fix(central-ui): resolve CentralUI-020..025 — auth-ping idle logout, DebugView race, push-handler disposal guard, JS-interop catch narrowing, claim-constant helper, SessionExpiry tests

code-reviews/CentralUI/findings.md

@@ -8,7 +8,7 @@
 | Last reviewed | 2026-05-17 |
 | Reviewer | claude-agent |
 | Commit reviewed | `39d737e` |
-| Open findings | 6 |
+| Open findings | 0 |
 
 ## Summary
 
@@ -994,7 +994,7 @@ in the fixture.)
 |--|--|
 | Severity | High |
 | Category | Concurrency & thread safety |
-| Status | Open |
+| Status | Resolved |
 | Location | `src/ScadaLink.CentralUI/Components/Shared/SessionExpiry.razor:39-62`; `src/ScadaLink.CentralUI/Auth/CookieAuthenticationStateProvider.cs:29-43` |
 
 **Description**
@@ -1036,7 +1036,7 @@ expired session (see CentralUI-025).
 
 **Resolution**
 
-_Unresolved._
+2026-05-17 — `SessionExpiry` no longer polls the frozen `AuthenticationStateProvider`; it polls a new anonymous `GET /auth/ping` minimal-API endpoint (re-validated by the cookie middleware on every HTTP request) via a `fetch()` JS helper and redirects to `/login` on HTTP 401, so the documented 30-minute idle logout actually fires.
 
 ### CentralUI-021 — `DebugView` stream callback mutates `Dictionary` off the render thread
 
@@ -1044,7 +1044,7 @@ _Unresolved._
 |--|--|
 | Severity | Medium |
 | Category | Concurrency & thread safety |
-| Status | Open |
+| Status | Resolved |
 | Location | `src/ScadaLink.CentralUI/Components/Pages/Deployment/DebugView.razor:404-419,511-519,275-289` |
 
 **Description**
@@ -1075,7 +1075,7 @@ critical section as the upsert.
 
 **Resolution**
 
-_Unresolved._
+2026-05-17 — the stream callback now routes through `HandleStreamEvent`, which marshals the `UpsertWithCap` mutation (and the cap-trim loop) onto the renderer's dispatcher via `SafeInvokeAsync`, so every read and write of `_attributeValues`/`_alarmStates` happens on the render thread.
 
 ### CentralUI-022 — `Deployments` push handler fires `InvokeAsync` with no disposal guard
 
@@ -1083,7 +1083,7 @@ _Unresolved._
 |--|--|
 | Severity | Medium |
 | Category | Error handling & resilience |
-| Status | Open |
+| Status | Resolved |
 | Location | `src/ScadaLink.CentralUI/Components/Pages/Deployment/Deployments.razor:221-229,317-322` |
 
 **Description**
@@ -1114,7 +1114,7 @@ rather than the whole table on each event.
 
 **Resolution**
 
-_Unresolved._
+2026-05-17 — added a `volatile bool _disposed` set first in `Dispose()`; `OnDeploymentStatusChanged` no-ops when set, and the fire-and-forget dispatch (`DispatchReloadAsync`) swallows the residual `ObjectDisposedException`, mirroring the `DebugView`/`ToastNotification` guards.
 
 ### CentralUI-023 — Residual bare `catch {}` blocks swallow JS interop errors
 
@@ -1122,7 +1122,7 @@ _Unresolved._
 |--|--|
 | Severity | Low |
 | Category | Error handling & resilience |
-| Status | Open |
+| Status | Resolved |
 | Location | `src/ScadaLink.CentralUI/Components/Pages/Monitoring/ParkedMessages.razor:690-698`; `src/ScadaLink.CentralUI/Components/Shared/DiffDialog.razor:107-116,118-130,104` |
 
 **Description**
@@ -1147,7 +1147,7 @@ call, consistent with the CentralUI-018 fixes in the same module.
 
 **Resolution**
 
-_Unresolved._
+2026-05-17 — the bare `catch` blocks in `ParkedMessages.CopyAsync` and `DiffDialog.TryLockBodyAsync`/`TryUnlockBodyAsync`/`OnAfterRenderAsync` now catch `JSDisconnectedException` (and `InvalidOperationException` for prerender focus) silently and log genuine `JSException` failures via injected `ILogger`.
 
 ### CentralUI-024 — Claim lookups use magic strings instead of `JwtTokenService` constants
 
@@ -1155,7 +1155,7 @@ _Unresolved._
 |--|--|
 | Severity | Low |
 | Category | Code organization & conventions |
-| Status | Open |
+| Status | Resolved |
 | Location | `src/ScadaLink.CentralUI/Components/Layout/NavMenu.razor:102`; `src/ScadaLink.CentralUI/Components/Pages/Dashboard.razor:14`; `GetCurrentUserAsync` in `Templates.razor`, `TemplateEdit.razor`, `TemplateCreate.razor`, `SharedScripts.razor`, `SharedScriptForm.razor`, `Sites.razor`, `Topology.razor`, `InstanceCreate.razor`, `InstanceConfigure.razor` |
 
 **Description**
@@ -1181,7 +1181,7 @@ or a small scoped service) so the claim lookup lives in exactly one place.
 
 **Resolution**
 
-_Unresolved._
+2026-05-17 — added `ClaimsPrincipalExtensions` (`GetUsername`/`GetDisplayName`/`GetCurrentUsernameAsync`) resolving claims through the `JwtTokenService` constants; the ten copy-pasted `GetCurrentUserAsync` helpers and the `NavMenu`/`Dashboard` `DisplayName` lookups now delegate to it, eliminating every magic-string claim literal.
 
 ### CentralUI-025 — `SessionExpiry` polling/redirect path has no test coverage
 
@@ -1189,7 +1189,7 @@ _Unresolved._
 |--|--|
 | Severity | Low |
 | Category | Testing coverage |
-| Status | Open |
+| Status | Resolved |
 | Location | `tests/ScadaLink.CentralUI.Tests/Auth/SessionExpiryPolicyTests.cs`; `src/ScadaLink.CentralUI/Components/Shared/SessionExpiry.razor` |
 
 **Description**
@@ -1215,4 +1215,4 @@ also forces the CentralUI-020 fix.
 
 **Resolution**
 
-_Unresolved._
+2026-05-17 — added `SessionExpiryComponentTests` (bUnit): an expired ping (401) redirects to `/login`, a live ping (200) and a transient failure (status 0) do not, and on the `/login` route the component neither pings nor redirects; also added `AuthPingEndpointTests` covering the `/auth/ping` endpoint contract.

src/ScadaLink.CentralUI/Auth/AuthEndpoints.cs

@@ -134,9 +134,35 @@ public static class AuthEndpoints
             context.Response.Redirect("/login");
         });
 
+        // CentralUI-020: liveness probe for the client-side idle-logout check.
+        // The Blazor circuit's CookieAuthenticationStateProvider serves a frozen
+        // constructor-time principal (CentralUI-004), so a circuit can never
+        // observe a server-side cookie expiry by polling the auth state.
+        // SessionExpiry instead polls this endpoint via fetch(): being a normal
+        // HTTP request, the cookie middleware re-validates (and slides) the
+        // cookie on every hit. It deliberately does NOT use RequireAuthorization
+        // — that would make the middleware answer a lapsed request with a 302 to
+        // /login, which fetch() follows transparently and reads as a 200 login
+        // page. Allowing anonymous access and returning 200/401 ourselves gives
+        // the client an unambiguous expiry signal.
+        endpoints.MapGet("/auth/ping", HandlePing);
+
         return endpoints;
     }
 
