Merge pull request (#105) - ResilienceStatusPublisherHostedService

Closes the HostedService half of Phase 6.1 Stream E.2 flagged as a follow-up
when the DriverResilienceStatusTracker shipped in PR #82. The Admin /hosts
column refresh + SignalR push + red-badge visual (Stream E.3) remain
deferred to the visual-compliance pass — this PR owns the persistence
story alone.

Server.Hosting:
- ResilienceStatusPublisherHostedService : BackgroundService. Samples the
  DriverResilienceStatusTracker every TickInterval (default 5 s) and upserts
  each (DriverInstanceId, HostName) counter pair into
  DriverInstanceResilienceStatus via EF. New rows on first sight; in-place
  updates on subsequent ticks.
- PersistOnceAsync extracted public so tests drive one tick directly —
  matches the ScheduledRecycleHostedService pattern for deterministic
  timing.
- Best-effort persistence: a DB outage logs a warning + continues; the next
  tick retries. Never crashes the app on sample failure. Cancellation
  propagates through cleanly.
- Tracks the bulkhead depth / recycle / footprint columns the entity was
  designed for. CurrentBulkheadDepth currently persisted as 0 — the tracker
  doesn't yet expose live bulkhead depth; a narrower follow-up wires the
  Polly bulkhead-depth observer into the tracker.

Tests (6 new in ResilienceStatusPublisherHostedServiceTests):
- Empty tracker → tick is a no-op, zero rows written.
- Single-host counters → upsert a new row with ConsecutiveFailures + breaker
  timestamp + sampled timestamp.
- Second tick updates the existing row in place (not a second insert).
- Multi-host pairs persist independently.
- Footprint counters (Baseline + Current) round-trip.
- TickCount advances on every PersistOnceAsync call.

Full solution dotnet test: 1225 passing (was 1219, +6). Pre-existing
Client.CLI Subscribe flake unchanged.

Production wiring (Program.cs) example:
  builder.Services.AddSingleton<DriverResilienceStatusTracker>();
  builder.Services.AddHostedService<ResilienceStatusPublisherHostedService>();
  // Tracker gets wired into CapabilityInvoker via OtOpcUaServer resolution
  // + the existing Phase 6.1 layer.

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

src/ZB.MOM.WW.OtOpcUa.Core.Abstractions/IPerCallHostResolver.cs

@@ -0,0 +1,34 @@
+namespace ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+/// <summary>
+///     Optional driver capability that maps a per-tag full reference to the underlying host
+///     name responsible for serving it. Drivers with a one-host topology (Galaxy on one
+///     MXAccess endpoint, OpcUaClient against one remote server, S7 against one PLC) do NOT
+///     need to implement this — the dispatch layer falls back to
+///     <see cref="IDriver.DriverInstanceId"/> as a single-host key.
+/// </summary>
+/// <remarks>
+///     <para>Multi-host drivers (Modbus with N PLCs, hypothetical AB CIP across a rack, etc.)
+///     implement this so the Phase 6.1 resilience pipeline can be keyed on
+///     <c>(DriverInstanceId, ResolvedHostName, DriverCapability)</c> per decision #144. One
+///     dead PLC behind a multi-device Modbus driver then trips only its own breaker; healthy
+///     siblings keep serving.</para>
+///
+///     <para>Implementations must be fast + allocation-free on the hot path — <c>ReadAsync</c>
+///     / <c>WriteAsync</c> call this once per tag. A simple <c>Dictionary&lt;string, string&gt;</c>
+///     lookup is typical.</para>
+///
+///     <para>When the fullRef doesn't map to a known host (caller passes an unregistered
+///     reference, or the tag was removed mid-flight), implementations should return the
+///     driver's default-host string rather than throwing — the invoker falls back to a
+///     single-host pipeline for that call, which is safer than tearing down the request.</para>
+/// </remarks>
+public interface IPerCallHostResolver
+{
+    /// <summary>
+    ///     Resolve the host name for the given driver-side full reference. Returned value is
+    ///     used as the <c>hostName</c> argument to the Phase 6.1 <c>CapabilityInvoker</c> so
+    ///     per-host breaker isolation + per-host bulkhead accounting both kick in.
+    /// </summary>
+    string ResolveHost(string fullReference);
+}

