbLegacyTagCreateParams("10.0.0.5", 44818, "1,0", "slc500", "N7:0", TimeSpan.FromSeconds(2))) { Value = 1 };
+        var factory = new FakeAbLegacyTagFactory { Customise = _ => tagRef };
+        var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            Devices = [new AbLegacyDeviceOptions("ab://10.0.0.5/1,0")],
+            Tags = [new AbLegacyTagDefinition("X", "ab://10.0.0.5/1,0", "N7:0", AbLegacyDataType.Int)],
+            Probe = new AbLegacyProbeOptions { Enabled = false },
+        }, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var events = new ConcurrentQueue<DataChangeEventArgs>();
+        drv.OnDataChange += (_, e) => events.Enqueue(e);
+
+        var handle = await drv.SubscribeAsync(["X"], TimeSpan.FromMilliseconds(100), CancellationToken.None);
+        await WaitForAsync(() => events.Count >= 1, TimeSpan.FromSeconds(1));
+        await drv.UnsubscribeAsync(handle, CancellationToken.None);
+
+        var afterUnsub = events.Count;
+        tagRef.Value = 999;
+        await Task.Delay(300);
+        events.Count.ShouldBe(afterUnsub);
+    }
+
+    // ---- IHostConnectivityProbe ----
+
+    [Fact]
+    public async Task GetHostStatuses_returns_one_per_device()
+    {
+        var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            Devices =
+            [
+                new AbLegacyDeviceOptions("ab://10.0.0.5/1,0"),
+                new AbLegacyDeviceOptions("ab://10.0.0.6/1,0"),
+            ],
+            Probe = new AbLegacyProbeOptions { Enabled = false },
+        }, "drv-1");
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        drv.GetHostStatuses().Count.ShouldBe(2);
+    }
+
+    [Fact]
+    public async Task Probe_transitions_to_Running_on_successful_read()
+    {
+        var factory = new FakeAbLegacyTagFactory { Customise = p => new FakeAbLegacyTag(p) };
+        var transitions = new ConcurrentQueue<HostStatusChangedEventArgs>();
+        var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            Devices = [new AbLegacyDeviceOptions("ab://10.0.0.5/1,0")],
+            Probe = new AbLegacyProbeOptions
+            {
+                Enabled = true, Interval = TimeSpan.FromMilliseconds(100),
+                Timeout = TimeSpan.FromMilliseconds(50), ProbeAddress = "S:0",
+            },
+        }, "drv-1", factory);
+        drv.OnHostStatusChanged += (_, e) => transitions.Enqueue(e);
+
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        await WaitForAsync(() => transitions.Any(t => t.NewState == HostState.Running), TimeSpan.FromSeconds(2));
+
+        drv.GetHostStatuses().Single().State.ShouldBe(HostState.Running);
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+
+    [Fact]
+    public async Task Probe_transitions_to_Stopped_on_read_failure()
+    {
+        var factory = new FakeAbLegacyTagFactory { Customise = p => new FakeAbLegacyTag(p) { ThrowOnRead = true } };
+        var transitions = new ConcurrentQueue<HostStatusChangedEventArgs>();
+        var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            Devices = [new AbLegacyDeviceOptions("ab://10.0.0.5/1,0")],
+            Probe = new AbLegacyProbeOptions
+            {
+                Enabled = true, Interval = TimeSpan.FromMilliseconds(100),
+                Timeout = TimeSpan.FromMilliseconds(50), ProbeAddress = "S:0",
+            },
+        }, "drv-1", factory);
+        drv.OnHostStatusChanged += (_, e) => transitions.Enqueue(e);
+
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        await WaitForAsync(() => transitions.Any(t => t.NewState == HostState.Stopped), TimeSpan.FromSeconds(2));
+
+        drv.GetHostStatuses().Single().State.ShouldBe(HostState.Stopped);
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+
+    [Fact]
+    public async Task Probe_disabled_when_ProbeAddress_is_null()
+    {
+        var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            Devices = [new AbLegacyDeviceOptions("ab://10.0.0.5/1,0")],
+            Probe = new AbLegacyProbeOptions { Enabled = true, ProbeAddress = null },
+        }, "drv-1");
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        await Task.Delay(200);
+
+        drv.GetHostStatuses().Single().State.ShouldBe(HostState.Unknown);
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+
+    // ---- IPerCallHostResolver ----
+
+    [Fact]
+    public async Task ResolveHost_returns_declared_device_for_known_tag()
+    {
+        var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            Devices =
+            [
+                new AbLegacyDeviceOptions("ab://10.0.0.5/1,0"),
+                new AbLegacyDeviceOptions("ab://10.0.0.6/1,0"),
+            ],
+            Tags =
+            [
+                new AbLegacyTagDefinition("A", "ab://10.0.0.5/1,0", "N7:0", AbLegacyDataType.Int),
+                new AbLegacyTagDefinition("B", "ab://10.0.0.6/1,0", "N7:0", AbLegacyDataType.Int),
+            ],
+            Probe = new AbLegacyProbeOptions { Enabled = false },
+        }, "drv-1");
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        drv.ResolveHost("A").ShouldBe("ab://10.0.0.5/1,0");
+        drv.ResolveHost("B").ShouldBe("ab://10.0.0.6/1,0");
+    }
+
+    [Fact]
+    public async Task ResolveHost_falls_back_to_first_device_for_unknown()
+    {
+        var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            Devices = [new AbLegacyDeviceOptions("ab://10.0.0.5/1,0")],
+            Probe = new AbLegacyProbeOptions { Enabled = false },
+        }, "drv-1");
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        drv.ResolveHost("missing").ShouldBe("ab://10.0.0.5/1,0");
+    }
+
+    [Fact]
+    public async Task ResolveHost_falls_back_to_DriverInstanceId_when_no_devices()
+    {
+        var drv = new AbLegacyDriver(new AbLegacyDriverOptions(), "drv-1");
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        drv.ResolveHost("anything").ShouldBe("drv-1");
+    }
+
+    // ---- helpers ----
+
+    private static async Task WaitForAsync(Func<bool> condition, TimeSpan timeout)
+    {
+        var deadline = DateTime.UtcNow + timeout;
+        while (!condition() && DateTime.UtcNow < deadline)
+            await Task.Delay(20);
+    }
+
+    private sealed class RecordingBuilder : IAddressSpaceBuilder
+    {
+        public List<(string BrowseName, string DisplayName)> Folders { get; } = new();
+        public List<(string BrowseName, DriverAttributeInfo Info)> Variables { get; } = new();
+
+        public IAddressSpaceBuilder Folder(string browseName, string displayName)
+        { Folders.Add((browseName, displayName)); return this; }
+
+        public IVariableHandle Variable(string browseName, string displayName, DriverAttributeInfo info)
+        { Variables.Add((browseName, info)); return new Handle(info.FullName); }
+
+        public void AddProperty(string _, DriverDataType __, object? ___) { }
+
+        private sealed class Handle(string fullRef) : IVariableHandle
+        {
+            public string FullReference => fullRef;
+            public IAlarmConditionSink MarkAsAlarmCondition(AlarmConditionInfo info) => new NullSink();
+        }
+        private sealed class NullSink : IAlarmConditionSink { public void OnTransition(AlarmEventArgs args) { } }
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/AbLegacyReadWriteTests.cs

@@ -0,0 +1,256 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Driver.AbLegacy;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests;
+
+[Trait("Category", "Unit")]
+public sealed class AbLegacyReadWriteTests
+{
+    private static (AbLegacyDriver drv, FakeAbLegacyTagFactory factory) NewDriver(params AbLegacyTagDefinition[] tags)
+    {
+        var factory = new FakeAbLegacyTagFactory();
+        var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            Devices = [new AbLegacyDeviceOptions("ab://10.0.0.5/1,0")],
+            Tags = tags,
+        }, "drv-1", factory);
+        return (drv, factory);
+    }
+
+    // ---- Read ----
+
+    [Fact]
+    public async Task Unknown_reference_maps_to_BadNodeIdUnknown()
+    {
+        var (drv, _) = NewDriver();
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var snapshots = await drv.ReadAsync(["missing"], CancellationToken.None);
+        snapshots.Single().StatusCode.ShouldBe(AbLegacyStatusMapper.BadNodeIdUnknown);
+    }
+
+    [Fact]
+    public async Task Successful_N_file_read_returns_Good_value()
+    {
+        var (drv, factory) = NewDriver(
+            new AbLegacyTagDefinition("Counter", "ab://10.0.0.5/1,0", "N7:0", AbLegacyDataType.Int));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = p => new FakeAbLegacyTag(p) { Value = 42 };
+
+        var snapshots = await drv.ReadAsync(["Counter"], CancellationToken.None);
+
+        snapshots.Single().StatusCode.ShouldBe(AbLegacyStatusMapper.Good);
+        snapshots.Single().Value.ShouldBe(42);
+        factory.Tags["N7:0"].InitializeCount.ShouldBe(1);
+        factory.Tags["N7:0"].ReadCount.ShouldBe(1);
+    }
+
+    [Fact]
+    public async Task Repeat_read_reuses_runtime()
+    {
+        var (drv, factory) = NewDriver(
+            new AbLegacyTagDefinition("X", "ab://10.0.0.5/1,0", "N7:0", AbLegacyDataType.Int));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = p => new FakeAbLegacyTag(p) { Value = 1 };
+
+        await drv.ReadAsync(["X"], CancellationToken.None);
+        await drv.ReadAsync(["X"], CancellationToken.None);
+
+        factory.Tags["N7:0"].InitializeCount.ShouldBe(1);
+        factory.Tags["N7:0"].ReadCount.ShouldBe(2);
+    }
+
+    [Fact]
+    public async Task NonZero_libplctag_status_maps_via_AbLegacyStatusMapper()
+    {
+        var (drv, factory) = NewDriver(
+            new AbLegacyTagDefinition("X", "ab://10.0.0.5/1,0", "N7:0", AbLegacyDataType.Int));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = p => new FakeAbLegacyTag(p) { Status = -14 };
+
+        var snapshots = await drv.ReadAsync(["X"], CancellationToken.None);
+        snapshots.Single().StatusCode.ShouldBe(AbLegacyStatusMapper.BadNodeIdUnknown);
+    }
+
+    [Fact]
+    public async Task Read_exception_surfaces_BadCommunicationError()
+    {
+        var (drv, factory) = NewDriver(
+            new AbLegacyTagDefinition("X", "ab://10.0.0.5/1,0", "N7:0", AbLegacyDataType.Int));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = p => new FakeAbLegacyTag(p) { ThrowOnRead = true };
+
+        var snapshots = await drv.ReadAsync(["X"], CancellationToken.None);
+        snapshots.Single().StatusCode.ShouldBe(AbLegacyStatusMapper.BadCommunicationError);
+        drv.GetHealth().State.ShouldBe(DriverState.Degraded);
+    }
+
+    [Fact]
+    public async Task Batched_reads_preserve_order()
+    {
+        var (drv, factory) = NewDriver(
+            new AbLegacyTagDefinition("A", "ab://10.0.0.5/1,0", "N7:0", AbLegacyDataType.Int),
+            new AbLegacyTagDefinition("B", "ab://10.0.0.5/1,0", "F8:0", AbLegacyDataType.Float),
+            new AbLegacyTagDefinition("C", "ab://10.0.0.5/1,0", "ST9:0", AbLegacyDataType.String));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = p => p.TagName switch
+        {
+            "N7:0" => new FakeAbLegacyTag(p) { Value = 1 },
+            "F8:0" => new FakeAbLegacyTag(p) { Value = 3.14f },
+            _ => new FakeAbLegacyTag(p) { Value = "hello" },
+        };
+
+        var snapshots = await drv.ReadAsync(["A", "B", "C"], CancellationToken.None);
+
+        snapshots.Count.ShouldBe(3);
+        snapshots[0].Value.ShouldBe(1);
+        snapshots[1].Value.ShouldBe(3.14f);
+        snapshots[2].Value.ShouldBe("hello");
+    }
+
+    [Fact]
+    public async Task Read_TagCreateParams_composed_from_device_and_profile()
+    {
+        var (drv, factory) = NewDriver(
+            new AbLegacyTagDefinition("X", "ab://10.0.0.5/1,0", "N7:5", AbLegacyDataType.Int));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        await drv.ReadAsync(["X"], CancellationToken.None);
+
+        var p = factory.Tags["N7:5"].CreationParams;
+        p.Gateway.ShouldBe("10.0.0.5");
+        p.Port.ShouldBe(44818);
+        p.CipPath.ShouldBe("1,0");
+        p.LibplctagPlcAttribute.ShouldBe("slc500");
+        p.TagName.ShouldBe("N7:5");
+    }
+
+    // ---- Write ----
+
+    [Fact]
+    public async Task Non_writable_tag_rejects_with_BadNotWritable()
+    {
+        var (drv, _) = NewDriver(
+            new AbLegacyTagDefinition("RO", "ab://10.0.0.5/1,0", "N7:0", AbLegacyDataType.Int, Writable: false));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var results = await drv.WriteAsync(
+            [new WriteRequest("RO", 1)], CancellationToken.None);
+        results.Single().StatusCode.ShouldBe(AbLegacyStatusMapper.BadNotWritable);
+    }
+
+    [Fact]
+    public async Task Successful_N_file_write_encodes_and_flushes()
+    {
+        var (drv, factory) = NewDriver(
+            new AbLegacyTagDefinition("X", "ab://10.0.0.5/1,0", "N7:0", AbLegacyDataType.Int));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var results = await drv.WriteAsync(
+            [new WriteRequest("X", 123)], CancellationToken.None);
+
+        results.Single().StatusCode.ShouldBe(AbLegacyStatusMapper.Good);
+        factory.Tags["N7:0"].Value.ShouldBe(123);
+        factory.Tags["N7:0"].WriteCount.ShouldBe(1);
+    }
+
+    [Fact]
+    public async Task Bit_within_word_write_rejected_as_BadNotSupported()
+    {
+        var factory = new FakeAbLegacyTagFactory { Customise = p => new RmwThrowingFake(p) };
+        var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            Devices = [new AbLegacyDeviceOptions("ab://10.0.0.5/1,0")],
+            Tags = [new AbLegacyTagDefinition("Bit3", "ab://10.0.0.5/1,0", "N7:0/3", AbLegacyDataType.Bit)],
+        }, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var results = await drv.WriteAsync(
+            [new WriteRequest("Bit3", true)], CancellationToken.None);
+
+        results.Single().StatusCode.ShouldBe(AbLegacyStatusMapper.BadNotSupported);
+    }
+
+    [Fact]
+    public async Task Write_exception_surfaces_BadCommunicationError()
+    {
+        var (drv, factory) = NewDriver(
+            new AbLegacyTagDefinition("X", "ab://10.0.0.5/1,0", "N7:0", AbLegacyDataType.Int));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = p => new FakeAbLegacyTag(p) { ThrowOnWrite = true };
+
+        var results = await drv.WriteAsync(
+            [new WriteRequest("X", 1)], CancellationToken.None);
+        results.Single().StatusCode.ShouldBe(AbLegacyStatusMapper.BadCommunicationError);
+    }
+
+    [Fact]
+    public async Task Batch_write_preserves_order_across_outcomes()
+    {
+        var factory = new FakeAbLegacyTagFactory();
+        var drv = new AbLegacyDriver(new AbLegacyDriverOptions
+        {
+            Devices = [new AbLegacyDeviceOptions("ab://10.0.0.5/1,0")],
+            Tags =
+            [
+                new AbLegacyTagDefinition("A", "ab://10.0.0.5/1,0", "N7:0", AbLegacyDataType.Int),
+                new AbLegacyTagDefinition("B", "ab://10.0.0.5/1,0", "N7:1", AbLegacyDataType.Int, Writable: false),
+            ],
+        }, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var results = await drv.WriteAsync(
+        [
+            new WriteRequest("A", 1),
+            new WriteRequest("B", 2),
+            new WriteRequest("Unknown", 3),
+        ], CancellationToken.None);
+
+        results.Count.ShouldBe(3);
+        results[0].StatusCode.ShouldBe(AbLegacyStatusMapper.Good);
+        results[1].StatusCode.ShouldBe(AbLegacyStatusMapper.BadNotWritable);
+        results[2].StatusCode.ShouldBe(AbLegacyStatusMapper.BadNodeIdUnknown);
+    }
+
+    [Fact]
+    public async Task Cancellation_propagates()
+    {
+        var (drv, factory) = NewDriver(
+            new AbLegacyTagDefinition("X", "ab://10.0.0.5/1,0", "N7:0", AbLegacyDataType.Int));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = p => new FakeAbLegacyTag(p)
+        {
+            ThrowOnRead = true,
+            Exception = new OperationCanceledException(),
+        };
+
+        await Should.ThrowAsync<OperationCanceledException>(
+            () => drv.ReadAsync(["X"], CancellationToken.None));
+    }
+
+    [Fact]
+    public async Task ShutdownAsync_disposes_runtimes()
+    {
+        var (drv, factory) = NewDriver(
+            new AbLegacyTagDefinition("A", "ab://10.0.0.5/1,0", "N7:0", AbLegacyDataType.Int));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = p => new FakeAbLegacyTag(p) { Value = 1 };
+
+        await drv.ReadAsync(["A"], CancellationToken.None);
+        await drv.ShutdownAsync(CancellationToken.None);
+
+        factory.Tags["N7:0"].Disposed.ShouldBeTrue();
+    }
+
+    private sealed class RmwThrowingFake(AbLegacyTagCreateParams p) : FakeAbLegacyTag(p)
+    {
+        public override void EncodeValue(AbLegacyDataType type, int? bitIndex, object? value)
+        {
+            if (type == AbLegacyDataType.Bit && bitIndex is not null)
+                throw new NotSupportedException("bit-within-word RMW deferred");
+            Value = value;
+        }
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/FakeAbLegacyTag.cs