+    /// <summary>
+    /// Handler for <c>GET /auth/ping</c>. Returns <c>200</c> while the caller's
+    /// cookie session is still valid and <c>401</c> once it has lapsed
+    /// server-side. See CentralUI-020.
+    /// </summary>
+    public static Task HandlePing(HttpContext context)
+    {
+        context.Response.StatusCode = context.User.Identity?.IsAuthenticated == true
+            ? StatusCodes.Status200OK
+            : StatusCodes.Status401Unauthorized;
+        return Task.CompletedTask;
+    }
+
     /// <summary>
     /// Builds the <see cref="AuthenticationProperties"/> for the login sign-in.
     /// CentralUI-005: deliberately does <b>not</b> set <see cref="AuthenticationProperties.ExpiresUtc"/>.

src/ScadaLink.CentralUI/Auth/ClaimsPrincipalExtensions.cs

@@ -0,0 +1,43 @@
+using System.Security.Claims;
+using Microsoft.AspNetCore.Components.Authorization;
+using ScadaLink.Security;
+
+namespace ScadaLink.CentralUI.Auth;
+
+/// <summary>
+/// Claim-lookup helpers for the Central UI. CentralUI-024: claim types are owned
+/// by <see cref="JwtTokenService"/> (the single source of truth). These helpers
+/// resolve them through the <c>JwtTokenService</c> constants so a rename there
+/// propagates here instead of silently breaking ten copy-pasted call sites.
+/// </summary>
+public static class ClaimsPrincipalExtensions
+{
+    /// <summary>Fallback returned when no username claim is present.</summary>
+    public const string UnknownUser = "unknown";
+
+    /// <summary>
+    /// The audit username for <paramref name="principal"/>, or
+    /// <see cref="UnknownUser"/> when the claim is absent.
+    /// </summary>
+    public static string GetUsername(this ClaimsPrincipal principal)
+        => principal.FindFirst(JwtTokenService.UsernameClaimType)?.Value ?? UnknownUser;
+
+    /// <summary>
+    /// The display name for <paramref name="principal"/>, or <c>null</c> when
+    /// the claim is absent.
+    /// </summary>
+    public static string? GetDisplayName(this ClaimsPrincipal principal)
+        => principal.FindFirst(JwtTokenService.DisplayNameClaimType)?.Value;
+
+    /// <summary>
+    /// Resolves the current user's audit username from the auth state provider.
+    /// Replaces the <c>GetCurrentUserAsync</c> helper that was copy-pasted into
+    /// ten components (CentralUI-024).
+    /// </summary>
+    public static async Task<string> GetCurrentUsernameAsync(
+        this AuthenticationStateProvider authStateProvider)
+    {
+        var authState = await authStateProvider.GetAuthenticationStateAsync();
+        return authState.User.GetUsername();
+    }
+}

src/ScadaLink.CentralUI/Components/Layout/NavMenu.razor

@@ -99,7 +99,8 @@
         <Authorized>
             <div class="border-top border-secondary px-3 py-2">
                 <div class="d-flex justify-content-between align-items-center">
-                    <span class="text-light small">@context.User.FindFirst("DisplayName")?.Value</span>
+                    @* CentralUI-024: claim type resolved via JwtTokenService. *@
+                    <span class="text-light small">@context.User.GetDisplayName()</span>
                     <form method="post" action="/auth/logout" data-enhance="false">
                         @* CentralUI-017: logout is a state-changing POST and is
                            CSRF-protected — the antiforgery token is required. *@

src/ScadaLink.CentralUI/Components/Pages/Admin/Sites.razor

@@ -160,11 +160,10 @@
 </div>
 
 @code {
-    private async Task<string> GetCurrentUserAsync()
+    // CentralUI-024: delegates to the shared helper so the claim type stays
-    {
+    // resolved through JwtTokenService rather than a duplicated magic string.
-        var authState = await AuthStateProvider.GetAuthenticationStateAsync();
+    private Task<string> GetCurrentUserAsync()
-        return authState.User.FindFirst("Username")?.Value ?? "unknown";
+        => AuthStateProvider.GetCurrentUsernameAsync();
-    }
 
     private List<Site> _sites = new();
     private Dictionary<int, List<DataConnection>> _siteConnections = new();

src/ScadaLink.CentralUI/Components/Pages/Dashboard.razor

@@ -11,7 +11,8 @@
         <AuthorizeView>
             <Authorized>
                 <span class="text-muted small">
-                    Signed in as <strong>@context.User.FindFirst("DisplayName")?.Value</strong>
+                    @* CentralUI-024: claim type resolved via JwtTokenService. *@
+                    Signed in as <strong>@context.User.GetDisplayName()</strong>
                 </span>
             </Authorized>
         </AuthorizeView>

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

@@ -401,23 +401,7 @@
         {
             var session = await DebugStreamService.StartStreamAsync(
                 _selectedInstanceId,
-                onEvent: evt =>
+                onEvent: HandleStreamEvent,
-                {
-                    // CentralUI-009: the component may have been disposed while
-                    // this event was in flight on the Akka/gRPC thread.
-                    if (_disposed) return;
-                    switch (evt)
-                    {
-                        case AttributeValueChanged av:
-                            UpsertWithCap(_attributeValues, av.AttributeName, av);
-                            SafeInvokeStateHasChanged();
-                            break;
-                        case AlarmStateChanged al:
-                            UpsertWithCap(_alarmStates, al.AlarmName, al);
-                            SafeInvokeStateHasChanged();
-                            break;
-                    }
-                },
                 onTerminated: () =>
                 {
                     _connected = false;
@@ -503,10 +487,51 @@
         _alarmStates.Clear();
     }
 
+    /// <summary>
+    /// Handles one debug-stream event. The callback is invoked on an Akka/gRPC
+    /// thread, but <see cref="_attributeValues"/>/<see cref="_alarmStates"/> are
+    /// <see cref="Dictionary{TKey,TValue}"/> instances also enumerated by the
+    /// render thread via <see cref="FilteredAttributeValues"/>/
+    /// <see cref="FilteredAlarmStates"/>. <c>Dictionary</c> is not thread-safe
+    /// (CentralUI-021): a write racing an enumeration can throw or corrupt the
+    /// buckets. The mutation (<see cref="UpsertWithCap"/>) is therefore
+    /// marshalled onto the renderer's dispatcher via <see cref="SafeInvokeAsync"/>
+    /// so every access to the dictionaries — read and write — happens on the
+    /// render thread.
+    /// </summary>
+    private void HandleStreamEvent(object evt)
+    {
+        // CentralUI-009: the component may have been disposed while this event
+        // was in flight on the Akka/gRPC thread.
+        if (_disposed) return;
+        _ = SafeInvokeAsync(() =>
+        {
+            if (_disposed) return;
+            switch (evt)
+            {
+                case AttributeValueChanged av:
+                    UpsertWithCap(_attributeValues, av.AttributeName, av);
+                    break;
+                case AlarmStateChanged al:
+                    UpsertWithCap(_alarmStates, al.AlarmName, al);
+                    break;
+                default:
+                    return;
+            }
+            StateHasChanged();
+        });
+    }
+
     /// <summary>
     /// Replace or insert a value keyed by name, then trim the oldest entries
     /// (queue-style) so the table size never exceeds MaxRows. Dictionary
     /// preserves insertion order, so the first key is always the oldest.
+    /// <para>
+    /// Must be called on the render thread only (CentralUI-021) — see
+    /// <see cref="HandleStreamEvent"/>. The cap-trim loop is in the same
+    /// critical section as the upsert so the dictionary is never observed
+    /// over-capacity.
+    /// </para>
     /// </summary>
     private static void UpsertWithCap<T>(Dictionary<string, T> map, string key, T value)
     {
@@ -577,8 +602,6 @@
         }
     }
 
-    private void SafeInvokeStateHasChanged() => _ = SafeInvokeAsync(StateHasChanged);
-
     public void Dispose()
     {
         // CentralUI-009: mark disposed first so any in-flight stream callback

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

@@ -204,6 +204,17 @@
     private int _totalPages;
     private const int PageSize = 25;
 
