Phase 6.1 Stream A remaining — IPerCallHostResolver + DriverNodeManager per-call host dispatch (decision #144)

Closes the per-device isolation gap flagged at the Phase 6.1 Stream A wire-up
(PR #78 used driver.DriverInstanceId as the pipeline host for every call, so
multi-host drivers like Modbus with N PLCs shared one pipeline — one dead PLC
poisoned sibling breakers). Decision #144 requires per-device isolation; this
PR wires it without breaking single-host drivers.

Core.Abstractions:
- IPerCallHostResolver interface. Optional driver capability. Drivers with
  multi-host topology (Modbus across N PLCs, AB CIP across a rack, etc.)
  implement this; single-host drivers (Galaxy, S7 against one PLC, OpcUaClient
  against one remote server) leave it alone. Must be fast + allocation-free
  — called once per tag on the hot path. Unknown refs return empty so dispatch
  falls back to single-host without throwing.

Server/OpcUa/DriverNodeManager:
- Captures `driver as IPerCallHostResolver` at construction alongside the
  existing capability casts.
- New `ResolveHostFor(fullReference)` helper returns either the resolver's
  answer or the driver's DriverInstanceId (single-host fallback). Empty /
  whitespace resolver output also falls back to DriverInstanceId.
- Every dispatch site now passes `ResolveHostFor(fullRef)` to the invoker
  instead of `_driver.DriverInstanceId` — OnReadValue, OnWriteValue, all four
  HistoryRead paths. The HistoryRead Events path tolerates fullRef=null and
  falls back to DriverInstanceId for those cluster-wide event queries.
- Drivers without IPerCallHostResolver observe zero behavioural change:
  every call still keys on DriverInstanceId, same as before.

Tests (4 new PerCallHostResolverDispatchTests, all pass):
- DeadPlc_DoesNotOpenBreaker_For_HealthyPlc_With_Resolver — 2 PLCs behind
  one driver; hammer the dead PLC past its breaker threshold; assert the
  healthy PLC's first call succeeds on its first attempt (decision #144).
- EmptyString / unknown-ref fallback behaviour documented via test.
- WithoutResolver_SameHost_Shares_One_Pipeline — regression guard for the
  single-host pre-existing behaviour.
- WithResolver_TwoHosts_Get_Two_Pipelines — builds the CachedPipelineCount
  assertion to confirm the shared-builder cache keys correctly.

Full solution dotnet test: 1219 passing (was 1215, +4). Pre-existing
Client.CLI Subscribe flake unchanged.

Adoption: Modbus driver (#120 follow-up), AB CIP / AB Legacy / TwinCAT
drivers (also #120) implement the interface and return the per-tag PLC host
string. Single-host drivers stay silent and pay zero cost.

Remaining sub-items of #160 still deferred:
- IAlarmSource.SubscribeAlarmsAsync + AcknowledgeAsync invoker wrapping.
  Non-trivial because alarm subscription is push-based from driver through
  IAlarmConditionSink — the wrap has to happen at the driver-to-server glue
  rather than a synchronous dispatch site.
- Roslyn analyzer asserting every capability-interface call routes through
  CapabilityInvoker. Substantial (separate analyzer project + test harness);
  noise-value ratio favors shipping this post-v2-GA once the coverage is
  known-stable.

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

src/ZB.MOM.WW.OtOpcUa.Configuration/Entities/DriverInstance.cs

@@ -27,6 +27,24 @@ public sealed class DriverInstance
     /// <summary>Schemaless per-driver-type JSON config. Validated against registered JSON schema at draft-publish time (decision #91).</summary>
     public required string DriverConfig { get; set; }
 
+    /// <summary>
+    ///     Optional per-instance overrides for the Phase 6.1 shared Polly resilience pipeline.
+    ///     Null = use the driver's tier defaults (decision #143). When populated, expected shape:
+    ///     <code>
+    ///     {
+    ///       "bulkheadMaxConcurrent": 16,
+    ///       "bulkheadMaxQueue": 64,
+    ///       "capabilityPolicies": {
+    ///         "Read":  { "timeoutSeconds": 5, "retryCount": 5, "breakerFailureThreshold": 3 },
+    ///         "Write": { "timeoutSeconds": 5, "retryCount": 0, "breakerFailureThreshold": 5 }
+    ///       }
+    ///     }
+    ///     </code>
+    ///     Parsed at startup by <c>DriverResilienceOptionsParser</c>; every key is optional +
+    ///     unrecognised keys are ignored so future shapes land without a migration.
+    /// </summary>
+    public string? ResilienceConfig { get; set; }
+
     public ConfigGeneration? Generation { get; set; }
     public ServerCluster? Cluster { get; set; }
 }

src/ZB.MOM.WW.OtOpcUa.Configuration/Migrations/20260419161932_AddDriverInstanceResilienceConfig.cs

