From 53d222e0f76469c0699573fad65f02e68a41f0b1 Mon Sep 17 00:00:00 2001
From: Joseph Doherty <dohejw01@gmail.com>
Date: Thu, 16 Jul 2026 04:29:37 -0400
Subject: [PATCH] =?UTF-8?q?feat(driver-calc):=20B2-WP7=20Calculation=20dri?=
 =?UTF-8?q?ver=20=E2=80=94=20IDependencyConsumer=20+=20triggers=20+=20depl?=
 =?UTF-8?q?oy=20cycle=20gate?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Adds the Calculation pseudo-driver (tags computed by C# scripts over other tags' live
values) plus the host seam that feeds it:

- IDependencyConsumer capability interface (Core.Abstractions) + DriverTypeNames.Calculation.
- CalculationDriver : IDriver, ISubscribable, IReadable, IDependencyConsumer — change-gate +
  dedupe (VirtualTagActor parity), timer-group scheduler, Bad-transition + script-log emission,
  Good recovery; reuses the T0-4 CalculationEvaluator.
- DriverHostActor spawns a DependencyConsumerMuxAdapter per dependency-consuming driver,
  registering its refs on the per-node DependencyMuxActor and forwarding DependencyValueChanged
  → OnDependencyValue; re-registers on every apply, torn down with the driver.
- Factory + probe registered in DriverFactoryBootstrap (keeps the T0-3 guard green); guard test
  csproj references the driver so the bin-scan discovers the factory.
- DeploymentArtifact injects the resolved scriptSource (scriptId → SourceCode) into a calc tag's
  delivered TagConfig so the host-blind driver can compile it.
- DraftValidator deploy gates: CalculationScriptMissing / CalculationScriptNotFound (scriptId
  existence) + CalculationDependencyCycle (DependencyGraph.DetectCycles over calc→calc edges).
- Tests: driver units (dep-ref extraction, change-gate, dedupe, Bad+script-log+recovery, timer,
  read), tag-config parsing, DraftValidator gates (self/2-cycle/cross-driver-terminal), and a
  Runtime integration test proving values FLOW mux → adapter → driver → calc-of-calc end-to-end.

Claude-Session: https://claude.ai/code/session_01LVneM3eh1UtJxEisFXgmox
---
 .../Validation/DraftSnapshot.cs               |   4 +
 .../Validation/DraftSnapshotFactory.cs        |   1 +
 .../Validation/DraftValidator.cs              |  99 +++++
 .../ZB.MOM.WW.OtOpcUa.Configuration.csproj    |  10 +-
 .../DriverTypeNames.cs                        |   4 +
 .../IDependencyConsumer.cs                    |  44 ++
 .../CalculationDriver.cs                      | 384 ++++++++++++++++++
 .../CalculationDriverFactoryExtensions.cs     |  96 +++++
 .../CalculationDriverOptions.cs               |  20 +
 .../CalculationDriverProbe.cs                 |  45 ++
 .../CalculationTagDefinition.cs               |  85 ++++
 .../CalculationTimerScheduler.cs              | 110 +++++
 ...B.MOM.WW.OtOpcUa.Driver.Calculation.csproj |   1 +
 .../Drivers/DriverFactoryBootstrap.cs         |  13 +-
 .../ZB.MOM.WW.OtOpcUa.Host.csproj             |   1 +
 .../Drivers/DeploymentArtifact.cs             |  50 +++
 .../Drivers/DriverHostActor.cs                |  39 ++
 .../DependencyConsumerMuxAdapter.cs           |  71 ++++
 .../DraftValidatorCalculationTests.cs         | 156 +++++++
 ....WW.OtOpcUa.Core.Abstractions.Tests.csproj |   1 +
 .../CalculationDriverTests.cs                 | 187 +++++++++
 .../CalculationTagDefinitionTests.cs          |  55 +++
 .../Drivers/CalculationDependencyFlowTests.cs |  82 ++++
 .../ZB.MOM.WW.OtOpcUa.Runtime.Tests.csproj    |   3 +
 24 files changed, 1558 insertions(+), 3 deletions(-)
 create mode 100644 src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/IDependencyConsumer.cs
 create mode 100644 src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationDriver.cs
 create mode 100644 src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationDriverFactoryExtensions.cs
 create mode 100644 src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationDriverOptions.cs
 create mode 100644 src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationDriverProbe.cs
 create mode 100644 src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationTagDefinition.cs
 create mode 100644 src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationTimerScheduler.cs
 create mode 100644 src/Server/ZB.MOM.WW.OtOpcUa.Runtime/VirtualTags/DependencyConsumerMuxAdapter.cs
 create mode 100644 tests/Core/ZB.MOM.WW.OtOpcUa.Configuration.Tests/DraftValidatorCalculationTests.cs
 create mode 100644 tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation.Tests/CalculationDriverTests.cs
 create mode 100644 tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation.Tests/CalculationTagDefinitionTests.cs
 create mode 100644 tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Drivers/CalculationDependencyFlowTests.cs

diff --git a/src/Core/ZB.MOM.WW.OtOpcUa.Configuration/Validation/DraftSnapshot.cs b/src/Core/ZB.MOM.WW.OtOpcUa.Configuration/Validation/DraftSnapshot.cs
index 9fa9dad7..4bed38ba 100644