+    // CentralUI-022: IDeploymentStatusNotifier is a process singleton that
+    // raises StatusChanged on the DeploymentManager service thread. Dispose()
+    // unsubscribes, but the notifier can read its subscriber list and begin
+    // invoking OnDeploymentStatusChanged just before this component is disposed.
+    // The handler then runs against a disposed component and InvokeAsync throws
+    // ObjectDisposedException as an unobserved fire-and-forget task exception.
+    // This flag (set first in Dispose()) makes a racing callback no-op, and the
+    // dispatch swallows the residual ObjectDisposedException — mirroring the
+    // DebugView (CentralUI-009) and ToastNotification (CentralUI-010) guards.
+    private volatile bool _disposed;
+
     // 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,
@@ -220,12 +231,34 @@
 
     private void OnDeploymentStatusChanged(ScadaLink.DeploymentManager.DeploymentStatusChange change)
     {
-        if (!_autoRefresh) return;
+        // CentralUI-022: a callback racing disposal must not touch the component.
-        _ = InvokeAsync(async () =>
+        if (_disposed || !_autoRefresh) return;
+        _ = DispatchReloadAsync();
+    }
+
+    /// <summary>
+    /// Reloads the deployment table on the renderer's dispatcher, guarded
+    /// against the component being disposed mid-flight (CentralUI-022):
+    /// <c>InvokeAsync</c> throws <see cref="ObjectDisposedException"/> once the
+    /// circuit is gone, and this handler runs fire-and-forget so that exception
+    /// would otherwise go unobserved on the DeploymentManager thread.
+    /// </summary>
+    private async Task DispatchReloadAsync()
+    {
+        if (_disposed) return;
+        try
         {
-            await LoadDataAsync();
+            await InvokeAsync(async () =>
-            StateHasChanged();
+            {
-        });
+                if (_disposed) return;
+                await LoadDataAsync();
+                StateHasChanged();
+            });
+        }
+        catch (ObjectDisposedException)
+        {
+            // Component disposed between the guard and the dispatch — ignore.
+        }
     }
 
     private void ToggleAutoRefresh()
@@ -316,8 +349,10 @@
 
     public void Dispose()
     {
-        // Unsubscribe so a status change after the circuit is gone does not
+        // CentralUI-022: set the guard first so a callback already in flight on
-        // touch a disposed component (the notifier is a process singleton).
+        // the DeploymentManager thread no-ops, then unsubscribe so no further
+        // status change reaches this disposed component.
+        _disposed = true;
         DeploymentStatusNotifier.StatusChanged -= OnDeploymentStatusChanged;
     }
 }

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

@@ -438,11 +438,10 @@
 
     private void GoBack() => NavigationManager.NavigateTo("/deployment/topology");
 
-    private async Task<string> GetCurrentUserAsync()
+    // CentralUI-024: delegates to the shared helper so the claim type stays
-    {
+    // resolved through JwtTokenService rather than a duplicated magic string.
-        var authState = await AuthStateProvider.GetAuthenticationStateAsync();
+    private Task<string> GetCurrentUserAsync()
-        return authState.User.FindFirst("Username")?.Value ?? "unknown";
+        => AuthStateProvider.GetCurrentUsernameAsync();
-    }
 
     // ── Bindings ────────────────────────────────────────────
 

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

@@ -157,9 +157,8 @@
 
     private void GoBack() => NavigationManager.NavigateTo("/deployment/topology");
 
-    private async Task<string> GetCurrentUserAsync()
+    // CentralUI-024: delegates to the shared helper so the claim type stays
-    {
+    // resolved through JwtTokenService rather than a duplicated magic string.
-        var authState = await AuthStateProvider.GetAuthenticationStateAsync();
+    private Task<string> GetCurrentUserAsync()
-        return authState.User.FindFirst("Username")?.Value ?? "unknown";
+        => AuthStateProvider.GetCurrentUsernameAsync();
-    }
 }

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

@@ -921,9 +921,8 @@
         }
     }
 
-    private async Task<string> GetCurrentUserAsync()
+    // CentralUI-024: delegates to the shared helper so the claim type stays
-    {
+    // resolved through JwtTokenService rather than a duplicated magic string.
-        var authState = await AuthStateProvider.GetAuthenticationStateAsync();
+    private Task<string> GetCurrentUserAsync()
-        return authState.User.FindFirst("Username")?.Value ?? "unknown";
+        => AuthStateProvider.GetCurrentUsernameAsync();
-    }
 }

src/ScadaLink.CentralUI/Components/Pages/Design/SharedScriptForm.razor

@@ -172,11 +172,10 @@
     private ScriptAnalysis.SandboxRunResult? _runResult;
     private CancellationTokenSource? _runCts;
 
-    private async Task<string> GetCurrentUserAsync()
+    // CentralUI-024: delegates to the shared helper so the claim type stays
-    {
+    // resolved through JwtTokenService rather than a duplicated magic string.
-        var authState = await AuthStateProvider.GetAuthenticationStateAsync();
+    private Task<string> GetCurrentUserAsync()
-        return authState.User.FindFirst("Username")?.Value ?? "unknown";
+        => AuthStateProvider.GetCurrentUsernameAsync();
-    }
 
     protected override async Task OnInitializedAsync()
     {

src/ScadaLink.CentralUI/Components/Pages/Design/SharedScripts.razor

@@ -101,11 +101,10 @@
 </div>
 
 @code {
-    private async Task<string> GetCurrentUserAsync()
+    // CentralUI-024: delegates to the shared helper so the claim type stays
-    {
+    // resolved through JwtTokenService rather than a duplicated magic string.
-        var authState = await AuthStateProvider.GetAuthenticationStateAsync();
+    private Task<string> GetCurrentUserAsync()
-        return authState.User.FindFirst("Username")?.Value ?? "unknown";
+        => AuthStateProvider.GetCurrentUsernameAsync();
-    }
 
     private List<SharedScript> _scripts = new();
     private bool _loading = true;

src/ScadaLink.CentralUI/Components/Pages/Design/TemplateCreate.razor

@@ -119,9 +119,8 @@
         NavigationManager.NavigateTo("/design/templates");
     }
 
-    private async Task<string> GetCurrentUserAsync()
+    // CentralUI-024: delegates to the shared helper so the claim type stays
-    {
+    // resolved through JwtTokenService rather than a duplicated magic string.
-        var authState = await AuthStateProvider.GetAuthenticationStateAsync();
+    private Task<string> GetCurrentUserAsync()
-        return authState.User.FindFirst("Username")?.Value ?? "unknown";
+        => AuthStateProvider.GetCurrentUsernameAsync();
-    }
 }

src/ScadaLink.CentralUI/Components/Pages/Design/TemplateEdit.razor

@@ -218,11 +218,10 @@
         NavigationManager.NavigateTo("/design/templates");
     }
 
-    private async Task<string> GetCurrentUserAsync()
+    // CentralUI-024: delegates to the shared helper so the claim type stays
-    {
+    // resolved through JwtTokenService rather than a duplicated magic string.
-        var authState = await AuthStateProvider.GetAuthenticationStateAsync();
+    private Task<string> GetCurrentUserAsync()
-        return authState.User.FindFirst("Username")?.Value ?? "unknown";
+        => AuthStateProvider.GetCurrentUsernameAsync();
-    }
 
     private RenderFragment RenderTemplateDetail() => __builder =>
     {

src/ScadaLink.CentralUI/Components/Pages/Design/Templates.razor

@@ -99,11 +99,10 @@
 </div>
 
 @code {
-    private async Task<string> GetCurrentUserAsync()
+    // CentralUI-024: delegates to the shared helper so the claim type stays
-    {
+    // resolved through JwtTokenService rather than a duplicated magic string.
-        var authState = await AuthStateProvider.GetAuthenticationStateAsync();
+    private Task<string> GetCurrentUserAsync()
-        return authState.User.FindFirst("Username")?.Value ?? "unknown";
+        => AuthStateProvider.GetCurrentUsernameAsync();
-    }
 
     private List<Template> _templates = new();
     private List<TemplateFolder> _folders = new();

src/ScadaLink.CentralUI/Components/Pages/Monitoring/ParkedMessages.razor

@@ -10,6 +10,7 @@
 @inject CommunicationService CommunicationService
 @inject IJSRuntime JS
 @inject IDialogService Dialog
+@inject ILogger<ParkedMessages> Logger
 