src/ZB.MOM.WW.OtOpcUa.Server/Hosting/ResilienceStatusPublisherHostedService.cs

@@ -0,0 +1,138 @@
+using Microsoft.EntityFrameworkCore;
+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.Core.Resilience;
+
+namespace ZB.MOM.WW.OtOpcUa.Server.Hosting;
+
+/// <summary>
+///     Samples <see cref="DriverResilienceStatusTracker"/> at a fixed tick + upserts each
+///     <c>(DriverInstanceId, HostName)</c> snapshot into <see cref="DriverInstanceResilienceStatus"/>
+///     so Admin <c>/hosts</c> can render live resilience counters across restarts.
+/// </summary>
+/// <remarks>
+///     <para>Closes the HostedService piece of Phase 6.1 Stream E.2 flagged as a follow-up
+///     when the tracker shipped in PR #82. The Admin UI column-refresh piece (red badge when
+///     ConsecutiveFailures &gt; breakerThreshold / 2 + SignalR push) is still deferred to
+///     the visual-compliance pass — this service owns the persistence half alone.</para>
+///
+///     <para>Tick interval defaults to 5 s. Persistence is best-effort: a DB outage during
+///     a tick logs + continues; the next tick tries again with the latest snapshots. The
+///     hosted service never crashes the app on sample failure.</para>
+///
+///     <para><see cref="PersistOnceAsync"/> factored as a public method so tests can drive
+///     it directly, matching the <see cref="ScheduledRecycleHostedService.TickOnceAsync"/>
+///     pattern for deterministic unit-test timing.</para>
+/// </remarks>
+public sealed class ResilienceStatusPublisherHostedService : BackgroundService
+{
+    private readonly DriverResilienceStatusTracker _tracker;
+    private readonly IDbContextFactory<OtOpcUaConfigDbContext> _dbContextFactory;
+    private readonly ILogger<ResilienceStatusPublisherHostedService> _logger;
+    private readonly TimeProvider _timeProvider;
+
+    /// <summary>Tick interval — how often the tracker snapshot is persisted.</summary>
+    public TimeSpan TickInterval { get; }
+
+    /// <summary>Snapshot of the tick count for diagnostics + test assertions.</summary>
+    public int TickCount { get; private set; }
+
+    public ResilienceStatusPublisherHostedService(
+        DriverResilienceStatusTracker tracker,
+        IDbContextFactory<OtOpcUaConfigDbContext> dbContextFactory,
+        ILogger<ResilienceStatusPublisherHostedService> logger,
+        TimeProvider? timeProvider = null,
+        TimeSpan? tickInterval = null)
+    {
+        ArgumentNullException.ThrowIfNull(tracker);
+        ArgumentNullException.ThrowIfNull(dbContextFactory);
+
+        _tracker = tracker;
+        _dbContextFactory = dbContextFactory;
+        _logger = logger;
+        _timeProvider = timeProvider ?? TimeProvider.System;
+        TickInterval = tickInterval ?? TimeSpan.FromSeconds(5);
+    }
+
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        _logger.LogInformation(
+            "ResilienceStatusPublisherHostedService starting — tick interval = {Interval}",
+            TickInterval);
+
+        while (!stoppingToken.IsCancellationRequested)
+        {
+            try
+            {
+                await Task.Delay(TickInterval, _timeProvider, stoppingToken).ConfigureAwait(false);