--- a/src/Core/ZB.MOM.WW.OtOpcUa.Configuration/Validation/DraftSnapshot.cs
+++ b/src/Core/ZB.MOM.WW.OtOpcUa.Configuration/Validation/DraftSnapshot.cs
@@ -55,6 +55,10 @@ public sealed class DraftSnapshot
     public IReadOnlyList<VirtualTag> VirtualTags { get; init; } = [];
     /// <summary>Equipment-bound scripted alarms. Part of the UNS effective-leaf uniqueness set.</summary>
     public IReadOnlyList<ScriptedAlarm> ScriptedAlarms { get; init; } = [];
+
+    /// <summary>User-authored scripts (shared by VirtualTags, ScriptedAlarms, and Calculation tags). Drives
+    /// the WP7 Calculation gates: <c>scriptId</c> existence + the calc→calc dependency-cycle check.</summary>
+    public IReadOnlyList<Script> Scripts { get; init; } = [];
     /// <summary>Gets the list of poll groups.</summary>
     public IReadOnlyList<PollGroup> PollGroups { get; init; } = [];
 
diff --git a/src/Core/ZB.MOM.WW.OtOpcUa.Configuration/Validation/DraftSnapshotFactory.cs b/src/Core/ZB.MOM.WW.OtOpcUa.Configuration/Validation/DraftSnapshotFactory.cs
index 2325944d..d10dfc82 100644
--- a/src/Core/ZB.MOM.WW.OtOpcUa.Configuration/Validation/DraftSnapshotFactory.cs
+++ b/src/Core/ZB.MOM.WW.OtOpcUa.Configuration/Validation/DraftSnapshotFactory.cs
@@ -50,6 +50,7 @@ public static class DraftSnapshotFactory
             UnsTagReferences   = await db.UnsTagReferences.AsNoTracking().ToListAsync(ct),
             VirtualTags        = await db.VirtualTags.AsNoTracking().ToListAsync(ct),
             ScriptedAlarms     = await db.ScriptedAlarms.AsNoTracking().ToListAsync(ct),
+            Scripts            = await db.Scripts.AsNoTracking().ToListAsync(ct),
             PollGroups         = await db.PollGroups.AsNoTracking().ToListAsync(ct),
             PriorEquipment     = [],   // intentional: no prior-generation table to diff against at this level
             ActiveReservations = await db.ExternalIdReservations
diff --git a/src/Core/ZB.MOM.WW.OtOpcUa.Configuration/Validation/DraftValidator.cs b/src/Core/ZB.MOM.WW.OtOpcUa.Configuration/Validation/DraftValidator.cs
index 097f56d1..86174ef1 100644
--- a/src/Core/ZB.MOM.WW.OtOpcUa.Configuration/Validation/DraftValidator.cs
+++ b/src/Core/ZB.MOM.WW.OtOpcUa.Configuration/Validation/DraftValidator.cs
@@ -2,6 +2,7 @@ using System.Text.RegularExpressions;
 using ZB.MOM.WW.OtOpcUa.Commons.Types;
 using ZB.MOM.WW.OtOpcUa.Configuration.Entities;
 using ZB.MOM.WW.OtOpcUa.Configuration.Enums;
+using ZB.MOM.WW.OtOpcUa.Core.VirtualTags;
 
 namespace ZB.MOM.WW.OtOpcUa.Configuration.Validation;
 
@@ -38,9 +39,107 @@ public static class DraftValidator
         ValidateRawNameCharset(draft, errors);
         ValidateHistorizedTagnameLength(draft, errors);
         ValidateUnsEffectiveLeafUniqueness(draft, errors);
+        ValidateCalculationTags(draft, errors);
         return errors;
     }
 
+    /// <summary>WP7 Calculation-driver deploy gates. For every tag bound to a <c>Calculation</c> driver:
+    /// <list type="number">
+    ///   <item><b>scriptId existence</b> — the tag's <c>TagConfig.scriptId</c> must be present and resolve to
+    ///     a <see cref="Script"/> row in the draft.</item>
+    ///   <item><b>Cycle gate (hard error)</b> — build the calc→calc edge set (a calc tag → its
+    ///     <c>ctx.GetTag</c> deps that are <b>themselves</b> Calculation tags; cross-driver refs are terminal,
+    ///     not edges) and run <see cref="DependencyGraph.DetectCycles"/> (Tarjan SCC). Any SCC / self-loop is a
+    ///     deploy error naming the cycle members — an undetected calc cycle is a live oscillation loop.</item>
+    /// </list>
+    /// Compile is deliberately NOT hard-gated (VirtualTag parity — the editor's live diagnostics mirror it and
+    /// a runtime compile failure lands as Bad quality + a script-log).</summary>
+    private static void ValidateCalculationTags(DraftSnapshot draft, List<ValidationError> errors)
+    {
+        var driverTypeByInstance = draft.DriverInstances
+            .GroupBy(d => d.DriverInstanceId, StringComparer.Ordinal)
+            .ToDictionary(g => g.Key, g => g.First().DriverType, StringComparer.Ordinal);
+        var driverTypeByDevice = draft.Devices
+            .GroupBy(d => d.DeviceId, StringComparer.Ordinal)
+            .ToDictionary(
+                g => g.Key,
+                g => driverTypeByInstance.TryGetValue(g.First().DriverInstanceId, out var dt) ? dt : null,
+                StringComparer.Ordinal);
+
+        var resolver = BuildRawPathResolver(draft);
+        var scriptExists = new HashSet<string>(draft.Scripts.Select(s => s.ScriptId), StringComparer.Ordinal);
+        var scriptSourceById = draft.Scripts
+            .GroupBy(s => s.ScriptId, StringComparer.Ordinal)
+            .ToDictionary(g => g.Key, g => g.First().SourceCode, StringComparer.Ordinal);
+
+        // Identify calc tags (tags on a Calculation-typed device) + their RawPath + scriptId in one pass.
