AbCip IAlarmSource via ALMD projection (#177) — feature-flagged OFF by default; when enabled, polls declared ALMD UDT member fields + raises OnAlarmEvent on 0→1 + 1→0 transitions. Closes task #177. The AB CIP driver now implements IAlarmSource so the generic-driver alarm dispatch path (PR 14's sinks + the Server.Security.AuthorizationGate AlarmSubscribe/AlarmAck invoker wrapping) can treat AB-backed alarms uniformly with Galaxy + OpcUaClient + FOCAS. Projection is ALMD-only in this pass: the Logix ALMD (digital alarm) instruction's UDT shape is well-understood (InFaulted + Acked + Severity + In + Cfg_ProgTime at stable member names) so the polled-read + state-diff pattern fits without concessions. ALMA (analog alarm) deferred to a follow-up because its HHLimit/HLimit/LLimit/LLLimit threshold + In value semantics deserve their own design pass — raising on threshold-crossing is not the same shape as raising on InFaulted-edge. AbCipDriverOptions gains two knobs: EnableAlarmProjection (default false) + AlarmPollInterval (default 1s). Explicit opt-in because projection semantics don't exactly mirror Rockwell FT Alarm & Events; shops running FT Live should leave this off + take alarms through the native A&E route. AbCipAlarmProjection is the state machine: per-subscription background loop polls the source-node set via the driver's public ReadAsync — which gains the #194 whole-UDT optimization for free when ALMDs are declared with their standard member set, so one poll tick reads (N alarms × 2 members) = N libplctag round-trips rather than 2N. Per-tick state diff: compare InFaulted + Severity against last-seen, fire raise (0→1) / clear (1→0) with AlarmSeverity bucketed via the 1-1000 Logix severity scale (≤250 Low, ≤500 Medium, ≤750 High, rest Critical — matches OpcUaClient's MapSeverity shape). ConditionId is {sourceNode}#active — matches a single active-branch per alarm which is all ALMD supports; when Cfg_ProgTime-based branch identity becomes interesting (re-raise after ack with new timestamp), a richer ConditionId pass can land. Subscribe-while-disabled returns a handle wrapping id=0 — capability negotiation (the server queries IAlarmSource presence at driver-load time) still succeeds, the alarm surface just never fires. Unsubscribe cancels the sub's CTS + awaits its loop; ShutdownAsync cancels every sub on its way out so a driver reload doesn't leak poll tasks. AcknowledgeAsync routes through the driver's existing WriteAsync path — per-ack writes {SourceNodeId}.Acked = true (the simpler semantic; operators whose ladder watches AckCmd + rising-edge can wire a client-side pulse until a driver-level edge-mode knob lands). Best-effort — per-ack faults are swallowed so one bad ack doesn't poison the whole batch. Six new AbCipAlarmProjectionTests: detector flags ALMD signature + skips non-signature UDTs + atomics; severity mapping matches OPC UA A&C bucket boundaries; feature-flag OFF returns a handle but never touches the fake runtime (proving no background polling happens); feature-flag ON fires a raise event on 0→1; clear event fires on 1→0 after a prior raise; unsubscribe stops the poll loop (ReadCount doesn't grow past cancel + at most one straggler read). Driver builds 0 errors; AbCip.Tests 233/233 (was 227, +6 new). Task #177 closed — the last pending AB CIP follow-up is now #194 (already shipped). Remaining pending fleet-wide: #150 (Galaxy MXAccess failover hardware) + #199 (UnsTab Playwright smoke).

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

src/ZB.MOM.WW.OtOpcUa.Driver.AbCip/AbCipDriver.cs

@@ -21,7 +21,7 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.AbCip;
 ///     <see cref="PlcTagHandle"/> and reconnects each device.</para>
 /// </remarks>
 public sealed class AbCipDriver : IDriver, IReadable, IWritable, ITagDiscovery, ISubscribable,
-    IHostConnectivityProbe, IPerCallHostResolver, IDisposable, IAsyncDisposable
+    IHostConnectivityProbe, IPerCallHostResolver, IAlarmSource, IDisposable, IAsyncDisposable
 {
     private readonly AbCipDriverOptions _options;
     private readonly string _driverInstanceId;
@@ -32,10 +32,15 @@ public sealed class AbCipDriver : IDriver, IReadable, IWritable, ITagDiscovery,
     private readonly PollGroupEngine _poll;
     private readonly Dictionary<string, DeviceState> _devices = new(StringComparer.OrdinalIgnoreCase);
     private readonly Dictionary<string, AbCipTagDefinition> _tagsByName = new(StringComparer.OrdinalIgnoreCase);
+    private readonly AbCipAlarmProjection _alarmProjection;
     private DriverHealth _health = new(DriverState.Unknown, null, null);
 