@@ -0,0 +1,37 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace ZB.MOM.WW.OtOpcUa.Configuration.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddDriverInstanceResilienceConfig : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AddColumn<string>(
+                name: "ResilienceConfig",
+                table: "DriverInstance",
+                type: "nvarchar(max)",
+                nullable: true);
+
+            migrationBuilder.AddCheckConstraint(
+                name: "CK_DriverInstance_ResilienceConfig_IsJson",
+                table: "DriverInstance",
+                sql: "ResilienceConfig IS NULL OR ISJSON(ResilienceConfig) = 1");
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropCheckConstraint(
+                name: "CK_DriverInstance_ResilienceConfig_IsJson",
+                table: "DriverInstance");
+
+            migrationBuilder.DropColumn(
+                name: "ResilienceConfig",
+                table: "DriverInstance");
+        }
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Configuration/Migrations/OtOpcUaConfigDbContextModelSnapshot.cs

@@ -413,6 +413,9 @@ namespace ZB.MOM.WW.OtOpcUa.Configuration.Migrations
                         .HasMaxLength(64)
                         .HasColumnType("nvarchar(64)");
 
+                    b.Property<string>("ResilienceConfig")
+                        .HasColumnType("nvarchar(max)");
+
                     b.HasKey("DriverInstanceRowId");
 
                     b.HasIndex("ClusterId");
@@ -431,6 +434,8 @@ namespace ZB.MOM.WW.OtOpcUa.Configuration.Migrations
                     b.ToTable("DriverInstance", null, t =>
                         {
                             t.HasCheckConstraint("CK_DriverInstance_DriverConfig_IsJson", "ISJSON(DriverConfig) = 1");
+
+                            t.HasCheckConstraint("CK_DriverInstance_ResilienceConfig_IsJson", "ResilienceConfig IS NULL OR ISJSON(ResilienceConfig) = 1");
                         });
                 });
 

src/ZB.MOM.WW.OtOpcUa.Configuration/OtOpcUaConfigDbContext.cs

@@ -251,6 +251,8 @@ public sealed class OtOpcUaConfigDbContext(DbContextOptions<OtOpcUaConfigDbConte
             {
                 t.HasCheckConstraint("CK_DriverInstance_DriverConfig_IsJson",
                     "ISJSON(DriverConfig) = 1");
+                t.HasCheckConstraint("CK_DriverInstance_ResilienceConfig_IsJson",
+                    "ResilienceConfig IS NULL OR ISJSON(ResilienceConfig) = 1");
             });
             e.HasKey(x => x.DriverInstanceRowId);
             e.Property(x => x.DriverInstanceRowId).HasDefaultValueSql("NEWSEQUENTIALID()");
@@ -260,6 +262,7 @@ public sealed class OtOpcUaConfigDbContext(DbContextOptions<OtOpcUaConfigDbConte
             e.Property(x => x.Name).HasMaxLength(128);
             e.Property(x => x.DriverType).HasMaxLength(32);
             e.Property(x => x.DriverConfig).HasColumnType("nvarchar(max)");
+            e.Property(x => x.ResilienceConfig).HasColumnType("nvarchar(max)");
 
             e.HasOne(x => x.Generation).WithMany().HasForeignKey(x => x.GenerationId).OnDelete(DeleteBehavior.Restrict);
             e.HasOne(x => x.Cluster).WithMany().HasForeignKey(x => x.ClusterId).OnDelete(DeleteBehavior.Restrict);

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.Core/OpcUa/IdentificationFolderBuilder.cs