@@ -0,0 +1,59 @@
+using ZB.MOM.WW.OtOpcUa.Driver.AbLegacy;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests;
+
+internal class FakeAbLegacyTag : IAbLegacyTagRuntime
+{
+    public AbLegacyTagCreateParams CreationParams { get; }
+    public object? Value { get; set; }
+    public int Status { get; set; }
+    public bool ThrowOnInitialize { get; set; }
+    public bool ThrowOnRead { get; set; }
+    public bool ThrowOnWrite { get; set; }
+    public Exception? Exception { get; set; }
+    public int InitializeCount { get; private set; }
+    public int ReadCount { get; private set; }
+    public int WriteCount { get; private set; }
+    public bool Disposed { get; private set; }
+
+    public FakeAbLegacyTag(AbLegacyTagCreateParams p) => CreationParams = p;
+
+    public virtual Task InitializeAsync(CancellationToken ct)
+    {
+        InitializeCount++;
+        if (ThrowOnInitialize) throw Exception ?? new InvalidOperationException();
+        return Task.CompletedTask;
+    }
+
+    public virtual Task ReadAsync(CancellationToken ct)
+    {
+        ReadCount++;
+        if (ThrowOnRead) throw Exception ?? new InvalidOperationException();
+        return Task.CompletedTask;
+    }
+
+    public virtual Task WriteAsync(CancellationToken ct)
+    {
+        WriteCount++;
+        if (ThrowOnWrite) throw Exception ?? new InvalidOperationException();
+        return Task.CompletedTask;
+    }
+
+    public virtual int GetStatus() => Status;
+    public virtual object? DecodeValue(AbLegacyDataType type, int? bitIndex) => Value;
+    public virtual void EncodeValue(AbLegacyDataType type, int? bitIndex, object? value) => Value = value;
+    public virtual void Dispose() => Disposed = true;
+}
+
+internal sealed class FakeAbLegacyTagFactory : IAbLegacyTagFactory
+{
+    public Dictionary<string, FakeAbLegacyTag> Tags { get; } = new(StringComparer.OrdinalIgnoreCase);
+    public Func<AbLegacyTagCreateParams, FakeAbLegacyTag>? Customise { get; set; }
+
+    public IAbLegacyTagRuntime Create(AbLegacyTagCreateParams p)
+    {
+        var fake = Customise?.Invoke(p) ?? new FakeAbLegacyTag(p);
+        Tags[p.TagName] = fake;
+        return fake;
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FakeFocasClient.cs

@@ -0,0 +1,69 @@
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests;
+
+internal class FakeFocasClient : IFocasClient
+{
+    public bool IsConnected { get; private set; }
+    public int ConnectCount { get; private set; }
+    public int DisposeCount { get; private set; }
+    public bool ThrowOnConnect { get; set; }
+    public bool ThrowOnRead { get; set; }
+    public bool ThrowOnWrite { get; set; }
+    public bool ProbeResult { get; set; } = true;
+    public Exception? Exception { get; set; }
+
+    public Dictionary<string, object?> Values { get; } = new(StringComparer.OrdinalIgnoreCase);
+    public Dictionary<string, uint> ReadStatuses { get; } = new(StringComparer.OrdinalIgnoreCase);
+    public Dictionary<string, uint> WriteStatuses { get; } = new(StringComparer.OrdinalIgnoreCase);
+    public List<(FocasAddress addr, FocasDataType type, object? value)> WriteLog { get; } = new();
+
+    public virtual Task ConnectAsync(FocasHostAddress address, TimeSpan timeout, CancellationToken ct)
+    {
+        ConnectCount++;
+        if (ThrowOnConnect) throw Exception ?? new InvalidOperationException();
+        IsConnected = true;
+        return Task.CompletedTask;
+    }
+
+    public virtual Task<(object? value, uint status)> ReadAsync(
+        FocasAddress address, FocasDataType type, CancellationToken ct)
+    {
+        if (ThrowOnRead) throw Exception ?? new InvalidOperationException();
+        var key = address.Canonical;
+        var status = ReadStatuses.TryGetValue(key, out var s) ? s : FocasStatusMapper.Good;
+        var value = Values.TryGetValue(key, out var v) ? v : null;
+        return Task.FromResult((value, status));
+    }
+
+    public virtual Task<uint> WriteAsync(
+        FocasAddress address, FocasDataType type, object? value, CancellationToken ct)
+    {
+        if (ThrowOnWrite) throw Exception ?? new InvalidOperationException();
+        WriteLog.Add((address, type, value));
+        Values[address.Canonical] = value;
+        var status = WriteStatuses.TryGetValue(address.Canonical, out var s) ? s : FocasStatusMapper.Good;
+        return Task.FromResult(status);
+    }
+
+    public virtual Task<bool> ProbeAsync(CancellationToken ct) => Task.FromResult(ProbeResult);
+
+    public virtual void Dispose()
+    {
+        DisposeCount++;
+        IsConnected = false;
+    }
+}
+
+internal sealed class FakeFocasClientFactory : IFocasClientFactory
+{
+    public List<FakeFocasClient> Clients { get; } = new();
+    public Func<FakeFocasClient>? Customise { get; set; }
+
+    public IFocasClient Create()
+    {
+        var c = Customise?.Invoke() ?? new FakeFocasClient();
+        Clients.Add(c);
+        return c;
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FocasCapabilityTests.cs

