fix(central-ui): resolve CentralUI-006 — push-based deployment status via IDeploymentStatusNotifier, remove 10s polling timer

code-reviews/CentralUI/findings.md

@@ -8,7 +8,7 @@
 | Last reviewed | 2026-05-16 |
 | Reviewer | claude-agent |
 | Commit reviewed | `9c60592` |
-| Open findings | 1 |
+| Open findings | 0 |
 
 ## Summary
 
@@ -318,7 +318,7 @@ longer imposes a fixed absolute cap. `dotnet build ScadaLink.slnx` clean;
 |--|--|
 | Severity | Medium |
 | Category | Design-document adherence |
-| Status | Open |
+| Status | Resolved |
 | Location | `src/ScadaLink.CentralUI/Components/Pages/Deployment/Deployments.razor:196-216` |
 
 **Description**
@@ -341,16 +341,59 @@ If polling is kept as a fallback, fetch only changed/in-progress records.
 
 **Resolution**
 
-_Unresolved — a genuine SignalR-push fix requires an event source in another
+Resolved 2026-05-16 (commit `<pending>`) — cross-module fix (CentralUI +
-module._ Verified 2026-05-16: `Deployments.razor` does poll every 10s, contrary
+DeploymentManager), explicitly authorized. Root cause confirmed against the
-to the design doc. But a real push implementation needs the **Deployment
+source: `Deployments.razor` ran a `Timer` (`OnInitializedAsync` → `StartTimer`,
-Manager** module (`ScadaLink.DeploymentManager` — `DeploymentService` /
+10s interval) that, every tick and for every open Blazor circuit, reloaded all
-`ArtifactDeploymentService` write the `DeploymentRecord` rows) to raise a
+deployment records (`GetAllDeploymentRecordsAsync`) and the full instance map
-status-change event/observable that the page subscribes to; there is no such
+(`GetAllInstancesAsync`) — contradicting Component-CentralUI "Real-Time Updates"
-event today and no CentralUI-only seam to subscribe to. Building that event
+("transitions push to the UI immediately via SignalR … no polling required").
-source is out of scope for a CentralUI-only review. Left Open and surfaced for a
+
-follow-up that adds a deployment-status broadcaster in DeploymentManager (or a
+**Process/DI topology confirmed.** `ScadaLink.Host/Program.cs` calls both
-design-doc amendment acknowledging the polling fallback).
+`AddDeploymentManager()` (line 75) and `AddCentralUI()` (line 77) on the same
+`builder.Services` — DeploymentManager and the Central UI run **in the same
+central Host process**, so a DI singleton is genuinely shared between the
+DeploymentManager services and the Blazor circuit's scoped components. The
+shared-singleton seam is real; no out-of-process fallback was needed.
+
+**What was implemented — push-based updates.** A new
+`IDeploymentStatusNotifier` (`ScadaLink.DeploymentManager/IDeploymentStatusNotifier.cs`)
+with a C# `event Action<DeploymentStatusChange>` and a small payload
+(`DeploymentStatusChange` = deployment id + instance id + new status). Its
+implementation `DeploymentStatusNotifier` invokes each subscriber in isolation
+and swallows/logs handler exceptions so a faulting circuit cannot break the
+deployment pipeline. It is registered as a **singleton** in `AddDeploymentManager`
+(`ServiceCollectionExtensions`). Every place `DeploymentService` writes a
+`DeploymentRecord` status now raises the notifier: the `Pending` create, the
+`InProgress` update, the site-response terminal update, the `Failed` cleanup
+write in the catch block, and the `DeploymentManager-006` reconciled-`Success`
+write — five call sites via a private `NotifyStatusChange` helper.
+`ArtifactDeploymentService` was inspected and writes only
+`SystemArtifactDeploymentRecord` rows, which `Deployments.razor` does not
+display, so it correctly raises nothing. `Deployments.razor` no longer has a
+`Timer`: `OnInitializedAsync` subscribes to `IDeploymentStatusNotifier.StatusChanged`,
+the handler reloads via `InvokeAsync(StateHasChanged)` (the notifier event is
+raised on the DeploymentManager service thread), and `Dispose` unsubscribes.
+Blazor Server pushes the re-render to the browser over its SignalR circuit
+automatically — satisfying the documented design. The existing "Pause/Resume
+updates" toggle now gates whether incoming push events are acted on, and
+"Refresh" still forces a manual reload. CLAUDE.md UI rules kept: Blazor Server +
+Bootstrap, custom components, no third-party frameworks.
+
+Regression tests fail against the pre-fix code and pass after. DeploymentManager
+(`DeploymentStatusNotifierTests`): `DeployInstanceAsync_RaisesStatusChange_ForEveryRecordStatusWrite`
+(pre-fix: no notifier, fails to compile / silent), plus
+`NotifyStatusChanged_WithNoSubscribers_DoesNotThrow` and
+`NotifyStatusChanged_ThrowingSubscriber_DoesNotBreakOtherSubscribers`;
+`ServiceCollectionExtensionsTests.AddDeploymentManager_RegistersDeploymentStatusNotifier_AsSingleton`
+pins the shared-singleton seam. CentralUI (`DeploymentsPushUpdateTests`):
+`Deployments_DoesNotPoll_HasNoRefreshTimer` (pre-fix: the `_refreshTimer` field
+existed — confirmed failing), `Deployments_StatusChange_TriggersReload`, and
+`Deployments_Dispose_UnsubscribesFromNotifier`. `dotnet build ScadaLink.slnx`
+clean (0 warnings); `tests/ScadaLink.DeploymentManager.Tests` 76 passed,
+`tests/ScadaLink.CentralUI.Tests` 257 passed. (`TopologyPageTests`' DI fixture
+was also updated to register the new notifier, since it constructs the real
+`DeploymentService`.)
 
