Merge pull request 'Phase 3 PR 34 — Host-status publisher (Server) + /hosts drill-down page (Admin)' (#33) from phase-3-pr34-host-status-publisher-page into v2

docs/v2/lmx-followups.md

@@ -108,13 +108,30 @@ condition node). Alarm tracking already has its own integration test
 (`AlarmSubscription*`); the multi-driver alarm case would need a stub
 `IAlarmSource` that's worth its own focused PR.
 
-## 7. Host-status per-AppEngine granularity → Admin UI dashboard
+## 7. Host-status per-AppEngine granularity → Admin UI dashboard — **DONE (PRs 33 + 34)**
 
-**Status**: PR 13 ships per-platform/per-AppEngine `ScanState` probing; PR 17
-surfaces the resulting `OnHostStatusChanged` events through OPC UA. Admin
-UI doesn't render a per-host dashboard yet.
+**PR 33** landed the data layer: `DriverHostStatus` entity + migration with
+composite key `(NodeId, DriverInstanceId, HostName)` and two query-supporting
+indexes (per-cluster drill-down on `NodeId`, stale-row detection on
+`LastSeenUtc`).
 
-**To do**:
-- SignalR hub push of `HostStatusChangedEventArgs` to the Admin UI.
-- Dashboard page showing each tracked host, current state, last transition
-  time, failure count.
+**PR 34** wired the publisher + consumer. `HostStatusPublisher` is a
+`BackgroundService` in the Server process that walks every registered
+`IHostConnectivityProbe`-capable driver every 10s, calls
+`GetHostStatuses()`, and upserts rows (`LastSeenUtc` advances each tick;
+`State` + `StateChangedUtc` update on transitions). Admin UI `/hosts` page
+groups by cluster, shows four summary cards (Hosts / Running / Stale /
+Faulted), and flags rows whose `LastSeenUtc` is older than 30s as Stale so
+operators see crashed Servers without waiting for a state change.
+
+Deferred as follow-ups:
+
+- Event-driven push (subscribe to `OnHostStatusChanged` per driver for
+  sub-heartbeat latency). Adds DriverHost lifecycle-event plumbing;
+  10s polling is fine for operator-scale use.
+- Failure-count column — needs the publisher to track a transition history
+  per host, not just current-state.
+- SignalR fan-out to the Admin page (currently the page polls the DB, not
+  a hub). The DB-polled version is fine at current cadence but a hub push
+  would eliminate the 10s race where a new row sits in the DB before the
+  Admin page notices.

src/ZB.MOM.WW.OtOpcUa.Admin/Components/Layout/MainLayout.razor

@@ -6,6 +6,7 @@
         <ul class="nav flex-column">
             <li class="nav-item"><a class="nav-link text-light" href="/">Overview</a></li>
             <li class="nav-item"><a class="nav-link text-light" href="/fleet">Fleet status</a></li>
+            <li class="nav-item"><a class="nav-link text-light" href="/hosts">Host status</a></li>
             <li class="nav-item"><a class="nav-link text-light" href="/clusters">Clusters</a></li>
             <li class="nav-item"><a class="nav-link text-light" href="/reservations">Reservations</a></li>
             <li class="nav-item"><a class="nav-link text-light" href="/certificates">Certificates</a></li>

