diff --git a/archreview/plans/R2-04-failure-visibility-plan.md.tasks.json b/archreview/plans/R2-04-failure-visibility-plan.md.tasks.json
index 20ea2898..3249880b 100644
--- a/archreview/plans/R2-04-failure-visibility-plan.md.tasks.json
+++ b/archreview/plans/R2-04-failure-visibility-plan.md.tasks.json
@@ -13,7 +13,7 @@
     { "id": "T9", "subject": "PrimaryGatePolicy pure class + truth-table tests + otopcua.redundancy.primary_gate_denied counter (03/S4)", "status": "completed", "blockedBy": [] },
     { "id": "T10", "subject": "Wire DriverHostActor gates (:977/:1039/:1095) through PrimaryGatePolicy with member-count provider + S5 log-once", "status": "completed", "blockedBy": ["T9"] },
     { "id": "T11", "subject": "DriverHostActorPrimaryGateTests: deny-on-unknown multi-node, allow single-node, ack/emit variants, meter tags", "status": "completed", "blockedBy": ["T10"] },
-    { "id": "T12", "subject": "ScriptedAlarmHostActor alerts-emit gate adopts PrimaryGatePolicy (consistency extension)", "status": "pending", "blockedBy": ["T9"] },
+    { "id": "T12", "subject": "ScriptedAlarmHostActor alerts-emit gate adopts PrimaryGatePolicy (consistency extension)", "status": "completed", "blockedBy": ["T9"] },
     { "id": "T13", "subject": "In-process 2-node delivery-path test (TwoNodeClusterHarness): DPS-delivered snapshot drives the gate", "status": "pending", "blockedBy": ["T11"] },
     { "id": "T14", "subject": "docs/Redundancy.md: gate policy table, boot-window client experience, new meters, Galaxy fail-closed semantics", "status": "pending", "blockedBy": [] },
     { "id": "T15", "subject": "LIVE GATE: 2-node docker-dev rig verify (ServiceLevel 240/100, boot-window write rejected+reverted, single /alerts row)", "status": "pending", "blockedBy": ["T10", "T11", "T12", "T13"] }
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/ScriptedAlarms/ScriptedAlarmHostActor.cs b/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/ScriptedAlarms/ScriptedAlarmHostActor.cs
index 7d93e51d..a8d790b8 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/ScriptedAlarms/ScriptedAlarmHostActor.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/ScriptedAlarms/ScriptedAlarmHostActor.cs
@@ -3,11 +3,13 @@ using Akka.Cluster.Tools.PublishSubscribe;
 using Akka.Event;
 using ZB.MOM.WW.OtOpcUa.Commons.Messages.Alerts;
 using ZB.MOM.WW.OtOpcUa.Commons.Messages.Redundancy;
+using ZB.MOM.WW.OtOpcUa.Commons.Observability;
 using ZB.MOM.WW.OtOpcUa.Commons.OpcUa;
 using ZB.MOM.WW.OtOpcUa.Commons.Types;
 using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
 using ZB.MOM.WW.OtOpcUa.Core.ScriptedAlarms;
 using ZB.MOM.WW.OtOpcUa.OpcUaServer;
+using ZB.MOM.WW.OtOpcUa.Runtime.Drivers;
 using ZB.MOM.WW.OtOpcUa.Runtime.OpcUa;
 using ZB.MOM.WW.OtOpcUa.Runtime.VirtualTags;
 
@@ -104,10 +106,16 @@ public sealed class ScriptedAlarmHostActor : ReceiveActor
 
     /// <summary>Cached local <see cref="RedundancyRole"/> from the latest <see cref="RedundancyStateChanged"/>
     /// snapshot (null = unknown until the first snapshot arrives, or no <see cref="_localNode"/> wired). The
-    /// cluster-wide <c>alerts</c> publish in <see cref="OnEngineEmission"/> is gated on this: only the Primary
-    /// publishes (default-emit while unknown so single-node deploys + the boot window never drop transitions).</summary>
+    /// cluster-wide <c>alerts</c> publish in <see cref="OnEngineEmission"/> resolves this through
+    /// <see cref="Drivers.PrimaryGatePolicy"/>: only the Primary publishes; an unknown role default-emits on a
+    /// single-driver cluster but default-DENIES on a multi-driver one, so the dual-primary boot window can't
+    /// historize duplicate AVEVA alarm rows (archreview 03/S4).</summary>
     private RedundancyRole? _localRole;
 