 ### CentralUI-007 — Monitoring nav links to Deployment-only pages are shown to all roles
 

src/ScadaLink.CentralUI/Components/Pages/Deployment/Deployments.razor

@@ -8,6 +8,7 @@
 @inject IDeploymentManagerRepository DeploymentManagerRepository
 @inject ITemplateEngineRepository TemplateEngineRepository
 @inject ScadaLink.CentralUI.Auth.SiteScopeService SiteScope
+@inject ScadaLink.DeploymentManager.IDeploymentStatusNotifier DeploymentStatusNotifier
 @implements IDisposable
 
 <div class="container-fluid mt-3">
@@ -196,47 +197,42 @@
     private Dictionary<int, string> _instanceNames = new();
     private bool _loading = true;
     private string? _errorMessage;
-    private Timer? _refreshTimer;
     private bool _autoRefresh = true;
     private readonly HashSet<string> _expandedErrors = new();
 
     private int _currentPage = 1;
     private int _totalPages;
     private const int PageSize = 25;
-    private static readonly TimeSpan RefreshInterval = TimeSpan.FromSeconds(10);
+
+    // CentralUI-006: deployment status updates are push-based, not polled.
+    // DeploymentManager raises IDeploymentStatusNotifier.StatusChanged on every
+    // deployment-record status write; this page subscribes to it and reloads,
+    // and Blazor Server pushes the re-render to the browser over its SignalR
+    // circuit — satisfying the design's "no polling required" requirement.
+    // The notifier event is raised on the DeploymentManager service thread, so
+    // the handler marshals onto the renderer via InvokeAsync.
 
     protected override async Task OnInitializedAsync()
     {
         await LoadDataAsync();
-        StartTimer();
+        DeploymentStatusNotifier.StatusChanged += OnDeploymentStatusChanged;
     }
 