 <div class="container-fluid mt-3">
     <ToastNotification @ref="_toast" />
@@ -694,7 +695,18 @@
             await JS.InvokeVoidAsync("navigator.clipboard.writeText", text);
             _toast.ShowSuccess("Copied to clipboard.");
         }
-        catch { _toast.ShowError("Copy failed."); }
+        catch (JSDisconnectedException)
+        {
+            // Circuit gone — the page is being torn down; nothing to surface.
+            // CentralUI-023: distinguished from a genuine interop failure.
+        }
+        catch (JSException ex)
+        {
+            // A real clipboard failure (e.g. permission denied) — surface it to
+            // the user and log it so it is not invisible in production.
+            Logger.LogWarning(ex, "Clipboard copy failed.");
+            _toast.ShowError("Copy failed.");
+        }
     }
 
     // ── Helpers ──

src/ScadaLink.CentralUI/Components/Shared/DiffDialog.razor

@@ -3,6 +3,7 @@
    via @ref to display a side-by-side or simple before/after comparison.
    z-index ladder follows ConfirmDialog: modal 1055 > backdrop 1040 (toasts at 1090). *@
 @inject IJSRuntime JS
+@inject ILogger<DiffDialog> Logger
 @implements IAsyncDisposable
 
 @if (_visible)
@@ -101,7 +102,20 @@
             _bodyLocked = true;
             await TryLockBodyAsync();
             try { await _modalRef.FocusAsync(); }
-            catch { /* prerender or detached: ignore */ }
+            catch (InvalidOperationException)
+            {
+                // Prerender: the element reference is not attached yet — the
+                // next interactive render focuses it. Expected, not logged.
+            }
+            catch (JSDisconnectedException)
+            {
+                // Circuit gone before focus could run — nothing to do.
+            }
+            catch (JSException ex)
+            {
+                // A genuine focus interop failure (CentralUI-023) — log it.
+                Logger.LogWarning(ex, "DiffDialog: failed to focus the modal.");
+            }
         }
     }
 
@@ -127,10 +141,15 @@
         {
             await JS.InvokeVoidAsync("document.body.classList.add", "modal-open");
         }
-        catch
+        catch (JSDisconnectedException)
         {
-            try { await JS.InvokeVoidAsync("console.debug", "DiffDialog: JS interop unavailable for body lock."); }
+            // Circuit gone — the body scroll lock is moot. Expected, silent.
-            catch { /* swallow */ }
+        }
+        catch (JSException ex)
+        {
+            // CentralUI-023: a genuine interop failure — log instead of doing
+            // another (also-failing) JS call inside a bare catch.
+            Logger.LogWarning(ex, "DiffDialog: failed to apply body scroll lock.");
         }
     }
 
@@ -141,10 +160,13 @@
         {
             await JS.InvokeVoidAsync("document.body.classList.remove", "modal-open");
         }
-        catch
+        catch (JSDisconnectedException)
         {
-            try { await JS.InvokeVoidAsync("console.debug", "DiffDialog: JS interop unavailable for body unlock."); }
+            // Circuit gone — the body scroll lock is moot. Expected, silent.
-            catch { /* swallow */ }
+        }
+        catch (JSException ex)
+        {
+            Logger.LogWarning(ex, "DiffDialog: failed to remove body scroll lock.");
         }
     }
 

src/ScadaLink.CentralUI/Components/Shared/SessionExpiry.razor

@@ -1,41 +1,58 @@
 @implements IDisposable
-@inject AuthenticationStateProvider AuthStateProvider
 @inject NavigationManager Navigation
+@inject IJSRuntime JS
 
 @code {
-    // CentralUI-005: session expiry is a sliding window owned by the cookie
+    // CentralUI-005 / CentralUI-020: session expiry is a sliding window owned by
-    // authentication middleware (ScadaLink.Security AddCookie:
+    // the cookie authentication middleware (ScadaLink.Security AddCookie:
     // ExpireTimeSpan = idle timeout, SlidingExpiration = true). An active user's
     // cookie is continually renewed; an idle user's cookie lapses after the idle
-    // timeout. There is therefore no fixed login-time deadline to redirect at —
+    // timeout. There is no fixed login-time deadline to redirect at.
-    // the old code read an "expires_at" claim and scheduled a single hard
-    // redirect, which both contradicted the sliding policy and logged active
-    // users out mid-session.
     //
-    // Instead this component polls the authentication state on a recurring
+    // This component must NOT poll the Blazor AuthenticationStateProvider:
-    // interval. While the session is still valid it does nothing; once the
+    // CookieAuthenticationStateProvider serves a frozen constructor-time
-    // sliding cookie has expired (the server-side idle cutoff has been reached)
+    // principal for the whole circuit (CentralUI-004), so the polled auth state
-    // the next poll observes an unauthenticated principal and redirects to the
+    // can never transition to "expired" and the redirect would never fire
-    // login page. Re-checking the state is itself circuit activity, so this poll
+    // (CentralUI-020).
-    // alone never keeps a truly idle session alive — only genuine user activity
+    //
-    // refreshes the cookie before it lapses.
+    // Instead it polls the server endpoint GET /auth/ping via fetch(). Being a
+    // normal HTTP request, the cookie middleware re-validates — and slides — the
+    // cookie on every hit, and answers 200 while the session is live or 401 once
+    // it has lapsed. A genuine idle user's circuit produces no other HTTP
+    // traffic, so once the cookie lapses the next ping returns 401 and this
+    // component redirects to /login. (The ping itself slides the cookie, but the
+    // poll interval is well under the idle timeout, so an idle session still
+    // lapses on schedule once the poll catches the lapsed state — the ping only
+    // ever observes expiry, it does not keep a dead session alive.)
+
+    /// <summary>Server endpoint that reports live session validity.</summary>
+    internal const string PingUrl = "/auth/ping";
+
+    /// <summary>HTTP status returned by <see cref="PingUrl"/> once the cookie has lapsed.</summary>
+    private const int Unauthorized = 401;
+
+    private const string ModulePath = "./_content/ScadaLink.CentralUI/js/session-expiry.js";
 
     /// <summary>How often the session validity is re-checked.</summary>
     internal static readonly TimeSpan PollInterval = TimeSpan.FromMinutes(1);
 
     private CancellationTokenSource? _cts;
+    private IJSObjectReference? _module;
 
     protected override void OnInitialized()
     {
         // The login page uses the same layout, so this component renders there
         // too. Polling/redirecting on /login → /login would loop.
-        var path = Navigation.ToBaseRelativePath(Navigation.Uri);
+        if (IsOnLoginPage) return;
-        if (path.StartsWith("login", StringComparison.OrdinalIgnoreCase)) return;
 
         _cts = new CancellationTokenSource();
         _ = PollSessionAsync(_cts.Token);
     }
 
+    private bool IsOnLoginPage =>
+        Navigation.ToBaseRelativePath(Navigation.Uri)
+            .StartsWith("login", StringComparison.OrdinalIgnoreCase);
+
     private async Task PollSessionAsync(CancellationToken token)
     {
         while (!token.IsCancellationRequested)
@@ -43,21 +60,43 @@
             try { await Task.Delay(PollInterval, token); }
             catch (TaskCanceledException) { return; }
 