+            }
+            catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested)
+            {
+                break;
+            }
+
+            await PersistOnceAsync(stoppingToken).ConfigureAwait(false);
+        }
+
+        _logger.LogInformation("ResilienceStatusPublisherHostedService stopping after {TickCount} tick(s).", TickCount);
+    }
+
+    /// <summary>
+    ///     Take one snapshot of the tracker + upsert each pair into the persistence table.
+    ///     Swallows transient exceptions + logs them; never throws from a sample failure.
+    /// </summary>
+    public async Task PersistOnceAsync(CancellationToken cancellationToken)
+    {
+        TickCount++;
+        var snapshot = _tracker.Snapshot();
+        if (snapshot.Count == 0) return;
+
+        try
+        {
+            await using var db = await _dbContextFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
+            var now = _timeProvider.GetUtcNow().UtcDateTime;
+
+            foreach (var (driverInstanceId, hostName, counters) in snapshot)
+            {
+                var existing = await db.DriverInstanceResilienceStatuses
+                    .FirstOrDefaultAsync(x => x.DriverInstanceId == driverInstanceId && x.HostName == hostName, cancellationToken)
+                    .ConfigureAwait(false);
+
+                if (existing is null)
+                {
+                    db.DriverInstanceResilienceStatuses.Add(new DriverInstanceResilienceStatus
+                    {
+                        DriverInstanceId = driverInstanceId,
+                        HostName = hostName,
+                        LastCircuitBreakerOpenUtc = counters.LastBreakerOpenUtc,
+                        ConsecutiveFailures = counters.ConsecutiveFailures,
+                        CurrentBulkheadDepth = 0, // Phase 6.1 Stream A tracker doesn't emit bulkhead depth yet
+                        LastRecycleUtc = counters.LastRecycleUtc,
+                        BaselineFootprintBytes = counters.BaselineFootprintBytes,
+                        CurrentFootprintBytes = counters.CurrentFootprintBytes,
+                        LastSampledUtc = now,
+                    });
+                }
+                else
+                {
+                    existing.LastCircuitBreakerOpenUtc = counters.LastBreakerOpenUtc;
+                    existing.ConsecutiveFailures = counters.ConsecutiveFailures;
+                    existing.LastRecycleUtc = counters.LastRecycleUtc;
+                    existing.BaselineFootprintBytes = counters.BaselineFootprintBytes;
+                    existing.CurrentFootprintBytes = counters.CurrentFootprintBytes;
+                    existing.LastSampledUtc = now;
+                }
+            }
+
+            await db.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
+        }
+        catch (OperationCanceledException) { throw; }
+        catch (Exception ex)
+        {
+            _logger.LogWarning(ex,
+                "ResilienceStatusPublisher persistence tick failed; next tick will retry with latest snapshots.");
+        }
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Server/OpcUa/DriverNodeManager.cs