-    private void StartTimer()
+    private void OnDeploymentStatusChanged(ScadaLink.DeploymentManager.DeploymentStatusChange change)
     {
-        _refreshTimer?.Dispose();
+        if (!_autoRefresh) return;
-        _refreshTimer = new Timer(_ =>
+        _ = InvokeAsync(async () =>
         {
-            InvokeAsync(async () =>
+            await LoadDataAsync();
-            {
+            StateHasChanged();
-                if (!_autoRefresh) return;
+        });
-                await LoadDataAsync();
-                StateHasChanged();
-            });
-        }, null, RefreshInterval, RefreshInterval);
     }
 
     private void ToggleAutoRefresh()
     {
+        // When paused, incoming push notifications are ignored; "Refresh" still
+        // forces a manual reload. No timer is involved either way.
         _autoRefresh = !_autoRefresh;
-        if (_autoRefresh)
-        {
-            StartTimer();
-        }
-        else
-        {
-            _refreshTimer?.Dispose();
-            _refreshTimer = null;
-        }
     }
 
     private bool IsErrorExpanded(string deploymentId) => _expandedErrors.Contains(deploymentId);
@@ -320,6 +316,8 @@
 
     public void Dispose()
     {
-        _refreshTimer?.Dispose();
+        // Unsubscribe so a status change after the circuit is gone does not
+        // touch a disposed component (the notifier is a process singleton).
+        DeploymentStatusNotifier.StatusChanged -= OnDeploymentStatusChanged;
     }
 }

src/ScadaLink.DeploymentManager/DeploymentService.cs

@@ -41,6 +41,7 @@ public class DeploymentService
     private readonly OperationLockManager _lockManager;
     private readonly IAuditService _auditService;
     private readonly DiffService _diffService;
+    private readonly IDeploymentStatusNotifier _statusNotifier;
     private readonly DeploymentManagerOptions _options;
     private readonly ILogger<DeploymentService> _logger;
 
@@ -60,6 +61,7 @@ public class DeploymentService
         OperationLockManager lockManager,
         IAuditService auditService,
         DiffService diffService,
+        IDeploymentStatusNotifier statusNotifier,
         IOptions<DeploymentManagerOptions> options,
         ILogger<DeploymentService> logger)
     {
@@ -70,10 +72,21 @@ public class DeploymentService
         _lockManager = lockManager;
         _auditService = auditService;
         _diffService = diffService;
+        _statusNotifier = statusNotifier;
         _options = options.Value;
         _logger = logger;
     }
 
+    /// <summary>
+    /// CentralUI-006: raises a push notification that a deployment record's
+    /// status was just persisted, so the Central UI deployment-status page can
+    /// re-render over its SignalR circuit instead of polling. Called at every
+    /// point a <see cref="DeploymentRecord"/> status is written.
+    /// </summary>
+    private void NotifyStatusChange(DeploymentRecord record) =>
+        _statusNotifier.NotifyStatusChanged(
+            new DeploymentStatusChange(record.DeploymentId, record.InstanceId, record.Status));
+
     /// <summary>
     /// Resolves the site's string identifier from the numeric DB ID.
     /// The communication layer routes by string identifier (e.g. "site-a"), not DB ID.
@@ -155,11 +168,13 @@ public class DeploymentService
 
         await _repository.AddDeploymentRecordAsync(record, cancellationToken);
         await _repository.SaveChangesAsync(cancellationToken);
+        NotifyStatusChange(record);
 
         // Update status to InProgress
         record.Status = DeploymentStatus.InProgress;
         await _repository.UpdateDeploymentRecordAsync(record, cancellationToken);
         await _repository.SaveChangesAsync(cancellationToken);
+        NotifyStatusChange(record);
 
         try
         {
@@ -187,6 +202,7 @@ public class DeploymentService
             // non-Success record while the site is running the new config.
             await _repository.UpdateDeploymentRecordAsync(record, cancellationToken);
             await _repository.SaveChangesAsync(cancellationToken);
+            NotifyStatusChange(record);
 
             if (response.Status == DeploymentStatus.Success)
             {
@@ -253,6 +269,7 @@ public class DeploymentService
             {
                 await _repository.UpdateDeploymentRecordAsync(record, CancellationToken.None);
                 await _repository.SaveChangesAsync(CancellationToken.None);
+                NotifyStatusChange(record);
 