@@ -0,0 +1,91 @@
+using ZB.MOM.WW.OtOpcUa.Configuration.Entities;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.OpcUa;
+
+/// <summary>
+///     Phase 6.4 Stream D: materializes the OPC 40010 Machinery companion-spec Identification
+///     sub-folder under an Equipment node. Reads the nine decision-#139 columns off the
+///     <see cref="Equipment"/> row and emits one property per non-null field.
+/// </summary>
+/// <remarks>
+///     <para>Pure-function shape — testable without a real OPC UA node manager. The caller
+///     passes the builder scoped to the Equipment node; this class handles the Identification
+///     sub-folder creation + per-field <see cref="IAddressSpaceBuilder.AddProperty"/> calls.</para>
+///
+///     <para>ACL binding: the sub-folder + its properties inherit the Equipment scope's
+///     grants (no new scope level). Phase 6.2's trie treats them as part of the Equipment
+///     ScopeId — a user with Equipment-level grant reads Identification; a user without the
+///     grant gets BadUserAccessDenied on both the Equipment node + its Identification variables.
+///     See <c>docs/v2/acl-design.md</c> §Identification cross-reference.</para>
+///
+///     <para>The nine fields per decision #139 are exposed exactly when they carry a non-null
+///     value. A row with all nine null produces no Identification sub-folder at all — the
+///     caller can use <see cref="HasAnyFields(Equipment)"/> to skip the Folder call entirely
+///     and avoid a pointless empty folder appearing in browse trees.</para>
+/// </remarks>
+public static class IdentificationFolderBuilder
+{
+    /// <summary>Browse + display name of the sub-folder — fixed per OPC 40010 convention.</summary>
+    public const string FolderName = "Identification";
+
+    /// <summary>
+    ///     Canonical decision #139 field set exposed in the Identification sub-folder. Order
+    ///     matches the decision-log entry so any browse-order reader can cross-reference
+    ///     without re-sorting.
+    /// </summary>
+    public static IReadOnlyList<string> FieldNames { get; } = new[]
+    {
+        "Manufacturer", "Model", "SerialNumber",
+        "HardwareRevision", "SoftwareRevision",
+        "YearOfConstruction", "AssetLocation",
+        "ManufacturerUri", "DeviceManualUri",
+    };
+
+    /// <summary>True when the equipment row has at least one non-null Identification field.</summary>
+    public static bool HasAnyFields(Equipment equipment)
+    {
+        ArgumentNullException.ThrowIfNull(equipment);
+        return equipment.Manufacturer is not null
+            || equipment.Model is not null
+            || equipment.SerialNumber is not null
+            || equipment.HardwareRevision is not null
+            || equipment.SoftwareRevision is not null
+            || equipment.YearOfConstruction is not null
+            || equipment.AssetLocation is not null
+            || equipment.ManufacturerUri is not null
+            || equipment.DeviceManualUri is not null;
+    }
+
+    /// <summary>
+    ///     Build the Identification sub-folder under <paramref name="equipmentBuilder"/>. No-op
+    ///     when every field is null. Returns the sub-folder builder (or null when no-op) so
+    ///     callers can attach additional nodes underneath if needed.
+    /// </summary>
+    public static IAddressSpaceBuilder? Build(IAddressSpaceBuilder equipmentBuilder, Equipment equipment)
+    {
+        ArgumentNullException.ThrowIfNull(equipmentBuilder);
+        ArgumentNullException.ThrowIfNull(equipment);
+
+        if (!HasAnyFields(equipment)) return null;
+
+        var folder = equipmentBuilder.Folder(FolderName, FolderName);
+        AddIfPresent(folder, "Manufacturer",       DriverDataType.String,   equipment.Manufacturer);
+        AddIfPresent(folder, "Model",              DriverDataType.String,   equipment.Model);
+        AddIfPresent(folder, "SerialNumber",       DriverDataType.String,   equipment.SerialNumber);
+        AddIfPresent(folder, "HardwareRevision",   DriverDataType.String,   equipment.HardwareRevision);
+        AddIfPresent(folder, "SoftwareRevision",   DriverDataType.String,   equipment.SoftwareRevision);
+        AddIfPresent(folder, "YearOfConstruction", DriverDataType.Int32,
+            equipment.YearOfConstruction is null ? null : (object)(int)equipment.YearOfConstruction.Value);
+        AddIfPresent(folder, "AssetLocation",      DriverDataType.String,   equipment.AssetLocation);
+        AddIfPresent(folder, "ManufacturerUri",    DriverDataType.String,   equipment.ManufacturerUri);
+        AddIfPresent(folder, "DeviceManualUri",    DriverDataType.String,   equipment.DeviceManualUri);
+        return folder;
+    }
+
+    private static void AddIfPresent(IAddressSpaceBuilder folder, string name, DriverDataType dataType, object? value)
+    {
+        if (value is null) return;
+        folder.AddProperty(name, dataType, value);
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Core/Resilience/DriverResilienceOptionsParser.cs