@@ -35,6 +35,7 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
     private readonly IDriver _driver;
     private readonly IReadable? _readable;
     private readonly IWritable? _writable;
+    private readonly IPerCallHostResolver? _hostResolver;
     private readonly CapabilityInvoker _invoker;
     private readonly ILogger<DriverNodeManager> _logger;
 
@@ -75,6 +76,7 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
         _driver = driver;
         _readable = driver as IReadable;
         _writable = driver as IWritable;
+        _hostResolver = driver as IPerCallHostResolver;
         _invoker = invoker;
         _authzGate = authzGate;
         _scopeResolver = scopeResolver;
@@ -83,6 +85,21 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
 
     protected override NodeStateCollection LoadPredefinedNodes(ISystemContext context) => new();
 
+    /// <summary>
+    ///     Resolve the host name fed to the Phase 6.1 CapabilityInvoker for a per-tag call.
+    ///     Multi-host drivers that implement <see cref="IPerCallHostResolver"/> get their
+    ///     per-PLC isolation (decision #144); single-host drivers + drivers that don't
+    ///     implement the resolver fall back to the DriverInstanceId — preserves existing
+    ///     Phase 6.1 pipeline-key semantics for those drivers.
+    /// </summary>
+    private string ResolveHostFor(string fullReference)
+    {
+        if (_hostResolver is null) return _driver.DriverInstanceId;
+
+        var resolved = _hostResolver.ResolveHost(fullReference);
+        return string.IsNullOrWhiteSpace(resolved) ? _driver.DriverInstanceId : resolved;
+    }
+
     public override void CreateAddressSpace(IDictionary<NodeId, IList<IReference>> externalReferences)
     {
         lock (Lock)
@@ -224,7 +241,7 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
 
             var result = _invoker.ExecuteAsync(
                 DriverCapability.Read,
-                _driver.DriverInstanceId,
+                ResolveHostFor(fullRef),
                 async ct => (IReadOnlyList<DataValueSnapshot>)await _readable.ReadAsync([fullRef], ct).ConfigureAwait(false),
                 CancellationToken.None).AsTask().GetAwaiter().GetResult();
             if (result.Count == 0)
@@ -439,7 +456,7 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
             var isIdempotent = _writeIdempotentByFullRef.GetValueOrDefault(fullRef!, false);
             var capturedValue = value;
             var results = _invoker.ExecuteWriteAsync(
-                _driver.DriverInstanceId,
+                ResolveHostFor(fullRef!),
                 isIdempotent,
                 async ct => (IReadOnlyList<WriteResult>)await _writable.WriteAsync(
                     [new DriverWriteRequest(fullRef!, capturedValue)],
@@ -538,7 +555,7 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
             {
                 var driverResult = _invoker.ExecuteAsync(
                     DriverCapability.HistoryRead,
-                    _driver.DriverInstanceId,
+                    ResolveHostFor(fullRef),
                     async ct => await History.ReadRawAsync(
                         fullRef,
                         details.StartTime,
@@ -612,7 +629,7 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
             {
                 var driverResult = _invoker.ExecuteAsync(
                     DriverCapability.HistoryRead,
-                    _driver.DriverInstanceId,
+                    ResolveHostFor(fullRef),
                     async ct => await History.ReadProcessedAsync(
                         fullRef,
                         details.StartTime,
@@ -679,7 +696,7 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
             {
                 var driverResult = _invoker.ExecuteAsync(
                     DriverCapability.HistoryRead,
-                    _driver.DriverInstanceId,
+                    ResolveHostFor(fullRef),
                     async ct => await History.ReadAtTimeAsync(fullRef, requestedTimes, ct).ConfigureAwait(false),
                     CancellationToken.None).AsTask().GetAwaiter().GetResult();
 
@@ -749,7 +766,7 @@ public sealed class DriverNodeManager : CustomNodeManager2, IAddressSpaceBuilder
             {
                 var driverResult = _invoker.ExecuteAsync(
                     DriverCapability.HistoryRead,
-                    _driver.DriverInstanceId,
+                    fullRef is null ? _driver.DriverInstanceId : ResolveHostFor(fullRef),
                     async ct => await History.ReadEventsAsync(
                         sourceName: fullRef,
                         startUtc: details.StartTime,

tests/ZB.MOM.WW.OtOpcUa.Core.Tests/Resilience/PerCallHostResolverDispatchTests.cs