                 await _auditService.LogAsync(user, "DeployFailed", "Instance", instanceId.ToString(),
                     instance.UniqueName, new { DeploymentId = deploymentId, Error = ex.Message },
@@ -624,6 +641,7 @@ public class DeploymentService
             prior.CompletedAt = DateTimeOffset.UtcNow;
             await _repository.UpdateDeploymentRecordAsync(prior, cancellationToken);
             await _repository.SaveChangesAsync(cancellationToken);
+            NotifyStatusChange(prior);
 
             await _auditService.LogAsync(prior.DeployedBy, "DeployReconciled", "Instance",
                 instance.Id.ToString(), instance.UniqueName,

src/ScadaLink.DeploymentManager/DeploymentStatusNotifier.cs

@@ -0,0 +1,51 @@
+using Microsoft.Extensions.Logging;
+
+namespace ScadaLink.DeploymentManager;
+
+/// <summary>
+/// Default <see cref="IDeploymentStatusNotifier"/> implementation. A simple
+/// in-process event broadcaster: registered as a DI singleton so it is shared
+/// between the central-process <see cref="DeploymentService"/> and the Central
+/// UI's Blazor circuits (CentralUI-006).
+///
+/// A throwing subscriber must never break the deployment pipeline, so each
+/// handler is invoked individually and its exceptions are caught and logged.
+/// </summary>
+public sealed class DeploymentStatusNotifier : IDeploymentStatusNotifier
+{
+    private readonly ILogger<DeploymentStatusNotifier> _logger;
+
+    public DeploymentStatusNotifier(ILogger<DeploymentStatusNotifier> logger)
+    {
+        _logger = logger;
+    }
+
+    /// <inheritdoc />
+    public event Action<DeploymentStatusChange>? StatusChanged;
+
+    /// <inheritdoc />
+    public void NotifyStatusChanged(DeploymentStatusChange change)
+    {
+        var handlers = StatusChanged;
+        if (handlers == null)
+            return;
+
+        // Invoke each subscriber in isolation: one faulting handler (e.g. a
+        // disposed Blazor circuit) must not stop the others from being notified
+        // and must not propagate back into the deployment pipeline.
+        foreach (var handler in handlers.GetInvocationList())
+        {
+            try
+            {
+                ((Action<DeploymentStatusChange>)handler)(change);
+            }
+            catch (Exception ex)
+            {
+                _logger.LogWarning(ex,
+                    "A deployment-status-change subscriber threw for deployment {DeploymentId} " +
+                    "(status {Status}); continuing with remaining subscribers",
+                    change.DeploymentId, change.Status);
+            }
+        }
+    }
+}

src/ScadaLink.DeploymentManager/IDeploymentStatusNotifier.cs

@@ -0,0 +1,49 @@
+using ScadaLink.Commons.Types.Enums;
+
+namespace ScadaLink.DeploymentManager;
+
+/// <summary>
+/// Payload describing a single deployment-record status change. Kept small —
+/// just the deployment identity, the owning instance, and the new status — so
+/// it is cheap to raise on the hot path and cheap for subscribers to handle.
+/// </summary>
+/// <param name="DeploymentId">The unique deployment ID whose status changed.</param>
+/// <param name="InstanceId">The instance the deployment record belongs to.</param>
+/// <param name="Status">The status the deployment record was just written with.</param>
+public readonly record struct DeploymentStatusChange(
+    string DeploymentId,
+    int InstanceId,
+    DeploymentStatus Status);
+
+/// <summary>
+/// CentralUI-006: push-based deployment-status change notification.
+///
+/// The design (Component-CentralUI "Real-Time Updates") requires deployment
+/// status transitions to push to the UI immediately via SignalR, with no
+/// polling. <see cref="DeploymentService"/> raises <see cref="StatusChanged"/>
+/// whenever it writes a <see cref="Commons.Entities.Deployment.DeploymentRecord"/>
+/// status; the Central UI's deployment-status page subscribes to it and
+/// re-renders over its existing Blazor Server SignalR circuit.
+///
+/// Registered as a DI singleton (see <see cref="ServiceCollectionExtensions.AddDeploymentManager"/>)
+/// so the scoped <see cref="DeploymentService"/> and the Blazor circuit's
+/// scoped page component share the same instance — both run in the same
+/// central Host process.
+/// </summary>
+public interface IDeploymentStatusNotifier
+{
+    /// <summary>
+    /// Raised after a deployment record's status has been written. Handlers run
+    /// synchronously on the caller's thread; subscribers must not block and
+    /// should marshal any UI work onto their own dispatcher.
+    /// </summary>
+    event Action<DeploymentStatusChange>? StatusChanged;
+
+    /// <summary>
+    /// Raises <see cref="StatusChanged"/>. Called by <see cref="DeploymentService"/>
+    /// at every point a deployment record's status is persisted. A throwing
+    /// subscriber must not break the deployment pipeline, so handler exceptions
+    /// are swallowed by the implementation.
+    /// </summary>
+    void NotifyStatusChanged(DeploymentStatusChange change);
+}