@@ -0,0 +1,239 @@
+using System.Collections.Concurrent;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests;
+
+[Trait("Category", "Unit")]
+public sealed class FocasCapabilityTests
+{
+    // ---- ITagDiscovery ----
+
+    [Fact]
+    public async Task DiscoverAsync_emits_pre_declared_tags()
+    {
+        var builder = new RecordingBuilder();
+        var drv = new FocasDriver(new FocasDriverOptions
+        {
+            Devices = [new FocasDeviceOptions("focas://10.0.0.5:8193", DeviceName: "Lathe-1")],
+            Tags =
+            [
+                new FocasTagDefinition("Run", "focas://10.0.0.5:8193", "R100", FocasDataType.Byte),
+                new FocasTagDefinition("Alarm", "focas://10.0.0.5:8193", "R200", FocasDataType.Byte, Writable: false),
+            ],
+            Probe = new FocasProbeOptions { Enabled = false },
+        }, "drv-1", new FakeFocasClientFactory());
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        await drv.DiscoverAsync(builder, CancellationToken.None);
+
+        builder.Folders.ShouldContain(f => f.BrowseName == "FOCAS");
+        builder.Folders.ShouldContain(f => f.BrowseName == "focas://10.0.0.5:8193" && f.DisplayName == "Lathe-1");
+        builder.Variables.Single(v => v.BrowseName == "Run").Info.SecurityClass.ShouldBe(SecurityClassification.Operate);
+        builder.Variables.Single(v => v.BrowseName == "Alarm").Info.SecurityClass.ShouldBe(SecurityClassification.ViewOnly);
+    }
+
+    // ---- ISubscribable ----
+
+    [Fact]
+    public async Task Subscribe_initial_poll_raises_OnDataChange()
+    {
+        var factory = new FakeFocasClientFactory
+        {
+            Customise = () => new FakeFocasClient { Values = { ["R100"] = (sbyte)42 } },
+        };
+        var drv = new FocasDriver(new FocasDriverOptions
+        {
+            Devices = [new FocasDeviceOptions("focas://10.0.0.5:8193")],
+            Tags = [new FocasTagDefinition("X", "focas://10.0.0.5:8193", "R100", FocasDataType.Byte)],
+            Probe = new FocasProbeOptions { Enabled = false },
+        }, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var events = new ConcurrentQueue<DataChangeEventArgs>();
+        drv.OnDataChange += (_, e) => events.Enqueue(e);
+
+        var handle = await drv.SubscribeAsync(["X"], TimeSpan.FromMilliseconds(200), CancellationToken.None);
+        await WaitForAsync(() => events.Count >= 1, TimeSpan.FromSeconds(2));
+
+        events.First().Snapshot.Value.ShouldBe((sbyte)42);
+        await drv.UnsubscribeAsync(handle, CancellationToken.None);
+    }
+
+    [Fact]
+    public async Task ShutdownAsync_cancels_active_subscriptions()
+    {
+        var factory = new FakeFocasClientFactory
+        {
+            Customise = () => new FakeFocasClient { Values = { ["R100"] = (sbyte)1 } },
+        };
+        var drv = new FocasDriver(new FocasDriverOptions
+        {
+            Devices = [new FocasDeviceOptions("focas://10.0.0.5:8193")],
+            Tags = [new FocasTagDefinition("X", "focas://10.0.0.5:8193", "R100", FocasDataType.Byte)],
+            Probe = new FocasProbeOptions { Enabled = false },
+        }, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var events = new ConcurrentQueue<DataChangeEventArgs>();
+        drv.OnDataChange += (_, e) => events.Enqueue(e);
+
+        _ = await drv.SubscribeAsync(["X"], TimeSpan.FromMilliseconds(100), CancellationToken.None);
+        await WaitForAsync(() => events.Count >= 1, TimeSpan.FromSeconds(1));
+        await drv.ShutdownAsync(CancellationToken.None);
+
+        var afterShutdown = events.Count;
+        await Task.Delay(200);
+        events.Count.ShouldBe(afterShutdown);
+    }
+
+    // ---- IHostConnectivityProbe ----
+
+    [Fact]
+    public async Task GetHostStatuses_returns_entry_per_device()
+    {
+        var drv = new FocasDriver(new FocasDriverOptions
+        {
+            Devices =
+            [
+                new FocasDeviceOptions("focas://10.0.0.5:8193"),
+                new FocasDeviceOptions("focas://10.0.0.6:8193"),
+            ],
+            Probe = new FocasProbeOptions { Enabled = false },
+        }, "drv-1", new FakeFocasClientFactory());
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        drv.GetHostStatuses().Count.ShouldBe(2);
+    }
+
+    [Fact]
+    public async Task Probe_transitions_to_Running_on_success()
+    {
+        var factory = new FakeFocasClientFactory
+        {
+            Customise = () => new FakeFocasClient { ProbeResult = true },
+        };
+        var transitions = new ConcurrentQueue<HostStatusChangedEventArgs>();
+        var drv = new FocasDriver(new FocasDriverOptions
+        {
+            Devices = [new FocasDeviceOptions("focas://10.0.0.5:8193")],
+            Probe = new FocasProbeOptions
+            {
+                Enabled = true, Interval = TimeSpan.FromMilliseconds(100),
+                Timeout = TimeSpan.FromMilliseconds(50),
+            },
+        }, "drv-1", factory);
+        drv.OnHostStatusChanged += (_, e) => transitions.Enqueue(e);
+
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        await WaitForAsync(() => transitions.Any(t => t.NewState == HostState.Running), TimeSpan.FromSeconds(2));
+
+        drv.GetHostStatuses().Single().State.ShouldBe(HostState.Running);
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+
+    [Fact]
+    public async Task Probe_transitions_to_Stopped_on_failure()
+    {
+        var factory = new FakeFocasClientFactory
+        {
+            Customise = () => new FakeFocasClient { ProbeResult = false },
+        };
+        var transitions = new ConcurrentQueue<HostStatusChangedEventArgs>();
+        var drv = new FocasDriver(new FocasDriverOptions
+        {
+            Devices = [new FocasDeviceOptions("focas://10.0.0.5:8193")],
+            Probe = new FocasProbeOptions
+            {
+                Enabled = true, Interval = TimeSpan.FromMilliseconds(100),
+                Timeout = TimeSpan.FromMilliseconds(50),
+            },
+        }, "drv-1", factory);
+        drv.OnHostStatusChanged += (_, e) => transitions.Enqueue(e);
+
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        await WaitForAsync(() => transitions.Any(t => t.NewState == HostState.Stopped), TimeSpan.FromSeconds(2));
+
+        drv.GetHostStatuses().Single().State.ShouldBe(HostState.Stopped);
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+
+    // ---- IPerCallHostResolver ----
+
+    [Fact]
+    public async Task ResolveHost_returns_declared_device_for_known_tag()
+    {
+        var drv = new FocasDriver(new FocasDriverOptions
+        {
+            Devices =
+            [
+                new FocasDeviceOptions("focas://10.0.0.5:8193"),
+                new FocasDeviceOptions("focas://10.0.0.6:8193"),
+            ],
+            Tags =
+            [
+                new FocasTagDefinition("A", "focas://10.0.0.5:8193", "R100", FocasDataType.Byte),
+                new FocasTagDefinition("B", "focas://10.0.0.6:8193", "R100", FocasDataType.Byte),
+            ],
+            Probe = new FocasProbeOptions { Enabled = false },
+        }, "drv-1", new FakeFocasClientFactory());
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        drv.ResolveHost("A").ShouldBe("focas://10.0.0.5:8193");
+        drv.ResolveHost("B").ShouldBe("focas://10.0.0.6:8193");
+    }
+
+    [Fact]
+    public async Task ResolveHost_falls_back_to_first_device_for_unknown()
+    {
+        var drv = new FocasDriver(new FocasDriverOptions
+        {
+            Devices = [new FocasDeviceOptions("focas://10.0.0.5:8193")],
+            Probe = new FocasProbeOptions { Enabled = false },
+        }, "drv-1", new FakeFocasClientFactory());
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        drv.ResolveHost("missing").ShouldBe("focas://10.0.0.5:8193");
+    }
+
+    [Fact]
+    public async Task ResolveHost_falls_back_to_DriverInstanceId_when_no_devices()
+    {
+        var drv = new FocasDriver(new FocasDriverOptions(), "drv-1", new FakeFocasClientFactory());
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        drv.ResolveHost("anything").ShouldBe("drv-1");
+    }
+
+    // ---- helpers ----
+
+    private static async Task WaitForAsync(Func<bool> condition, TimeSpan timeout)
+    {
+        var deadline = DateTime.UtcNow + timeout;
+        while (!condition() && DateTime.UtcNow < deadline)
+            await Task.Delay(20);
+    }
+
+    private sealed class RecordingBuilder : IAddressSpaceBuilder
+    {
+        public List<(string BrowseName, string DisplayName)> Folders { get; } = new();
+        public List<(string BrowseName, DriverAttributeInfo Info)> Variables { get; } = new();
+
+        public IAddressSpaceBuilder Folder(string browseName, string displayName)
+        { Folders.Add((browseName, displayName)); return this; }
+
+        public IVariableHandle Variable(string browseName, string displayName, DriverAttributeInfo info)
+        { Variables.Add((browseName, info)); return new Handle(info.FullName); }
+
+        public void AddProperty(string _, DriverDataType __, object? ___) { }
+
+        private sealed class Handle(string fullRef) : IVariableHandle
+        {
+            public string FullReference => fullRef;
+            public IAlarmConditionSink MarkAsAlarmCondition(AlarmConditionInfo info) => new NullSink();
+        }
+        private sealed class NullSink : IAlarmConditionSink { public void OnTransition(AlarmEventArgs args) { } }
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FocasReadWriteTests.cs

@@ -0,0 +1,261 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests;
+
+[Trait("Category", "Unit")]
+public sealed class FocasReadWriteTests
+{
+    private static (FocasDriver drv, FakeFocasClientFactory factory) NewDriver(params FocasTagDefinition[] tags)
+    {
+        var factory = new FakeFocasClientFactory();
+        var drv = new FocasDriver(new FocasDriverOptions
+        {
+            Devices = [new FocasDeviceOptions("focas://10.0.0.5:8193")],
+            Tags = tags,
+            Probe = new FocasProbeOptions { Enabled = false },
+        }, "drv-1", factory);
+        return (drv, factory);
+    }
+
+    // ---- Read ----
+
+    [Fact]
+    public async Task Unknown_reference_maps_to_BadNodeIdUnknown()
+    {
+        var (drv, _) = NewDriver();
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var snapshots = await drv.ReadAsync(["missing"], CancellationToken.None);
+        snapshots.Single().StatusCode.ShouldBe(FocasStatusMapper.BadNodeIdUnknown);
+    }
+
+    [Fact]
+    public async Task Successful_PMC_read_returns_Good_value()
+    {
+        var (drv, factory) = NewDriver(
+            new FocasTagDefinition("Run", "focas://10.0.0.5:8193", "R100", FocasDataType.Byte));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = () => new FakeFocasClient { Values = { ["R100"] = (sbyte)5 } };
+
+        var snapshots = await drv.ReadAsync(["Run"], CancellationToken.None);
+        snapshots.Single().StatusCode.ShouldBe(FocasStatusMapper.Good);
+        snapshots.Single().Value.ShouldBe((sbyte)5);
+    }
+
+    [Fact]
+    public async Task Parameter_read_routes_through_FocasAddress_Parameter_kind()
+    {
+        var (drv, factory) = NewDriver(
+            new FocasTagDefinition("Accel", "focas://10.0.0.5:8193", "PARAM:1820", FocasDataType.Int32));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = () => new FakeFocasClient { Values = { ["PARAM:1820"] = 1500 } };
+
+        var snapshots = await drv.ReadAsync(["Accel"], CancellationToken.None);
+        snapshots.Single().StatusCode.ShouldBe(FocasStatusMapper.Good);
+        snapshots.Single().Value.ShouldBe(1500);
+    }
+
+    [Fact]
+    public async Task Macro_read_routes_through_FocasAddress_Macro_kind()
+    {
+        var (drv, factory) = NewDriver(
+            new FocasTagDefinition("CustomVar", "focas://10.0.0.5:8193", "MACRO:500", FocasDataType.Float64));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = () => new FakeFocasClient { Values = { ["MACRO:500"] = 3.14159 } };
+
+        var snapshots = await drv.ReadAsync(["CustomVar"], CancellationToken.None);
+        snapshots.Single().Value.ShouldBe(3.14159);
+    }
+
+    [Fact]
+    public async Task Repeat_read_reuses_connection()
+    {
+        var (drv, factory) = NewDriver(
+            new FocasTagDefinition("X", "focas://10.0.0.5:8193", "R100", FocasDataType.Byte));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = () => new FakeFocasClient { Values = { ["R100"] = (sbyte)1 } };
+
+        await drv.ReadAsync(["X"], CancellationToken.None);
+        await drv.ReadAsync(["X"], CancellationToken.None);
+
+        factory.Clients.Count.ShouldBe(1);
+        factory.Clients[0].ConnectCount.ShouldBe(1);
+    }
+
+    [Fact]
+    public async Task FOCAS_error_status_maps_via_status_mapper()
+    {
+        var (drv, factory) = NewDriver(
+            new FocasTagDefinition("Ghost", "focas://10.0.0.5:8193", "R999", FocasDataType.Byte));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = () =>
+        {
+            var c = new FakeFocasClient();
+            c.ReadStatuses["R999"] = FocasStatusMapper.BadNodeIdUnknown;
+            return c;
+        };
+
+        var snapshots = await drv.ReadAsync(["Ghost"], CancellationToken.None);
+        snapshots.Single().StatusCode.ShouldBe(FocasStatusMapper.BadNodeIdUnknown);
+    }
+
+    [Fact]
+    public async Task Read_exception_surfaces_BadCommunicationError()
+    {
+        var (drv, factory) = NewDriver(
+            new FocasTagDefinition("X", "focas://10.0.0.5:8193", "R100", FocasDataType.Byte));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = () => new FakeFocasClient { ThrowOnRead = true };
+
+        var snapshots = await drv.ReadAsync(["X"], CancellationToken.None);
+        snapshots.Single().StatusCode.ShouldBe(FocasStatusMapper.BadCommunicationError);
+        drv.GetHealth().State.ShouldBe(DriverState.Degraded);
+    }
+
+    [Fact]
+    public async Task Connect_failure_disposes_client_and_surfaces_BadCommunicationError()
+    {
+        var (drv, factory) = NewDriver(
+            new FocasTagDefinition("X", "focas://10.0.0.5:8193", "R100", FocasDataType.Byte));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = () => new FakeFocasClient { ThrowOnConnect = true };
+
+        var snapshots = await drv.ReadAsync(["X"], CancellationToken.None);
+        snapshots.Single().StatusCode.ShouldBe(FocasStatusMapper.BadCommunicationError);
+        factory.Clients[0].DisposeCount.ShouldBe(1);
+    }
+
+    [Fact]
+    public async Task Batched_reads_preserve_order_across_areas()
+    {
+        var (drv, factory) = NewDriver(
+            new FocasTagDefinition("A", "focas://10.0.0.5:8193", "R100", FocasDataType.Byte),
+            new FocasTagDefinition("B", "focas://10.0.0.5:8193", "PARAM:1820", FocasDataType.Int32),
+            new FocasTagDefinition("C", "focas://10.0.0.5:8193", "MACRO:500", FocasDataType.Float64));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = () => new FakeFocasClient
+        {
+            Values =
+            {
+                ["R100"] = (sbyte)5,
+                ["PARAM:1820"] = 1500,
+                ["MACRO:500"] = 2.718,
+            },
+        };
+
+        var snapshots = await drv.ReadAsync(["A", "B", "C"], CancellationToken.None);
+        snapshots[0].Value.ShouldBe((sbyte)5);
+        snapshots[1].Value.ShouldBe(1500);
+        snapshots[2].Value.ShouldBe(2.718);
+    }
+
+    // ---- Write ----
+
+    [Fact]
+    public async Task Non_writable_tag_rejected_with_BadNotWritable()
+    {
+        var (drv, _) = NewDriver(
+            new FocasTagDefinition("RO", "focas://10.0.0.5:8193", "R100", FocasDataType.Byte, Writable: false));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var results = await drv.WriteAsync(
+            [new WriteRequest("RO", 1)], CancellationToken.None);
+        results.Single().StatusCode.ShouldBe(FocasStatusMapper.BadNotWritable);
+    }
+
+    [Fact]
+    public async Task Successful_write_logs_address_type_value()
+    {
+        var (drv, factory) = NewDriver(
+            new FocasTagDefinition("Speed", "focas://10.0.0.5:8193", "R100", FocasDataType.Int16));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var results = await drv.WriteAsync(
+            [new WriteRequest("Speed", (short)1800)], CancellationToken.None);
+
+        results.Single().StatusCode.ShouldBe(FocasStatusMapper.Good);
+        var write = factory.Clients[0].WriteLog.Single();
+        write.addr.Canonical.ShouldBe("R100");
+        write.type.ShouldBe(FocasDataType.Int16);
+        write.value.ShouldBe((short)1800);
+    }
+
+    [Fact]
+    public async Task Write_status_code_maps_via_FocasStatusMapper()
+    {
+        var (drv, factory) = NewDriver(
+            new FocasTagDefinition("Protected", "focas://10.0.0.5:8193", "R100", FocasDataType.Byte));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = () =>
+        {
+            var c = new FakeFocasClient();
+            c.WriteStatuses["R100"] = FocasStatusMapper.BadNotWritable;
+            return c;
+        };
+
+        var results = await drv.WriteAsync(
+            [new WriteRequest("Protected", (sbyte)1)], CancellationToken.None);
+        results.Single().StatusCode.ShouldBe(FocasStatusMapper.BadNotWritable);
+    }
+
+    [Fact]
+    public async Task Batch_write_preserves_order_across_outcomes()
+    {
+        var factory = new FakeFocasClientFactory();
+        var drv = new FocasDriver(new FocasDriverOptions
+        {
+            Devices = [new FocasDeviceOptions("focas://10.0.0.5:8193")],
+            Tags =
+            [
+                new FocasTagDefinition("A", "focas://10.0.0.5:8193", "R100", FocasDataType.Byte),
+                new FocasTagDefinition("B", "focas://10.0.0.5:8193", "R101", FocasDataType.Byte, Writable: false),
+            ],
+            Probe = new FocasProbeOptions { Enabled = false },
+        }, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var results = await drv.WriteAsync(
+        [
+            new WriteRequest("A", (sbyte)1),
+            new WriteRequest("B", (sbyte)2),
+            new WriteRequest("Unknown", (sbyte)3),
+        ], CancellationToken.None);
+
+        results[0].StatusCode.ShouldBe(FocasStatusMapper.Good);
+        results[1].StatusCode.ShouldBe(FocasStatusMapper.BadNotWritable);
+        results[2].StatusCode.ShouldBe(FocasStatusMapper.BadNodeIdUnknown);
+    }
+
+    [Fact]
+    public async Task Cancellation_propagates()
+    {
+        var (drv, factory) = NewDriver(
+            new FocasTagDefinition("X", "focas://10.0.0.5:8193", "R100", FocasDataType.Byte));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = () => new FakeFocasClient
+        {
+            ThrowOnRead = true,
+            Exception = new OperationCanceledException(),
+        };
+
+        await Should.ThrowAsync<OperationCanceledException>(
+            () => drv.ReadAsync(["X"], CancellationToken.None));
+    }
+
+    [Fact]
+    public async Task ShutdownAsync_disposes_client()
+    {
+        var (drv, factory) = NewDriver(
+            new FocasTagDefinition("X", "focas://10.0.0.5:8193", "R100", FocasDataType.Byte));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = () => new FakeFocasClient { Values = { ["R100"] = (sbyte)1 } };
+
+        await drv.ReadAsync(["X"], CancellationToken.None);
+        await drv.ShutdownAsync(CancellationToken.None);
+
+        factory.Clients[0].DisposeCount.ShouldBe(1);
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FocasScaffoldingTests.cs