+        var calcTags = new List<(Tag Tag, string? RawPath, string? ScriptId)>();
+        var calcRawPaths = new HashSet<string>(StringComparer.Ordinal);
+        foreach (var t in draft.Tags)
+        {
+            if (!driverTypeByDevice.TryGetValue(t.DeviceId, out var dt)
+                || !string.Equals(dt, Core.Abstractions.DriverTypeNames.Calculation, StringComparison.Ordinal))
+                continue;
+            var rawPath = resolver.TryBuildTagPath(t.DeviceId, t.TagGroupId, t.Name);
+            calcTags.Add((t, rawPath, ParseScriptId(t.TagConfig)));
+            if (rawPath is not null) calcRawPaths.Add(rawPath);
+        }
+        if (calcTags.Count == 0) return;
+
+        // Rule 1 — scriptId existence.
+        foreach (var (t, _, scriptId) in calcTags)
+        {
+            if (string.IsNullOrWhiteSpace(scriptId))
+                errors.Add(new("CalculationScriptMissing",
+                    $"Calculation tag '{t.TagId}' has no 'scriptId' in its TagConfig", t.TagId));
+            else if (!scriptExists.Contains(scriptId!))
+                errors.Add(new("CalculationScriptNotFound",
+                    $"Calculation tag '{t.TagId}' references script '{scriptId}', which does not exist in the draft",
+                    t.TagId));
+        }
+
+        // Rule 2 — cycle gate. Edges run from a calc tag to each dep that is ITSELF a calc tag.
+        var graph = new DependencyGraph();
+        foreach (var (_, rawPath, scriptId) in calcTags)
+        {
+            if (rawPath is null) continue; // broken chain — flagged by the charset rule; not a graph node
+            var source = scriptId is not null && scriptSourceById.TryGetValue(scriptId, out var src) ? src : null;
+            var calcDeps = EquipmentScriptPaths.ExtractDependencyRefs(source)
+                .Where(calcRawPaths.Contains)
+                .ToHashSet(StringComparer.Ordinal);
+            graph.Add(rawPath, calcDeps);
+        }
+        foreach (var cycle in graph.DetectCycles())
+            errors.Add(new("CalculationDependencyCycle",
+                "Calculation tags form a dependency cycle (members: " + string.Join(", ", cycle) +
+                "); a calc→calc cycle is a live oscillation loop and must be broken before deploy",
+                cycle.Count > 0 ? cycle[0] : null));
+    }
+
+    /// <summary>Extract the <c>scriptId</c> string from a calc tag's schemaless <c>TagConfig</c> JSON. Never
+    /// throws — malformed/blank/non-object JSON or an absent/non-string <c>scriptId</c> yields null.</summary>
+    private static string? ParseScriptId(string? tagConfig)
+    {
+        if (string.IsNullOrWhiteSpace(tagConfig)) return null;
+        try
+        {
+            using var doc = System.Text.Json.JsonDocument.Parse(tagConfig);
+            var root = doc.RootElement;
+            if (root.ValueKind != System.Text.Json.JsonValueKind.Object) return null;
+            if (root.TryGetProperty("scriptId", out var el)
+                && el.ValueKind == System.Text.Json.JsonValueKind.String)
+            {
+                var v = el.GetString();
+                return string.IsNullOrWhiteSpace(v) ? null : v;
+            }
+            return null;
+        }
+        catch (System.Text.Json.JsonException)
+        {
+            return null;
+        }
+    }
+
     /// <summary>Builds the shared <see cref="RawPathResolver"/> from the draft's raw topology so the
     /// tagname-length rule computes the SAME RawPath the deploy artifact injects into drivers.</summary>
     private static RawPathResolver BuildRawPathResolver(DraftSnapshot draft)
diff --git a/src/Core/ZB.MOM.WW.OtOpcUa.Configuration/ZB.MOM.WW.OtOpcUa.Configuration.csproj b/src/Core/ZB.MOM.WW.OtOpcUa.Configuration/ZB.MOM.WW.OtOpcUa.Configuration.csproj
index 4b014f63..4c8b187f 100644
--- a/src/Core/ZB.MOM.WW.OtOpcUa.Configuration/ZB.MOM.WW.OtOpcUa.Configuration.csproj
+++ b/src/Core/ZB.MOM.WW.OtOpcUa.Configuration/ZB.MOM.WW.OtOpcUa.Configuration.csproj
@@ -7,7 +7,12 @@
         <LangVersion>latest</LangVersion>
         <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
         <GenerateDocumentationFile>true</GenerateDocumentationFile>
-        <NoWarn>$(NoWarn);CS1591</NoWarn>
+        <!-- WP7: the calc deploy-gate reuses the pure DependencyGraph (Tarjan SCC) from Core.VirtualTags,
+             whose closure includes Microsoft.CodeAnalysis.CSharp.Scripting 4.12.0 (== CodeAnalysis.Common
+             4.12.0), while EF's transitive CodeAnalysis.Common 5.0.0 wins resolution. Suppress NU1608 — the
+             only surface Configuration touches (DependencyGraph.DetectCycles) has ZERO Roslyn dependency, so
+             the version skew never runs. Mirrors the identical suppression + rationale in the Host csproj. -->
+        <NoWarn>$(NoWarn);CS1591;NU1608</NoWarn>
         <RootNamespace>ZB.MOM.WW.OtOpcUa.Configuration</RootNamespace>
     </PropertyGroup>
 
@@ -30,6 +35,9 @@
         <!-- R2-11 (01/C-1): consume the shared TagConfigIntent.Parse byte-parity authority in Commons.