src/ScadaLink.DeploymentManager/ServiceCollectionExtensions.cs

@@ -27,6 +27,14 @@ public static class ServiceCollectionExtensions
         // the declared option-class defaults apply.
         services.AddOptions<DeploymentManagerOptions>();
         services.AddSingleton<OperationLockManager>();
+
+        // CentralUI-006: push-based deployment-status notification. Registered
+        // as a singleton so the scoped DeploymentService and the Central UI's
+        // scoped Blazor page component share one instance — both run in the
+        // same central Host process. The deployment-status page subscribes to
+        // it instead of polling the database every 10 seconds.
+        services.AddSingleton<IDeploymentStatusNotifier, DeploymentStatusNotifier>();
+
         services.AddScoped<IFlatteningPipeline, FlatteningPipeline>();
         services.AddScoped<DeploymentService>();
         services.AddScoped<ArtifactDeploymentService>();

tests/ScadaLink.CentralUI.Tests/Deployment/DeploymentsPushUpdateTests.cs

@@ -0,0 +1,112 @@
+using System.Reflection;
+using System.Security.Claims;
+using Bunit;
+using Microsoft.AspNetCore.Components.Authorization;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging.Abstractions;
+using NSubstitute;
+using ScadaLink.CentralUI.Auth;
+using ScadaLink.Commons.Entities.Deployment;
+using ScadaLink.Commons.Entities.Instances;
+using ScadaLink.Commons.Interfaces.Repositories;
+using ScadaLink.Commons.Types.Enums;
+using ScadaLink.DeploymentManager;
+using DeploymentsPage = ScadaLink.CentralUI.Components.Pages.Deployment.Deployments;
+
+namespace ScadaLink.CentralUI.Tests.Deployment;
+
+/// <summary>
+/// Regression tests for CentralUI-006. Component-CentralUI "Real-Time Updates"
+/// states deployment status transitions push to the UI immediately via SignalR
+/// with no polling. The page previously ran a 10-second <c>Timer</c> that
+/// reloaded every deployment record + instance map per tick. The fix removes
+/// the timer and subscribes to <see cref="IDeploymentStatusNotifier"/>, which
+/// <c>DeploymentService</c> raises on every deployment-record status write;
+/// Blazor Server then pushes the re-render over its SignalR circuit.
+/// </summary>
+public class DeploymentsPushUpdateTests : BunitContext
+{
+    private IDeploymentManagerRepository _deployRepo = null!;
+    private ITemplateEngineRepository _templateRepo = null!;
+    private DeploymentStatusNotifier _notifier = null!;
+
+    private void RegisterServices()
+    {
+        _deployRepo = Substitute.For<IDeploymentManagerRepository>();
+        _templateRepo = Substitute.For<ITemplateEngineRepository>();
+        _notifier = new DeploymentStatusNotifier(NullLogger<DeploymentStatusNotifier>.Instance);
+
+        _templateRepo.GetAllInstancesAsync(Arg.Any<CancellationToken>())
+            .Returns(new List<Instance>
+            {
+                new("Inst-1") { Id = 1, SiteId = 1 }
+            });
+        _deployRepo.GetAllDeploymentRecordsAsync(Arg.Any<CancellationToken>())
+            .Returns(new List<DeploymentRecord>());
+
+        Services.AddSingleton(_deployRepo);
+        Services.AddSingleton(_templateRepo);
+        Services.AddSingleton<IDeploymentStatusNotifier>(_notifier);
+
+        var identity = new ClaimsIdentity(
+            new[] { new Claim(ClaimTypes.Name, "deployer") }, "TestCookie");
+        var stubAuth = new StubAuthStateProvider(
+            new AuthenticationState(new ClaimsPrincipal(identity)));
+        Services.AddSingleton<AuthenticationStateProvider>(stubAuth);
