src/MxGateway.Server/Grpc/MxAccessGatewayService.cs

@@ -20,8 +20,10 @@ public sealed class MxAccessGatewayService(
     MxAccessGrpcMapper mapper,
     IEventStreamService eventStreamService,
     GatewayMetrics metrics,
-    ILogger<MxAccessGatewayService> logger) : MxAccessGateway.MxAccessGatewayBase
+    ILogger<MxAccessGatewayService> logger,
+    IAlarmRpcDispatcher? alarmRpcDispatcher = null) : MxAccessGateway.MxAccessGatewayBase
 {
+    private readonly IAlarmRpcDispatcher alarmRpcDispatcher = alarmRpcDispatcher ?? new NotWiredAlarmRpcDispatcher();
     /// <inheritdoc />
     public override async Task<OpenSessionReply> OpenSession(
         OpenSessionRequest request,
@@ -167,7 +169,7 @@ public sealed class MxAccessGatewayService(
     ///     UNIMPLEMENTED, so the .NET / Python / Go / Java / Rust SDK call sites land
     ///     on a stable surface.
     /// </remarks>
-    public override Task<AcknowledgeAlarmReply> AcknowledgeAlarm(
+    public override async Task<AcknowledgeAlarmReply> AcknowledgeAlarm(
         AcknowledgeAlarmRequest request,
         ServerCallContext context)
     {
@@ -187,13 +189,13 @@ public sealed class MxAccessGatewayService(
             // gRPC NotFound by the caller's MapException.
             _ = ResolveSession(request.SessionId);
 
-            return Task.FromResult(new AcknowledgeAlarmReply
-            {
-                SessionId = request.SessionId,
-                CorrelationId = request.ClientCorrelationId,
-                ProtocolStatus = MxAccessGrpcMapper.Ok("AcknowledgeAlarm accepted; worker dispatch pending PR A.2."),
-                DiagnosticMessage = "Gateway-side AcknowledgeAlarm contract is live (PR A.3); worker-side MxAccess Acknowledge call ships in PR A.2.",
-            });
+            // PR A.6 — delegate to the alarm dispatcher. NotWiredAlarmRpcDispatcher
+            // (default) returns OK + a worker-pending diagnostic. Production
+            // WorkerAlarmRpcDispatcher (dev-rig follow-up) routes through the
+            // worker IPC to AlarmClient.AlarmAckByGUID with full operator-identity
+            // fidelity.
+            return await alarmRpcDispatcher.AcknowledgeAsync(request, context.CancellationToken)
+                .ConfigureAwait(false);
         }
         catch (Exception exception) when (exception is not RpcException)
         {
@@ -210,7 +212,7 @@ public sealed class MxAccessGatewayService(
     ///     handler will translate the request into a WorkerCommand and stream the
     ///     resulting snapshots.
     /// </remarks>
-    public override Task QueryActiveAlarms(
+    public override async Task QueryActiveAlarms(
         QueryActiveAlarmsRequest request,
         IServerStreamWriter<ActiveAlarmSnapshot> responseStream,
         ServerCallContext context)
@@ -224,9 +226,18 @@ public sealed class MxAccessGatewayService(
             }
             _ = ResolveSession(request.SessionId);
 
-            // Empty stream — PR A.4 implements ConditionRefresh server-side once the
-            // worker's QueryActiveAlarmsCommand is available.
-            return Task.CompletedTask;
+            // PR A.7 — delegate to the alarm dispatcher. NotWiredAlarmRpcDispatcher
+            // (default) yields an empty stream. Production WorkerAlarmRpcDispatcher
+            // (dev-rig follow-up) walks the worker's IMxAccessAlarmConsumer
+            // SnapshotActiveAlarms output and translates each AlarmRecord into an
+            // ActiveAlarmSnapshot.
+            await foreach (ActiveAlarmSnapshot snapshot in alarmRpcDispatcher
+                .QueryActiveAlarmsAsync(request, context.CancellationToken)
+                .WithCancellation(context.CancellationToken)
+                .ConfigureAwait(false))
+            {
+                await responseStream.WriteAsync(snapshot).ConfigureAwait(false);
+            }
         }
         catch (Exception exception) when (exception is not RpcException)
         {

src/MxGateway.Server/Sessions/IAlarmRpcDispatcher.cs

@@ -0,0 +1,41 @@
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+using MxGateway.Contracts.Proto;
+
+namespace MxGateway.Server.Sessions;
+
+/// <summary>
+///     PR A.6 / A.7 — gateway-side dispatcher for the alarm-RPC surface.
+///     Bridges the public <c>AcknowledgeAlarm</c> + <c>QueryActiveAlarms</c>
+///     gRPC handlers to the worker process that hosts
+///     <c>IMxAccessAlarmConsumer</c>.
+/// </summary>
+/// <remarks>
+///     <para>
+///         Production implementations live in <c>WorkerAlarmRpcDispatcher</c>
+///         (this PR ships a not-yet-wired default that returns a clear
+///         worker-pending diagnostic) and route through the existing
+///         worker-pipe IPC. Tests inject a fake to exercise the gateway
+///         handler shape without spinning up a worker process.
+///     </para>
+///     <para>
+///         The dispatcher is session-scoped: every call resolves the
+///         session and forwards to that session's worker. The handler
+///         constructs the <see cref="AcknowledgeAlarmReply"/> /
+///         <see cref="ActiveAlarmSnapshot"/> stream from the dispatcher's
+///         output without further translation.
+///     </para>
+/// </remarks>
+public interface IAlarmRpcDispatcher
+{
+    /// <summary>Forward an Acknowledge to the worker that owns the session.</summary>
+    Task<AcknowledgeAlarmReply> AcknowledgeAsync(
+        AcknowledgeAlarmRequest request,
+        CancellationToken cancellationToken);
+
+    /// <summary>Walk active alarms on the worker that owns the session.</summary>
+    IAsyncEnumerable<ActiveAlarmSnapshot> QueryActiveAlarmsAsync(
+        QueryActiveAlarmsRequest request,
+        CancellationToken cancellationToken);
+}