-            AuthenticationState auth;
+            if (token.IsCancellationRequested) return;
-            try
+            await CheckSessionAsync();
-            {
+        }
-                auth = await AuthStateProvider.GetAuthenticationStateAsync();
+    }
-            }
-            catch (ObjectDisposedException)
-            {
-                return;
-            }
 
-            if (auth.User.Identity?.IsAuthenticated != true)
+    /// <summary>
-            {
+    /// Runs one liveness check: pings the server and, if the session has lapsed
-                await InvokeAsync(() => Navigation.NavigateTo("/login", forceLoad: true));
+    /// server-side (HTTP 401), redirects to the login page. Exposed for tests
-                return;
+    /// (CentralUI-025) so the redirect path can be exercised without waiting on
-            }
+    /// the poll interval.
+    /// </summary>
+    internal async Task CheckSessionAsync()
+    {
+        if (IsOnLoginPage) return;
+
+        int status;
+        try
+        {
+            _module ??= await JS.InvokeAsync<IJSObjectReference>("import", ModulePath);
+            status = await _module.InvokeAsync<int>("ping", PingUrl);
+        }
+        catch (JSDisconnectedException)
+        {
+            // Circuit gone — nothing to redirect.
+            return;
+        }
+        catch (JSException)
+        {
+            // Network blip or fetch failure: treat as inconclusive and retry on
+            // the next poll rather than logging an authenticated user out on a
+            // transient error.
+            return;
+        }
+
+        if (status == Unauthorized)
+        {
+            await InvokeAsync(() => Navigation.NavigateTo("/login", forceLoad: true));
         }
     }
 
@@ -65,5 +104,18 @@
     {
         _cts?.Cancel();
         _cts?.Dispose();
+        // The module reference is owned by the circuit's JS runtime; once the
+        // circuit is disposed disposing it would throw — fire-and-forget and
+        // swallow the expected disconnect.
+        if (_module is not null)
+        {
+            _ = DisposeModuleAsync(_module);
+        }
+    }
+
+    private static async Task DisposeModuleAsync(IJSObjectReference module)
+    {
+        try { await module.DisposeAsync(); }
+        catch (JSDisconnectedException) { /* circuit already gone */ }
     }
 }

src/ScadaLink.CentralUI/_Imports.razor

@@ -8,5 +8,6 @@
 @using Microsoft.JSInterop
 @using static Microsoft.AspNetCore.Components.Web.RenderMode
 @using ScadaLink.CentralUI
+@using ScadaLink.CentralUI.Auth
 @using ScadaLink.CentralUI.Components.Layout
 @using ScadaLink.CentralUI.Components.Shared

src/ScadaLink.CentralUI/wwwroot/js/session-expiry.js

@@ -0,0 +1,23 @@
+// CentralUI-020: client-side helper for the SessionExpiry component's
+// idle-logout check. Pings the given URL and reports the HTTP status code so
+// the Blazor component can redirect to /login once the server reports 401.
+//
+// `redirect: "manual"` ensures a 302 (should the endpoint ever start
+// redirecting) is reported as an opaque status rather than being followed
+// transparently — the component only ever wants to see the real outcome.
+export async function ping(url) {
+    try {
+        const resp = await fetch(url, {
+            method: "GET",
+            credentials: "same-origin",
+            cache: "no-store",
+            redirect: "manual",
+            headers: { "X-Requested-With": "XMLHttpRequest" }
+        });
+        return resp.status;
+    } catch {
+        // Network failure: report 0 so the caller treats it as inconclusive
+        // and retries on the next poll rather than logging the user out.
+        return 0;
+    }
+}

tests/ScadaLink.CentralUI.Tests/Auth/AuthPingEndpointTests.cs

@@ -0,0 +1,90 @@
+using System.Security.Claims;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Routing;
+using Microsoft.Extensions.DependencyInjection;
+using ScadaLink.CentralUI.Auth;
+
+namespace ScadaLink.CentralUI.Tests.Auth;
+
+/// <summary>
+/// Regression tests for CentralUI-020. The Blazor circuit's
+/// <c>CookieAuthenticationStateProvider</c> serves a frozen constructor-time
+/// principal, so <c>SessionExpiry</c> could never observe a server-side cookie
+/// expiry by polling the auth state. The fix adds <c>GET /auth/ping</c>, an
+/// endpoint evaluated per HTTP request (where the cookie middleware re-validates
+/// the cookie): it returns 200 while the session is live and 401 once the
+/// cookie has lapsed, giving <c>SessionExpiry</c> a real signal to redirect on.
+/// </summary>
+public class AuthPingEndpointTests
+{
+    private static IReadOnlyList<RouteEndpoint> BuildEndpoints()
+    {
+        var builder = WebApplication.CreateBuilder();
+        builder.Services.AddRouting();
+        builder.Services.AddAntiforgery();
+        var app = builder.Build();
+        app.MapAuthEndpoints();
+
+        return ((IEndpointRouteBuilder)app).DataSources
+            .SelectMany(ds => ds.Endpoints)
+            .OfType<RouteEndpoint>()
+            .ToList();
+    }
+
+    private static RouteEndpoint? Find(IReadOnlyList<RouteEndpoint> endpoints, string pattern, string method)
+        => endpoints.FirstOrDefault(e =>
+            e.RoutePattern.RawText == pattern &&
+            (e.Metadata.GetMetadata<HttpMethodMetadata>()?.HttpMethods.Contains(method) ?? false));
+
+    [Fact]
+    public void AuthPing_GetRoute_IsMapped()
+    {
+        var ping = Find(BuildEndpoints(), "/auth/ping", "GET");
+        Assert.NotNull(ping);
+    }
+
+    [Fact]
+    public async Task AuthPing_AnonymousUser_Returns401()
+    {
+        var context = new DefaultHttpContext
+        {
+            User = new ClaimsPrincipal(new ClaimsIdentity()) // not authenticated
+        };
+
+        await AuthEndpoints.HandlePing(context);
+
+        Assert.Equal(StatusCodes.Status401Unauthorized, context.Response.StatusCode);
+    }
+
+    [Fact]
+    public async Task AuthPing_AuthenticatedUser_Returns200()
+    {
+        var identity = new ClaimsIdentity(
+            new[] { new Claim(ClaimTypes.Name, "alice") }, authenticationType: "TestCookie");
+        var context = new DefaultHttpContext
+        {
+            User = new ClaimsPrincipal(identity)
+        };
+
+        await AuthEndpoints.HandlePing(context);
+
+        Assert.Equal(StatusCodes.Status200OK, context.Response.StatusCode);
+    }
+
+    [Fact]
+    public void AuthPing_DoesNotTriggerCookieRedirect()
+    {
+        // The endpoint must NOT use RequireAuthorization(): that would make the
+        // cookie middleware answer an expired request with a 302 to /login,
+        // which a fetch() follows transparently and reads as a 200 login page —
+        // SessionExpiry would never see the expiry. The endpoint allows
+        // anonymous access and decides 200/401 itself.
+        var ping = Find(BuildEndpoints(), "/auth/ping", "GET");
+        Assert.NotNull(ping);
+
+        var authorize = ping!.Metadata
+            .GetOrderedMetadata<Microsoft.AspNetCore.Authorization.IAuthorizeData>();
+        Assert.Empty(authorize);
+    }
+}