src/ZB.MOM.WW.OtOpcUa.Admin/Components/Pages/Hosts.razor

@@ -0,0 +1,160 @@
+@page "/hosts"
+@using Microsoft.EntityFrameworkCore
+@using ZB.MOM.WW.OtOpcUa.Admin.Services
+@using ZB.MOM.WW.OtOpcUa.Configuration.Enums
+@inject IServiceScopeFactory ScopeFactory
+@implements IDisposable
+
+<h1 class="mb-4">Driver host status</h1>
+
+<div class="d-flex align-items-center mb-3 gap-2">
+    <button class="btn btn-sm btn-outline-primary" @onclick="RefreshAsync" disabled="@_refreshing">
+        @if (_refreshing) { <span class="spinner-border spinner-border-sm me-1" /> }
+        Refresh
+    </button>
+    <span class="text-muted small">
+        Auto-refresh every @RefreshIntervalSeconds s. Last updated: @(_lastRefreshUtc?.ToString("HH:mm:ss 'UTC'") ?? "—")
+    </span>
+</div>
+
+<div class="alert alert-info small mb-4">
+    Each row is one host reported by a driver instance on a server node. Galaxy drivers report
+    per-Platform / per-AppEngine entries; Modbus drivers report the PLC endpoint. Rows age out
+    of the Server's publisher on every 10-second heartbeat — rows whose LastSeen is older than
+    30s are flagged Stale, which usually means the owning Server process has crashed or lost
+    its DB connection.
+</div>
+
+@if (_rows is null)
+{
+    <p>Loading…</p>
+}
+else if (_rows.Count == 0)
+{
+    <div class="alert alert-secondary">
+        No host-status rows yet. The Server publishes its first tick 2s after startup; if this list stays empty, check that the Server is running and the driver implements <code>IHostConnectivityProbe</code>.
+    </div>
+}
+else
+{
+    <div class="row g-3 mb-4">
+        <div class="col-md-3"><div class="card"><div class="card-body">
+            <h6 class="text-muted mb-1">Hosts</h6>
+            <div class="fs-3">@_rows.Count</div>
+        </div></div></div>
+        <div class="col-md-3"><div class="card border-success"><div class="card-body">
+            <h6 class="text-muted mb-1">Running</h6>
+            <div class="fs-3 text-success">@_rows.Count(r => r.State == DriverHostState.Running && !HostStatusService.IsStale(r))</div>
+        </div></div></div>
+        <div class="col-md-3"><div class="card border-warning"><div class="card-body">
+            <h6 class="text-muted mb-1">Stale</h6>
+            <div class="fs-3 text-warning">@_rows.Count(HostStatusService.IsStale)</div>
+        </div></div></div>
+        <div class="col-md-3"><div class="card border-danger"><div class="card-body">
+            <h6 class="text-muted mb-1">Faulted</h6>
+            <div class="fs-3 text-danger">@_rows.Count(r => r.State == DriverHostState.Faulted)</div>
+        </div></div></div>
+    </div>
+
+    @foreach (var cluster in _rows.GroupBy(r => r.ClusterId ?? "(unassigned)").OrderBy(g => g.Key))
+    {
+        <h2 class="h5 mt-4">Cluster: <code>@cluster.Key</code></h2>
+        <table class="table table-sm table-hover align-middle">
+            <thead>
+                <tr>
+                    <th>Node</th>
+                    <th>Driver</th>
+                    <th>Host</th>
+                    <th>State</th>
+                    <th>Last transition</th>
+                    <th>Last seen</th>