src/MxGateway.Server/Sessions/NotWiredAlarmRpcDispatcher.cs

@@ -0,0 +1,52 @@
+using System.Collections.Generic;
+using System.Runtime.CompilerServices;
+using System.Threading;
+using System.Threading.Tasks;
+using MxGateway.Contracts.Proto;
+using MxGateway.Server.Grpc;
+
+namespace MxGateway.Server.Sessions;
+
+/// <summary>
+///     PR A.6 / A.7 — default <see cref="IAlarmRpcDispatcher"/> shipped while
+///     the worker-side AlarmClient event subscription is gated on dev-rig
+///     validation. Acknowledges with a structured "worker-pending"
+///     diagnostic and yields an empty active-alarm stream.
+/// </summary>
+/// <remarks>
+///     <para>
+///         Replaces the inline diagnostic strings in
+///         <c>MxAccessGatewayService.AcknowledgeAlarm</c> /
+///         <c>QueryActiveAlarms</c> from PR A.3 with an injectable seam.
+///         When the worker dispatcher (PR A.6/A.7 dev-rig follow-up) lands,
+///         <c>WorkerAlarmRpcDispatcher</c> replaces this implementation in
+///         the DI container and the same handler shape comes alive without
+///         further changes to the public RPC surface.
+///     </para>
+/// </remarks>
+public sealed class NotWiredAlarmRpcDispatcher : IAlarmRpcDispatcher
+{
+    /// <inheritdoc />
+    public Task<AcknowledgeAlarmReply> AcknowledgeAsync(
+        AcknowledgeAlarmRequest request,
+        CancellationToken cancellationToken)
+    {
+        return Task.FromResult(new AcknowledgeAlarmReply
+        {
+            SessionId = request.SessionId,
+            CorrelationId = request.ClientCorrelationId,
+            ProtocolStatus = MxAccessGrpcMapper.Ok("AcknowledgeAlarm accepted; worker dispatch pending dev-rig wiring."),
+            DiagnosticMessage = "Gateway-side AcknowledgeAlarm accepted; the worker-side AlarmClient consumer (PR A.5) is in place but the dispatcher hookup is gated on validating the AVEVA alarm-provider event subscription on the dev rig.",
+        });
+    }
+
+    /// <inheritdoc />
+#pragma warning disable CS1998 // Async method lacks 'await' operators — empty stream is intentional.
+    public async IAsyncEnumerable<ActiveAlarmSnapshot> QueryActiveAlarmsAsync(
+        QueryActiveAlarmsRequest request,
+        [EnumeratorCancellation] CancellationToken cancellationToken)
+    {
+        yield break;
+    }
+#pragma warning restore CS1998
+}

src/MxGateway.Tests/Gateway/Sessions/NotWiredAlarmRpcDispatcherTests.cs

@@ -0,0 +1,54 @@
+using System.Threading;
+using System.Threading.Tasks;
+using MxGateway.Contracts.Proto;
+using MxGateway.Server.Sessions;
+
+namespace MxGateway.Tests.Gateway.Sessions;
+
+/// <summary>
+///     PR A.6 / A.7 — pins the not-yet-wired dispatcher's behaviour:
+///     AcknowledgeAsync returns OK with a worker-pending diagnostic and
+///     QueryActiveAlarmsAsync yields an empty stream. Production
+///     <c>WorkerAlarmRpcDispatcher</c> (dev-rig follow-up) replaces this
+///     impl in DI without changing the gateway handler shape.
+/// </summary>
+public sealed class NotWiredAlarmRpcDispatcherTests
+{
+    [Fact]
+    public async Task AcknowledgeAsync_returns_ok_with_worker_pending_diagnostic()
+    {
+        IAlarmRpcDispatcher dispatcher = new NotWiredAlarmRpcDispatcher();
+
+        AcknowledgeAlarmReply reply = await dispatcher.AcknowledgeAsync(
+            new AcknowledgeAlarmRequest
+            {
+                SessionId = "session-1",
+                ClientCorrelationId = "corr-1",
+                AlarmFullReference = "Tank01.Level.HiHi",
+                Comment = "investigating",
+                OperatorUser = "alice",
+            },
+            CancellationToken.None);
+
+        Assert.Equal(ProtocolStatusCode.Ok, reply.ProtocolStatus.Code);
+        Assert.Equal("session-1", reply.SessionId);
+        Assert.Equal("corr-1", reply.CorrelationId);
+        Assert.Contains("worker", reply.DiagnosticMessage, System.StringComparison.OrdinalIgnoreCase);
+    }
+
+    [Fact]
+    public async Task QueryActiveAlarmsAsync_yields_no_snapshots()
+    {
+        IAlarmRpcDispatcher dispatcher = new NotWiredAlarmRpcDispatcher();
+
+        int count = 0;
+        await foreach (ActiveAlarmSnapshot _ in dispatcher.QueryActiveAlarmsAsync(
+            new QueryActiveAlarmsRequest { SessionId = "session-1" },
+            CancellationToken.None))
+        {
+            count++;
+        }
+
+        Assert.Equal(0, count);
+    }
+}