+    /// <summary>Test seam (archreview 03/S4): overrides the count of Up <c>driver</c>-role cluster members the
+    /// alerts-emit gate reads while the role is unknown. Null ⇒ read the live cluster state.</summary>
+    private readonly Func<int>? _driverMemberCountProvider;
+
     /// <summary>Monotonic load generation, bumped on every <see cref="OnApply"/>. The continuation that
     /// pipes back an <see cref="AlarmsLoaded"/> captures the generation it was started under; a stale
     /// completion (an earlier generation arriving after a newer apply) is discarded in
@@ -136,8 +144,9 @@ public sealed class ScriptedAlarmHostActor : ReceiveActor
         IActorRef? mux,
         DependencyMuxTagUpstreamSource upstream,
         ScriptedAlarmEngine engine,
-        NodeId? localNode = null) =>
-        Akka.Actor.Props.Create(() => new ScriptedAlarmHostActor(publishActor, mux, upstream, engine, localNode));
+        NodeId? localNode = null,
+        Func<int>? driverMemberCountProvider = null) =>
+        Akka.Actor.Props.Create(() => new ScriptedAlarmHostActor(publishActor, mux, upstream, engine, localNode, driverMemberCountProvider));
 
     /// <summary>Initializes a new instance of the <see cref="ScriptedAlarmHostActor"/> class.</summary>
     /// <param name="publishActor">The OPC UA publish actor emissions are bridged to.</param>
@@ -147,12 +156,16 @@ public sealed class ScriptedAlarmHostActor : ReceiveActor
     /// <param name="localNode">The local cluster node id, used to read this node's <see cref="RedundancyRole"/>
     /// from the <c>redundancy-state</c> topic so only the Primary publishes the cluster-wide <c>alerts</c>
     /// transition. Null leaves the role unknown ⇒ default-emit (single-node deploys + tests).</param>
+    /// <param name="driverMemberCountProvider">Test seam (archreview 03/S4): overrides the count of Up
+    /// <c>driver</c>-role cluster members the alerts-emit gate reads while the role is unknown. Null reads
+    /// the live cluster state (0 on a non-cluster ActorRefProvider ⇒ single-node default-emit).</param>
     public ScriptedAlarmHostActor(
         IActorRef publishActor,
         IActorRef? mux,
         DependencyMuxTagUpstreamSource upstream,
         ScriptedAlarmEngine engine,
-        NodeId? localNode = null)
+        NodeId? localNode = null,
+        Func<int>? driverMemberCountProvider = null)
     {
         ArgumentNullException.ThrowIfNull(publishActor);
         ArgumentNullException.ThrowIfNull(upstream);
@@ -162,6 +175,7 @@ public sealed class ScriptedAlarmHostActor : ReceiveActor
         _upstream = upstream;
         _engine = engine;
         _localNode = localNode;
+        _driverMemberCountProvider = driverMemberCountProvider;
 
         // OnEvent fires on the engine's worker thread. NEVER touch Context / actor state here —
         // marshal onto the actor thread via the thread-safe Self.Tell. Keep the handler in a field
@@ -307,18 +321,45 @@ public sealed class ScriptedAlarmHostActor : ReceiveActor
             // suppress only the sink write. This publish (and the live `/alerts` fan-out) is NOT gated on it.
             HistorizeToAveva: e.HistorizeToAveva);
 
-        // Warm-standby dedup: only the Primary (driver-role leader) publishes the cluster-wide
-        // transition. Default-emit until told we are Secondary/Detached so single-node deploys + the
-        // boot window never drop transitions. The OPC UA node write above + inbound command processing
-        // stay ungated (the secondary keeps its address space + engine state warm for failover).
-        if (_localRole is RedundancyRole.Secondary or RedundancyRole.Detached)
+        // Warm-standby dedup: only the Primary publishes the cluster-wide transition (archreview 03/S4 —
+        // same PrimaryGatePolicy as DriverHostActor). A KNOWN Secondary/Detached is denied; an UNKNOWN role
+        // default-emits on a single-driver cluster but default-DENIES on a multi-driver one (so the
+        // dual-primary boot window can't historize duplicate AVEVA alarm rows). The OPC UA node write above +
+        // inbound command processing stay ungated (the secondary keeps its state warm for failover).
+        if (!PrimaryGatePolicy.ShouldServiceAsPrimary(_localRole, DriverMemberCount()))
         {
+            OtOpcUaTelemetry.PrimaryGateDenied.Add(1,
+                new KeyValuePair<string, object?>("site", "alarm-emit"),
+                new KeyValuePair<string, object?>("reason", _localRole switch
+                {
+                    RedundancyRole.Secondary => "secondary",
+                    RedundancyRole.Detached => "detached",
+                    _ => "role-unknown",
+                }));
             return;
         }
 