              Cycle-safe — Commons has zero in-repo ProjectReferences. -->
         <ProjectReference Include="..\ZB.MOM.WW.OtOpcUa.Commons\ZB.MOM.WW.OtOpcUa.Commons.csproj"/>
+        <!-- WP7: the deploy-gate cycle check reuses DependencyGraph (Tarjan SCC) for the calc→calc
+             dependency-cycle rule. Cycle-safe — Core.VirtualTags does not reference Configuration. -->
+        <ProjectReference Include="..\ZB.MOM.WW.OtOpcUa.Core.VirtualTags\ZB.MOM.WW.OtOpcUa.Core.VirtualTags.csproj"/>
     </ItemGroup>
 
 </Project>
diff --git a/src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/DriverTypeNames.cs b/src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/DriverTypeNames.cs
index 2e166a21..d4ba0417 100644
--- a/src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/DriverTypeNames.cs
+++ b/src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/DriverTypeNames.cs
@@ -50,6 +50,9 @@ public static class DriverTypeNames
     /// <summary>AVEVA System Platform (Wonderware) Galaxy driver, via the mxaccessgw gateway.</summary>
     public const string Galaxy = "GalaxyMxGateway";
 
+    /// <summary>Calculation pseudo-driver — tags computed by C# scripts over other tags' live values.</summary>
+    public const string Calculation = "Calculation";
+
     /// <summary>
     ///     Every driver-type string declared above, for callers that need to enumerate
     ///     the full set (e.g. validation of an authored <c>DriverType</c>).
@@ -64,5 +67,6 @@ public static class DriverTypeNames
         FOCAS,
         OpcUaClient,
         Galaxy,
+        Calculation,
     ];
 }
diff --git a/src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/IDependencyConsumer.cs b/src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/IDependencyConsumer.cs
new file mode 100644
index 00000000..e3261ceb
--- /dev/null
+++ b/src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/IDependencyConsumer.cs
@@ -0,0 +1,44 @@
+namespace ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+/// <summary>
+///     Optional composable driver capability: the driver consumes <b>other</b> tags' live values.
+///     The host registers the declared <see cref="DependencyRefs"/> with its per-node dependency mux
+///     and forwards every matching value change into <see cref="OnDependencyValue"/> — the seam that
+///     lets a host-blind driver (e.g. the <c>Calculation</c> pseudo-driver) read the address space's
+///     live values without any cross-driver plumbing of its own.
+/// </summary>
+/// <remarks>
+///     <para>
+///         The mechanism mirrors how a <c>VirtualTagActor</c> registers interest on the
+///         <c>DependencyMuxActor</c>: the mux already receives every driver's
+///         <c>AttributeValuePublished</c> keyed by wire-ref (under v3, RawPath), so a driver that
+///         implements this interface simply piggy-backs on that fan-out. A calc tag's computed output
+///         re-enters the mux via the ordinary driver publish path, so calc-of-calc chains work with no
+///         extra machinery — which is exactly why the deploy-time cycle gate is mandatory.
+///     </para>
+///     <para>
+///         Implementations of <see cref="OnDependencyValue"/> are invoked from an actor context and
+///         <b>must be non-blocking</b> — do the work inline and cheaply (the compile cache makes
+///         steady-state calc evaluation a bounded method invocation), never block on I/O.
+///     </para>
+/// </remarks>
+public interface IDependencyConsumer
+{
+    /// <summary>
+    ///     Wire-refs (RawPaths) this driver needs fed to it, derived from its authored tags. The host
+    ///     re-reads this after <see cref="IDriver.InitializeAsync"/> / <see cref="IDriver.ReinitializeAsync"/>
+    ///     and (re)registers the set with its dependency mux on every apply, so a tag/script edit that
+    ///     changes the set converges without a bespoke notification.
+    /// </summary>
+    IReadOnlyCollection<string> DependencyRefs { get; }
+
+    /// <summary>
+    ///     Host push of a single dependency value change. Called from an actor context, so the
+    ///     implementation must be non-blocking.