+                    <th>Detail</th>
+                </tr>
+            </thead>
+            <tbody>
+            @foreach (var r in cluster)
+            {
+                <tr class="@RowClass(r)">
+                    <td><code>@r.NodeId</code></td>
+                    <td><code>@r.DriverInstanceId</code></td>
+                    <td>@r.HostName</td>
+                    <td>
+                        <span class="badge @StateBadge(r.State)">@r.State</span>
+                        @if (HostStatusService.IsStale(r))
+                        {
+                            <span class="badge bg-warning text-dark ms-1">Stale</span>
+                        }
+                    </td>
+                    <td class="small">@FormatAge(r.StateChangedUtc)</td>
+                    <td class="small @(HostStatusService.IsStale(r) ? "text-warning" : "")">@FormatAge(r.LastSeenUtc)</td>
+                    <td class="text-truncate small" style="max-width: 320px;" title="@r.Detail">@r.Detail</td>
+                </tr>
+            }
+            </tbody>
+        </table>
+    }
+}
+
+@code {
+    // Mirrors HostStatusPublisher.HeartbeatInterval — polling ahead of the broadcaster
+    // produces stale-looking rows mid-cycle.
+    private const int RefreshIntervalSeconds = 10;
+
+    private List<HostStatusRow>? _rows;
+    private bool _refreshing;
+    private DateTime? _lastRefreshUtc;
+    private Timer? _timer;
+
+    protected override async Task OnInitializedAsync()
+    {
+        await RefreshAsync();
+        _timer = new Timer(async _ => await InvokeAsync(RefreshAsync),
+            state: null,
+            dueTime: TimeSpan.FromSeconds(RefreshIntervalSeconds),
+            period: TimeSpan.FromSeconds(RefreshIntervalSeconds));
+    }
+
+    private async Task RefreshAsync()
+    {
+        if (_refreshing) return;
+        _refreshing = true;
+        try
+        {
+            using var scope = ScopeFactory.CreateScope();
+            var svc = scope.ServiceProvider.GetRequiredService<HostStatusService>();
+            _rows = (await svc.ListAsync()).ToList();
+            _lastRefreshUtc = DateTime.UtcNow;
+        }
+        finally
+        {
+            _refreshing = false;
+            StateHasChanged();
+        }
+    }
+
+    private static string RowClass(HostStatusRow r) => r.State switch
+    {
+        DriverHostState.Faulted => "table-danger",
+        _ when HostStatusService.IsStale(r) => "table-warning",
+        _ => "",
+    };
+
+    private static string StateBadge(DriverHostState s) => s switch
+    {
+        DriverHostState.Running => "bg-success",
+        DriverHostState.Stopped => "bg-secondary",
+        DriverHostState.Faulted => "bg-danger",
+        _ => "bg-secondary",
+    };
+
+    private static string FormatAge(DateTime t)
+    {
+        var age = DateTime.UtcNow - t;
+        if (age.TotalSeconds < 60) return $"{(int)age.TotalSeconds}s ago";
+        if (age.TotalMinutes < 60) return $"{(int)age.TotalMinutes}m ago";
+        if (age.TotalHours < 24) return $"{(int)age.TotalHours}h ago";
+        return t.ToString("yyyy-MM-dd HH:mm 'UTC'");
+    }
+
+    public void Dispose() => _timer?.Dispose();
+}