+        Services.AddScoped(_ => new SiteScopeService(stubAuth));
+    }
+
+    private sealed class StubAuthStateProvider : AuthenticationStateProvider
+    {
+        private readonly AuthenticationState _state;
+        public StubAuthStateProvider(AuthenticationState state) => _state = state;
+        public override Task<AuthenticationState> GetAuthenticationStateAsync()
+            => Task.FromResult(_state);
+    }
+
+    [Fact]
+    public void Deployments_DoesNotPoll_HasNoRefreshTimer()
+    {
+        // The 10-second polling Timer must be gone — push replaces polling.
+        var timerField = typeof(DeploymentsPage).GetField(
+            "_refreshTimer", BindingFlags.Instance | BindingFlags.NonPublic);
+
+        Assert.Null(timerField);
+    }
+
+    [Fact]
+    public void Deployments_StatusChange_TriggersReload()
+    {
+        RegisterServices();
+        var cut = Render<DeploymentsPage>();
+
+        // Initial load: instances + records each fetched once.
+        _deployRepo.ClearReceivedCalls();
+        _templateRepo.ClearReceivedCalls();
+
+        // A deployment status write in DeploymentManager raises the notifier;
+        // the page must reload in response (no polling timer involved).
+        _notifier.NotifyStatusChanged(
+            new DeploymentStatusChange("dep-1", 1, DeploymentStatus.Success));
+
+        cut.WaitForAssertion(() =>
+            _deployRepo.Received().GetAllDeploymentRecordsAsync(Arg.Any<CancellationToken>()));
+    }
+
+    [Fact]
+    public void Deployments_Dispose_UnsubscribesFromNotifier()
+    {
+        RegisterServices();
+        var cut = Render<DeploymentsPage>();
+
+        cut.Instance.Dispose();
+        _deployRepo.ClearReceivedCalls();
+
+        // After disposal, a status change must NOT touch the disposed component.
+        _notifier.NotifyStatusChanged(
+            new DeploymentStatusChange("dep-2", 1, DeploymentStatus.Failed));
+
+        _deployRepo.DidNotReceive()
+            .GetAllDeploymentRecordsAsync(Arg.Any<CancellationToken>());
+    }
+}

tests/ScadaLink.CentralUI.Tests/TopologyPageTests.cs

@@ -57,6 +57,11 @@ public class TopologyPageTests : BunitContext
         // DeploymentService gained a DiffService dependency (DeploymentManager
         // contract change); register it so the page's DI graph resolves.
         Services.AddScoped<ScadaLink.TemplateEngine.Flattening.DiffService>();
+        // CentralUI-006: DeploymentService now also depends on the
+        // deployment-status notifier (a process singleton in production).
+        Services.AddSingleton<ScadaLink.DeploymentManager.IDeploymentStatusNotifier>(
+            new ScadaLink.DeploymentManager.DeploymentStatusNotifier(
+                NullLogger<ScadaLink.DeploymentManager.DeploymentStatusNotifier>.Instance));
         Services.AddScoped<DeploymentService>();
         Services.AddScoped<AreaService>();
         Services.AddScoped<InstanceService>();

tests/ScadaLink.DeploymentManager.Tests/DeploymentServiceTests.cs

@@ -47,7 +47,9 @@ public class DeploymentServiceTests : TestKit
         var siteRepo = Substitute.For<ISiteRepository>();
         _service = new DeploymentService(
             _repo, siteRepo, _pipeline, _comms, _lockManager, _audit,
-            new DiffService(), options,
+            new DiffService(),
+            new DeploymentStatusNotifier(NullLogger<DeploymentStatusNotifier>.Instance),
+            options,
             NullLogger<DeploymentService>.Instance);
     }
 