+    /// </summary>
+    /// <param name="rawPath">The changed dependency's wire-ref (RawPath).</param>
+    /// <param name="value">The new value (may be null).</param>
+    /// <param name="statusCode">The OPC UA status code carried with the value (0 = Good).</param>
+    /// <param name="timestampUtc">The source timestamp of the change.</param>
+    void OnDependencyValue(string rawPath, object? value, uint statusCode, DateTime timestampUtc);
+}
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationDriver.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationDriver.cs
new file mode 100644
index 00000000..bc551e7c
--- /dev/null
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationDriver.cs
@@ -0,0 +1,384 @@
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Logging.Abstractions;
+using Serilog;
+using ZB.MOM.WW.OtOpcUa.Commons.Engines;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Calculation;
+
+/// <summary>
+///     The <c>Calculation</c> pseudo-driver. Its tags are ordinary raw tags whose value is <b>computed</b>
+///     by a C# script over other tags' live values — there is no backend, no endpoint, no discovery, no
+///     writes. It implements:
+///     <list type="bullet">
+///       <item><see cref="IDriver"/> — lifecycle + always-Connected health.</item>
+///       <item><see cref="IDependencyConsumer"/> — the host feeds it the other tags' live values.</item>
+///       <item><see cref="ISubscribable"/> — computed values flow out via <see cref="OnDataChange"/>
+///       exactly like any driver, so the ordinary node fan-out + the mux re-entry (calc-of-calc) apply.</item>
+///       <item><see cref="IReadable"/> — on-demand read returns the last computed snapshot
+///       (<c>BadWaitingForInitialData</c> before the first evaluation).</item>
+///     </list>
+///
+///     <para>
+///         <b>Triggers.</b> A tag re-evaluates on any of its declared dependencies changing (change-trigger,
+///         gated exactly like <c>VirtualTagActor</c>: nothing publishes until every declared dep has arrived
+///         at least once, and equal results are deduped) and/or on a timer (one timer per interval group).
+///     </para>
+///     <para>
+///         <b>Error semantics (mini-design §6).</b> An evaluator <c>Failure</c> publishes <b>Bad</b> quality
+///         carrying the last-known value, once per Good→Bad transition and only after all deps have arrived,
+///         and emits a <c>ScriptLogEntry</c> on the <c>script-logs</c> topic (via the injected
+///         <see cref="ScriptRootLogger"/>'s <c>ScriptLogTopicSink</c>). Recovery to Good is force-published.
+///         A historized Bad records <c>BadInternalError</c>.
+///     </para>
+/// </summary>
+public sealed class CalculationDriver : IDriver, IDependencyConsumer, ISubscribable, IReadable, IDisposable
+{
+    // OPC UA status codes surfaced by the calc driver.
+    private const uint StatusGood = 0u;
+    private const uint StatusBadWaitingForInitialData = 0x80320000u;
+    private const uint StatusBadInternalError = 0x80020000u;
+
+    private readonly string _driverInstanceId;
+    private readonly CalculationDriverOptions _options;
+    private readonly ILogger<CalculationDriver> _logger;
+    private readonly ScriptRootLogger _scriptRoot;
+    private readonly CalculationEvaluator _evaluator;
+
+    // Authored calc tags, keyed by RawPath (identity + evaluation id). Built once at construction so
+    // DependencyRefs is available BEFORE InitializeAsync (the host reads it when spawning the mux-adapter).
+    private readonly Dictionary<string, CalculationTagDefinition> _tagsByRawPath = new(StringComparer.Ordinal);
+
+    // rawPath (a dependency) → the calc tags that read it AND are change-triggered. Drives OnDependencyValue.
+    private readonly Dictionary<string, List<string>> _changeDependents = new(StringComparer.Ordinal);
+
+    // Union of every tag's declared dependency refs — the interest set the host registers on the mux.
+    private readonly IReadOnlyCollection<string> _dependencyRefs;
+
+    // Live evaluation state. Guarded by _lock: OnDependencyValue (actor thread) and timer ticks
+    // (pool threads) can both drive an evaluation, so all state mutation is serialized.