     public event EventHandler<DataChangeEventArgs>? OnDataChange;
     public event EventHandler<HostStatusChangedEventArgs>? OnHostStatusChanged;
+    public event EventHandler<AlarmEventArgs>? OnAlarmEvent;
+
+    /// <summary>Internal seam for the alarm projection to raise events through the driver.</summary>
+    internal void InvokeAlarmEvent(AlarmEventArgs args) => OnAlarmEvent?.Invoke(this, args);
 
     public AbCipDriver(AbCipDriverOptions options, string driverInstanceId,
         IAbCipTagFactory? tagFactory = null,
@@ -52,6 +57,7 @@ public sealed class AbCipDriver : IDriver, IReadable, IWritable, ITagDiscovery,
             reader: ReadAsync,
             onChange: (handle, tagRef, snapshot) =>
                 OnDataChange?.Invoke(this, new DataChangeEventArgs(handle, tagRef, snapshot)));
+        _alarmProjection = new AbCipAlarmProjection(this, _options.AlarmPollInterval);
     }
 
     /// <summary>
@@ -162,6 +168,7 @@ public sealed class AbCipDriver : IDriver, IReadable, IWritable, ITagDiscovery,
 
     public async Task ShutdownAsync(CancellationToken cancellationToken)
     {
+        await _alarmProjection.DisposeAsync().ConfigureAwait(false);
         await _poll.DisposeAsync().ConfigureAwait(false);
         foreach (var state in _devices.Values)
         {
@@ -187,6 +194,39 @@ public sealed class AbCipDriver : IDriver, IReadable, IWritable, ITagDiscovery,
         return Task.CompletedTask;
     }
 
+    // ---- IAlarmSource (ALMD projection, #177) ----
+
+    /// <summary>
+    ///     Subscribe to ALMD alarm transitions on <paramref name="sourceNodeIds"/>. Each id
+    ///     names a declared ALMD UDT tag; the projection polls the tag's <c>InFaulted</c> +
+    ///     <c>Severity</c> members at <see cref="AbCipDriverOptions.AlarmPollInterval"/> and
+    ///     fires <see cref="OnAlarmEvent"/> on 0→1 (raise) + 1→0 (clear) transitions.
+    ///     Feature-gated — when <see cref="AbCipDriverOptions.EnableAlarmProjection"/> is
+    ///     <c>false</c> (the default), returns a handle wrapping a no-op subscription so
+    ///     capability negotiation still works; <see cref="OnAlarmEvent"/> never fires.
+    /// </summary>
+    public Task<IAlarmSubscriptionHandle> SubscribeAlarmsAsync(
+        IReadOnlyList<string> sourceNodeIds, CancellationToken cancellationToken)
+    {
+        if (!_options.EnableAlarmProjection)
+        {
+            var disabled = new AbCipAlarmSubscriptionHandle(0);
+            return Task.FromResult<IAlarmSubscriptionHandle>(disabled);
+        }
+        return _alarmProjection.SubscribeAsync(sourceNodeIds, cancellationToken);
+    }
+
+    public Task UnsubscribeAlarmsAsync(IAlarmSubscriptionHandle handle, CancellationToken cancellationToken) =>
+        _options.EnableAlarmProjection
+            ? _alarmProjection.UnsubscribeAsync(handle, cancellationToken)
+            : Task.CompletedTask;
+
+    public Task AcknowledgeAsync(
+        IReadOnlyList<AlarmAcknowledgeRequest> acknowledgements, CancellationToken cancellationToken) =>
+        _options.EnableAlarmProjection
+            ? _alarmProjection.AcknowledgeAsync(acknowledgements, cancellationToken)
+            : Task.CompletedTask;
+
     // ---- IHostConnectivityProbe ----
 
     public IReadOnlyList<HostConnectivityStatus> GetHostStatuses() =>