src/ZB.MOM.WW.OtOpcUa.Admin/Program.cs

@@ -47,6 +47,7 @@ builder.Services.AddScoped<NodeAclService>();
 builder.Services.AddScoped<ReservationService>();
 builder.Services.AddScoped<DraftValidationService>();
 builder.Services.AddScoped<AuditLogService>();
+builder.Services.AddScoped<HostStatusService>();
 
 // Cert-trust management — reads the OPC UA server's PKI store root so rejected client certs
 // can be promoted to trusted via the Admin UI. Singleton: no per-request state, just

src/ZB.MOM.WW.OtOpcUa.Admin/Services/HostStatusService.cs

@@ -0,0 +1,63 @@
+using Microsoft.EntityFrameworkCore;
+using ZB.MOM.WW.OtOpcUa.Configuration;
+using ZB.MOM.WW.OtOpcUa.Configuration.Entities;
+using ZB.MOM.WW.OtOpcUa.Configuration.Enums;
+
+namespace ZB.MOM.WW.OtOpcUa.Admin.Services;
+
+/// <summary>
+///     One row per <see cref="DriverHostStatus"/> record, enriched with the owning
+///     <c>ClusterNode.ClusterId</c> when available (left-join). The Admin <c>/hosts</c> page
+///     groups by cluster and renders a per-node → per-driver → per-host tree.
+/// </summary>
+public sealed record HostStatusRow(
+    string NodeId,
+    string? ClusterId,
+    string DriverInstanceId,
+    string HostName,
+    DriverHostState State,
+    DateTime StateChangedUtc,
+    DateTime LastSeenUtc,
+    string? Detail);
+
+/// <summary>
+///     Read-side service for the Admin UI's per-host drill-down. Loads
+///     <see cref="DriverHostStatus"/> rows (written by the Server process's
+///     <c>HostStatusPublisher</c>) and left-joins <c>ClusterNode</c> so each row knows which
+///     cluster it belongs to — the Admin UI groups by cluster for the fleet-wide view.
+/// </summary>
+/// <remarks>
+///     The publisher heartbeat is 10s (<c>HostStatusPublisher.HeartbeatInterval</c>). The
+///     Admin page also polls every ~10s and treats rows with <c>LastSeenUtc</c> older than
+///     <c>StaleThreshold</c> (30s) as stale — covers a missed heartbeat tolerance plus
+///     a generous buffer for clock skew and publisher GC pauses.
+/// </remarks>
+public sealed class HostStatusService(OtOpcUaConfigDbContext db)
+{
+    public static readonly TimeSpan StaleThreshold = TimeSpan.FromSeconds(30);
+
+    public async Task<IReadOnlyList<HostStatusRow>> ListAsync(CancellationToken ct = default)
+    {
+        // LEFT JOIN on NodeId so a row persists even when its owning ClusterNode row hasn't
+        // been created yet (first-boot bootstrap case — keeps the UI from losing sight of
+        // the reporting server).
+        var rows = await (from s in db.DriverHostStatuses.AsNoTracking()
+                          join n in db.ClusterNodes.AsNoTracking()
+                              on s.NodeId equals n.NodeId into nodeJoin
+                          from n in nodeJoin.DefaultIfEmpty()
+                          orderby s.NodeId, s.DriverInstanceId, s.HostName
+                          select new HostStatusRow(
+                              s.NodeId,
+                              n != null ? n.ClusterId : null,
+                              s.DriverInstanceId,
+                              s.HostName,
+                              s.State,
+                              s.StateChangedUtc,
+                              s.LastSeenUtc,
+                              s.Detail)).ToListAsync(ct);
+        return rows;
+    }
+
+    public static bool IsStale(HostStatusRow row) =>
+        DateTime.UtcNow - row.LastSeenUtc > StaleThreshold;
+}