@@ -0,0 +1,116 @@
+using System.Text.Json;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Resilience;
+
+/// <summary>
+///     Parses the <c>DriverInstance.ResilienceConfig</c> JSON column into a
+///     <see cref="DriverResilienceOptions"/> instance layered on top of the tier defaults.
+///     Every key in the JSON is optional; missing keys fall back to the tier defaults from
+///     <see cref="DriverResilienceOptions.GetTierDefaults(DriverTier)"/>.
+/// </summary>
+/// <remarks>
+///     <para>Example JSON shape per Phase 6.1 Stream A.2:</para>
+///     <code>
+///     {
+///       "bulkheadMaxConcurrent": 16,
+///       "bulkheadMaxQueue": 64,
+///       "capabilityPolicies": {
+///         "Read":  { "timeoutSeconds": 5, "retryCount": 5, "breakerFailureThreshold": 3 },
+///         "Write": { "timeoutSeconds": 5, "retryCount": 0, "breakerFailureThreshold": 5 }
+///       }
+///     }
+///     </code>
+///
+///     <para>Unrecognised keys + values are ignored so future shapes land without a migration.
+///     Per-capability overrides are layered on top of tier defaults — a partial policy (only
+///     some of TimeoutSeconds/RetryCount/BreakerFailureThreshold) fills in the other fields
+///     from the tier default for that capability.</para>
+///
+///     <para>Parser failures (malformed JSON, type mismatches) fall back to pure tier defaults
+///     + surface through an out-parameter diagnostic. Callers may log the diagnostic but should
+///     NOT fail driver startup — a misconfigured ResilienceConfig should never brick a
+///     working driver.</para>
+/// </remarks>
+public static class DriverResilienceOptionsParser
+{
+    private static readonly JsonSerializerOptions JsonOpts = new()
+    {
+        PropertyNameCaseInsensitive = true,
+        AllowTrailingCommas = true,
+        ReadCommentHandling = JsonCommentHandling.Skip,
+    };
+
+    /// <summary>
+    ///     Parse the JSON payload layered on <paramref name="tier"/>'s defaults. Returns the
+    ///     effective options; <paramref name="parseDiagnostic"/> is null on success, or a
+    ///     human-readable error message when the JSON was malformed (options still returned
+    ///     = tier defaults).
+    /// </summary>
+    public static DriverResilienceOptions ParseOrDefaults(
+        DriverTier tier,
+        string? resilienceConfigJson,
+        out string? parseDiagnostic)
+    {
+        parseDiagnostic = null;
+        var baseDefaults = DriverResilienceOptions.GetTierDefaults(tier);
+        var baseOptions = new DriverResilienceOptions { Tier = tier, CapabilityPolicies = baseDefaults };
+
+        if (string.IsNullOrWhiteSpace(resilienceConfigJson))
+            return baseOptions;
+
+        ResilienceConfigShape? shape;
+        try
+        {
+            shape = JsonSerializer.Deserialize<ResilienceConfigShape>(resilienceConfigJson, JsonOpts);
+        }
+        catch (JsonException ex)
+        {
+            parseDiagnostic = $"ResilienceConfig JSON malformed; falling back to tier {tier} defaults. Detail: {ex.Message}";
+            return baseOptions;
+        }
+
+        if (shape is null) return baseOptions;
+
+        var merged = new Dictionary<DriverCapability, CapabilityPolicy>(baseDefaults);
+        if (shape.CapabilityPolicies is not null)
+        {
+            foreach (var (capName, overridePolicy) in shape.CapabilityPolicies)
+            {
+                if (!Enum.TryParse<DriverCapability>(capName, ignoreCase: true, out var capability))
+                {
+                    parseDiagnostic ??= $"Unknown capability '{capName}' in ResilienceConfig; skipped.";
+                    continue;
+                }
+
+                var basePolicy = merged[capability];
+                merged[capability] = new CapabilityPolicy(
+                    TimeoutSeconds: overridePolicy.TimeoutSeconds ?? basePolicy.TimeoutSeconds,
+                    RetryCount: overridePolicy.RetryCount ?? basePolicy.RetryCount,
+                    BreakerFailureThreshold: overridePolicy.BreakerFailureThreshold ?? basePolicy.BreakerFailureThreshold);
+            }
+        }
+
+        return new DriverResilienceOptions
+        {
+            Tier = tier,
+            CapabilityPolicies = merged,
+            BulkheadMaxConcurrent = shape.BulkheadMaxConcurrent ?? baseOptions.BulkheadMaxConcurrent,
+            BulkheadMaxQueue = shape.BulkheadMaxQueue ?? baseOptions.BulkheadMaxQueue,
+        };
+    }
+
+    private sealed class ResilienceConfigShape
+    {
+        public int? BulkheadMaxConcurrent { get; set; }
+        public int? BulkheadMaxQueue { get; set; }
+        public Dictionary<string, CapabilityPolicyShape>? CapabilityPolicies { get; set; }
+    }
+
+    private sealed class CapabilityPolicyShape
+    {
+        public int? TimeoutSeconds { get; set; }
+        public int? RetryCount { get; set; }
+        public int? BreakerFailureThreshold { get; set; }
+    }
+}