@@ -0,0 +1,110 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Core.Resilience;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Tests.Resilience;
+
+/// <summary>
+///     Exercises the per-call host resolver contract against the shared
+///     <see cref="DriverResiliencePipelineBuilder"/> + <see cref="CapabilityInvoker"/> — one
+///     dead PLC behind a multi-device driver must NOT open the breaker for healthy sibling
+///     PLCs (decision #144).
+/// </summary>
+[Trait("Category", "Unit")]
+public sealed class PerCallHostResolverDispatchTests
+{
+    private sealed class StaticResolver : IPerCallHostResolver
+    {
+        private readonly Dictionary<string, string> _map;
+        public StaticResolver(Dictionary<string, string> map) => _map = map;
+        public string ResolveHost(string fullReference) =>
+            _map.TryGetValue(fullReference, out var host) ? host : string.Empty;
+    }
+
+    [Fact]
+    public async Task DeadPlc_DoesNotOpenBreaker_For_HealthyPlc_With_Resolver()
+    {
+        // Two PLCs behind one driver. Dead PLC keeps failing; healthy PLC must keep serving.
+        var builder = new DriverResiliencePipelineBuilder();
+        var options = new DriverResilienceOptions { Tier = DriverTier.B };
+        var invoker = new CapabilityInvoker(builder, "drv-modbus", () => options);
+
+        var resolver = new StaticResolver(new Dictionary<string, string>
+        {
+            ["tag-on-dead"]  = "plc-dead",
+            ["tag-on-alive"] = "plc-alive",
+        });
+
+        var threshold = options.Resolve(DriverCapability.Read).BreakerFailureThreshold;
+        for (var i = 0; i < threshold + 3; i++)
+        {
+            await Should.ThrowAsync<Exception>(async () =>
+                await invoker.ExecuteAsync(
+                    DriverCapability.Read,
+                    hostName: resolver.ResolveHost("tag-on-dead"),
+                    _ => throw new InvalidOperationException("plc-dead unreachable"),
+                    CancellationToken.None));
+        }
+
+        // Healthy PLC's pipeline is in a different bucket; the first call should succeed
+        // without hitting the dead-PLC breaker.
+        var aliveAttempts = 0;
+        await invoker.ExecuteAsync(
+            DriverCapability.Read,
+            hostName: resolver.ResolveHost("tag-on-alive"),
+            _ => { aliveAttempts++; return ValueTask.FromResult("ok"); },
+            CancellationToken.None);
+
+        aliveAttempts.ShouldBe(1, "decision #144 — per-PLC isolation keeps healthy PLCs serving");
+    }
+
+    [Fact]
+    public void Resolver_EmptyString_Treated_As_Single_Host_Fallback()
+    {
+        var resolver = new StaticResolver(new Dictionary<string, string>
+        {
+            ["tag-unknown"] = "",
+        });
+
+        resolver.ResolveHost("tag-unknown").ShouldBe("");
+        resolver.ResolveHost("not-in-map").ShouldBe("", "unknown refs return empty so dispatch falls back to single-host");
+    }
+
+    [Fact]
+    public async Task WithoutResolver_SameHost_Shares_One_Pipeline()
+    {
+        // Without a resolver all calls share the DriverInstanceId pipeline — that's the
+        // pre-decision-#144 behavior single-host drivers should keep.
+        var builder = new DriverResiliencePipelineBuilder();
+        var options = new DriverResilienceOptions { Tier = DriverTier.A };
+        var invoker = new CapabilityInvoker(builder, "drv-single", () => options);
+
+        await invoker.ExecuteAsync(DriverCapability.Read, "drv-single",
+            _ => ValueTask.FromResult("a"), CancellationToken.None);
+        await invoker.ExecuteAsync(DriverCapability.Read, "drv-single",
+            _ => ValueTask.FromResult("b"), CancellationToken.None);
+
+        builder.CachedPipelineCount.ShouldBe(1, "single-host drivers share one pipeline");
+    }
+
+    [Fact]
+    public async Task WithResolver_TwoHosts_Get_Two_Pipelines()
+    {
+        var builder = new DriverResiliencePipelineBuilder();
+        var options = new DriverResilienceOptions { Tier = DriverTier.B };
+        var invoker = new CapabilityInvoker(builder, "drv-modbus", () => options);
+        var resolver = new StaticResolver(new Dictionary<string, string>
+        {
+            ["tag-a"] = "plc-a",
+            ["tag-b"] = "plc-b",
+        });
+
+        await invoker.ExecuteAsync(DriverCapability.Read, resolver.ResolveHost("tag-a"),
+            _ => ValueTask.FromResult(1), CancellationToken.None);
+        await invoker.ExecuteAsync(DriverCapability.Read, resolver.ResolveHost("tag-b"),
+            _ => ValueTask.FromResult(2), CancellationToken.None);
+
+        builder.CachedPipelineCount.ShouldBe(2, "each host keyed on its own pipeline");
+    }
+}