@@ -0,0 +1,229 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests;
+
+[Trait("Category", "Unit")]
+public sealed class FocasScaffoldingTests
+{
+    // ---- FocasHostAddress ----
+
+    [Theory]
+    [InlineData("focas://10.0.0.5:8193", "10.0.0.5", 8193)]
+    [InlineData("focas://10.0.0.5", "10.0.0.5", 8193)]                         // default port
+    [InlineData("focas://cnc-01.factory.internal:8193", "cnc-01.factory.internal", 8193)]
+    [InlineData("focas://10.0.0.5:12345", "10.0.0.5", 12345)]
+    [InlineData("FOCAS://10.0.0.5:8193", "10.0.0.5", 8193)]                    // case-insensitive scheme
+    public void HostAddress_parses_valid(string input, string host, int port)
+    {
+        var parsed = FocasHostAddress.TryParse(input);
+        parsed.ShouldNotBeNull();
+        parsed.Host.ShouldBe(host);
+        parsed.Port.ShouldBe(port);
+    }
+
+    [Theory]
+    [InlineData(null)]
+    [InlineData("")]
+    [InlineData("http://10.0.0.5/")]
+    [InlineData("focas:10.0.0.5:8193")]          // missing //
+    [InlineData("focas://")]                     // empty body
+    [InlineData("focas://10.0.0.5:0")]           // port 0
+    [InlineData("focas://10.0.0.5:65536")]       // port out of range
+    [InlineData("focas://10.0.0.5:abc")]         // non-numeric port
+    public void HostAddress_rejects_invalid(string? input)
+    {
+        FocasHostAddress.TryParse(input).ShouldBeNull();
+    }
+
+    [Fact]
+    public void HostAddress_ToString_strips_default_port()
+    {
+        new FocasHostAddress("10.0.0.5", 8193).ToString().ShouldBe("focas://10.0.0.5");
+        new FocasHostAddress("10.0.0.5", 12345).ToString().ShouldBe("focas://10.0.0.5:12345");
+    }
+
+    // ---- FocasAddress ----
+
+    [Theory]
+    [InlineData("X0.0", FocasAreaKind.Pmc, "X", 0, 0)]
+    [InlineData("X0", FocasAreaKind.Pmc, "X", 0, null)]
+    [InlineData("Y10", FocasAreaKind.Pmc, "Y", 10, null)]
+    [InlineData("F20.3", FocasAreaKind.Pmc, "F", 20, 3)]
+    [InlineData("G54", FocasAreaKind.Pmc, "G", 54, null)]
+    [InlineData("R100", FocasAreaKind.Pmc, "R", 100, null)]
+    [InlineData("D200", FocasAreaKind.Pmc, "D", 200, null)]
+    [InlineData("C300", FocasAreaKind.Pmc, "C", 300, null)]
+    [InlineData("K400", FocasAreaKind.Pmc, "K", 400, null)]
+    [InlineData("A500", FocasAreaKind.Pmc, "A", 500, null)]
+    [InlineData("E600", FocasAreaKind.Pmc, "E", 600, null)]
+    [InlineData("T50.4", FocasAreaKind.Pmc, "T", 50, 4)]
+    public void Address_parses_PMC_forms(string input, FocasAreaKind kind, string letter, int num, int? bit)
+    {
+        var a = FocasAddress.TryParse(input);
+        a.ShouldNotBeNull();
+        a.Kind.ShouldBe(kind);
+        a.PmcLetter.ShouldBe(letter);
+        a.Number.ShouldBe(num);
+        a.BitIndex.ShouldBe(bit);
+    }
+
+    [Theory]
+    [InlineData("PARAM:1020", FocasAreaKind.Parameter, 1020, null)]
+    [InlineData("PARAM:1815/0", FocasAreaKind.Parameter, 1815, 0)]
+    [InlineData("PARAM:1815/31", FocasAreaKind.Parameter, 1815, 31)]
+    public void Address_parses_parameter_forms(string input, FocasAreaKind kind, int num, int? bit)
+    {
+        var a = FocasAddress.TryParse(input);
+        a.ShouldNotBeNull();
+        a.Kind.ShouldBe(kind);
+        a.PmcLetter.ShouldBeNull();
+        a.Number.ShouldBe(num);
+        a.BitIndex.ShouldBe(bit);
+    }
+
+    [Theory]
+    [InlineData("MACRO:100", FocasAreaKind.Macro, 100)]
+    [InlineData("MACRO:500", FocasAreaKind.Macro, 500)]
+    public void Address_parses_macro_forms(string input, FocasAreaKind kind, int num)
+    {
+        var a = FocasAddress.TryParse(input);
+        a.ShouldNotBeNull();
+        a.Kind.ShouldBe(kind);
+        a.Number.ShouldBe(num);
+        a.BitIndex.ShouldBeNull();
+    }
+
+    [Theory]
+    [InlineData(null)]
+    [InlineData("")]
+    [InlineData("   ")]
+    [InlineData("Z0")]                   // unknown PMC letter
+    [InlineData("X")]                    // missing number
+    [InlineData("X-1")]                  // negative number
+    [InlineData("Xabc")]                 // non-numeric
+    [InlineData("X0.8")]                 // bit out of range (0-7)
+    [InlineData("X0.-1")]                // negative bit
+    [InlineData("PARAM:")]               // missing number
+    [InlineData("PARAM:1815/32")]        // bit out of range (0-31)
+    [InlineData("MACRO:abc")]            // non-numeric
+    public void Address_rejects_invalid_forms(string? input)
+    {
+        FocasAddress.TryParse(input).ShouldBeNull();
+    }
+
+    [Theory]
+    [InlineData("X0.0")]
+    [InlineData("R100")]
+    [InlineData("F20.3")]
+    [InlineData("PARAM:1020")]
+    [InlineData("PARAM:1815/0")]
+    [InlineData("MACRO:100")]
+    public void Address_Canonical_roundtrips(string input)
+    {
+        var parsed = FocasAddress.TryParse(input);
+        parsed.ShouldNotBeNull();
+        parsed.Canonical.ShouldBe(input);
+    }
+
+    // ---- FocasDataType ----
+
+    [Fact]
+    public void DataType_mapping_covers_atomic_focas_types()
+    {
+        FocasDataType.Bit.ToDriverDataType().ShouldBe(DriverDataType.Boolean);
+        FocasDataType.Int16.ToDriverDataType().ShouldBe(DriverDataType.Int32);
+        FocasDataType.Int32.ToDriverDataType().ShouldBe(DriverDataType.Int32);
+        FocasDataType.Float32.ToDriverDataType().ShouldBe(DriverDataType.Float32);
+        FocasDataType.Float64.ToDriverDataType().ShouldBe(DriverDataType.Float64);
+        FocasDataType.String.ToDriverDataType().ShouldBe(DriverDataType.String);
+    }
+
+    // ---- FocasStatusMapper ----
+
+    [Theory]
+    [InlineData(0, FocasStatusMapper.Good)]
+    [InlineData(3, FocasStatusMapper.BadOutOfRange)]         // EW_NUMBER
+    [InlineData(4, FocasStatusMapper.BadOutOfRange)]         // EW_LENGTH
+    [InlineData(5, FocasStatusMapper.BadNotWritable)]        // EW_PROT
+    [InlineData(6, FocasStatusMapper.BadNotSupported)]       // EW_NOOPT
+    [InlineData(8, FocasStatusMapper.BadNodeIdUnknown)]      // EW_DATA
+    [InlineData(-1, FocasStatusMapper.BadDeviceFailure)]     // EW_BUSY
+    [InlineData(-8, FocasStatusMapper.BadInternalError)]     // EW_HANDLE
+    [InlineData(-16, FocasStatusMapper.BadCommunicationError)] // EW_SOCKET
+    [InlineData(999, FocasStatusMapper.BadCommunicationError)] // unknown → generic
+    public void StatusMapper_covers_known_focas_returns(int ret, uint expected)
+    {
+        FocasStatusMapper.MapFocasReturn(ret).ShouldBe(expected);
+    }
+
+    // ---- FocasDriver ----
+
+    [Fact]
+    public void DriverType_is_FOCAS()
+    {
+        var drv = new FocasDriver(new FocasDriverOptions(), "drv-1");
+        drv.DriverType.ShouldBe("FOCAS");
+        drv.DriverInstanceId.ShouldBe("drv-1");
+    }
+
+    [Fact]
+    public async Task InitializeAsync_parses_device_addresses()
+    {
+        var drv = new FocasDriver(new FocasDriverOptions
+        {
+            Devices =
+            [
+                new FocasDeviceOptions("focas://10.0.0.5:8193"),
+                new FocasDeviceOptions("focas://10.0.0.6:12345", DeviceName: "CNC-2"),
+            ],
+        }, "drv-1");
+
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        drv.DeviceCount.ShouldBe(2);
+        drv.GetDeviceState("focas://10.0.0.5:8193")!.ParsedAddress.Port.ShouldBe(8193);
+        drv.GetDeviceState("focas://10.0.0.6:12345")!.Options.DeviceName.ShouldBe("CNC-2");
+    }
+
+    [Fact]
+    public async Task InitializeAsync_malformed_address_faults()
+    {
+        var drv = new FocasDriver(new FocasDriverOptions
+        {
+            Devices = [new FocasDeviceOptions("not-an-address")],
+        }, "drv-1");
+
+        await Should.ThrowAsync<InvalidOperationException>(
+            () => drv.InitializeAsync("{}", CancellationToken.None));
+        drv.GetHealth().State.ShouldBe(DriverState.Faulted);
+    }
+
+    [Fact]
+    public async Task ShutdownAsync_clears_devices()
+    {
+        var drv = new FocasDriver(new FocasDriverOptions
+        {
+            Devices = [new FocasDeviceOptions("focas://10.0.0.5:8193")],
+            Probe = new FocasProbeOptions { Enabled = false },
+        }, "drv-1");
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        await drv.ShutdownAsync(CancellationToken.None);
+        drv.DeviceCount.ShouldBe(0);
+        drv.GetHealth().State.ShouldBe(DriverState.Unknown);
+    }
+
+    // ---- UnimplementedFocasClientFactory ----
+
+    [Fact]
+    public void Default_factory_throws_on_Create_with_deployment_pointer()
+    {
+        var factory = new UnimplementedFocasClientFactory();
+        var ex = Should.Throw<NotSupportedException>(() => factory.Create());
+        ex.Message.ShouldContain("Fwlib32.dll");
+        ex.Message.ShouldContain("licensed");
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FwlibNativeHelperTests.cs