+    private readonly object _lock = new();
+    private readonly Dictionary<string, object?> _depValues = new(StringComparer.Ordinal);
+    private readonly HashSet<string> _arrivedDeps = new(StringComparer.Ordinal);
+    private readonly Dictionary<string, TagState> _stateByRawPath = new(StringComparer.Ordinal);
+
+    private CalculationTimerScheduler? _timers;
+    private volatile bool _running;
+    private DateTime? _lastComputeUtc;
+    private bool _disposed;
+
+    /// <summary>Occurs when a calc tag's computed value changes (or transitions Good↔Bad).</summary>
+    public event EventHandler<DataChangeEventArgs>? OnDataChange;
+
+    /// <summary>Initializes a new <see cref="CalculationDriver"/>.</summary>
+    /// <param name="options">Bound options carrying the authored raw calc tags.</param>
+    /// <param name="driverInstanceId">Stable logical id of this driver instance.</param>
+    /// <param name="scriptRoot">Root script logger — user <c>ctx.Logger</c> output + failure entries fan out
+    /// to the <c>script-logs</c> topic through its <c>ScriptLogTopicSink</c>. When null a no-op logger is used.</param>
+    /// <param name="logger">Host-side diagnostics logger; defaults to the null logger.</param>
+    public CalculationDriver(
+        CalculationDriverOptions options,
+        string driverInstanceId,
+        ScriptRootLogger? scriptRoot = null,
+        ILogger<CalculationDriver>? logger = null)
+    {
+        ArgumentNullException.ThrowIfNull(options);
+        ArgumentException.ThrowIfNullOrWhiteSpace(driverInstanceId);
+        _options = options;
+        _driverInstanceId = driverInstanceId;
+        _logger = logger ?? NullLogger<CalculationDriver>.Instance;
+        _scriptRoot = scriptRoot ?? new ScriptRootLogger(new LoggerConfiguration().CreateLogger());
+        _evaluator = new CalculationEvaluator(
+            _logger is ILogger<CalculationEvaluator> el ? el : NullLogger<CalculationEvaluator>.Instance,
+            _scriptRoot,
+            _options.RunTimeout);
+
+        BuildTagTable();
+        _dependencyRefs = _tagsByRawPath.Values
+            .SelectMany(t => t.DependencyRefs)
+            .Distinct(StringComparer.Ordinal)
+            .ToArray();
+    }
+
+    private void BuildTagTable()
+    {
+        foreach (var entry in _options.RawTags)
+        {
+            if (!CalculationTagDefinition.TryFromTagConfig(entry.TagConfig, entry.RawPath, out var def))
+            {
+                _logger.LogWarning(
+                    "Calculation {Driver}: raw tag {RawPath} has no scriptId; skipping (not a calc tag)",
+                    _driverInstanceId, entry.RawPath);
+                continue;
+            }
+            if (string.IsNullOrWhiteSpace(def.ScriptSource))
+            {
+                _logger.LogWarning(
+                    "Calculation {Driver}: calc tag {RawPath} (script {Script}) has no resolved scriptSource; " +
+                    "it will not compute until the deploy artifact injects the script source",
+                    _driverInstanceId, entry.RawPath, def.ScriptId);
+            }
+            _tagsByRawPath[entry.RawPath] = def;
+            _stateByRawPath[entry.RawPath] = new TagState();
+            if (def.ChangeTriggered)
+            {
+                foreach (var dep in def.DependencyRefs)
+                {
+                    if (!_changeDependents.TryGetValue(dep, out var list))
+                        _changeDependents[dep] = list = new List<string>();
+                    if (!list.Contains(entry.RawPath, StringComparer.Ordinal)) list.Add(entry.RawPath);
+                }
+            }
+        }
+    }
+
+    // ---- IDriver ----
+
+    /// <inheritdoc />
+    public string DriverInstanceId => _driverInstanceId;
+
+    /// <inheritdoc />
+    public string DriverType => DriverTypeNames.Calculation;
+
+    /// <inheritdoc />
+    public Task InitializeAsync(string driverConfigJson, CancellationToken cancellationToken)
+    {
+        _running = true;
+        StartTimers();
+        _logger.LogInformation(
+            "Calculation {Driver}: initialized with {TagCount} calc tag(s), {DepCount} distinct dependency ref(s)",
+            _driverInstanceId, _tagsByRawPath.Count, _dependencyRefs.Count);
+        return Task.CompletedTask;
+    }
+
+    /// <inheritdoc />
+    public Task ReinitializeAsync(string driverConfigJson, CancellationToken cancellationToken)
+    {
+        // The authored tag table is fixed at construction (a RawTags change respawns the driver, mirroring
+        // the fleet's factory-built-options pattern). Reinit drops compiled scripts (IScriptCacheOwner
+        // contract — stops collectible ALCs accreting) + re-arms timers so the calc set stays live.
+        StopTimers();
+        _evaluator.ClearCompiledScripts();
+        _running = true;
+        StartTimers();
+        return Task.CompletedTask;
+    }
+
+    /// <inheritdoc />
+    public Task ShutdownAsync(CancellationToken cancellationToken)
+    {
+        _running = false;
+        StopTimers();
+        return Task.CompletedTask;
+    }
+
+    /// <inheritdoc />
+    public DriverHealth GetHealth() => new(DriverState.Healthy, _lastComputeUtc, null);
+
+    /// <inheritdoc />
+    public long GetMemoryFootprint() => 0;
+
+    /// <inheritdoc />
+    public Task FlushOptionalCachesAsync(CancellationToken cancellationToken)
+    {
+        // The compile cache is the only optional cache; dropping it is safe (recompiled on next eval).
+        _evaluator.ClearCompiledScripts();
+        return Task.CompletedTask;
+    }
+
+    // ---- IDependencyConsumer ----
+
+    /// <inheritdoc />
+    public IReadOnlyCollection<string> DependencyRefs => _dependencyRefs;
+
+    /// <inheritdoc />
+    public void OnDependencyValue(string rawPath, object? value, uint statusCode, DateTime timestampUtc)
+    {
+        if (!_running) return;
+        List<string>? dependents;
+        lock (_lock)
+        {
+            _depValues[rawPath] = value;
+            _arrivedDeps.Add(rawPath);
+            if (!_changeDependents.TryGetValue(rawPath, out dependents) || dependents.Count == 0) return;
+            // Evaluate each change-triggered dependent inline under the lock (the compile cache makes this
+            // a bounded method invocation — the same "fast enough to run inline" contract as the VT evaluator).
