refactor(driver-pages): address Phase 6/8 deep-review findings

- Topic-name drift fix: DriverHealthChanged.TopicName and
  DriverControlTopic.Name now live on the message contracts in
  Commons. AkkaDriverHealthPublisher, DriverStatusSignalRBridge,
  DriverHostActor, and AdminOperationsActor all delegate to the
  single constant so a rename can't silently desynchronise
  publisher and subscriber.
- DriverStatusPanel._opResultClearTimer switched from
  System.Timers.Timer to System.Threading.Timer + awaited
  DisposeAsync. Prevents an in-flight 8s clear-callback from
  invoking StateHasChanged on a component whose hub has already
  been released.
- PublishHealthSnapshot deduplicates against the last published
  (state, lastSuccess, lastError, errorCount) fingerprint. The
  30s heartbeat no longer floods the SignalR layer with identical
  Healthy snapshots — newly-joined clients still warm up via the
  snapshot store on JoinDriver.

src/Core/ZB.MOM.WW.OtOpcUa.Commons/Messages/Admin/RestartDriver.cs

@@ -1,5 +1,16 @@
 namespace ZB.MOM.WW.OtOpcUa.Commons.Messages.Admin;
 
+/// <summary>
+///     Shared DPS topic for driver-control commands (<see cref="RestartDriver"/>,
+///     <see cref="ReconnectDriver"/>). Publishers (AdminOperationsActor) and subscribers
+///     (DriverHostActor) reference this single constant so renames can't silently
+///     desynchronise.
+/// </summary>
+public static class DriverControlTopic
+{
+    public const string Name = "driver-control";
+}
+
 /// <summary>
 ///     AdminUI → AdminOperationsActor: restart the driver actor for one instance.
 ///     A restart fully stops and respawns the actor — loses in-memory state, may briefly

src/Core/ZB.MOM.WW.OtOpcUa.Commons/Messages/Drivers/DriverHealthChanged.cs

@@ -20,4 +20,12 @@ public sealed record DriverHealthChanged(
     DateTime? LastSuccessfulReadUtc,
     string? LastError,
     int ErrorCount5Min,
-    DateTime PublishedUtc);
+    DateTime PublishedUtc)
+{
+    /// <summary>
+    ///     DPS topic name. Both the runtime <c>AkkaDriverHealthPublisher</c> and the AdminUI
+    ///     <c>DriverStatusSignalRBridge</c> reference this single constant so renames can't
+    ///     silently desynchronise publisher and subscriber.
+    /// </summary>
+    public const string TopicName = "driver-health";
+}

src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Drivers/DriverStatusPanel.razor

@@ -157,7 +157,7 @@
     private bool _showRestartConfirm;
     private string? _opResultMessage;
     private bool _opResultOk;
-    private System.Timers.Timer? _opResultClearTimer;
+    private System.Threading.Timer? _opResultClearTimer;
 
     protected override async Task OnInitializedAsync()
     {
@@ -257,24 +257,23 @@
     {
         _opResultOk = ok;
         _opResultMessage = message;
-        // Auto-clear the result chip after 8 s.
+        // Auto-clear the result chip after 8 s. System.Threading.Timer is used (not
+        // System.Timers.Timer) so DisposeAsync can drain any in-flight callback.
         _opResultClearTimer?.Dispose();
-        _opResultClearTimer = new System.Timers.Timer(8_000) { AutoReset = false };
-        _opResultClearTimer.Elapsed += async (_, _) =>
+        _opResultClearTimer = new System.Threading.Timer(_ =>
         {
             _opResultMessage = null;
-            await InvokeAsync(StateHasChanged);
-        };
-        _opResultClearTimer.Start();
+            InvokeAsync(StateHasChanged);
+        }, null, TimeSpan.FromSeconds(8), Timeout.InfiniteTimeSpan);
     }
 
     public async ValueTask DisposeAsync()
     {
-        // Drain the timer first so an in-flight callback can't invoke StateHasChanged on
-        // a component that's already releasing its hub. System.Threading.Timer implements
-        // IAsyncDisposable in .NET 6+; the async dispose awaits any in-flight callback.
+        // Drain BOTH timers first so an in-flight callback can't invoke StateHasChanged on
+        // a component whose hub has already been released. System.Threading.Timer's async
+        // dispose awaits any in-flight callback (.NET 6+).
         if (_timer is not null) await _timer.DisposeAsync();
-        _opResultClearTimer?.Dispose();
+        if (_opResultClearTimer is not null) await _opResultClearTimer.DisposeAsync();
         if (_hub is not null) await _hub.DisposeAsync();
     }
 

src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Hubs/DriverStatusSignalRBridge.cs

