Phase 3 PR 34 — Host-status publisher (Server) + /hosts drill-down page (Admin). Closes LMX follow-up #7 by wiring together the data layer from PR 33. Server.HostStatusPublisher is a BackgroundService that walks every driver registered in DriverHost every 10 seconds, skips drivers that don't implement IHostConnectivityProbe, calls GetHostStatuses() on each probe-capable driver, and upserts one DriverHostStatus row per (NodeId, DriverInstanceId, HostName) into the central config DB. Upsert path: SingleOrDefaultAsync on the composite PK; if no row exists, Add a new one; if a row exists, LastSeenUtc advances unconditionally (heartbeat) and State + StateChangedUtc update only on transitions so Admin UI can distinguish 'still reporting, still Running' from 'freshly transitioned to Running'. MapState translates Core.Abstractions.HostState to Configuration.Enums.DriverHostState (intentional duplicate enum — Configuration project stays free of driver-runtime deps per PR 33's choice). If a driver's GetHostStatuses throws, log warning and skip that driver this tick — never take down the Server on a publisher failure. If the DB is unreachable, log warning + retry next heartbeat (no buffering — next tick's current-state snapshot is more useful than replaying stale transitions after a long outage). 2-second startup delay so NodeBootstrap's RegisterAsync calls land before the first publish tick, then tick runs immediately so a freshly-started Server surfaces its host topology in the Admin UI without waiting a full interval.

Polling chosen over event-driven for initial scope: simpler, matches Admin UI consumer cadence, avoids DriverHost lifecycle-event plumbing that doesn't exist today. Event-driven push for sub-heartbeat latency is a straightforward follow-up.
Admin.Services.HostStatusService left-joins DriverHostStatus against ClusterNode on NodeId so rows persist even when the ClusterNode entry doesn't exist yet (first-boot bootstrap case). StaleThreshold = 30s — covers one missed publisher heartbeat plus a generous buffer for clock skew and GC pauses. Admin Components/Pages/Hosts.razor — FleetAdmin-visible page grouped by cluster (handles the '(unassigned)' case for rows without a matching ClusterNode). Four summary cards (Hosts / Running / Stale / Faulted); per-cluster table with Node / Driver / Host / State + Stale-badge / Last-transition / Last-seen / Detail columns; 10s auto-refresh via IServiceScopeFactory timer pattern matching FleetStatusPoller + Fleet dashboard (PR 27). Row-class highlighting: Faulted → table-danger, Stale → table-warning, else default. State badge maps DriverHostState enum to bootstrap color classes. Sidebar link added between 'Fleet status' and 'Clusters'.
Server csproj adds Microsoft.EntityFrameworkCore.SqlServer 10.0.0 + registers OtOpcUaConfigDbContext in Program.cs scoped via NodeOptions.ConfigDbConnectionString (no Admin-style manual SQL raw — the DbContext is the only access path, keeps migrations owner-of-record).
Tests — HostStatusPublisherTests (4 new Integration cases, uses per-run throwaway DB matching the FleetStatusPollerTests pattern): publisher upserts one row per host from each probe-capable driver and skips non-probe drivers; second tick advances LastSeenUtc without creating duplicate rows (upsert pattern verified end-to-end); state change between ticks updates State AND StateChangedUtc (datetime2(3) rounds to millisecond precision so comparison uses 1ms tolerance — documented inline); MapState translates every HostState enum member. Server.Tests Integration: 4 new tests pass. Admin build clean, Admin.Tests Unit still 23 / 0. docs/v2/lmx-followups.md item #7 marked DONE with three explicit deferred items (event-driven push, failure-count column, SignalR fan-out).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

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;
+}