@@ -577,6 +579,7 @@ public class DeploymentServiceTests : TestKit
         return new DeploymentService(
             _repo, siteRepo, _pipeline, comms, _lockManager, _audit,
             new DiffService(),
+            new DeploymentStatusNotifier(NullLogger<DeploymentStatusNotifier>.Instance),
             Options.Create(new DeploymentManagerOptions { OperationLockTimeout = TimeSpan.FromSeconds(5) }),
             NullLogger<DeploymentService>.Instance);
     }
@@ -792,6 +795,7 @@ public class DeploymentServiceTests : TestKit
         var service = new DeploymentService(
             _repo, siteRepo, _pipeline, comms, _lockManager, _audit,
             new DiffService(),
+            new DeploymentStatusNotifier(NullLogger<DeploymentStatusNotifier>.Instance),
             Options.Create(new DeploymentManagerOptions
             {
                 OperationLockTimeout = TimeSpan.FromSeconds(5),

tests/ScadaLink.DeploymentManager.Tests/DeploymentStatusNotifierTests.cs

@@ -0,0 +1,114 @@
+using Akka.TestKit.Xunit2;
+using Microsoft.Extensions.Logging.Abstractions;
+using Microsoft.Extensions.Options;
+using NSubstitute;
+using ScadaLink.Commons.Entities.Deployment;
+using ScadaLink.Commons.Entities.Instances;
+using ScadaLink.Commons.Interfaces.Repositories;
+using ScadaLink.Commons.Interfaces.Services;
+using ScadaLink.Commons.Types;
+using ScadaLink.Commons.Types.Enums;
+using ScadaLink.Commons.Types.Flattening;
+using ScadaLink.Communication;
+using ScadaLink.TemplateEngine.Flattening;
+
+namespace ScadaLink.DeploymentManager.Tests;
+
+/// <summary>
+/// CentralUI-006: regression tests proving <see cref="DeploymentService"/>
+/// raises <see cref="IDeploymentStatusNotifier.StatusChanged"/> whenever it
+/// writes a deployment record's status. This is the event source the Central
+/// UI deployment-status page subscribes to instead of polling.
+/// </summary>
+public class DeploymentStatusNotifierTests : TestKit
+{
+    private readonly IDeploymentManagerRepository _repo;
+    private readonly IFlatteningPipeline _pipeline;
+    private readonly CommunicationService _comms;
+    private readonly OperationLockManager _lockManager;
+    private readonly IAuditService _audit;
+    private readonly DeploymentStatusNotifier _notifier;
+    private readonly DeploymentService _service;
+
+    public DeploymentStatusNotifierTests()
+    {
+        _repo = Substitute.For<IDeploymentManagerRepository>();
+        _pipeline = Substitute.For<IFlatteningPipeline>();
+        _comms = new CommunicationService(
+            Options.Create(new CommunicationOptions()),
+            NullLogger<CommunicationService>.Instance);
+        _lockManager = new OperationLockManager();
+        _audit = Substitute.For<IAuditService>();
+        _notifier = new DeploymentStatusNotifier(NullLogger<DeploymentStatusNotifier>.Instance);
+
+        var options = Options.Create(new DeploymentManagerOptions
+        {
+            OperationLockTimeout = TimeSpan.FromSeconds(5)
+        });
+
+        var siteRepo = Substitute.For<ISiteRepository>();
+        _service = new DeploymentService(
+            _repo, siteRepo, _pipeline, _comms, _lockManager, _audit,
+            new DiffService(), _notifier, options,
+            NullLogger<DeploymentService>.Instance);
+    }
+
+    [Fact]
+    public async Task DeployInstanceAsync_RaisesStatusChange_ForEveryRecordStatusWrite()
+    {
+        var instance = new Instance("TestInst") { Id = 7, SiteId = 1, State = InstanceState.NotDeployed };
+        _repo.GetInstanceByIdAsync(7).Returns(instance);
+