@@ -15,7 +15,7 @@ namespace ZB.MOM.WW.OtOpcUa.AdminUI.Hubs;
 /// </summary>
 public sealed class DriverStatusSignalRBridge : ReceiveActor
 {
-    public const string TopicName = "driver-health";
+    public const string TopicName = DriverHealthChanged.TopicName;
 
     private readonly IHubContext<DriverStatusHub> _hub;
     private readonly IDriverStatusSnapshotStore _store;

src/Server/ZB.MOM.WW.OtOpcUa.ControlPlane/AdminOperations/AdminOperationsActor.cs

@@ -178,7 +178,7 @@ public sealed class AdminOperationsActor : ReceiveActor
         {
             // Broadcast to every DriverHostActor on every node via the driver-control DPS topic.
             // Only the host that owns the instance will act; others ignore it (id not found in _children).
-            DistributedPubSub.Get(Context.System).Mediator.Tell(new Publish("driver-control", msg));
+            DistributedPubSub.Get(Context.System).Mediator.Tell(new Publish(DriverControlTopic.Name, msg));
 
             await using var db = await _dbFactory.CreateDbContextAsync();
             db.ConfigEdits.Add(new ConfigEdit
@@ -208,7 +208,7 @@ public sealed class AdminOperationsActor : ReceiveActor
         try
         {
             // Broadcast to every DriverHostActor; only the one owning the instance reacts.
-            DistributedPubSub.Get(Context.System).Mediator.Tell(new Publish("driver-control", msg));
+            DistributedPubSub.Get(Context.System).Mediator.Tell(new Publish(DriverControlTopic.Name, msg));
 
             await using var db = await _dbFactory.CreateDbContextAsync();
             db.ConfigEdits.Add(new ConfigEdit

src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/AkkaDriverHealthPublisher.cs

@@ -12,8 +12,9 @@ namespace ZB.MOM.WW.OtOpcUa.Runtime.Drivers;
 /// </summary>
 public sealed class AkkaDriverHealthPublisher : IDriverHealthPublisher
 {
-    /// <summary>The DistributedPubSub topic name for driver-health snapshots.</summary>
-    public const string TopicName = "driver-health";
+    /// <summary>The DistributedPubSub topic name for driver-health snapshots — single source
+    /// of truth on the message contract itself.</summary>
+    public const string TopicName = DriverHealthChanged.TopicName;
 
     private readonly ActorSystem _system;
 

src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/DriverHostActor.cs

@@ -37,7 +37,7 @@ public sealed class DriverHostActor : ReceiveActor, IWithTimers
 {
     public const string DeploymentsTopic = "deployments";
     public const string DeploymentAcksTopic = "deployment-acks";
-    public const string DriverControlTopic = "driver-control";
+    public const string DriverControlTopic = ZB.MOM.WW.OtOpcUa.Commons.Messages.Admin.DriverControlTopic.Name;
     public static readonly TimeSpan ReconnectInterval = TimeSpan.FromSeconds(30);
 
     private readonly IDbContextFactory<OtOpcUaConfigDbContext> _dbFactory;

src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/DriverInstanceActor.cs

@@ -434,13 +434,22 @@ public sealed class DriverInstanceActor : ReceiveActor, IWithTimers
     ///     Polls <see cref="IDriver.GetHealth"/> and forwards the snapshot to the health publisher.
     ///     Called on every observable state change and by the periodic <see cref="HealthPollTick"/>
     ///     so the AdminUI snapshot store is warmed up for newly-joined SignalR clients.
+    ///     Deduplicates: if the resulting (state, lastSuccess, lastError, errorCount) tuple matches
+    ///     the last publish, this call is a no-op. Stops flood-publishing identical Healthy snapshots
+    ///     every 30s when nothing has changed. Newly-joined SignalR clients still get the current
+    ///     snapshot via <c>DriverStatusHub.JoinDriver</c> which reads the store directly.
     /// </summary>
     private void PublishHealthSnapshot()
     {
         try
         {
             var health = _driver.GetHealth();
-            _healthPublisher.Publish(_clusterId, _driverInstanceId, health, ErrorCount5Min());
+            var errorCount = ErrorCount5Min();
+            var fingerprint = (health.State, health.LastSuccessfulRead, health.LastError, errorCount);
+            if (_lastPublishedFingerprint is { } prev && prev.Equals(fingerprint))
+                return;
+            _lastPublishedFingerprint = fingerprint;
+            _healthPublisher.Publish(_clusterId, _driverInstanceId, health, errorCount);
         }
         catch (Exception ex)
         {
@@ -448,6 +457,9 @@ public sealed class DriverInstanceActor : ReceiveActor, IWithTimers
         }
     }
 
+    /// <summary>Fingerprint of the last <see cref="PublishHealthSnapshot"/> call; null until first publish.</summary>
+    private (DriverState State, DateTime? LastSuccess, string? LastError, int ErrorCount)? _lastPublishedFingerprint;
+
     /// <inheritdoc />
     protected override void PostStop()
     {