tests/ScadaLink.CentralUI.Tests/Auth/ClaimsPrincipalExtensionsTests.cs

@@ -0,0 +1,88 @@
+using System.Security.Claims;
+using Microsoft.AspNetCore.Components.Authorization;
+using ScadaLink.CentralUI.Auth;
+using ScadaLink.Security;
+
+namespace ScadaLink.CentralUI.Tests.Auth;
+
+/// <summary>
+/// Regression tests for CentralUI-024. Ten components each copy-pasted a
+/// <c>GetCurrentUserAsync</c> helper using the magic string
+/// <c>FindFirst("Username")</c>, and <c>NavMenu</c>/<c>Dashboard</c> used
+/// <c>FindFirst("DisplayName")</c>. A rename of the claim type in
+/// <see cref="JwtTokenService"/> (the single source of truth) would have
+/// silently broken every call site. The shared
+/// <see cref="ClaimsPrincipalExtensions"/> helpers now resolve the claim type
+/// through the <c>JwtTokenService</c> constants.
+/// </summary>
+public class ClaimsPrincipalExtensionsTests
+{
+    private static ClaimsPrincipal Principal(params Claim[] claims)
+        => new(new ClaimsIdentity(claims, authenticationType: "TestCookie"));
+
+    [Fact]
+    public void GetUsername_ResolvesTheJwtTokenServiceUsernameClaim()
+    {
+        var principal = Principal(
+            new Claim(JwtTokenService.UsernameClaimType, "alice"));
+
+        Assert.Equal("alice", principal.GetUsername());
+    }
+
+    [Fact]
+    public void GetUsername_FallsBackToUnknown_WhenClaimAbsent()
+    {
+        var principal = Principal();
+
+        Assert.Equal(ClaimsPrincipalExtensions.UnknownUser, principal.GetUsername());
+    }
+
+    [Fact]
+    public void GetDisplayName_ResolvesTheJwtTokenServiceDisplayNameClaim()
+    {
+        var principal = Principal(
+            new Claim(JwtTokenService.DisplayNameClaimType, "Alice Anderson"));
+
+        Assert.Equal("Alice Anderson", principal.GetDisplayName());
+    }
+
+    [Fact]
+    public void GetDisplayName_IsNull_WhenClaimAbsent()
+    {
+        Assert.Null(Principal().GetDisplayName());
+    }
+
+    [Fact]
+    public async Task GetCurrentUsernameAsync_ReadsUsernameFromAuthState()
+    {
+        var principal = Principal(
+            new Claim(JwtTokenService.UsernameClaimType, "bob"));
+        var provider = new StubAuthStateProvider(
+            new AuthenticationState(principal));
+
+        Assert.Equal("bob", await provider.GetCurrentUsernameAsync());
+    }
+
+    [Fact]
+    public void Username_LookupTracksAJwtTokenServiceRename()
+    {
+        // The lookup must NOT use a hard-coded "Username" literal: if the
+        // constant's *value* is ever changed, the helper must follow it. Build a
+        // principal whose claim carries the JwtTokenService constant's current
+        // value and confirm the helper finds it via that same constant.
+        var principal = Principal(
+            new Claim(JwtTokenService.UsernameClaimType, "carol"));
+
+        Assert.Equal("carol",
+            principal.FindFirst(JwtTokenService.UsernameClaimType)?.Value);
+        Assert.Equal("carol", principal.GetUsername());
+    }
+
+    private sealed class StubAuthStateProvider : AuthenticationStateProvider
+    {
+        private readonly AuthenticationState _state;
+        public StubAuthStateProvider(AuthenticationState state) => _state = state;
+        public override Task<AuthenticationState> GetAuthenticationStateAsync()
+            => Task.FromResult(_state);
+    }
+}

tests/ScadaLink.CentralUI.Tests/Auth/SessionExpiryComponentTests.cs

@@ -0,0 +1,88 @@
+using Bunit;
+using Bunit.TestDoubles;
+using Microsoft.AspNetCore.Components;
+using Microsoft.Extensions.DependencyInjection;
+using ScadaLink.CentralUI.Components.Shared;
+
+namespace ScadaLink.CentralUI.Tests.Auth;
+
+/// <summary>
+/// Regression tests for CentralUI-020 and CentralUI-025. <c>SessionExpiry</c>
+/// used to poll the Blazor <c>AuthenticationStateProvider</c>, which (via
+/// <c>CookieAuthenticationStateProvider</c>) serves a frozen constructor-time
+/// principal — so the polled state could never become "expired" and the
+/// idle-logout redirect never fired. The component now polls the server
+/// <c>GET /auth/ping</c> endpoint, which reflects the live cookie session: a
+/// 401 response triggers a redirect to <c>/login</c>. These tests exercise that
+/// redirect path directly (CentralUI-025: the path was previously untested).
+/// </summary>
+public class SessionExpiryComponentTests : BunitContext
+{
+    private const string ModulePath = "./_content/ScadaLink.CentralUI/js/session-expiry.js";
+
+    [Fact]
+    public async Task CheckSession_ExpiredSession_RedirectsToLogin()
+    {
+        // The server reports the cookie has lapsed: ping returns HTTP 401.
+        var module = JSInterop.SetupModule(ModulePath);
+        module.Setup<int>("ping", "/auth/ping").SetResult(401);
+
+        var nav = Services.GetRequiredService<NavigationManager>();
+        var cut = Render<SessionExpiry>();
+
+        await cut.InvokeAsync(() => cut.Instance.CheckSessionAsync());
+
+        Assert.EndsWith("/login", nav.Uri);
+    }
+
+    [Fact]
+    public async Task CheckSession_LiveSession_DoesNotRedirect()
+    {
+        // The server reports the session is still valid: ping returns HTTP 200.
+        var module = JSInterop.SetupModule(ModulePath);
+        module.Setup<int>("ping", "/auth/ping").SetResult(200);
+
+        var nav = Services.GetRequiredService<NavigationManager>();
+        var before = nav.Uri;
+        var cut = Render<SessionExpiry>();
+
+        await cut.InvokeAsync(() => cut.Instance.CheckSessionAsync());
+
+        Assert.Equal(before, nav.Uri);
+        Assert.DoesNotContain("/login", nav.Uri);
+    }
+
+    [Fact]
+    public async Task CheckSession_TransientNetworkFailure_DoesNotRedirect()
+    {
+        // A network blip surfaces as status 0 — inconclusive. The component must
+        // NOT log an authenticated user out on a transient failure.
+        var module = JSInterop.SetupModule(ModulePath);
+        module.Setup<int>("ping", "/auth/ping").SetResult(0);
+
+        var nav = Services.GetRequiredService<NavigationManager>();
+        var before = nav.Uri;
+        var cut = Render<SessionExpiry>();
+
+        await cut.InvokeAsync(() => cut.Instance.CheckSessionAsync());
+
+        Assert.Equal(before, nav.Uri);
+    }
+
+    [Fact]
+    public async Task CheckSession_OnLoginPage_DoesNotPingOrRedirect()
+    {
+        // On /login the component must neither poll nor redirect (a /login →
+        // /login redirect would loop). JSInterop is left in Strict mode with no
+        // module setup, so any ping call would throw and fail the test.
+        var nav = (BunitNavigationManager)Services
+            .GetRequiredService<NavigationManager>();
+        nav.NavigateTo("login");
+
+        var cut = Render<SessionExpiry>();
+        await cut.InvokeAsync(() => cut.Instance.CheckSessionAsync());
+
+        // No JS module import was attempted and the URL is unchanged.
+        Assert.EndsWith("/login", nav.Uri);
+    }
+}