+            foreach (var calcRawPath in dependents)
+                EvaluateTag(calcRawPath, timestampUtc);
+        }
+    }
+
+    // ---- ISubscribable ----
+
+    /// <inheritdoc />
+    public Task<ISubscriptionHandle> SubscribeAsync(
+        IReadOnlyList<string> fullReferences, TimeSpan publishingInterval, CancellationToken cancellationToken)
+    {
+        ArgumentNullException.ThrowIfNull(fullReferences);
+        var handle = new CalculationSubscriptionHandle($"calc-{Guid.NewGuid():N}");
+        // Initial-data callback (OPC UA convention): surface the current snapshot for each subscribed calc
+        // tag so a freshly-materialised node shows BadWaitingForInitialData until its first evaluation lands.
+        foreach (var reference in fullReferences)
+        {
+            var snapshot = ReadOne(reference);
+            OnDataChange?.Invoke(this, new DataChangeEventArgs(handle, reference, snapshot));
+        }
+        return Task.FromResult<ISubscriptionHandle>(handle);
+    }
+
+    /// <inheritdoc />
+    public Task UnsubscribeAsync(ISubscriptionHandle handle, CancellationToken cancellationToken)
+        => Task.CompletedTask;
+
+    // ---- IReadable ----
+
+    /// <inheritdoc />
+    public Task<IReadOnlyList<DataValueSnapshot>> ReadAsync(
+        IReadOnlyList<string> fullReferences, CancellationToken cancellationToken)
+    {
+        ArgumentNullException.ThrowIfNull(fullReferences);
+        var results = new DataValueSnapshot[fullReferences.Count];
+        for (var i = 0; i < fullReferences.Count; i++)
+            results[i] = ReadOne(fullReferences[i]);
+        return Task.FromResult<IReadOnlyList<DataValueSnapshot>>(results);
+    }
+
+    private DataValueSnapshot ReadOne(string reference)
+    {
+        var now = DateTime.UtcNow;
+        lock (_lock)
+        {
+            if (!_stateByRawPath.TryGetValue(reference, out var st) || !st.HasValue)
+                return new DataValueSnapshot(null, StatusBadWaitingForInitialData, null, now);
+            var status = st.LastPublishedBad ? StatusBadInternalError : StatusGood;
+            return new DataValueSnapshot(st.LastValue, status, st.LastTimestampUtc, st.LastTimestampUtc);
+        }
+    }
+
+    // ---- evaluation ----
+
+    /// <summary>Timer-trigger entry point — evaluates a single calc tag. Guards the lock itself (called
+    /// from a pool thread, unlike the change path which is already under the lock).</summary>
+    private void EvaluateTagLocked(string rawPath)
+    {
+        if (!_running) return;
+        lock (_lock) EvaluateTag(rawPath, DateTime.UtcNow);
+    }
+
+    /// <summary>Evaluate one calc tag and publish the outcome. MUST be called under <see cref="_lock"/>.</summary>
+    private void EvaluateTag(string rawPath, DateTime timestampUtc)
+    {
+        if (!_tagsByRawPath.TryGetValue(rawPath, out var def)) return;
+        if (string.IsNullOrWhiteSpace(def.ScriptSource)) return; // unresolved script — never computes (logged at init)
+
+        var st = _stateByRawPath[rawPath];
+
+        // Change-gate (mini-design §4): publish nothing until every declared dep has arrived at least once.
+        var allArrived = def.DependencyRefs.All(_arrivedDeps.Contains);
+
+        // Build the per-tag dependency snapshot (only its declared reads, current values).
+        var deps = new Dictionary<string, object?>(StringComparer.Ordinal);
+        foreach (var dep in def.DependencyRefs)
+            if (_depValues.TryGetValue(dep, out var v)) deps[dep] = v;
+
+        var result = _evaluator.Evaluate(rawPath, def.ScriptSource, deps);
+
+        if (!result.Success)
+        {
+            OnEvaluationFailed(def, st, result.Reason ?? "evaluator failure", allArrived, timestampUtc);
+            return;
+        }
+
+        if (!allArrived) return; // change-trigger warm-up: hold until inputs are ready
+
+        // Value dedup — but bypass it while recovering from Bad so a recovery whose value equals the
+        // pre-failure value still republishes Good (otherwise the node would stay Bad forever).
+        if (!st.LastPublishedBad && st.HasValue && Equals(st.LastValue, result.Value))
+            return;
+
+        st.HasValue = true;
+        st.LastValue = result.Value;
+        st.LastPublishedBad = false;
+        st.LastTimestampUtc = timestampUtc;
+        _lastComputeUtc = DateTime.UtcNow;
+        Publish(rawPath, result.Value, StatusGood, timestampUtc);
+    }
+
+    /// <summary>Failure tail (mirrors <c>VirtualTagActor</c> 02/S13): always emits the per-failure
+    /// script-log; additionally publishes a Bad snapshot — carrying the last-known value — once per
+    /// Good→Bad transition and only after every declared dependency has arrived.</summary>
+    private void OnEvaluationFailed(
+        CalculationTagDefinition def, TagState st, string reason, bool allArrived, DateTime timestampUtc)
+    {
+        PublishScriptLog(def, reason);
+        if (st.LastPublishedBad || !allArrived) return;
+
+        st.LastPublishedBad = true;
+        st.LastTimestampUtc = timestampUtc;
+        // Carry the last-known value (null if none) with Bad quality.