@@ -0,0 +1,100 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests;
+
+/// <summary>
+///     Tests for the managed helpers inside FwlibNative + FwlibFocasClient that don't require the
+///     licensed Fwlib32.dll — letter→ADR_* mapping, FocasDataType→data-type mapping, byte encoding.
+///     The actual P/Invoke calls can only run where the DLL is present; field testing covers those.
+/// </summary>
+[Trait("Category", "Unit")]
+public sealed class FwlibNativeHelperTests
+{
+    [Theory]
+    [InlineData("G", 0)]
+    [InlineData("F", 1)]
+    [InlineData("Y", 2)]
+    [InlineData("X", 3)]
+    [InlineData("A", 4)]
+    [InlineData("R", 5)]
+    [InlineData("T", 6)]
+    [InlineData("K", 7)]
+    [InlineData("C", 8)]
+    [InlineData("D", 9)]
+    [InlineData("E", 10)]
+    [InlineData("g", 0)] // case-insensitive
+    public void PmcAddrType_maps_every_valid_letter(string letter, short expected)
+    {
+        FocasPmcAddrType.FromLetter(letter).ShouldBe(expected);
+    }
+
+    [Theory]
+    [InlineData("Z")]
+    [InlineData("")]
+    [InlineData("XX")]
+    public void PmcAddrType_rejects_unknown_letters(string letter)
+    {
+        FocasPmcAddrType.FromLetter(letter).ShouldBeNull();
+    }
+
+    [Theory]
+    [InlineData(FocasDataType.Bit, 0)]   // byte
+    [InlineData(FocasDataType.Byte, 0)]
+    [InlineData(FocasDataType.Int16, 1)]  // word
+    [InlineData(FocasDataType.Int32, 2)]  // long
+    [InlineData(FocasDataType.Float32, 4)]
+    [InlineData(FocasDataType.Float64, 5)]
+    public void PmcDataType_maps_FocasDataType_to_FOCAS_code(FocasDataType input, short expected)
+    {
+        FocasPmcDataType.FromFocasDataType(input).ShouldBe(expected);
+    }
+
+    [Fact]
+    public void EncodePmcValue_Byte_writes_signed_byte_at_offset_0()
+    {
+        var buf = new byte[40];
+        FwlibFocasClient.EncodePmcValue(buf, FocasDataType.Byte, (sbyte)-5, bitIndex: null);
+        ((sbyte)buf[0]).ShouldBe((sbyte)-5);
+    }
+
+    [Fact]
+    public void EncodePmcValue_Int16_writes_little_endian()
+    {
+        var buf = new byte[40];
+        FwlibFocasClient.EncodePmcValue(buf, FocasDataType.Int16, (short)0x1234, bitIndex: null);
+        buf[0].ShouldBe((byte)0x34);
+        buf[1].ShouldBe((byte)0x12);
+    }
+
+    [Fact]
+    public void EncodePmcValue_Int32_writes_little_endian()
+    {
+        var buf = new byte[40];
+        FwlibFocasClient.EncodePmcValue(buf, FocasDataType.Int32, 0x12345678, bitIndex: null);
+        buf[0].ShouldBe((byte)0x78);
+        buf[1].ShouldBe((byte)0x56);
+        buf[2].ShouldBe((byte)0x34);
+        buf[3].ShouldBe((byte)0x12);
+    }
+
+    [Fact]
+    public void EncodePmcValue_Bit_throws_NotSupported_for_RMW_gap()
+    {
+        var buf = new byte[40];
+        Should.Throw<NotSupportedException>(() =>
+            FwlibFocasClient.EncodePmcValue(buf, FocasDataType.Bit, true, bitIndex: 3));
+    }
+
+    [Fact]
+    public void EncodeParamValue_Int32_writes_little_endian()
+    {
+        var buf = new byte[32];
+        FwlibFocasClient.EncodeParamValue(buf, FocasDataType.Int32, 0x0A0B0C0D);
+        buf[0].ShouldBe((byte)0x0D);
+        buf[1].ShouldBe((byte)0x0C);
+        buf[2].ShouldBe((byte)0x0B);
+        buf[3].ShouldBe((byte)0x0A);
+    }
+}

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

@@ -0,0 +1,31 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <TargetFramework>net10.0</TargetFramework>
+        <Nullable>enable</Nullable>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <IsPackable>false</IsPackable>
+        <IsTestProject>true</IsTestProject>
+        <RootNamespace>ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests</RootNamespace>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <PackageReference Include="xunit.v3" Version="1.1.0"/>
+        <PackageReference Include="Shouldly" Version="4.3.0"/>
+        <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0"/>
+        <PackageReference Include="xunit.runner.visualstudio" Version="3.0.2">
+            <PrivateAssets>all</PrivateAssets>
+            <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+        </PackageReference>
+    </ItemGroup>
+
+    <ItemGroup>
+        <ProjectReference Include="..\..\src\ZB.MOM.WW.OtOpcUa.Driver.FOCAS\ZB.MOM.WW.OtOpcUa.Driver.FOCAS.csproj"/>
+    </ItemGroup>
+
+    <ItemGroup>
+        <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-37gx-xxp4-5rgx"/>
+        <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-w3x6-4m5h-cxqf"/>
+    </ItemGroup>
+
+</Project>

tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests/FakeTwinCATClient.cs

@@ -0,0 +1,114 @@
+using ZB.MOM.WW.OtOpcUa.Driver.TwinCAT;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests;
+
+internal class FakeTwinCATClient : ITwinCATClient
+{
+    public bool IsConnected { get; private set; }
+    public int ConnectCount { get; private set; }
+    public int DisposeCount { get; private set; }
+    public bool ThrowOnConnect { get; set; }
+    public bool ThrowOnRead { get; set; }
+    public bool ThrowOnWrite { get; set; }
+    public bool ThrowOnProbe { get; set; }
+    public Exception? Exception { get; set; }
+    public Dictionary<string, object?> Values { get; } = new(StringComparer.OrdinalIgnoreCase);
+    public Dictionary<string, uint> ReadStatuses { get; } = new(StringComparer.OrdinalIgnoreCase);
+    public Dictionary<string, uint> WriteStatuses { get; } = new(StringComparer.OrdinalIgnoreCase);
+    public List<(string symbol, TwinCATDataType type, int? bit, object? value)> WriteLog { get; } = new();
+    public bool ProbeResult { get; set; } = true;
+
+    public virtual Task ConnectAsync(TwinCATAmsAddress address, TimeSpan timeout, CancellationToken ct)
+    {
+        ConnectCount++;
+        if (ThrowOnConnect) throw Exception ?? new InvalidOperationException();
+        IsConnected = true;
+        return Task.CompletedTask;
+    }
+
+    public virtual Task<(object? value, uint status)> ReadValueAsync(
+        string symbolPath, TwinCATDataType type, int? bitIndex, CancellationToken ct)
+    {
+        if (ThrowOnRead) throw Exception ?? new InvalidOperationException();
+        var status = ReadStatuses.TryGetValue(symbolPath, out var s) ? s : TwinCATStatusMapper.Good;
+        var value = Values.TryGetValue(symbolPath, out var v) ? v : null;
+        return Task.FromResult((value, status));
+    }
+
+    public virtual Task<uint> WriteValueAsync(
+        string symbolPath, TwinCATDataType type, int? bitIndex, object? value, CancellationToken ct)
+    {
+        if (ThrowOnWrite) throw Exception ?? new InvalidOperationException();
+        WriteLog.Add((symbolPath, type, bitIndex, value));
+        Values[symbolPath] = value;
+        var status = WriteStatuses.TryGetValue(symbolPath, out var s) ? s : TwinCATStatusMapper.Good;
+        return Task.FromResult(status);
+    }
+
+    public virtual Task<bool> ProbeAsync(CancellationToken ct)
+    {
+        if (ThrowOnProbe) return Task.FromResult(false);
+        return Task.FromResult(ProbeResult);
+    }
+
+    public virtual void Dispose()
+    {
+        DisposeCount++;
+        IsConnected = false;
+    }
+
+    // ---- notification fake ----
+
+    public List<FakeNotification> Notifications { get; } = new();
+    public bool ThrowOnAddNotification { get; set; }
+
+    public virtual Task<ITwinCATNotificationHandle> AddNotificationAsync(
+        string symbolPath, TwinCATDataType type, int? bitIndex, TimeSpan cycleTime,
+        Action<string, object?> onChange, CancellationToken cancellationToken)
+    {
+        if (ThrowOnAddNotification)
+            throw Exception ?? new InvalidOperationException("fake AddNotification failure");
+
+        var reg = new FakeNotification(symbolPath, type, bitIndex, onChange, this);
+        Notifications.Add(reg);
+        return Task.FromResult<ITwinCATNotificationHandle>(reg);
+    }
+
+    /// <summary>Fire a change event through the registered callback for <paramref name="symbolPath"/>.</summary>
+    public void FireNotification(string symbolPath, object? value)
+    {
+        foreach (var n in Notifications)
+            if (!n.Disposed && string.Equals(n.SymbolPath, symbolPath, StringComparison.OrdinalIgnoreCase))
+                n.OnChange(symbolPath, value);
+    }
+
+    public sealed class FakeNotification(
+        string symbolPath, TwinCATDataType type, int? bitIndex,
+        Action<string, object?> onChange, FakeTwinCATClient owner) : ITwinCATNotificationHandle
+    {
+        public string SymbolPath { get; } = symbolPath;
+        public TwinCATDataType Type { get; } = type;
+        public int? BitIndex { get; } = bitIndex;
+        public Action<string, object?> OnChange { get; } = onChange;
+        public bool Disposed { get; private set; }
+
+        public void Dispose()
+        {
+            Disposed = true;
+            owner.Notifications.Remove(this);
+        }
+    }
+}
+
+internal sealed class FakeTwinCATClientFactory : ITwinCATClientFactory
+{
+    public List<FakeTwinCATClient> Clients { get; } = new();
+    public Func<FakeTwinCATClient>? Customise { get; set; }
+
+    public ITwinCATClient Create()
+    {
+        var client = Customise?.Invoke() ?? new FakeTwinCATClient();
+        Clients.Add(client);
+        return client;
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests/TwinCATAmsAddressTests.cs

@@ -0,0 +1,59 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Driver.TwinCAT;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests;
+
+[Trait("Category", "Unit")]
+public sealed class TwinCATAmsAddressTests
+{
+    [Theory]
+    [InlineData("ads://5.23.91.23.1.1:851", "5.23.91.23.1.1", 851)]
+    [InlineData("ads://5.23.91.23.1.1:852", "5.23.91.23.1.1", 852)]
+    [InlineData("ads://5.23.91.23.1.1", "5.23.91.23.1.1", 851)]                  // default port
+    [InlineData("ads://127.0.0.1.1.1:851", "127.0.0.1.1.1", 851)]
+    [InlineData("ADS://5.23.91.23.1.1:851", "5.23.91.23.1.1", 851)]              // case-insensitive scheme
+    [InlineData("ads://10.0.0.1.1.1:10000", "10.0.0.1.1.1", 10000)]              // system service port
+    public void TryParse_accepts_valid_ams_addresses(string input, string netId, int port)
+    {
+        var parsed = TwinCATAmsAddress.TryParse(input);
+        parsed.ShouldNotBeNull();
+        parsed.NetId.ShouldBe(netId);
+        parsed.Port.ShouldBe(port);
+    }
+
+    [Theory]
+    [InlineData(null)]
+    [InlineData("")]
+    [InlineData("   ")]
+    [InlineData("tcp://5.23.91.23.1.1:851")]        // wrong scheme
+    [InlineData("ads:5.23.91.23.1.1:851")]          // missing //
+    [InlineData("ads://")]                           // empty body
+    [InlineData("ads://5.23.91.23.1:851")]           // only 5 octets
+    [InlineData("ads://5.23.91.23.1.1.1:851")]       // 7 octets
+    [InlineData("ads://5.23.91.256.1.1:851")]        // octet > 255
+    [InlineData("ads://5.23.91.23.1.1:0")]           // port 0
+    [InlineData("ads://5.23.91.23.1.1:65536")]       // port out of range
+    [InlineData("ads://5.23.91.23.1.1:abc")]         // non-numeric port
+    [InlineData("ads://a.b.c.d.e.f:851")]            // non-numeric octets
+    public void TryParse_rejects_invalid_forms(string? input)
+    {
+        TwinCATAmsAddress.TryParse(input).ShouldBeNull();
+    }
+
+    [Theory]
+    [InlineData("5.23.91.23.1.1", 851, "ads://5.23.91.23.1.1")]        // default port stripped
+    [InlineData("5.23.91.23.1.1", 852, "ads://5.23.91.23.1.1:852")]
+    public void ToString_canonicalises(string netId, int port, string expected)
+    {
+        new TwinCATAmsAddress(netId, port).ToString().ShouldBe(expected);
+    }
+
+    [Fact]
+    public void RoundTrip_is_stable()
+    {
+        const string input = "ads://5.23.91.23.1.1:852";
+        var parsed = TwinCATAmsAddress.TryParse(input)!;
+        TwinCATAmsAddress.TryParse(parsed.ToString()).ShouldBe(parsed);
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests/TwinCATCapabilityTests.cs