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,

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

@@ -27,6 +27,8 @@ public sealed class OpcUaApplicationHost : IAsyncDisposable
     private readonly AuthorizationGate? _authzGate;
     private readonly NodeScopeResolver? _scopeResolver;
     private readonly StaleConfigFlag? _staleConfigFlag;
+    private readonly Func<string, ZB.MOM.WW.OtOpcUa.Core.Abstractions.DriverTier>? _tierLookup;
+    private readonly Func<string, string?>? _resilienceConfigLookup;
     private readonly ILoggerFactory _loggerFactory;
     private readonly ILogger<OpcUaApplicationHost> _logger;
     private ApplicationInstance? _application;
@@ -39,7 +41,9 @@ public sealed class OpcUaApplicationHost : IAsyncDisposable
         DriverResiliencePipelineBuilder? pipelineBuilder = null,
         AuthorizationGate? authzGate = null,
         NodeScopeResolver? scopeResolver = null,
-        StaleConfigFlag? staleConfigFlag = null)
+        StaleConfigFlag? staleConfigFlag = null,
+        Func<string, ZB.MOM.WW.OtOpcUa.Core.Abstractions.DriverTier>? tierLookup = null,
+        Func<string, string?>? resilienceConfigLookup = null)
     {
         _options = options;
         _driverHost = driverHost;
@@ -48,6 +52,8 @@ public sealed class OpcUaApplicationHost : IAsyncDisposable
         _authzGate = authzGate;
         _scopeResolver = scopeResolver;
         _staleConfigFlag = staleConfigFlag;
+        _tierLookup = tierLookup;
+        _resilienceConfigLookup = resilienceConfigLookup;
         _loggerFactory = loggerFactory;
         _logger = logger;
     }
@@ -75,7 +81,8 @@ public sealed class OpcUaApplicationHost : IAsyncDisposable
                 $"OPC UA application certificate could not be validated or created in {_options.PkiStoreRoot}");
 
         _server = new OtOpcUaServer(_driverHost, _authenticator, _pipelineBuilder, _loggerFactory,
-            authzGate: _authzGate, scopeResolver: _scopeResolver);
+            authzGate: _authzGate, scopeResolver: _scopeResolver,
+            tierLookup: _tierLookup, resilienceConfigLookup: _resilienceConfigLookup);
         await _application.Start(_server).ConfigureAwait(false);
 
         _logger.LogInformation("OPC UA server started — endpoint={Endpoint} driverCount={Count}",

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

@@ -23,6 +23,8 @@ public sealed class OtOpcUaServer : StandardServer
     private readonly DriverResiliencePipelineBuilder _pipelineBuilder;
     private readonly AuthorizationGate? _authzGate;
     private readonly NodeScopeResolver? _scopeResolver;
+    private readonly Func<string, DriverTier>? _tierLookup;
+    private readonly Func<string, string?>? _resilienceConfigLookup;
     private readonly ILoggerFactory _loggerFactory;
     private readonly List<DriverNodeManager> _driverNodeManagers = new();
 
@@ -32,13 +34,17 @@ public sealed class OtOpcUaServer : StandardServer
         DriverResiliencePipelineBuilder pipelineBuilder,
         ILoggerFactory loggerFactory,
         AuthorizationGate? authzGate = null,
-        NodeScopeResolver? scopeResolver = null)
+        NodeScopeResolver? scopeResolver = null,
+        Func<string, DriverTier>? tierLookup = null,
+        Func<string, string?>? resilienceConfigLookup = null)
     {
         _driverHost = driverHost;
         _authenticator = authenticator;
         _pipelineBuilder = pipelineBuilder;
         _authzGate = authzGate;
         _scopeResolver = scopeResolver;
+        _tierLookup = tierLookup;
+        _resilienceConfigLookup = resilienceConfigLookup;
         _loggerFactory = loggerFactory;
     }
 
@@ -59,10 +65,16 @@ public sealed class OtOpcUaServer : StandardServer
             if (driver is null) continue;
 
             var logger = _loggerFactory.CreateLogger<DriverNodeManager>();
-            // Per-driver resilience options: default Tier A pending Stream B.1 which wires
-            // per-type tiers into DriverTypeRegistry. Read ResilienceConfig JSON from the
-            // DriverInstance row in a follow-up PR; for now every driver gets Tier A defaults.
-            var options = new DriverResilienceOptions { Tier = DriverTier.A };
+            // Per-driver resilience options: tier comes from lookup (Phase 6.1 Stream B.1
+            // DriverTypeRegistry in the prod wire-up) or falls back to Tier A. ResilienceConfig
+            // JSON comes from the DriverInstance row via the optional lookup Func; parser
+            // layers JSON overrides on top of tier defaults (Phase 6.1 Stream A.2).
+            var tier = _tierLookup?.Invoke(driver.DriverType) ?? DriverTier.A;
+            var resilienceJson = _resilienceConfigLookup?.Invoke(driver.DriverInstanceId);
+            var options = DriverResilienceOptionsParser.ParseOrDefaults(tier, resilienceJson, out var diag);
+            if (diag is not null)
+                logger.LogWarning("ResilienceConfig parse diagnostic for driver {DriverId}: {Diag}", driver.DriverInstanceId, diag);
+
             var invoker = new CapabilityInvoker(_pipelineBuilder, driver.DriverInstanceId, () => options, driver.DriverType);
             var manager = new DriverNodeManager(server, configuration, driver, invoker, logger,
                 authzGate: _authzGate, scopeResolver: _scopeResolver);