         _mediator.Tell(new Publish(AlertsTopic, evt));
     }
 
+    /// <summary>Count of Up cluster members carrying the <c>driver</c> role, for the alerts-emit gate. Uses
+    /// the injected test seam when present; otherwise reads the live cluster state guarded by try/catch so a
+    /// non-cluster ActorRefProvider yields 0 ⇒ the single-node default-emit posture (archreview 03/S4).</summary>
+    /// <returns>The number of Up driver-role members, or 0 when the cluster extension is unavailable.</returns>
+    private int DriverMemberCount()
+    {
+        if (_driverMemberCountProvider is not null) return _driverMemberCountProvider();
+        try
+        {
+            return Akka.Cluster.Cluster.Get(Context.System).State.Members
+                .Count(m => m.Status == Akka.Cluster.MemberStatus.Up && m.Roles.Contains(ServiceCollectionExtensions.DriverRole));
+        }
+        catch (Exception)
+        {
+            return 0;
+        }
+    }
+
     /// <summary>Caches this node's <see cref="RedundancyRole"/> from a cluster redundancy snapshot so
     /// <see cref="OnEngineEmission"/> can gate the cluster-wide <c>alerts</c> publish to the Primary. A
     /// snapshot that doesn't mention <see cref="_localNode"/> (or no local node wired) leaves the cached
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/ScriptedAlarms/ScriptedAlarmHostActorTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/ScriptedAlarms/ScriptedAlarmHostActorTests.cs
index 94e7a78c..2bd182bd 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/ScriptedAlarms/ScriptedAlarmHostActorTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/ScriptedAlarms/ScriptedAlarmHostActorTests.cs
@@ -519,6 +519,58 @@ public sealed class ScriptedAlarmHostActorTests : RuntimeActorTestBase
         evt.TransitionKind.ShouldBe("Activated");
     }
 
+    /// <summary>Boot-window multi-driver suppression (archreview 03/S4): role unknown + a real driver peer
+    /// (member count 2) ⇒ the alerts publish is DENIED (default-deny closes the dual-primary window that would
+    /// historize duplicate AVEVA rows), while the OPC UA node write stays ungated.</summary>
+    [Fact]
+    public void Unknown_role_multi_driver_suppresses_alerts_but_still_writes_opcua()
+    {
+        var publish = CreateTestProbe();
+        var mux = CreateTestProbe();
+        var alerts = CreateTestProbe();
+        SubscribeToAlerts(alerts);
+
+        var (host, _) = SpawnWithMemberCount(publish, mux, LocalNode, driverMemberCount: 2);
+        host.Tell(new ScriptedAlarmHostActor.ApplyScriptedAlarms(new[] { Plan(severity: 800) }));
+        mux.ExpectMsg<DependencyMuxActor.RegisterInterest>(Timeout);
+
+        // No snapshot sent ⇒ role unknown; count 2 ⇒ default-DENY.
+        host.Tell(new VirtualTagActor.DependencyValueChanged("M.T", 99, DateTime.UtcNow));
+
+        publish.FishForMessage<OpcUaPublishActor.AlarmStateUpdate>(m => m.State.Active, Timeout);
+        alerts.ExpectNoMsg(TimeSpan.FromMilliseconds(500));
+    }
+
+    /// <summary>Boot-window single-driver emit (archreview 03/S4): role unknown + no driver peer (member
+    /// count 1) ⇒ the alerts publish proceeds (single-node posture preserved).</summary>
+    [Fact]
+    public void Unknown_role_single_driver_publishes_alerts()
+    {
+        var publish = CreateTestProbe();
+        var mux = CreateTestProbe();
+        var alerts = CreateTestProbe();
+        SubscribeToAlerts(alerts);
+
+        var (host, _) = SpawnWithMemberCount(publish, mux, LocalNode, driverMemberCount: 1);
+        host.Tell(new ScriptedAlarmHostActor.ApplyScriptedAlarms(new[] { Plan(severity: 800) }));
+        mux.ExpectMsg<DependencyMuxActor.RegisterInterest>(Timeout);
+
+        host.Tell(new VirtualTagActor.DependencyValueChanged("M.T", 99, DateTime.UtcNow));
+
+        publish.FishForMessage<OpcUaPublishActor.AlarmStateUpdate>(m => m.State.Active, Timeout);
+        alerts.ExpectMsg<AlarmTransitionEvent>(Timeout).AlarmId.ShouldBe("alm-1");
+    }
+
+    private (IActorRef Host, DependencyMuxTagUpstreamSource Upstream) SpawnWithMemberCount(
+        TestProbe publish, TestProbe mux, NodeId localNode, int driverMemberCount)
+    {
+        var upstream = new DependencyMuxTagUpstreamSource();
+        var engine = BuildEngine(upstream);
+        var host = Sys.ActorOf(ScriptedAlarmHostActor.Props(
+            publish.Ref, mux.Ref, upstream, engine, localNode, driverMemberCountProvider: () => driverMemberCount));
+        return (host, upstream);
+    }
+
     /// <summary>Inbound command ungated by role (T1): the alerts-publish gate must NOT affect inbound
     /// command processing. Under a Secondary role, an AlarmCommand("Acknowledge") for an owned, active
     /// alarm still drives the engine — observed via the resulting AlarmStateUpdate(Acknowledged=true)