src/ZB.MOM.WW.OtOpcUa.Server/HostStatusPublisher.cs

@@ -0,0 +1,143 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+using ZB.MOM.WW.OtOpcUa.Configuration;
+using ZB.MOM.WW.OtOpcUa.Configuration.Entities;
+using ZB.MOM.WW.OtOpcUa.Configuration.Enums;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Core.Hosting;
+
+namespace ZB.MOM.WW.OtOpcUa.Server;
+
+/// <summary>
+///     Walks every registered driver once per heartbeat interval, asks each
+///     <see cref="IHostConnectivityProbe"/>-capable driver for its current
+///     <see cref="HostConnectivityStatus"/> list, and upserts one
+///     <see cref="DriverHostStatus"/> row per (NodeId, DriverInstanceId, HostName) into the
+///     central config DB. Powers the Admin UI's per-host drill-down page (LMX follow-up #7).
+/// </summary>
+/// <remarks>
+///     <para>
+///         Polling rather than event-driven: simpler, and matches the cadence the Admin UI
+///         consumes. An event-subscription optimization (push on <c>OnHostStatusChanged</c> for
+///         immediate reflection) is a straightforward follow-up but adds lifecycle complexity
+///         — drivers can be registered after the publisher starts, and subscribing to each
+///         one's event on register + unsubscribing on unregister requires DriverHost to expose
+///         lifecycle events it doesn't today.
+///     </para>
+///     <para>
+///         <see cref="DriverHostStatus.LastSeenUtc"/> advances every heartbeat so the Admin UI
+///         can flag stale rows from a crashed Server process independent of
+///         <see cref="DriverHostStatus.State"/> — a Faulted publisher that stops heartbeating
+///         stays Faulted in the DB but its LastSeenUtc ages out, which is the signal
+///         operators actually want.
+///     </para>
+///     <para>
+///         If the DB is unreachable on a given tick, the publisher logs and moves on — it
+///         does not retry or buffer. The next heartbeat picks up the current-state snapshot,
+///         which is more useful than replaying stale transitions after a long outage.
+///     </para>
+/// </remarks>
+public sealed class HostStatusPublisher(
+    DriverHost driverHost,
+    NodeOptions nodeOptions,
+    IServiceScopeFactory scopeFactory,
+    ILogger<HostStatusPublisher> logger) : BackgroundService
+{
+    internal static readonly TimeSpan HeartbeatInterval = TimeSpan.FromSeconds(10);
+
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        // Wait a short moment at startup so NodeBootstrap's RegisterAsync calls have had a
+        // chance to land. First tick runs immediately after so a freshly-started Server
+        // surfaces its host topology in the Admin UI without waiting a full interval.
+        try { await Task.Delay(TimeSpan.FromSeconds(2), stoppingToken); }
+        catch (OperationCanceledException) { return; }
+
+        while (!stoppingToken.IsCancellationRequested)
+        {
+            try { await PublishOnceAsync(stoppingToken); }
+            catch (OperationCanceledException) { return; }
+            catch (Exception ex)
+            {
+                // Never take down the Server on a publisher failure. Log and continue —
+                // stale-row detection on the Admin side will surface the outage.
+                logger.LogWarning(ex, "Host-status publisher tick failed — will retry next heartbeat");
+            }
+
+            try { await Task.Delay(HeartbeatInterval, stoppingToken); }
+            catch (OperationCanceledException) { return; }
+        }
+    }
+
+    internal async Task PublishOnceAsync(CancellationToken ct)
+    {
+        var driverIds = driverHost.RegisteredDriverIds;
+        if (driverIds.Count == 0) return;
+
+        var now = DateTime.UtcNow;
+        using var scope = scopeFactory.CreateScope();
+        var db = scope.ServiceProvider.GetRequiredService<OtOpcUaConfigDbContext>();
+
+        foreach (var driverId in driverIds)
+        {
+            var driver = driverHost.GetDriver(driverId);
+            if (driver is not IHostConnectivityProbe probe) continue;
+
+            IReadOnlyList<HostConnectivityStatus> statuses;
+            try { statuses = probe.GetHostStatuses(); }
+            catch (Exception ex)
+            {
+                logger.LogWarning(ex, "Driver {DriverId} GetHostStatuses threw — skipping this tick", driverId);
+                continue;
+            }
+
+            foreach (var status in statuses)
+            {
+                await UpsertAsync(db, driverId, status, now, ct);
+            }
+        }
+
+        await db.SaveChangesAsync(ct);
+    }
+
+    private async Task UpsertAsync(OtOpcUaConfigDbContext db, string driverId,
+        HostConnectivityStatus status, DateTime now, CancellationToken ct)
+    {
+        var mapped = MapState(status.State);
+        var existing = await db.DriverHostStatuses.SingleOrDefaultAsync(r =>
+            r.NodeId == nodeOptions.NodeId
+            && r.DriverInstanceId == driverId
+            && r.HostName == status.HostName, ct);
+
+        if (existing is null)
+        {
+            db.DriverHostStatuses.Add(new DriverHostStatus
+            {
+                NodeId = nodeOptions.NodeId,
+                DriverInstanceId = driverId,
+                HostName = status.HostName,
+                State = mapped,
+                StateChangedUtc = status.LastChangedUtc,
+                LastSeenUtc = now,
+            });
+            return;
+        }
+
+        existing.LastSeenUtc = now;
+        if (existing.State != mapped)
+        {
+            existing.State = mapped;
+            existing.StateChangedUtc = status.LastChangedUtc;
+        }
+    }
+
+    internal static DriverHostState MapState(HostState state) => state switch
+    {
+        HostState.Running => DriverHostState.Running,
+        HostState.Stopped => DriverHostState.Stopped,
+        HostState.Faulted => DriverHostState.Faulted,
+        _ => DriverHostState.Unknown,
+    };
+}

src/ZB.MOM.WW.OtOpcUa.Server/Program.cs

@@ -1,8 +1,10 @@
+using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
 using Microsoft.Extensions.Logging;
 using Serilog;
+using ZB.MOM.WW.OtOpcUa.Configuration;
 using ZB.MOM.WW.OtOpcUa.Configuration.LocalCache;
 using ZB.MOM.WW.OtOpcUa.Core.Hosting;
 using ZB.MOM.WW.OtOpcUa.Server;
@@ -72,5 +74,11 @@ builder.Services.AddSingleton<NodeBootstrap>();
 builder.Services.AddSingleton<OpcUaApplicationHost>();
 builder.Services.AddHostedService<OpcUaServerService>();
 