tests/ZB.MOM.WW.OtOpcUa.Configuration.Tests/SchemaComplianceTests.cs

@@ -78,6 +78,7 @@ WHERE  i.is_unique = 1 AND i.has_filter = 1;",
             "CK_ServerCluster_RedundancyMode_NodeCount",
             "CK_Device_DeviceConfig_IsJson",
             "CK_DriverInstance_DriverConfig_IsJson",
+            "CK_DriverInstance_ResilienceConfig_IsJson",
             "CK_PollGroup_IntervalMs_Min",
             "CK_Tag_TagConfig_IsJson",
             "CK_ConfigAuditLog_DetailsJson_IsJson",

tests/ZB.MOM.WW.OtOpcUa.Core.Tests/OpcUa/IdentificationFolderBuilderTests.cs

@@ -0,0 +1,158 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Configuration.Entities;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Core.OpcUa;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Tests.OpcUa;
+
+[Trait("Category", "Unit")]
+public sealed class IdentificationFolderBuilderTests
+{
+    private sealed class RecordingBuilder : IAddressSpaceBuilder
+    {
+        public List<(string BrowseName, string DisplayName)> Folders { get; } = [];
+        public List<(string BrowseName, DriverDataType DataType, object? Value)> Properties { get; } = [];
+
+        public IAddressSpaceBuilder Folder(string browseName, string displayName)
+        {
+            Folders.Add((browseName, displayName));
+            return this; // flat recording — identification fields land in the same bucket
+        }
+
+        public IVariableHandle Variable(string browseName, string displayName, DriverAttributeInfo attributeInfo)
+            => throw new NotSupportedException("Identification fields use AddProperty, not Variable");
+
+        public void AddProperty(string browseName, DriverDataType dataType, object? value)
+            => Properties.Add((browseName, dataType, value));
+    }
+
+    private static Equipment EmptyEquipment() => new()
+    {
+        EquipmentId = "EQ-000000000001",
+        DriverInstanceId = "drv-1",
+        UnsLineId = "line-1",
+        Name = "eq-1",
+        MachineCode = "machine_001",
+    };
+
+    private static Equipment FullyPopulatedEquipment() => new()
+    {
+        EquipmentId = "EQ-000000000001",
+        DriverInstanceId = "drv-1",
+        UnsLineId = "line-1",
+        Name = "eq-1",
+        MachineCode = "machine_001",
+        Manufacturer = "Siemens",
+        Model = "S7-1500",
+        SerialNumber = "SN-12345",
+        HardwareRevision = "Rev-A",
+        SoftwareRevision = "Fw-2.3.1",
+        YearOfConstruction = 2023,
+        AssetLocation = "Warsaw-West/Bldg-3",
+        ManufacturerUri = "https://siemens.example",
+        DeviceManualUri = "https://siemens.example/manual",
+    };
+
+    [Fact]
+    public void HasAnyFields_AllNull_ReturnsFalse()
+    {
+        IdentificationFolderBuilder.HasAnyFields(EmptyEquipment()).ShouldBeFalse();
+    }
+
+    [Fact]
+    public void HasAnyFields_OneNonNull_ReturnsTrue()
+    {
+        var eq = EmptyEquipment();
+        eq.SerialNumber = "SN-1";
+        IdentificationFolderBuilder.HasAnyFields(eq).ShouldBeTrue();
+    }
+
+    [Fact]
+    public void Build_AllNull_ReturnsNull_AndDoesNotEmit_Folder()