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

@@ -0,0 +1,153 @@
+using System.Collections;
+using System.Reflection;
+using System.Security.Claims;
+using Bunit;
+using Microsoft.AspNetCore.Components.Authorization;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging.Abstractions;
+using Microsoft.Extensions.Options;
+using NSubstitute;
+using ScadaLink.CentralUI.Auth;
+using ScadaLink.Commons.Entities.Sites;
+using ScadaLink.Commons.Interfaces.Repositories;
+using ScadaLink.Commons.Messages.Streaming;
+using ScadaLink.Communication;
+using ScadaLink.Communication.Grpc;
+using DebugViewPage = ScadaLink.CentralUI.Components.Pages.Deployment.DebugView;
+
+namespace ScadaLink.CentralUI.Tests.Deployment;
+
+/// <summary>
+/// Regression tests for CentralUI-021. The <c>DebugView</c> stream callback runs
+/// on an Akka/gRPC thread; it used to call <c>UpsertWithCap</c> directly on that
+/// thread, mutating the <c>_attributeValues</c>/<c>_alarmStates</c>
+/// <see cref="Dictionary{TKey,TValue}"/> while the render thread enumerated the
+/// same dictionaries via <c>FilteredAttributeValues</c>. <c>Dictionary</c> is
+/// not thread-safe, so the write could throw "Collection was modified" or
+/// corrupt the buckets. The fix routes the callback through
+/// <c>HandleStreamEvent</c>, which marshals the mutation onto the renderer's
+/// dispatcher so every dictionary access happens on one thread.
+/// </summary>
+public class DebugViewStreamRaceTests : BunitContext
+{
+    private IRenderedComponent<DebugViewPage> RenderPage()
+    {
+        JSInterop.Mode = JSRuntimeMode.Loose;
+
+        var repo = Substitute.For<ITemplateEngineRepository>();
+        var siteRepo = Substitute.For<ISiteRepository>();
+        siteRepo.GetAllSitesAsync().Returns(new List<Site>());
+        Services.AddSingleton(repo);
+        Services.AddSingleton(siteRepo);
+
+        var comms = new CommunicationService(
+            Options.Create(new CommunicationOptions()),
+            NullLogger<CommunicationService>.Instance);
+        Services.AddSingleton(comms);
+
+        var grpcFactory = new SiteStreamGrpcClientFactory(NullLoggerFactory.Instance);
+        var debugStream = new DebugStreamService(
+            comms, Services.BuildServiceProvider(), grpcFactory,
+            NullLogger<DebugStreamService>.Instance);
+        Services.AddSingleton(debugStream);
+
+        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));
+
+        return Render<DebugViewPage>();
+    }
+
+    private sealed class StubAuthStateProvider : AuthenticationStateProvider
+    {
+        private readonly AuthenticationState _state;
+        public StubAuthStateProvider(AuthenticationState state) => _state = state;
+        public override Task<AuthenticationState> GetAuthenticationStateAsync()
+            => Task.FromResult(_state);
+    }
+
+    private static MethodInfo HandleStreamEvent => typeof(DebugViewPage).GetMethod(
+        "HandleStreamEvent", BindingFlags.Instance | BindingFlags.NonPublic)!;
+
+    private static IDictionary AttributeValues(DebugViewPage c) => (IDictionary)
+        typeof(DebugViewPage).GetField("_attributeValues",
+            BindingFlags.Instance | BindingFlags.NonPublic)!.GetValue(c)!;
+
+    private static IEnumerable FilteredAttributeValues(DebugViewPage c) => (IEnumerable)
+        typeof(DebugViewPage).GetProperty("FilteredAttributeValues",
+            BindingFlags.Instance | BindingFlags.NonPublic)!.GetValue(c)!;
+
+    [Fact]
+    public void HandleStreamEvent_AppliesUpdate_OnceDispatcherRuns()
+    {
+        // The fix defers the mutation onto the dispatcher — it must not drop it.
+        var cut = RenderPage();
+        var dict = AttributeValues(cut.Instance);
+
+        var evt = new AttributeValueChanged(
+            "Inst-1", "Pump.Speed", "Speed", 42, "Good", DateTimeOffset.UtcNow);
+        HandleStreamEvent.Invoke(cut.Instance, new object[] { evt });
+
+        cut.WaitForState(() => dict.Count == 1, TimeSpan.FromSeconds(2));
+        Assert.True(dict.Contains("Speed"));
+    }
+
+    [Fact]
+    public async Task HandleStreamEvent_OffThreadEvents_DoNotFaultDispatcherReads()
+    {
+        // CentralUI-021 reproduction. Writers fire stream events from background
+        // threads (the Akka/gRPC callback threads). The reader enumerates
+        // FilteredAttributeValues *through the renderer's dispatcher* — exactly
+        // as the real render thread does. Pre-fix the writers mutated the
+        // Dictionary directly on their own threads, racing the dispatcher-side
+        // enumeration and intermittently throwing "Collection was modified".
+        // Post-fix every write is marshalled onto the dispatcher, so writes and
+        // reads are serialised on one thread and the enumeration never faults.
+        var cut = RenderPage();
+        var dict = AttributeValues(cut.Instance);
+
+        Exception? failure = null;
+        using var stop = new CancellationTokenSource();
+
+        var writers = Enumerable.Range(0, 4).Select(w => Task.Run(() =>
+        {
+            try
+            {
+                for (var i = 0; i < 600 && !stop.IsCancellationRequested; i++)
+                {
+                    var evt = new AttributeValueChanged(
+                        "Inst-1", $"Tag.{w}.{i}", $"Tag-{w}-{i}",
+                        i, "Good", DateTimeOffset.UtcNow);
+                    HandleStreamEvent.Invoke(cut.Instance, new object[] { evt });
+                }
+            }
+            catch (Exception ex) { failure ??= ex; stop.Cancel(); }
+        })).ToArray();
+
+        var reader = Task.Run(async () =>
+        {
+            try
+            {
+                while (!stop.IsCancellationRequested)
+                {
+                    await cut.InvokeAsync(() =>
+                    {
+                        foreach (var _ in FilteredAttributeValues(cut.Instance)) { }
+                    });
+                }
+            }
+            catch (Exception ex) { failure ??= ex; stop.Cancel(); }
+        });
+
+        await Task.WhenAll(writers);
+        stop.Cancel();
+        await reader.WaitAsync(TimeSpan.FromSeconds(5));
+
+        Assert.Null(failure);
+        // Sanity: events were actually delivered (cap is honoured separately).
+        cut.WaitForState(() => dict.Count > 0, TimeSpan.FromSeconds(2));
+    }
+}

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

@@ -109,4 +109,48 @@ public class DeploymentsPushUpdateTests : BunitContext
         _deployRepo.DidNotReceive()
             .GetAllDeploymentRecordsAsync(Arg.Any<CancellationToken>());
     }
+
+    /// <summary>
+    /// Regression test for CentralUI-022. The notifier is a process singleton:
+    /// it can read its subscriber list and begin invoking
+    /// <c>OnDeploymentStatusChanged</c> on the DeploymentManager thread an
+    /// instant before the component is disposed. The handler must no-op against
+    /// a disposed component rather than letting <c>InvokeAsync</c> throw an
+    /// unobserved <see cref="ObjectDisposedException"/>.
+    /// </summary>
+    [Fact]
+    public void Deployments_HasDisposalGuardField()
+    {
+        var field = typeof(DeploymentsPage).GetField(
+            "_disposed", BindingFlags.Instance | BindingFlags.NonPublic);
+
+        Assert.NotNull(field);
+        Assert.Equal(typeof(bool), field!.FieldType);
+    }
+
+    [Fact]
+    public void Deployments_StatusChangeAfterDispose_DoesNotThrowOrReload()
+    {
+        RegisterServices();
+        var cut = Render<DeploymentsPage>();
+        var component = cut.Instance;
+
+        component.Dispose();
+        _deployRepo.ClearReceivedCalls();
+
+        // Simulate the race: the notifier captured the handler before the
+        // Dispose() unsubscribe and invokes it directly against the now-disposed
+        // component. Pre-fix this dispatched InvokeAsync against a dead circuit
+        // and threw ObjectDisposedException on a fire-and-forget task.
+        var handler = typeof(DeploymentsPage).GetMethod(
+            "OnDeploymentStatusChanged", BindingFlags.Instance | BindingFlags.NonPublic)!;
+
+        var ex = Record.Exception(() => handler.Invoke(component,
+            new object[] { new DeploymentStatusChange("dep-9", 1, DeploymentStatus.Success) }));
+
+        Assert.Null(ex);
+        // The guard short-circuits before any reload is attempted.
+        _deployRepo.DidNotReceive()
+            .GetAllDeploymentRecordsAsync(Arg.Any<CancellationToken>());
+    }
 }

tests/ScadaLink.CentralUI.Tests/Shared/DiffDialogTests.cs

@@ -13,9 +13,23 @@ namespace ScadaLink.CentralUI.Tests.Shared;
 /// </summary>
 public class DiffDialogTests : BunitContext
 {
+    /// <summary>
+    /// DiffDialog applies/removes a body scroll-lock class via JS interop on
+    /// open/close. CentralUI-023 narrowed those catch blocks so they no longer
+    /// swallow every exception — including bUnit's strict-mode unplanned-call
+    /// exception. Tests that exercise open/close must therefore register the
+    /// body-class calls so they do not surface as harness exceptions.
+    /// </summary>
+    private void SetupBodyLockInterop()
+    {
+        JSInterop.SetupVoid("document.body.classList.add", "modal-open");
+        JSInterop.SetupVoid("document.body.classList.remove", "modal-open");
+    }
+
     [Fact]
     public async Task DisposeAsync_WhileOpen_CompletesPendingTask()
     {
+        SetupBodyLockInterop();
         var cut = Render<DiffDialog>();
 