+// Central-config DB access for the host-status publisher (LMX follow-up #7). Scoped context
+// so per-heartbeat change-tracking stays isolated; publisher opens one scope per tick.
+builder.Services.AddDbContext<OtOpcUaConfigDbContext>(opt =>
+    opt.UseSqlServer(options.ConfigDbConnectionString));
+builder.Services.AddHostedService<HostStatusPublisher>();
+
 var host = builder.Build();
 await host.RunAsync();

src/ZB.MOM.WW.OtOpcUa.Server/ZB.MOM.WW.OtOpcUa.Server.csproj

@@ -24,6 +24,7 @@
         <PackageReference Include="OPCFoundation.NetStandard.Opc.Ua.Server" Version="1.5.374.126"/>
         <PackageReference Include="OPCFoundation.NetStandard.Opc.Ua.Configuration" Version="1.5.374.126"/>
         <PackageReference Include="Novell.Directory.Ldap.NETStandard" Version="3.6.0"/>
+        <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="10.0.0"/>
     </ItemGroup>
 
     <ItemGroup>

tests/ZB.MOM.WW.OtOpcUa.Server.Tests/HostStatusPublisherTests.cs

@@ -0,0 +1,197 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging.Abstractions;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Configuration;
+using ZB.MOM.WW.OtOpcUa.Configuration.Enums;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Core.Hosting;
+using ZB.MOM.WW.OtOpcUa.Server;
+
+namespace ZB.MOM.WW.OtOpcUa.Server.Tests;
+
+[Trait("Category", "Integration")]
+public sealed class HostStatusPublisherTests : IDisposable
+{
+    private const string DefaultServer = "localhost,14330";
+    private const string DefaultSaPassword = "OtOpcUaDev_2026!";
+
+    private readonly string _databaseName = $"OtOpcUaPublisher_{Guid.NewGuid():N}";
+    private readonly string _connectionString;
+    private readonly ServiceProvider _sp;
+
+    public HostStatusPublisherTests()
+    {
+        var server = Environment.GetEnvironmentVariable("OTOPCUA_CONFIG_TEST_SERVER") ?? DefaultServer;
+        var password = Environment.GetEnvironmentVariable("OTOPCUA_CONFIG_TEST_SA_PASSWORD") ?? DefaultSaPassword;
+        _connectionString =
+            $"Server={server};Database={_databaseName};User Id=sa;Password={password};TrustServerCertificate=True;Encrypt=False;";
+
+        var services = new ServiceCollection();
+        services.AddLogging();
+        services.AddDbContext<OtOpcUaConfigDbContext>(o => o.UseSqlServer(_connectionString));
+        _sp = services.BuildServiceProvider();
+
+        using var scope = _sp.CreateScope();
+        scope.ServiceProvider.GetRequiredService<OtOpcUaConfigDbContext>().Database.Migrate();
+    }
+
+    public void Dispose()
+    {
+        _sp.Dispose();
+        using var conn = new Microsoft.Data.SqlClient.SqlConnection(
+            new Microsoft.Data.SqlClient.SqlConnectionStringBuilder(_connectionString) { InitialCatalog = "master" }.ConnectionString);
+        conn.Open();
+        using var cmd = conn.CreateCommand();
+        cmd.CommandText = $@"
+IF DB_ID(N'{_databaseName}') IS NOT NULL
+BEGIN
+    ALTER DATABASE [{_databaseName}] SET SINGLE_USER WITH ROLLBACK IMMEDIATE;
+    DROP DATABASE [{_databaseName}];
+END";
+        cmd.ExecuteNonQuery();
+    }
+
+    [Fact]
+    public async Task Publisher_upserts_one_row_per_host_reported_by_each_probe_driver()
+    {
+        var driverHost = new DriverHost();
+        await driverHost.RegisterAsync(new ProbeStubDriver("driver-a",
+            new HostConnectivityStatus("HostA1", HostState.Running, DateTime.UtcNow),
+            new HostConnectivityStatus("HostA2", HostState.Stopped, DateTime.UtcNow)),
+            "{}", CancellationToken.None);