@@ -0,0 +1,257 @@
+using System.Collections.Concurrent;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Driver.TwinCAT;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests;
+
+[Trait("Category", "Unit")]
+public sealed class TwinCATCapabilityTests
+{
+    // ---- ITagDiscovery ----
+
+    [Fact]
+    public async Task DiscoverAsync_emits_pre_declared_tags()
+    {
+        var builder = new RecordingBuilder();
+        var drv = new TwinCATDriver(new TwinCATDriverOptions
+        {
+            Devices = [new TwinCATDeviceOptions("ads://5.23.91.23.1.1:851", DeviceName: "Mach1")],
+            Tags =
+            [
+                new TwinCATTagDefinition("Speed", "ads://5.23.91.23.1.1:851", "MAIN.Speed", TwinCATDataType.DInt),
+                new TwinCATTagDefinition("Status", "ads://5.23.91.23.1.1:851", "GVL.Status", TwinCATDataType.Bool, Writable: false),
+            ],
+            Probe = new TwinCATProbeOptions { Enabled = false },
+        }, "drv-1");
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        await drv.DiscoverAsync(builder, CancellationToken.None);
+
+        builder.Folders.ShouldContain(f => f.BrowseName == "TwinCAT");
+        builder.Folders.ShouldContain(f => f.BrowseName == "ads://5.23.91.23.1.1:851" && f.DisplayName == "Mach1");
+        builder.Variables.Single(v => v.BrowseName == "Speed").Info.SecurityClass.ShouldBe(SecurityClassification.Operate);
+        builder.Variables.Single(v => v.BrowseName == "Status").Info.SecurityClass.ShouldBe(SecurityClassification.ViewOnly);
+    }
+
+    // ---- ISubscribable ----
+
+    [Fact]
+    public async Task Subscribe_initial_poll_raises_OnDataChange()
+    {
+        var factory = new FakeTwinCATClientFactory
+        {
+            Customise = () => new FakeTwinCATClient { Values = { ["MAIN.X"] = 42 } },
+        };
+        var drv = new TwinCATDriver(new TwinCATDriverOptions
+        {
+            Devices = [new TwinCATDeviceOptions("ads://5.23.91.23.1.1:851")],
+            Tags = [new TwinCATTagDefinition("X", "ads://5.23.91.23.1.1:851", "MAIN.X", TwinCATDataType.DInt)],
+            Probe = new TwinCATProbeOptions { Enabled = false },
+            UseNativeNotifications = false, // poll-mode test
+        }, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var events = new ConcurrentQueue<DataChangeEventArgs>();
+        drv.OnDataChange += (_, e) => events.Enqueue(e);
+
+        var handle = await drv.SubscribeAsync(["X"], TimeSpan.FromMilliseconds(200), CancellationToken.None);
+        await WaitForAsync(() => events.Count >= 1, TimeSpan.FromSeconds(2));
+
+        events.First().Snapshot.Value.ShouldBe(42);
+        await drv.UnsubscribeAsync(handle, CancellationToken.None);
+    }
+
+    [Fact]
+    public async Task ShutdownAsync_cancels_active_subscriptions()
+    {
+        var factory = new FakeTwinCATClientFactory
+        {
+            Customise = () => new FakeTwinCATClient { Values = { ["MAIN.X"] = 1 } },
+        };
+        var drv = new TwinCATDriver(new TwinCATDriverOptions
+        {
+            Devices = [new TwinCATDeviceOptions("ads://5.23.91.23.1.1:851")],
+            Tags = [new TwinCATTagDefinition("X", "ads://5.23.91.23.1.1:851", "MAIN.X", TwinCATDataType.DInt)],
+            Probe = new TwinCATProbeOptions { Enabled = false },
+            UseNativeNotifications = false, // poll-mode test
+        }, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var events = new ConcurrentQueue<DataChangeEventArgs>();
+        drv.OnDataChange += (_, e) => events.Enqueue(e);
+
+        _ = await drv.SubscribeAsync(["X"], TimeSpan.FromMilliseconds(100), CancellationToken.None);
+        await WaitForAsync(() => events.Count >= 1, TimeSpan.FromSeconds(1));
+        await drv.ShutdownAsync(CancellationToken.None);
+
+        var afterShutdown = events.Count;
+        await Task.Delay(200);
+        events.Count.ShouldBe(afterShutdown);
+    }
+
+    // ---- IHostConnectivityProbe ----
+
+    [Fact]
+    public async Task GetHostStatuses_returns_entry_per_device()
+    {
+        var drv = new TwinCATDriver(new TwinCATDriverOptions
+        {
+            Devices =
+            [
+                new TwinCATDeviceOptions("ads://5.23.91.23.1.1:851"),
+                new TwinCATDeviceOptions("ads://5.23.91.24.1.1:851"),
+            ],
+            Probe = new TwinCATProbeOptions { Enabled = false },
+        }, "drv-1");
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        drv.GetHostStatuses().Count.ShouldBe(2);
+    }
+
+    [Fact]
+    public async Task Probe_transitions_to_Running_on_successful_probe()
+    {
+        var factory = new FakeTwinCATClientFactory
+        {
+            Customise = () => new FakeTwinCATClient { ProbeResult = true },
+        };
+        var transitions = new ConcurrentQueue<HostStatusChangedEventArgs>();
+        var drv = new TwinCATDriver(new TwinCATDriverOptions
+        {
+            Devices = [new TwinCATDeviceOptions("ads://5.23.91.23.1.1:851")],
+            Probe = new TwinCATProbeOptions
+            {
+                Enabled = true, Interval = TimeSpan.FromMilliseconds(100),
+                Timeout = TimeSpan.FromMilliseconds(50),
+            },
+        }, "drv-1", factory);
+        drv.OnHostStatusChanged += (_, e) => transitions.Enqueue(e);
+
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        await WaitForAsync(() => transitions.Any(t => t.NewState == HostState.Running), TimeSpan.FromSeconds(2));
+
+        drv.GetHostStatuses().Single().State.ShouldBe(HostState.Running);
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+
+    [Fact]
+    public async Task Probe_transitions_to_Stopped_on_probe_failure()
+    {
+        var factory = new FakeTwinCATClientFactory
+        {
+            Customise = () => new FakeTwinCATClient { ProbeResult = false },
+        };
+        var transitions = new ConcurrentQueue<HostStatusChangedEventArgs>();
+        var drv = new TwinCATDriver(new TwinCATDriverOptions
+        {
+            Devices = [new TwinCATDeviceOptions("ads://5.23.91.23.1.1:851")],
+            Probe = new TwinCATProbeOptions
+            {
+                Enabled = true, Interval = TimeSpan.FromMilliseconds(100),
+                Timeout = TimeSpan.FromMilliseconds(50),
+            },
+        }, "drv-1", factory);
+        drv.OnHostStatusChanged += (_, e) => transitions.Enqueue(e);
+
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        await WaitForAsync(() => transitions.Any(t => t.NewState == HostState.Stopped), TimeSpan.FromSeconds(2));
+
+        drv.GetHostStatuses().Single().State.ShouldBe(HostState.Stopped);
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+
+    [Fact]
+    public async Task Probe_disabled_when_Enabled_is_false()
+    {
+        var factory = new FakeTwinCATClientFactory();
+        var drv = new TwinCATDriver(new TwinCATDriverOptions
+        {
+            Devices = [new TwinCATDeviceOptions("ads://5.23.91.23.1.1:851")],
+            Probe = new TwinCATProbeOptions { Enabled = false },
+        }, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        await Task.Delay(200);
+
+        drv.GetHostStatuses().Single().State.ShouldBe(HostState.Unknown);
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+
+    // ---- IPerCallHostResolver ----
+
+    [Fact]
+    public async Task ResolveHost_returns_declared_device_for_known_tag()
+    {
+        var drv = new TwinCATDriver(new TwinCATDriverOptions
+        {
+            Devices =
+            [
+                new TwinCATDeviceOptions("ads://5.23.91.23.1.1:851"),
+                new TwinCATDeviceOptions("ads://5.23.91.24.1.1:851"),
+            ],
+            Tags =
+            [
+                new TwinCATTagDefinition("A", "ads://5.23.91.23.1.1:851", "MAIN.A", TwinCATDataType.DInt),
+                new TwinCATTagDefinition("B", "ads://5.23.91.24.1.1:851", "MAIN.B", TwinCATDataType.DInt),
+            ],
+            Probe = new TwinCATProbeOptions { Enabled = false },
+        }, "drv-1");
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        drv.ResolveHost("A").ShouldBe("ads://5.23.91.23.1.1:851");
+        drv.ResolveHost("B").ShouldBe("ads://5.23.91.24.1.1:851");
+    }
+
+    [Fact]
+    public async Task ResolveHost_falls_back_to_first_device_for_unknown_ref()
+    {
+        var drv = new TwinCATDriver(new TwinCATDriverOptions
+        {
+            Devices = [new TwinCATDeviceOptions("ads://5.23.91.23.1.1:851")],
+            Probe = new TwinCATProbeOptions { Enabled = false },
+        }, "drv-1");
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        drv.ResolveHost("missing").ShouldBe("ads://5.23.91.23.1.1:851");
+    }
+
+    [Fact]
+    public async Task ResolveHost_falls_back_to_DriverInstanceId_when_no_devices()
+    {
+        var drv = new TwinCATDriver(new TwinCATDriverOptions(), "drv-1");
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        drv.ResolveHost("anything").ShouldBe("drv-1");
+    }
+
+    // ---- helpers ----
+
+    private static async Task WaitForAsync(Func<bool> condition, TimeSpan timeout)
+    {
+        var deadline = DateTime.UtcNow + timeout;
+        while (!condition() && DateTime.UtcNow < deadline)
+            await Task.Delay(20);
+    }
+
+    private sealed class RecordingBuilder : IAddressSpaceBuilder
+    {
+        public List<(string BrowseName, string DisplayName)> Folders { get; } = new();
+        public List<(string BrowseName, DriverAttributeInfo Info)> Variables { get; } = new();
+
+        public IAddressSpaceBuilder Folder(string browseName, string displayName)
+        { Folders.Add((browseName, displayName)); return this; }
+
+        public IVariableHandle Variable(string browseName, string displayName, DriverAttributeInfo info)
+        { Variables.Add((browseName, info)); return new Handle(info.FullName); }
+
+        public void AddProperty(string _, DriverDataType __, object? ___) { }
+
+        private sealed class Handle(string fullRef) : IVariableHandle
+        {
+            public string FullReference => fullRef;
+            public IAlarmConditionSink MarkAsAlarmCondition(AlarmConditionInfo info) => new NullSink();
+        }
+        private sealed class NullSink : IAlarmConditionSink { public void OnTransition(AlarmEventArgs args) { } }
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests/TwinCATDriverTests.cs

@@ -0,0 +1,107 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Driver.TwinCAT;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests;
+
+[Trait("Category", "Unit")]
+public sealed class TwinCATDriverTests
+{
+    [Fact]
+    public void DriverType_is_TwinCAT()
+    {
+        var drv = new TwinCATDriver(new TwinCATDriverOptions(), "drv-1");
+        drv.DriverType.ShouldBe("TwinCAT");
+        drv.DriverInstanceId.ShouldBe("drv-1");
+    }
+
+    [Fact]
+    public async Task InitializeAsync_parses_device_addresses()
+    {
+        var drv = new TwinCATDriver(new TwinCATDriverOptions
+        {
+            Devices =
+            [
+                new TwinCATDeviceOptions("ads://5.23.91.23.1.1:851"),
+                new TwinCATDeviceOptions("ads://10.0.0.1.1.1:852", DeviceName: "Machine2"),
+            ],
+        }, "drv-1");
+
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        drv.DeviceCount.ShouldBe(2);
+        drv.GetDeviceState("ads://5.23.91.23.1.1:851")!.ParsedAddress.Port.ShouldBe(851);
+        drv.GetDeviceState("ads://10.0.0.1.1.1:852")!.Options.DeviceName.ShouldBe("Machine2");
+    }
+
+    [Fact]
+    public async Task InitializeAsync_malformed_address_faults()
+    {
+        var drv = new TwinCATDriver(new TwinCATDriverOptions
+        {
+            Devices = [new TwinCATDeviceOptions("not-an-address")],
+        }, "drv-1");
+
+        await Should.ThrowAsync<InvalidOperationException>(
+            () => drv.InitializeAsync("{}", CancellationToken.None));
+        drv.GetHealth().State.ShouldBe(DriverState.Faulted);
+    }
+
+    [Fact]
+    public async Task ShutdownAsync_clears_devices()
+    {
+        var drv = new TwinCATDriver(new TwinCATDriverOptions
+        {
+            Devices = [new TwinCATDeviceOptions("ads://5.23.91.23.1.1:851")],
+            Probe = new TwinCATProbeOptions { Enabled = false },
+        }, "drv-1");
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        await drv.ShutdownAsync(CancellationToken.None);
+        drv.DeviceCount.ShouldBe(0);
+        drv.GetHealth().State.ShouldBe(DriverState.Unknown);
+    }
+
+    [Fact]
+    public async Task ReinitializeAsync_cycles_devices()
+    {
+        var drv = new TwinCATDriver(new TwinCATDriverOptions
+        {
+            Devices = [new TwinCATDeviceOptions("ads://5.23.91.23.1.1:851")],
+            Probe = new TwinCATProbeOptions { Enabled = false },
+        }, "drv-1");
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        await drv.ReinitializeAsync("{}", CancellationToken.None);
+
+        drv.DeviceCount.ShouldBe(1);
+        drv.GetHealth().State.ShouldBe(DriverState.Healthy);
+    }
+
+    [Fact]
+    public void DataType_mapping_covers_atomic_iec_types()
+    {
+        TwinCATDataType.Bool.ToDriverDataType().ShouldBe(DriverDataType.Boolean);
+        TwinCATDataType.DInt.ToDriverDataType().ShouldBe(DriverDataType.Int32);
+        TwinCATDataType.Real.ToDriverDataType().ShouldBe(DriverDataType.Float32);
+        TwinCATDataType.LReal.ToDriverDataType().ShouldBe(DriverDataType.Float64);
+        TwinCATDataType.String.ToDriverDataType().ShouldBe(DriverDataType.String);
+        TwinCATDataType.WString.ToDriverDataType().ShouldBe(DriverDataType.String);
+        TwinCATDataType.Time.ToDriverDataType().ShouldBe(DriverDataType.Int32);
+    }
+
+    [Theory]
+    [InlineData(0u, TwinCATStatusMapper.Good)]
+    [InlineData(1798u, TwinCATStatusMapper.BadNodeIdUnknown)]   // symbol not found
+    [InlineData(1808u, TwinCATStatusMapper.BadNotWritable)]     // access denied
+    [InlineData(1861u, TwinCATStatusMapper.BadTimeout)]         // sync timeout
+    [InlineData(1793u, TwinCATStatusMapper.BadOutOfRange)]      // invalid index group
+    [InlineData(1794u, TwinCATStatusMapper.BadOutOfRange)]      // invalid index offset
+    [InlineData(1792u, TwinCATStatusMapper.BadNotSupported)]    // service not supported
+    [InlineData(7u, TwinCATStatusMapper.BadCommunicationError)] // port unreachable
+    [InlineData(99999u, TwinCATStatusMapper.BadCommunicationError)] // unknown → generic comm fail
+    public void StatusMapper_covers_known_ads_error_codes(uint adsError, uint expected)
+    {
+        TwinCATStatusMapper.MapAdsError(adsError).ShouldBe(expected);
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests/TwinCATNativeNotificationTests.cs