+    {
+        var builder = new RecordingBuilder();
+
+        var result = IdentificationFolderBuilder.Build(builder, EmptyEquipment());
+
+        result.ShouldBeNull();
+        builder.Folders.ShouldBeEmpty("no Identification folder when every field is null");
+        builder.Properties.ShouldBeEmpty();
+    }
+
+    [Fact]
+    public void Build_FullyPopulated_EmitsAllNineFields()
+    {
+        var builder = new RecordingBuilder();
+
+        var result = IdentificationFolderBuilder.Build(builder, FullyPopulatedEquipment());
+
+        result.ShouldNotBeNull();
+        builder.Folders.ShouldContain(f => f.BrowseName == "Identification");
+        builder.Properties.Count.ShouldBe(9);
+        builder.Properties.Select(p => p.BrowseName).ShouldBe(
+            ["Manufacturer", "Model", "SerialNumber",
+             "HardwareRevision", "SoftwareRevision",
+             "YearOfConstruction", "AssetLocation",
+             "ManufacturerUri", "DeviceManualUri"],
+            "property order matches decision #139 exactly");
+    }
+
+    [Fact]
+    public void Build_OnlyNonNull_Are_Emitted()
+    {
+        var eq = EmptyEquipment();
+        eq.Manufacturer = "Siemens";
+        eq.SerialNumber = "SN-1";
+        eq.YearOfConstruction = 2024;
+        var builder = new RecordingBuilder();
+
+        IdentificationFolderBuilder.Build(builder, eq);
+
+        builder.Properties.Count.ShouldBe(3, "only the 3 non-null fields are exposed");
+        builder.Properties.Select(p => p.BrowseName).ShouldBe(
+            ["Manufacturer", "SerialNumber", "YearOfConstruction"]);
+    }
+
+    [Fact]
+    public void YearOfConstruction_Maps_Short_To_Int32_DriverDataType()
+    {
+        var eq = EmptyEquipment();
+        eq.YearOfConstruction = 2023;
+        var builder = new RecordingBuilder();
+
+        IdentificationFolderBuilder.Build(builder, eq);
+
+        var prop = builder.Properties.Single(p => p.BrowseName == "YearOfConstruction");
+        prop.DataType.ShouldBe(DriverDataType.Int32);
+        prop.Value.ShouldBe(2023, "short is widened to int for OPC UA Int32 representation");
+    }
+
+    [Fact]
+    public void Build_StringValues_RoundTrip()
+    {
+        var eq = FullyPopulatedEquipment();
+        var builder = new RecordingBuilder();
+
+        IdentificationFolderBuilder.Build(builder, eq);
+
+        builder.Properties.Single(p => p.BrowseName == "Manufacturer").Value.ShouldBe("Siemens");
+        builder.Properties.Single(p => p.BrowseName == "DeviceManualUri").Value.ShouldBe("https://siemens.example/manual");
+    }
+
+    [Fact]
+    public void FieldNames_Match_Decision139_Exactly()
+    {
+        IdentificationFolderBuilder.FieldNames.ShouldBe(
+            ["Manufacturer", "Model", "SerialNumber",
+             "HardwareRevision", "SoftwareRevision",
+             "YearOfConstruction", "AssetLocation",
+             "ManufacturerUri", "DeviceManualUri"]);
+    }
+
+    [Fact]
+    public void FolderName_Is_Identification()
+    {
+        IdentificationFolderBuilder.FolderName.ShouldBe("Identification");
+    }
+}