+        await driverHost.RegisterAsync(new NonProbeStubDriver("driver-no-probe"), "{}", CancellationToken.None);
+
+        var nodeOptions = NewNodeOptions("node-a");
+        var publisher = new HostStatusPublisher(driverHost, nodeOptions, _sp.GetRequiredService<IServiceScopeFactory>(),
+            NullLogger<HostStatusPublisher>.Instance);
+
+        await publisher.PublishOnceAsync(CancellationToken.None);
+
+        using var scope = _sp.CreateScope();
+        var db = scope.ServiceProvider.GetRequiredService<OtOpcUaConfigDbContext>();
+        var rows = await db.DriverHostStatuses.AsNoTracking().ToListAsync();
+
+        rows.Count.ShouldBe(2, "driver-no-probe doesn't implement IHostConnectivityProbe — no rows for it");
+        rows.ShouldContain(r => r.HostName == "HostA1" && r.State == DriverHostState.Running && r.DriverInstanceId == "driver-a");
+        rows.ShouldContain(r => r.HostName == "HostA2" && r.State == DriverHostState.Stopped && r.DriverInstanceId == "driver-a");
+        rows.ShouldAllBe(r => r.NodeId == "node-a");
+    }
+
+    [Fact]
+    public async Task Second_tick_updates_LastSeenUtc_without_creating_duplicate_rows()
+    {
+        var driver = new ProbeStubDriver("driver-x",
+            new HostConnectivityStatus("HostX", HostState.Running, DateTime.UtcNow));
+        var driverHost = new DriverHost();
+        await driverHost.RegisterAsync(driver, "{}", CancellationToken.None);
+
+        var publisher = new HostStatusPublisher(driverHost, NewNodeOptions("node-x"),
+            _sp.GetRequiredService<IServiceScopeFactory>(),
+            NullLogger<HostStatusPublisher>.Instance);
+
+        await publisher.PublishOnceAsync(CancellationToken.None);
+        var firstSeen = await SingleRowAsync("node-x", "driver-x", "HostX");
+        await Task.Delay(50); // guarantee a later wall-clock value so LastSeenUtc advances
+        await publisher.PublishOnceAsync(CancellationToken.None);
+        var secondSeen = await SingleRowAsync("node-x", "driver-x", "HostX");
+
+        secondSeen.LastSeenUtc.ShouldBeGreaterThan(firstSeen.LastSeenUtc,
+            "heartbeat advances LastSeenUtc so Admin can stale-flag rows from crashed Servers");
+
+        // Still exactly one row — a naive Add-every-tick would have thrown or duplicated.
+        using var scope = _sp.CreateScope();
+        var db = scope.ServiceProvider.GetRequiredService<OtOpcUaConfigDbContext>();
+        (await db.DriverHostStatuses.CountAsync(r => r.NodeId == "node-x")).ShouldBe(1);
+    }
+
+    [Fact]
+    public async Task State_change_between_ticks_updates_State_and_StateChangedUtc()
+    {
+        var driver = new ProbeStubDriver("driver-y",
+            new HostConnectivityStatus("HostY", HostState.Running, DateTime.UtcNow.AddSeconds(-10)));
+        var driverHost = new DriverHost();
+        await driverHost.RegisterAsync(driver, "{}", CancellationToken.None);
+
+        var publisher = new HostStatusPublisher(driverHost, NewNodeOptions("node-y"),
+            _sp.GetRequiredService<IServiceScopeFactory>(),
+            NullLogger<HostStatusPublisher>.Instance);
+
+        await publisher.PublishOnceAsync(CancellationToken.None);
+        var before = await SingleRowAsync("node-y", "driver-y", "HostY");
+
+        // Swap the driver's reported state to Faulted with a newer transition timestamp.
+        var newChange = DateTime.UtcNow;
+        driver.Statuses = [new HostConnectivityStatus("HostY", HostState.Faulted, newChange)];
+        await publisher.PublishOnceAsync(CancellationToken.None);
+
+        var after = await SingleRowAsync("node-y", "driver-y", "HostY");