@@ -0,0 +1,221 @@
+using System.Collections.Concurrent;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Driver.TwinCAT;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests;
+
+[Trait("Category", "Unit")]
+public sealed class TwinCATNativeNotificationTests
+{
+    private static (TwinCATDriver drv, FakeTwinCATClientFactory factory) NewNativeDriver(params TwinCATTagDefinition[] tags)
+    {
+        var factory = new FakeTwinCATClientFactory();
+        var drv = new TwinCATDriver(new TwinCATDriverOptions
+        {
+            Devices = [new TwinCATDeviceOptions("ads://5.23.91.23.1.1:851")],
+            Tags = tags,
+            Probe = new TwinCATProbeOptions { Enabled = false },
+            UseNativeNotifications = true,
+        }, "drv-1", factory);
+        return (drv, factory);
+    }
+
+    [Fact]
+    public async Task Native_subscribe_registers_one_notification_per_tag()
+    {
+        var (drv, factory) = NewNativeDriver(
+            new TwinCATTagDefinition("A", "ads://5.23.91.23.1.1:851", "MAIN.A", TwinCATDataType.DInt),
+            new TwinCATTagDefinition("B", "ads://5.23.91.23.1.1:851", "MAIN.B", TwinCATDataType.Real));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var handle = await drv.SubscribeAsync(["A", "B"], TimeSpan.FromMilliseconds(100), CancellationToken.None);
+        handle.DiagnosticId.ShouldStartWith("twincat-native-sub-");
+
+        factory.Clients[0].Notifications.Count.ShouldBe(2);
+        factory.Clients[0].Notifications.Select(n => n.SymbolPath).ShouldBe(["MAIN.A", "MAIN.B"], ignoreOrder: true);
+    }
+
+    [Fact]
+    public async Task Native_notification_fires_OnDataChange_with_pushed_value()
+    {
+        var (drv, factory) = NewNativeDriver(
+            new TwinCATTagDefinition("Speed", "ads://5.23.91.23.1.1:851", "MAIN.Speed", TwinCATDataType.DInt));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var events = new ConcurrentQueue<DataChangeEventArgs>();
+        drv.OnDataChange += (_, e) => events.Enqueue(e);
+
+        _ = await drv.SubscribeAsync(["Speed"], TimeSpan.FromMilliseconds(100), CancellationToken.None);
+
+        factory.Clients[0].FireNotification("MAIN.Speed", 4200);
+        factory.Clients[0].FireNotification("MAIN.Speed", 4201);
+
+        events.Count.ShouldBe(2);
+        events.Last().Snapshot.Value.ShouldBe(4201);
+        events.Last().FullReference.ShouldBe("Speed"); // driver-side reference, not ADS symbol
+    }
+
+    [Fact]
+    public async Task Native_unsubscribe_disposes_all_notifications()
+    {
+        var (drv, factory) = NewNativeDriver(
+            new TwinCATTagDefinition("A", "ads://5.23.91.23.1.1:851", "MAIN.A", TwinCATDataType.DInt),
+            new TwinCATTagDefinition("B", "ads://5.23.91.23.1.1:851", "MAIN.B", TwinCATDataType.DInt));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var handle = await drv.SubscribeAsync(["A", "B"], TimeSpan.FromMilliseconds(100), CancellationToken.None);
+        factory.Clients[0].Notifications.Count.ShouldBe(2);
+
+        await drv.UnsubscribeAsync(handle, CancellationToken.None);
+        factory.Clients[0].Notifications.ShouldBeEmpty();
+    }
+
+    [Fact]
+    public async Task Native_unsubscribe_halts_future_notifications()
+    {
+        var (drv, factory) = NewNativeDriver(
+            new TwinCATTagDefinition("X", "ads://5.23.91.23.1.1:851", "MAIN.X", TwinCATDataType.DInt));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var events = new ConcurrentQueue<DataChangeEventArgs>();
+        drv.OnDataChange += (_, e) => events.Enqueue(e);
+
+        var handle = await drv.SubscribeAsync(["X"], TimeSpan.FromMilliseconds(100), CancellationToken.None);
+        factory.Clients[0].FireNotification("MAIN.X", 1);
+        var snapshotFake = factory.Clients[0];
+        await drv.UnsubscribeAsync(handle, CancellationToken.None);
+
+        var afterUnsub = events.Count;
+        // After unsubscribe the fake's Notifications list is empty so FireNotification finds nothing
+        // to invoke. This mirrors the production contract — disposed handles no longer deliver.
+        snapshotFake.FireNotification("MAIN.X", 999);
+        events.Count.ShouldBe(afterUnsub);
+    }
+
+    [Fact]
+    public async Task Native_subscribe_failure_mid_registration_cleans_up_partial_state()
+    {
+        // Fail-on-second-call fake — first AddNotificationAsync succeeds, second throws.
+        // Subscribe's catch block must tear the first one down before rethrowing so no zombie
+        // notification lingers.
+        var fake = new FailAfterNAddsFake(new AbTagParamsIrrelevant(), succeedBefore: 1);
+        var factory = new FakeTwinCATClientFactory { Customise = () => fake };
+        var drv = new TwinCATDriver(new TwinCATDriverOptions
+        {
+            Devices = [new TwinCATDeviceOptions("ads://5.23.91.23.1.1:851")],
+            Tags =
+            [
+                new TwinCATTagDefinition("A", "ads://5.23.91.23.1.1:851", "MAIN.A", TwinCATDataType.DInt),
+                new TwinCATTagDefinition("B", "ads://5.23.91.23.1.1:851", "MAIN.B", TwinCATDataType.DInt),
+            ],
+            Probe = new TwinCATProbeOptions { Enabled = false },
+            UseNativeNotifications = true,
+        }, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        await Should.ThrowAsync<InvalidOperationException>(() =>
+            drv.SubscribeAsync(["A", "B"], TimeSpan.FromMilliseconds(100), CancellationToken.None));
+
+        // First registration succeeded then got torn down by the catch; second threw.
+        fake.AddCallCount.ShouldBe(2);
+        fake.Notifications.Count.ShouldBe(0); // partial handle cleaned up
+    }
+
+    private sealed class AbTagParamsIrrelevant { }
+
+    private sealed class FailAfterNAddsFake : FakeTwinCATClient
+    {
+        private readonly int _succeedBefore;
+        public int AddCallCount { get; private set; }
+
+        public FailAfterNAddsFake(AbTagParamsIrrelevant _, int succeedBefore) : base()
+        {
+            _succeedBefore = succeedBefore;
+        }
+
+        public override Task<ITwinCATNotificationHandle> AddNotificationAsync(
+            string symbolPath, TwinCATDataType type, int? bitIndex, TimeSpan cycleTime,
+            Action<string, object?> onChange, CancellationToken cancellationToken)
+        {
+            AddCallCount++;
+            if (AddCallCount > _succeedBefore)
+                throw new InvalidOperationException($"fake fail on call #{AddCallCount}");
+            return base.AddNotificationAsync(symbolPath, type, bitIndex, cycleTime, onChange, cancellationToken);
+        }
+    }
+
+    [Fact]
+    public async Task Native_shutdown_disposes_subscriptions()
+    {
+        var (drv, factory) = NewNativeDriver(
+            new TwinCATTagDefinition("X", "ads://5.23.91.23.1.1:851", "MAIN.X", TwinCATDataType.DInt));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        _ = await drv.SubscribeAsync(["X"], TimeSpan.FromMilliseconds(100), CancellationToken.None);
+        factory.Clients[0].Notifications.Count.ShouldBe(1);
+
+        await drv.ShutdownAsync(CancellationToken.None);
+        factory.Clients[0].Notifications.ShouldBeEmpty();
+    }
+
+    [Fact]
+    public async Task Poll_path_still_works_when_UseNativeNotifications_false()
+    {
+        var factory = new FakeTwinCATClientFactory
+        {
+            Customise = () => new FakeTwinCATClient { Values = { ["MAIN.X"] = 7 } },
+        };
+        var drv = new TwinCATDriver(new TwinCATDriverOptions
+        {
+            Devices = [new TwinCATDeviceOptions("ads://5.23.91.23.1.1:851")],
+            Tags = [new TwinCATTagDefinition("X", "ads://5.23.91.23.1.1:851", "MAIN.X", TwinCATDataType.DInt)],
+            Probe = new TwinCATProbeOptions { Enabled = false },
+            UseNativeNotifications = false,
+        }, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var events = new ConcurrentQueue<DataChangeEventArgs>();
+        drv.OnDataChange += (_, e) => events.Enqueue(e);
+
+        var handle = await drv.SubscribeAsync(["X"], TimeSpan.FromMilliseconds(150), CancellationToken.None);
+        await WaitForAsync(() => events.Count >= 1, TimeSpan.FromSeconds(2));
+
+        events.First().Snapshot.Value.ShouldBe(7);
+        factory.Clients[0].Notifications.ShouldBeEmpty(); // no native notifications on poll path
+        await drv.UnsubscribeAsync(handle, CancellationToken.None);
+    }
+
+    [Fact]
+    public async Task Subscribe_handle_DiagnosticId_indicates_native_vs_poll()
+    {
+        var (drvNative, _) = NewNativeDriver(
+            new TwinCATTagDefinition("X", "ads://5.23.91.23.1.1:851", "MAIN.X", TwinCATDataType.DInt));
+        await drvNative.InitializeAsync("{}", CancellationToken.None);
+        var nativeHandle = await drvNative.SubscribeAsync(["X"], TimeSpan.FromMilliseconds(100), CancellationToken.None);
+        nativeHandle.DiagnosticId.ShouldContain("native");
+
+        var factoryPoll = new FakeTwinCATClientFactory
+        {
+            Customise = () => new FakeTwinCATClient { Values = { ["MAIN.X"] = 1 } },
+        };
+        var drvPoll = new TwinCATDriver(new TwinCATDriverOptions
+        {
+            Devices = [new TwinCATDeviceOptions("ads://5.23.91.23.1.1:851")],
+            Tags = [new TwinCATTagDefinition("X", "ads://5.23.91.23.1.1:851", "MAIN.X", TwinCATDataType.DInt)],
+            Probe = new TwinCATProbeOptions { Enabled = false },
+            UseNativeNotifications = false,
+        }, "drv-1", factoryPoll);
+        await drvPoll.InitializeAsync("{}", CancellationToken.None);
+        var pollHandle = await drvPoll.SubscribeAsync(["X"], TimeSpan.FromMilliseconds(100), CancellationToken.None);
+        pollHandle.DiagnosticId.ShouldNotContain("native");
+    }
+
+    private static async Task WaitForAsync(Func<bool> condition, TimeSpan timeout)
+    {
+        var deadline = DateTime.UtcNow + timeout;
+        while (!condition() && DateTime.UtcNow < deadline)
+            await Task.Delay(20);
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests/TwinCATReadWriteTests.cs