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

@@ -0,0 +1,166 @@
+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;
+
+[Trait("Category", "Unit")]
+public sealed class DriverResilienceOptionsParserTests
+{
+    [Fact]
+    public void NullJson_ReturnsPureTierDefaults()
+    {
+        var options = DriverResilienceOptionsParser.ParseOrDefaults(DriverTier.A, null, out var diag);
+
+        diag.ShouldBeNull();
+        options.Tier.ShouldBe(DriverTier.A);
+        options.Resolve(DriverCapability.Read).ShouldBe(
+            DriverResilienceOptions.GetTierDefaults(DriverTier.A)[DriverCapability.Read]);
+    }
+
+    [Fact]
+    public void WhitespaceJson_ReturnsDefaults()
+    {
+        DriverResilienceOptionsParser.ParseOrDefaults(DriverTier.B, "   ", out var diag);
+        diag.ShouldBeNull();
+    }
+
+    [Fact]
+    public void MalformedJson_FallsBack_WithDiagnostic()
+    {
+        var options = DriverResilienceOptionsParser.ParseOrDefaults(DriverTier.A, "{not json", out var diag);
+
+        diag.ShouldNotBeNull();
+        diag.ShouldContain("malformed");
+        options.Tier.ShouldBe(DriverTier.A);
+        options.Resolve(DriverCapability.Read).ShouldBe(
+            DriverResilienceOptions.GetTierDefaults(DriverTier.A)[DriverCapability.Read]);
+    }
+
+    [Fact]
+    public void EmptyObject_ReturnsDefaults()
+    {
+        var options = DriverResilienceOptionsParser.ParseOrDefaults(DriverTier.A, "{}", out var diag);
+
+        diag.ShouldBeNull();
+        options.Resolve(DriverCapability.Write).ShouldBe(
+            DriverResilienceOptions.GetTierDefaults(DriverTier.A)[DriverCapability.Write]);
+    }
+
+    [Fact]
+    public void ReadOverride_MergedIntoTierDefaults()
+    {
+        var json = """
+            {
+              "capabilityPolicies": {
+                "Read": { "timeoutSeconds": 5, "retryCount": 7, "breakerFailureThreshold": 2 }
+              }
+            }
+            """;
+
+        var options = DriverResilienceOptionsParser.ParseOrDefaults(DriverTier.A, json, out var diag);
+
+        diag.ShouldBeNull();
+        var read = options.Resolve(DriverCapability.Read);
+        read.TimeoutSeconds.ShouldBe(5);
+        read.RetryCount.ShouldBe(7);
+        read.BreakerFailureThreshold.ShouldBe(2);
+
+        // Other capabilities untouched
+        options.Resolve(DriverCapability.Write).ShouldBe(
+            DriverResilienceOptions.GetTierDefaults(DriverTier.A)[DriverCapability.Write]);
+    }
+
+    [Fact]
+    public void PartialPolicy_FillsMissingFieldsFromTierDefault()
+    {
+        var json = """
+            {
+              "capabilityPolicies": {
+                "Read": { "retryCount": 10 }
+              }
+            }
+            """;
+
+        var options = DriverResilienceOptionsParser.ParseOrDefaults(DriverTier.A, json, out _);
+
+        var read = options.Resolve(DriverCapability.Read);
+        var tierDefault = DriverResilienceOptions.GetTierDefaults(DriverTier.A)[DriverCapability.Read];
+        read.RetryCount.ShouldBe(10);
+        read.TimeoutSeconds.ShouldBe(tierDefault.TimeoutSeconds, "partial override; timeout falls back to tier default");
+        read.BreakerFailureThreshold.ShouldBe(tierDefault.BreakerFailureThreshold);
+    }
+
+    [Fact]
+    public void BulkheadOverrides_AreHonored()
+    {
+        var json = """
+            { "bulkheadMaxConcurrent": 100, "bulkheadMaxQueue": 500 }
+            """;
+
+        var options = DriverResilienceOptionsParser.ParseOrDefaults(DriverTier.B, json, out _);
+
+        options.BulkheadMaxConcurrent.ShouldBe(100);
+        options.BulkheadMaxQueue.ShouldBe(500);
+    }
+
+    [Fact]
+    public void UnknownCapability_Surfaces_InDiagnostic_ButDoesNotFail()
+    {
+        var json = """
+            {
+              "capabilityPolicies": {
+                "InventedCapability": { "timeoutSeconds": 99 }
+              }
+            }
+            """;
+
+        var options = DriverResilienceOptionsParser.ParseOrDefaults(DriverTier.A, json, out var diag);
+
+        diag.ShouldNotBeNull();
+        diag.ShouldContain("InventedCapability");
+        // Known capabilities untouched.
+        options.Resolve(DriverCapability.Read).ShouldBe(
+            DriverResilienceOptions.GetTierDefaults(DriverTier.A)[DriverCapability.Read]);
+    }
+
+    [Fact]
+    public void PropertyNames_AreCaseInsensitive()
+    {
+        var json = """
+            { "BULKHEADMAXCONCURRENT": 42 }
+            """;
+
+        var options = DriverResilienceOptionsParser.ParseOrDefaults(DriverTier.A, json, out _);
+
+        options.BulkheadMaxConcurrent.ShouldBe(42);
+    }
+
+    [Fact]
+    public void CapabilityName_IsCaseInsensitive()
+    {
+        var json = """
+            { "capabilityPolicies": { "read": { "retryCount": 99 } } }
+            """;
+
+        var options = DriverResilienceOptionsParser.ParseOrDefaults(DriverTier.A, json, out var diag);
+
+        diag.ShouldBeNull();
+        options.Resolve(DriverCapability.Read).RetryCount.ShouldBe(99);
+    }
+
+    [Theory]
+    [InlineData(DriverTier.A)]
+    [InlineData(DriverTier.B)]
+    [InlineData(DriverTier.C)]
+    public void EveryTier_WithEmptyJson_RoundTrips_Its_Defaults(DriverTier tier)
+    {
+        var options = DriverResilienceOptionsParser.ParseOrDefaults(tier, "{}", out var diag);
+
+        diag.ShouldBeNull();
+        options.Tier.ShouldBe(tier);
+        foreach (var cap in Enum.GetValues<DriverCapability>())
+            options.Resolve(cap).ShouldBe(DriverResilienceOptions.GetTierDefaults(tier)[cap]);
+    }
+}

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");
+    }
+}