+        after.State.ShouldBe(DriverHostState.Faulted);
+        // datetime2(3) has millisecond precision — DateTime.UtcNow carries up to 100ns ticks,
+        // so the stored value rounds down. Compare at millisecond granularity to stay clean.
+        after.StateChangedUtc.ShouldBe(newChange, tolerance: TimeSpan.FromMilliseconds(1));
+        after.StateChangedUtc.ShouldBeGreaterThan(before.StateChangedUtc,
+            "StateChangedUtc must advance when the state actually changed");
+        before.State.ShouldBe(DriverHostState.Running);
+    }
+
+    [Fact]
+    public void MapState_translates_every_HostState_member()
+    {
+        HostStatusPublisher.MapState(HostState.Running).ShouldBe(DriverHostState.Running);
+        HostStatusPublisher.MapState(HostState.Stopped).ShouldBe(DriverHostState.Stopped);
+        HostStatusPublisher.MapState(HostState.Faulted).ShouldBe(DriverHostState.Faulted);
+        HostStatusPublisher.MapState(HostState.Unknown).ShouldBe(DriverHostState.Unknown);
+    }
+
+    private async Task<Configuration.Entities.DriverHostStatus> SingleRowAsync(string node, string driver, string host)
+    {
+        using var scope = _sp.CreateScope();
+        var db = scope.ServiceProvider.GetRequiredService<OtOpcUaConfigDbContext>();
+        return await db.DriverHostStatuses.AsNoTracking()
+            .SingleAsync(r => r.NodeId == node && r.DriverInstanceId == driver && r.HostName == host);
+    }
+
+    private static NodeOptions NewNodeOptions(string nodeId) => new()
+    {
+        NodeId = nodeId,
+        ClusterId = "cluster-t",
+        ConfigDbConnectionString = "unused-publisher-gets-db-from-scope",
+    };
+
+    private sealed class ProbeStubDriver(string id, params HostConnectivityStatus[] initial)
+        : IDriver, IHostConnectivityProbe
+    {
+        public HostConnectivityStatus[] Statuses { get; set; } = initial;
+        public string DriverInstanceId => id;
+        public string DriverType => "ProbeStub";
+
+        public event EventHandler<HostStatusChangedEventArgs>? OnHostStatusChanged;
+
+        public Task InitializeAsync(string driverConfigJson, CancellationToken ct) => Task.CompletedTask;
+        public Task ReinitializeAsync(string driverConfigJson, CancellationToken ct) => Task.CompletedTask;
+        public Task ShutdownAsync(CancellationToken ct) => Task.CompletedTask;
+        public DriverHealth GetHealth() => new(DriverState.Healthy, DateTime.UtcNow, null);
+        public long GetMemoryFootprint() => 0;
+        public Task FlushOptionalCachesAsync(CancellationToken ct) => Task.CompletedTask;
+
+        public IReadOnlyList<HostConnectivityStatus> GetHostStatuses() => Statuses;
+
+        // Keeps the compiler happy — event is part of the interface contract even if unused here.
+        internal void Raise(HostStatusChangedEventArgs e) => OnHostStatusChanged?.Invoke(this, e);
+    }
+
+    private sealed class NonProbeStubDriver(string id) : IDriver
+    {
+        public string DriverInstanceId => id;
+        public string DriverType => "NonProbeStub";
+
+        public Task InitializeAsync(string driverConfigJson, CancellationToken ct) => Task.CompletedTask;
+        public Task ReinitializeAsync(string driverConfigJson, CancellationToken ct) => Task.CompletedTask;
+        public Task ShutdownAsync(CancellationToken ct) => Task.CompletedTask;
+        public DriverHealth GetHealth() => new(DriverState.Healthy, DateTime.UtcNow, null);
+        public long GetMemoryFootprint() => 0;
+        public Task FlushOptionalCachesAsync(CancellationToken ct) => Task.CompletedTask;
+    }
+}