@@ -0,0 +1,255 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Driver.TwinCAT;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests;
+
+[Trait("Category", "Unit")]
+public sealed class TwinCATReadWriteTests
+{
+    private static (TwinCATDriver drv, FakeTwinCATClientFactory factory) NewDriver(params TwinCATTagDefinition[] tags)
+    {
+        var factory = new FakeTwinCATClientFactory();
+        var drv = new TwinCATDriver(new TwinCATDriverOptions
+        {
+            Devices = [new TwinCATDeviceOptions("ads://5.23.91.23.1.1:851")],
+            Tags = tags,
+            Probe = new TwinCATProbeOptions { Enabled = false },
+        }, "drv-1", factory);
+        return (drv, factory);
+    }
+
+    // ---- Read ----
+
+    [Fact]
+    public async Task Unknown_reference_maps_to_BadNodeIdUnknown()
+    {
+        var (drv, _) = NewDriver();
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var snapshots = await drv.ReadAsync(["missing"], CancellationToken.None);
+        snapshots.Single().StatusCode.ShouldBe(TwinCATStatusMapper.BadNodeIdUnknown);
+    }
+
+    [Fact]
+    public async Task Successful_DInt_read_returns_Good_value()
+    {
+        var (drv, factory) = NewDriver(
+            new TwinCATTagDefinition("Speed", "ads://5.23.91.23.1.1:851", "MAIN.Speed", TwinCATDataType.DInt));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = () => new FakeTwinCATClient { Values = { ["MAIN.Speed"] = 4200 } };
+
+        var snapshots = await drv.ReadAsync(["Speed"], CancellationToken.None);
+
+        snapshots.Single().StatusCode.ShouldBe(TwinCATStatusMapper.Good);
+        snapshots.Single().Value.ShouldBe(4200);
+        factory.Clients[0].ConnectCount.ShouldBe(1);
+        factory.Clients[0].IsConnected.ShouldBeTrue();
+    }
+
+    [Fact]
+    public async Task Repeat_read_reuses_connection()
+    {
+        var (drv, factory) = NewDriver(
+            new TwinCATTagDefinition("X", "ads://5.23.91.23.1.1:851", "GVL.X", TwinCATDataType.DInt));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = () => new FakeTwinCATClient { Values = { ["GVL.X"] = 1 } };
+
+        await drv.ReadAsync(["X"], CancellationToken.None);
+        await drv.ReadAsync(["X"], CancellationToken.None);
+        await drv.ReadAsync(["X"], CancellationToken.None);
+
+        // One client, one connect — subsequent calls reuse the connected client.
+        factory.Clients.Count.ShouldBe(1);
+        factory.Clients[0].ConnectCount.ShouldBe(1);
+    }
+
+    [Fact]
+    public async Task Read_with_ADS_error_maps_via_status_mapper()
+    {
+        var (drv, factory) = NewDriver(
+            new TwinCATTagDefinition("Ghost", "ads://5.23.91.23.1.1:851", "MAIN.Missing", TwinCATDataType.DInt));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = () =>
+        {
+            var c = new FakeTwinCATClient();
+            c.ReadStatuses["MAIN.Missing"] = TwinCATStatusMapper.BadNodeIdUnknown;
+            return c;
+        };
+
+        var snapshots = await drv.ReadAsync(["Ghost"], CancellationToken.None);
+        snapshots.Single().StatusCode.ShouldBe(TwinCATStatusMapper.BadNodeIdUnknown);
+    }
+
+    [Fact]
+    public async Task Read_exception_surfaces_BadCommunicationError()
+    {
+        var (drv, factory) = NewDriver(
+            new TwinCATTagDefinition("X", "ads://5.23.91.23.1.1:851", "MAIN.X", TwinCATDataType.DInt));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = () => new FakeTwinCATClient { ThrowOnRead = true };
+
+        var snapshots = await drv.ReadAsync(["X"], CancellationToken.None);
+        snapshots.Single().StatusCode.ShouldBe(TwinCATStatusMapper.BadCommunicationError);
+        drv.GetHealth().State.ShouldBe(DriverState.Degraded);
+    }
+
+    [Fact]
+    public async Task Connect_failure_surfaces_BadCommunicationError_and_disposes_client()
+    {
+        var (drv, factory) = NewDriver(
+            new TwinCATTagDefinition("X", "ads://5.23.91.23.1.1:851", "MAIN.X", TwinCATDataType.DInt));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = () => new FakeTwinCATClient { ThrowOnConnect = true };
+
+        var snapshots = await drv.ReadAsync(["X"], CancellationToken.None);
+        snapshots.Single().StatusCode.ShouldBe(TwinCATStatusMapper.BadCommunicationError);
+        factory.Clients[0].DisposeCount.ShouldBe(1);
+    }
+
+    [Fact]
+    public async Task Batched_reads_preserve_order()
+    {
+        var (drv, factory) = NewDriver(
+            new TwinCATTagDefinition("A", "ads://5.23.91.23.1.1:851", "MAIN.A", TwinCATDataType.DInt),
+            new TwinCATTagDefinition("B", "ads://5.23.91.23.1.1:851", "MAIN.B", TwinCATDataType.Real),
+            new TwinCATTagDefinition("C", "ads://5.23.91.23.1.1:851", "MAIN.C", TwinCATDataType.String));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = () => new FakeTwinCATClient
+        {
+            Values =
+            {
+                ["MAIN.A"] = 1,
+                ["MAIN.B"] = 3.14f,
+                ["MAIN.C"] = "hello",
+            },
+        };
+
+        var snapshots = await drv.ReadAsync(["A", "B", "C"], CancellationToken.None);
+        snapshots[0].Value.ShouldBe(1);
+        snapshots[1].Value.ShouldBe(3.14f);
+        snapshots[2].Value.ShouldBe("hello");
+    }
+
+    // ---- Write ----
+
+    [Fact]
+    public async Task Non_writable_tag_rejected_with_BadNotWritable()
+    {
+        var (drv, _) = NewDriver(
+            new TwinCATTagDefinition("RO", "ads://5.23.91.23.1.1:851", "MAIN.RO", TwinCATDataType.DInt, Writable: false));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var results = await drv.WriteAsync(
+            [new WriteRequest("RO", 1)], CancellationToken.None);
+        results.Single().StatusCode.ShouldBe(TwinCATStatusMapper.BadNotWritable);
+    }
+
+    [Fact]
+    public async Task Successful_write_logs_symbol_type_value()
+    {
+        var (drv, factory) = NewDriver(
+            new TwinCATTagDefinition("Speed", "ads://5.23.91.23.1.1:851", "MAIN.Speed", TwinCATDataType.DInt));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var results = await drv.WriteAsync(
+            [new WriteRequest("Speed", 4200)], CancellationToken.None);
+
+        results.Single().StatusCode.ShouldBe(TwinCATStatusMapper.Good);
+        var write = factory.Clients[0].WriteLog.Single();
+        write.symbol.ShouldBe("MAIN.Speed");
+        write.type.ShouldBe(TwinCATDataType.DInt);
+        write.value.ShouldBe(4200);
+    }
+
+    [Fact]
+    public async Task Write_with_ADS_error_surfaces_mapped_status()
+    {
+        var (drv, factory) = NewDriver(
+            new TwinCATTagDefinition("X", "ads://5.23.91.23.1.1:851", "MAIN.X", TwinCATDataType.DInt));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = () =>
+        {
+            var c = new FakeTwinCATClient();
+            c.WriteStatuses["MAIN.X"] = TwinCATStatusMapper.BadNotWritable;
+            return c;
+        };
+
+        var results = await drv.WriteAsync(
+            [new WriteRequest("X", 1)], CancellationToken.None);
+        results.Single().StatusCode.ShouldBe(TwinCATStatusMapper.BadNotWritable);
+    }
+
+    [Fact]
+    public async Task Write_exception_surfaces_BadCommunicationError()
+    {
+        var (drv, factory) = NewDriver(
+            new TwinCATTagDefinition("X", "ads://5.23.91.23.1.1:851", "MAIN.X", TwinCATDataType.DInt));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = () => new FakeTwinCATClient { ThrowOnWrite = true };
+
+        var results = await drv.WriteAsync(
+            [new WriteRequest("X", 1)], CancellationToken.None);
+        results.Single().StatusCode.ShouldBe(TwinCATStatusMapper.BadCommunicationError);
+    }
+
+    [Fact]
+    public async Task Batch_write_preserves_order_across_outcomes()
+    {
+        var factory = new FakeTwinCATClientFactory();
+        var drv = new TwinCATDriver(new TwinCATDriverOptions
+        {
+            Devices = [new TwinCATDeviceOptions("ads://5.23.91.23.1.1:851")],
+            Tags =
+            [
+                new TwinCATTagDefinition("A", "ads://5.23.91.23.1.1:851", "MAIN.A", TwinCATDataType.DInt),
+                new TwinCATTagDefinition("B", "ads://5.23.91.23.1.1:851", "MAIN.B", TwinCATDataType.DInt, Writable: false),
+            ],
+            Probe = new TwinCATProbeOptions { Enabled = false },
+        }, "drv-1", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var results = await drv.WriteAsync(
+        [
+            new WriteRequest("A", 1),
+            new WriteRequest("B", 2),
+            new WriteRequest("Unknown", 3),
+        ], CancellationToken.None);
+
+        results.Count.ShouldBe(3);
+        results[0].StatusCode.ShouldBe(TwinCATStatusMapper.Good);
+        results[1].StatusCode.ShouldBe(TwinCATStatusMapper.BadNotWritable);
+        results[2].StatusCode.ShouldBe(TwinCATStatusMapper.BadNodeIdUnknown);
+    }
+
+    [Fact]
+    public async Task Cancellation_propagates()
+    {
+        var (drv, factory) = NewDriver(
+            new TwinCATTagDefinition("X", "ads://5.23.91.23.1.1:851", "MAIN.X", TwinCATDataType.DInt));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = () => new FakeTwinCATClient
+        {
+            ThrowOnRead = true,
+            Exception = new OperationCanceledException(),
+        };
+
+        await Should.ThrowAsync<OperationCanceledException>(
+            () => drv.ReadAsync(["X"], CancellationToken.None));
+    }
+
+    [Fact]
+    public async Task ShutdownAsync_disposes_client()
+    {
+        var (drv, factory) = NewDriver(
+            new TwinCATTagDefinition("X", "ads://5.23.91.23.1.1:851", "MAIN.X", TwinCATDataType.DInt));
+        await drv.InitializeAsync("{}", CancellationToken.None);
+        factory.Customise = () => new FakeTwinCATClient { Values = { ["MAIN.X"] = 1 } };
+
+        await drv.ReadAsync(["X"], CancellationToken.None);
+        await drv.ShutdownAsync(CancellationToken.None);
+
+        factory.Clients[0].DisposeCount.ShouldBe(1);
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests/TwinCATSymbolPathTests.cs

@@ -0,0 +1,138 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Driver.TwinCAT;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests;
+
+[Trait("Category", "Unit")]
+public sealed class TwinCATSymbolPathTests
+{
+    [Fact]
+    public void Single_segment_global_variable_parses()
+    {
+        var p = TwinCATSymbolPath.TryParse("Counter");
+        p.ShouldNotBeNull();
+        p.Segments.Single().Name.ShouldBe("Counter");
+        p.ToAdsSymbolName().ShouldBe("Counter");
+    }
+
+    [Fact]
+    public void POU_dot_variable_parses()
+    {
+        var p = TwinCATSymbolPath.TryParse("MAIN.bStart");
+        p.ShouldNotBeNull();
+        p.Segments.Select(s => s.Name).ShouldBe(["MAIN", "bStart"]);
+        p.ToAdsSymbolName().ShouldBe("MAIN.bStart");
+    }
+
+    [Fact]
+    public void GVL_reference_parses()
+    {
+        var p = TwinCATSymbolPath.TryParse("GVL.Counter");
+        p.ShouldNotBeNull();
+        p.Segments.Select(s => s.Name).ShouldBe(["GVL", "Counter"]);
+        p.ToAdsSymbolName().ShouldBe("GVL.Counter");
+    }
+
+    [Fact]
+    public void Structured_member_access_splits()
+    {
+        var p = TwinCATSymbolPath.TryParse("Motor1.Status.Running");
+        p.ShouldNotBeNull();
+        p.Segments.Select(s => s.Name).ShouldBe(["Motor1", "Status", "Running"]);
+    }
+
+    [Fact]
+    public void Array_subscript_parses()
+    {
+        var p = TwinCATSymbolPath.TryParse("Data[5]");
+        p.ShouldNotBeNull();
+        p.Segments.Single().Subscripts.ShouldBe([5]);
+        p.ToAdsSymbolName().ShouldBe("Data[5]");
+    }
+
+    [Fact]
+    public void Multi_dim_array_subscript_parses()
+    {
+        var p = TwinCATSymbolPath.TryParse("Matrix[1,2]");
+        p.ShouldNotBeNull();
+        p.Segments.Single().Subscripts.ShouldBe([1, 2]);
+    }
+
+    [Fact]
+    public void Bit_access_captured_as_bit_index()
+    {
+        var p = TwinCATSymbolPath.TryParse("Flags.3");
+        p.ShouldNotBeNull();
+        p.Segments.Single().Name.ShouldBe("Flags");
+        p.BitIndex.ShouldBe(3);
+        p.ToAdsSymbolName().ShouldBe("Flags.3");
+    }
+
+    [Fact]
+    public void Bit_access_after_member_path()
+    {
+        var p = TwinCATSymbolPath.TryParse("GVL.Status.7");
+        p.ShouldNotBeNull();
+        p.Segments.Select(s => s.Name).ShouldBe(["GVL", "Status"]);
+        p.BitIndex.ShouldBe(7);
+    }
+
+    [Fact]
+    public void Combined_scope_member_subscript_bit()
+    {
+        var p = TwinCATSymbolPath.TryParse("MAIN.Motors[0].Status.5");
+        p.ShouldNotBeNull();
+        p.Segments.Select(s => s.Name).ShouldBe(["MAIN", "Motors", "Status"]);
+        p.Segments[1].Subscripts.ShouldBe([0]);
+        p.BitIndex.ShouldBe(5);
+        p.ToAdsSymbolName().ShouldBe("MAIN.Motors[0].Status.5");
+    }
+
+    [Theory]
+    [InlineData(null)]
+    [InlineData("")]
+    [InlineData("   ")]
+    [InlineData(".Motor")]              // leading dot
+    [InlineData("Motor.")]              // trailing dot
+    [InlineData("Motor.[0]")]           // empty segment
+    [InlineData("1bad")]                // ident starts with digit
+    [InlineData("Bad Name")]            // space in ident
+    [InlineData("Motor[]")]             // empty subscript
+    [InlineData("Motor[-1]")]           // negative subscript
+    [InlineData("Motor[a]")]            // non-numeric subscript
+    [InlineData("Motor[")]              // unbalanced bracket
+    [InlineData("Flags.32")]            // bit out of range (treated as ident → invalid shape)
+    public void Invalid_shapes_return_null(string? input)
+    {
+        TwinCATSymbolPath.TryParse(input).ShouldBeNull();
+    }
+
+    [Fact]
+    public void Underscore_prefix_idents_accepted()
+    {
+        TwinCATSymbolPath.TryParse("_internal_var")!.Segments.Single().Name.ShouldBe("_internal_var");
+    }
+
+    [Fact]
+    public void ToAdsSymbolName_roundtrips()
+    {
+        var cases = new[]
+        {
+            "Counter",
+            "MAIN.bStart",
+            "GVL.Counter",
+            "Motor1.Status.Running",
+            "Data[5]",
+            "Matrix[1,2]",
+            "Flags.3",
+            "MAIN.Motors[0].Status.5",
+        };
+        foreach (var c in cases)
+        {
+            var parsed = TwinCATSymbolPath.TryParse(c);
+            parsed.ShouldNotBeNull(c);
+            parsed.ToAdsSymbolName().ShouldBe(c);
+        }
+    }
+}

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

@@ -0,0 +1,31 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <TargetFramework>net10.0</TargetFramework>
+        <Nullable>enable</Nullable>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <IsPackable>false</IsPackable>
+        <IsTestProject>true</IsTestProject>
+        <RootNamespace>ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests</RootNamespace>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <PackageReference Include="xunit.v3" Version="1.1.0"/>
+        <PackageReference Include="Shouldly" Version="4.3.0"/>
+        <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0"/>
+        <PackageReference Include="xunit.runner.visualstudio" Version="3.0.2">
+            <PrivateAssets>all</PrivateAssets>
+            <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+        </PackageReference>
+    </ItemGroup>
+
+    <ItemGroup>
+        <ProjectReference Include="..\..\src\ZB.MOM.WW.OtOpcUa.Driver.TwinCAT\ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.csproj"/>
+    </ItemGroup>
+
+    <ItemGroup>
+        <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-37gx-xxp4-5rgx"/>
+        <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-w3x6-4m5h-cxqf"/>
+    </ItemGroup>
+
+</Project>