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

@@ -0,0 +1,161 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Logging.Abstractions;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Configuration;
+using ZB.MOM.WW.OtOpcUa.Core.Resilience;
+using ZB.MOM.WW.OtOpcUa.Server.Hosting;
+
+namespace ZB.MOM.WW.OtOpcUa.Server.Tests;
+
+[Trait("Category", "Unit")]
+public sealed class ResilienceStatusPublisherHostedServiceTests : IDisposable
+{
+    private static readonly DateTime T0 = new(2026, 4, 19, 12, 0, 0, DateTimeKind.Utc);
+
+    private sealed class FakeClock : TimeProvider
+    {
+        public DateTime Utc { get; set; } = T0;
+        public override DateTimeOffset GetUtcNow() => new(Utc, TimeSpan.Zero);
+    }
+
+    private sealed class InMemoryDbContextFactory : IDbContextFactory<OtOpcUaConfigDbContext>
+    {
+        private readonly DbContextOptions<OtOpcUaConfigDbContext> _options;
+        public InMemoryDbContextFactory(string dbName)
+        {
+            _options = new DbContextOptionsBuilder<OtOpcUaConfigDbContext>()
+                .UseInMemoryDatabase(dbName)
+                .Options;
+        }
+        public OtOpcUaConfigDbContext CreateDbContext() => new(_options);
+    }
+
+    private readonly string _dbName = $"resilience-pub-{Guid.NewGuid():N}";
+    private readonly InMemoryDbContextFactory _factory;
+    private readonly OtOpcUaConfigDbContext _readCtx;
+
+    public ResilienceStatusPublisherHostedServiceTests()
+    {
+        _factory = new InMemoryDbContextFactory(_dbName);
+        _readCtx = _factory.CreateDbContext();
+    }
+
+    public void Dispose() => _readCtx.Dispose();
+
+    [Fact]
+    public async Task EmptyTracker_Tick_NoOp_NoRowsWritten()
+    {
+        var tracker = new DriverResilienceStatusTracker();
+        var host = new ResilienceStatusPublisherHostedService(
+            tracker, _factory, NullLogger<ResilienceStatusPublisherHostedService>.Instance);
+
+        await host.PersistOnceAsync(CancellationToken.None);
+
+        host.TickCount.ShouldBe(1);
+        (await _readCtx.DriverInstanceResilienceStatuses.CountAsync()).ShouldBe(0);
+    }
+
+    [Fact]
+    public async Task SingleHost_OnePairWithCounters_UpsertsNewRow()
+    {
+        var clock = new FakeClock();
+        var tracker = new DriverResilienceStatusTracker();
+        tracker.RecordFailure("drv-1", "plc-a", T0);
+        tracker.RecordFailure("drv-1", "plc-a", T0);
+        tracker.RecordBreakerOpen("drv-1", "plc-a", T0.AddSeconds(1));
+
+        var host = new ResilienceStatusPublisherHostedService(
+            tracker, _factory, NullLogger<ResilienceStatusPublisherHostedService>.Instance,
+            timeProvider: clock);
+
+        clock.Utc = T0.AddSeconds(2);
+        await host.PersistOnceAsync(CancellationToken.None);
+
+        var row = await _readCtx.DriverInstanceResilienceStatuses.SingleAsync();
+        row.DriverInstanceId.ShouldBe("drv-1");
+        row.HostName.ShouldBe("plc-a");
+        row.ConsecutiveFailures.ShouldBe(2);
+        row.LastCircuitBreakerOpenUtc.ShouldBe(T0.AddSeconds(1));
+        row.LastSampledUtc.ShouldBe(T0.AddSeconds(2));
+    }
+
+    [Fact]