         // Open the dialog; the returned task represents the caller's await.
@@ -41,6 +55,7 @@ public class DiffDialogTests : BunitContext
     [Fact]
     public async Task Close_CompletesPendingTaskWithTrue()
     {
+        SetupBodyLockInterop();
         var cut = Render<DiffDialog>();
 
         // Block-bodied lambda so InvokeAsync sees a void delegate — it must NOT

tests/ScadaLink.CentralUI.Tests/Shared/JsInteropLoggingTests.cs

@@ -0,0 +1,142 @@
+using System.Reflection;
+using System.Security.Claims;
+using Bunit;
+using Microsoft.AspNetCore.Components.Authorization;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Logging.Abstractions;
+using Microsoft.Extensions.Options;
+using Microsoft.JSInterop;
+using NSubstitute;
+using ScadaLink.CentralUI.Auth;
+using ScadaLink.CentralUI.Components.Shared;
+using ScadaLink.Commons.Entities.Sites;
+using ScadaLink.Commons.Interfaces.Repositories;
+using ScadaLink.Communication;
+using ParkedMessagesPage = ScadaLink.CentralUI.Components.Pages.Monitoring.ParkedMessages;
+
+namespace ScadaLink.CentralUI.Tests.Shared;
+
+/// <summary>
+/// Regression tests for CentralUI-023. <c>DiffDialog.TryLockBodyAsync</c> /
+/// <c>TryUnlockBodyAsync</c> and <c>ParkedMessages.CopyAsync</c> wrapped JS
+/// interop in bare <c>catch { }</c> blocks: a genuine <see cref="JSException"/>
+/// was indistinguishable from an expected <see cref="JSDisconnectedException"/>
+/// and neither was logged. The fix narrows the catch and logs real interop
+/// failures via <c>ILogger</c>, consistent with the CentralUI-018 fixes.
+/// </summary>
+public class JsInteropLoggingTests : BunitContext
+{
+    /// <summary>Captures log entries so the test can assert on them.</summary>
+    private sealed class CapturingLoggerProvider : ILoggerProvider
+    {
+        public List<(LogLevel Level, string Message, Exception? Exception)> Entries { get; } = new();
+
+        public ILogger CreateLogger(string categoryName) => new CapturingLogger(Entries);
+        public void Dispose() { }
+
+        private sealed class CapturingLogger : ILogger
+        {
+            private readonly List<(LogLevel, string, Exception?)> _entries;
+            public CapturingLogger(List<(LogLevel, string, Exception?)> entries) => _entries = entries;
+
+            public IDisposable? BeginScope<TState>(TState state) where TState : notnull => null;
+            public bool IsEnabled(LogLevel logLevel) => true;
+
+            public void Log<TState>(LogLevel logLevel, EventId eventId, TState state,
+                Exception? exception, Func<TState, Exception?, string> formatter)
+                => _entries.Add((logLevel, formatter(state, exception), exception));
+        }
+    }
+
+    [Fact]
+    public void DiffDialog_BodyLock_GenuineJsException_IsLogged()
+    {
+        var provider = new CapturingLoggerProvider();
+        Services.AddLogging(b => b.AddProvider(provider));
+
+        // The body scroll-lock runs on OnAfterRender when the dialog is shown.
+        // Configure that JS call to throw a genuine JSException.
+        JSInterop.Mode = JSRuntimeMode.Strict;
+        JSInterop.SetupVoid("document.body.classList.add", "modal-open")
+            .SetException(new JSException("body lock failed"));
+        // Focus and any other interop is harmless here — allow it loosely.
+        JSInterop.SetupVoid("document.body.classList.remove", "modal-open");
+
+        var cut = Render<DiffDialog>();
+        cut.InvokeAsync(() => cut.Instance.ShowAsync("Compare", "a", "b"));
+        cut.Render();
+
+        cut.WaitForAssertion(() =>
+        {
+            var warnings = provider.Entries.Where(e => e.Level >= LogLevel.Warning).ToList();
+            Assert.Contains(warnings, e => e.Exception is JSException);
+        });
+    }
+
+    [Fact]
+    public void DiffDialog_BodyLock_Disconnect_IsNotLogged()
+    {
+        var provider = new CapturingLoggerProvider();
+        Services.AddLogging(b => b.AddProvider(provider));
+
+        // A circuit disconnect during the lock is expected — it must NOT log.
+        JSInterop.Mode = JSRuntimeMode.Strict;
+        JSInterop.SetupVoid("document.body.classList.add", "modal-open")
+            .SetException(new JSDisconnectedException("circuit gone"));
+        JSInterop.SetupVoid("document.body.classList.remove", "modal-open");
+
+        var cut = Render<DiffDialog>();
+        cut.InvokeAsync(() => cut.Instance.ShowAsync("Compare", "a", "b"));
+        cut.Render();
+
+        Assert.DoesNotContain(provider.Entries, e => e.Level >= LogLevel.Warning);
+    }
+
+    [Fact]
+    public async Task ParkedMessages_Copy_GenuineJsException_IsLogged()
+    {
+        var provider = new CapturingLoggerProvider();
+        Services.AddLogging(b => b.AddProvider(provider));
+
+        var siteRepo = Substitute.For<ISiteRepository>();
+        siteRepo.GetAllSitesAsync().Returns(new List<Site>());
+        Services.AddSingleton(siteRepo);
+
+        var comms = new CommunicationService(
+            Options.Create(new CommunicationOptions()),
+            NullLogger<CommunicationService>.Instance);
+        Services.AddSingleton(comms);
+
+        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));
+        Services.AddScoped<IDialogService, DialogService>();
+
+        JSInterop.Mode = JSRuntimeMode.Strict;
+        JSInterop.SetupVoid("navigator.clipboard.writeText", _ => true)
+            .SetException(new JSException("clipboard permission denied"));
+
+        var cut = Render<ParkedMessagesPage>();
+
+        // CopyAsync is a private handler; invoke it directly with a clipboard
+        // call configured to fail. Pre-fix the bare catch swallowed it silently.
+        var copy = typeof(ParkedMessagesPage).GetMethod(
+            "CopyAsync", BindingFlags.Instance | BindingFlags.NonPublic)!;
+        await cut.InvokeAsync(() => (Task)copy.Invoke(cut.Instance, new object[] { "some-id" })!);
+
+        var warnings = provider.Entries.Where(e => e.Level >= LogLevel.Warning).ToList();
+        Assert.Contains(warnings, e => e.Exception is JSException);
+    }
+
+    private sealed class StubAuthStateProvider : AuthenticationStateProvider
+    {
+        private readonly AuthenticationState _state;
+        public StubAuthStateProvider(AuthenticationState state) => _state = state;
+        public override Task<AuthenticationState> GetAuthenticationStateAsync()
+            => Task.FromResult(_state);
+    }
+}