+        var config = new FlattenedConfiguration { InstanceUniqueName = "TestInst" };
+        _pipeline.FlattenAndValidateAsync(7, Arg.Any<CancellationToken>())
+            .Returns(Result<FlatteningPipelineResult>.Success(
+                new FlatteningPipelineResult(config, "sha256:abc", ValidationResult.Success())));
+
+        var changes = new List<DeploymentStatusChange>();
+        _notifier.StatusChanged += c => changes.Add(c);
+
+        // _comms has no actor set, so the deploy reaches the catch block and
+        // the record ends Failed. The notifier must fire for the Pending,
+        // InProgress and Failed writes — not be silent (the pre-fix behaviour).
+        var result = await _service.DeployInstanceAsync(7, "admin");
+
+        Assert.True(result.IsFailure);
+        Assert.NotEmpty(changes);
+        Assert.All(changes, c => Assert.Equal(7, c.InstanceId));
+        Assert.Contains(changes, c => c.Status == DeploymentStatus.Pending);
+        Assert.Contains(changes, c => c.Status == DeploymentStatus.InProgress);
+        Assert.Contains(changes, c => c.Status == DeploymentStatus.Failed);
+
+        // All notifications carry the same deployment id (the one created here).
+        var deploymentId = changes[0].DeploymentId;
+        Assert.False(string.IsNullOrEmpty(deploymentId));
+        Assert.All(changes, c => Assert.Equal(deploymentId, c.DeploymentId));
+    }
+
+    [Fact]
+    public void NotifyStatusChanged_WithNoSubscribers_DoesNotThrow()
+    {
+        var notifier = new DeploymentStatusNotifier(NullLogger<DeploymentStatusNotifier>.Instance);
+
+        var ex = Record.Exception(() =>
+            notifier.NotifyStatusChanged(new DeploymentStatusChange("dep-1", 1, DeploymentStatus.Success)));
+
+        Assert.Null(ex);
+    }
+
+    [Fact]
+    public void NotifyStatusChanged_ThrowingSubscriber_DoesNotBreakOtherSubscribers()
+    {
+        var notifier = new DeploymentStatusNotifier(NullLogger<DeploymentStatusNotifier>.Instance);
+        var reached = false;
+
+        notifier.StatusChanged += _ => throw new InvalidOperationException("boom");
+        notifier.StatusChanged += _ => reached = true;
+
+        var ex = Record.Exception(() =>
+            notifier.NotifyStatusChanged(new DeploymentStatusChange("dep-2", 2, DeploymentStatus.InProgress)));
+
+        Assert.Null(ex);
+        Assert.True(reached, "a faulting subscriber must not stop later subscribers from being notified");
+    }
+}

tests/ScadaLink.DeploymentManager.Tests/ServiceCollectionExtensionsTests.cs

@@ -56,4 +56,25 @@ public class ServiceCollectionExtensionsTests
     {
         Assert.Equal("ScadaLink:DeploymentManager", ServiceCollectionExtensions.OptionsSection);
     }
+
+    // CentralUI-006: the deployment-status notifier must be a singleton so the
+    // scoped DeploymentService and the Central UI's scoped Blazor page share
+    // one instance — without that, a push notification raised by the service
+    // would never reach the page's subscription.
+    [Fact]
+    public void AddDeploymentManager_RegistersDeploymentStatusNotifier_AsSingleton()
+    {
+        var services = new ServiceCollection();
+        services.AddLogging();
+        services.AddDeploymentManager();
+
+        using var provider = services.BuildServiceProvider();
+
+        var fromRoot = provider.GetRequiredService<IDeploymentStatusNotifier>();
+        using var scope = provider.CreateScope();
+        var fromScope = scope.ServiceProvider.GetRequiredService<IDeploymentStatusNotifier>();
+
+        Assert.IsType<DeploymentStatusNotifier>(fromRoot);
+        Assert.Same(fromRoot, fromScope);
+    }
 }