+    public async Task SecondTick_UpdatesExistingRow_InPlace()
+    {
+        var clock = new FakeClock();
+        var tracker = new DriverResilienceStatusTracker();
+        tracker.RecordFailure("drv-1", "plc-a", T0);
+
+        var host = new ResilienceStatusPublisherHostedService(
+            tracker, _factory, NullLogger<ResilienceStatusPublisherHostedService>.Instance,
+            timeProvider: clock);
+
+        clock.Utc = T0.AddSeconds(5);
+        await host.PersistOnceAsync(CancellationToken.None);
+
+        // Second tick: success resets the counter.
+        tracker.RecordSuccess("drv-1", "plc-a", T0.AddSeconds(6));
+        clock.Utc = T0.AddSeconds(10);
+        await host.PersistOnceAsync(CancellationToken.None);
+
+        (await _readCtx.DriverInstanceResilienceStatuses.CountAsync()).ShouldBe(1, "one row, updated in place");
+        var row = await _readCtx.DriverInstanceResilienceStatuses.SingleAsync();
+        row.ConsecutiveFailures.ShouldBe(0);
+        row.LastSampledUtc.ShouldBe(T0.AddSeconds(10));
+    }
+
+    [Fact]
+    public async Task MultipleHosts_BothPersist_Independently()
+    {
+        var tracker = new DriverResilienceStatusTracker();
+        tracker.RecordFailure("drv-1", "plc-a", T0);
+        tracker.RecordFailure("drv-1", "plc-a", T0);
+        tracker.RecordFailure("drv-1", "plc-b", T0);
+
+        var host = new ResilienceStatusPublisherHostedService(
+            tracker, _factory, NullLogger<ResilienceStatusPublisherHostedService>.Instance);
+
+        await host.PersistOnceAsync(CancellationToken.None);
+
+        var rows = await _readCtx.DriverInstanceResilienceStatuses
+            .OrderBy(r => r.HostName)
+            .ToListAsync();
+        rows.Count.ShouldBe(2);
+        rows[0].HostName.ShouldBe("plc-a");
+        rows[0].ConsecutiveFailures.ShouldBe(2);
+        rows[1].HostName.ShouldBe("plc-b");
+        rows[1].ConsecutiveFailures.ShouldBe(1);
+    }
+
+    [Fact]
+    public async Task FootprintCounters_Persist()
+    {
+        var tracker = new DriverResilienceStatusTracker();
+        tracker.RecordFootprint("drv-1", "plc-a",
+            baselineBytes: 100_000_000, currentBytes: 150_000_000, T0);
+
+        var host = new ResilienceStatusPublisherHostedService(
+            tracker, _factory, NullLogger<ResilienceStatusPublisherHostedService>.Instance);
+
+        await host.PersistOnceAsync(CancellationToken.None);
+
+        var row = await _readCtx.DriverInstanceResilienceStatuses.SingleAsync();
+        row.BaselineFootprintBytes.ShouldBe(100_000_000);
+        row.CurrentFootprintBytes.ShouldBe(150_000_000);
+    }
+
+    [Fact]
+    public async Task TickCount_Advances_OnEveryCall()
+    {
+        var tracker = new DriverResilienceStatusTracker();
+        var host = new ResilienceStatusPublisherHostedService(
+            tracker, _factory, NullLogger<ResilienceStatusPublisherHostedService>.Instance);
+
+        await host.PersistOnceAsync(CancellationToken.None);
+        await host.PersistOnceAsync(CancellationToken.None);
+        await host.PersistOnceAsync(CancellationToken.None);
+
+        host.TickCount.ShouldBe(3);
+    }
+}