+        Publish(def.RawPath, st.HasValue ? st.LastValue : null, StatusBadInternalError, timestampUtc);
+    }
+
+    private void Publish(string rawPath, object? value, uint statusCode, DateTime timestampUtc)
+    {
+        var snapshot = new DataValueSnapshot(value, statusCode, timestampUtc, timestampUtc);
+        // Fired under _lock — the subscriber (DriverInstanceActor) marshals the event to its own thread,
+        // so there is no re-entrant call back into this driver.
+        OnDataChange?.Invoke(this, new DataChangeEventArgs(SharedHandle, rawPath, snapshot));
+    }
+
+    private void PublishScriptLog(CalculationTagDefinition def, string reason)
+    {
+        // Route through the script logger bound with ScriptId + the calc tag's RawPath (in the VirtualTagId
+        // slot the Script-log page attributes on). The ScriptRootLogger's ScriptLogTopicSink converts this
+        // Warning event into a ScriptLogEntry on the script-logs DPS topic — the driver needs no Akka access.
+        _scriptRoot.Logger
+            .ForContext(ScriptLoggerFactory.ScriptIdProperty, def.ScriptId)
+            .ForContext(ScriptLoggerFactory.VirtualTagIdProperty, def.RawPath)
+            .Warning("{Reason}", reason);
+    }
+
+    private void StartTimers()
+    {
+        var timed = _tagsByRawPath.Values.Where(t => t.TimerInterval is not null).ToArray();
+        if (timed.Length == 0) return;
+        _timers = new CalculationTimerScheduler(EvaluateTagLocked, _logger);
+        _timers.Start(timed);
+    }
+
+    private void StopTimers()
+    {
+        _timers?.Dispose();
+        _timers = null;
+    }
+
+    /// <summary>Test/diagnostic accessor: number of timer ticks skipped for in-flight groups.</summary>
+    internal long TimerSkippedTickCount => _timers?.SkippedTickCount ?? 0;
+
+    // A single shared handle for host-pushed publishes (change + timer). SubscribeAsync mints its own
+    // per-call handle for the initial-data callback; steady-state publishes reuse this so OnDataChange
+    // always carries a non-null handle.
+    private static readonly CalculationSubscriptionHandle SharedHandle = new("calc-shared");
+
+    /// <inheritdoc />
+    public void Dispose()
+    {
+        if (_disposed) return;
+        _disposed = true;
+        _running = false;
+        StopTimers();
+        _evaluator.Dispose();
+    }
+
+    /// <summary>Per-tag published state (guarded by <see cref="_lock"/>).</summary>
+    private sealed class TagState
+    {
+        public bool HasValue;
+        public object? LastValue;
+        public bool LastPublishedBad;
+        public DateTime LastTimestampUtc;
+    }
+
+    private sealed record CalculationSubscriptionHandle(string DiagnosticId) : ISubscriptionHandle;
+}
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationDriverFactoryExtensions.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationDriverFactoryExtensions.cs
new file mode 100644
index 00000000..ab10f06d
--- /dev/null
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationDriverFactoryExtensions.cs
@@ -0,0 +1,96 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using Microsoft.Extensions.Logging;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Core.Hosting;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Calculation;
+
+/// <summary>
+///     Static factory registration helper for <see cref="CalculationDriver"/>. The Server's
+///     <c>DriverFactoryBootstrap</c> calls <see cref="Register"/> once at startup; the bootstrapper then
+///     materialises <c>Calculation</c> DriverInstance rows into live driver instances. Mirrors
+///     <c>ModbusDriverFactoryExtensions</c>, with the addition of a <see cref="ScriptRootLogger"/> so a
+///     script failure fans out onto the <c>script-logs</c> topic (via the root logger's
+///     <c>ScriptLogTopicSink</c>) — the calc driver has no Akka access of its own.
+/// </summary>
+public static class CalculationDriverFactoryExtensions
+{
+    /// <summary>The <c>DriverInstance.DriverType</c> string this factory registers under.</summary>
+    public const string DriverTypeName = "Calculation";
+
+    private static readonly JsonSerializerOptions JsonOptions = new()
+    {
+        PropertyNameCaseInsensitive = true,
+        ReadCommentHandling = JsonCommentHandling.Skip,
+        AllowTrailingCommas = true,
+        Converters = { new JsonStringEnumConverter() },
+    };
+
+    /// <summary>
+    ///     Register the Calculation factory with the driver registry. The optional
+    ///     <paramref name="loggerFactory"/> + <paramref name="scriptRoot"/> are captured at registration
+    ///     time; both may be null (the guard test invokes <c>Register(registry)</c> reflectively with the
+    ///     trailing parameters defaulted), in which case the driver runs with the null logger + a no-op
+    ///     script-logger.
+    /// </summary>
+    /// <param name="registry">The driver factory registry to register with.</param>
+    /// <param name="loggerFactory">Optional logger factory for per-instance diagnostics loggers.</param>
+    /// <param name="scriptRoot">Optional root script logger (fans failure entries onto the <c>script-logs</c> topic).</param>
+    public static void Register(
+        DriverFactoryRegistry registry,
+        ILoggerFactory? loggerFactory = null,
+        ScriptRootLogger? scriptRoot = null)
+    {
+        ArgumentNullException.ThrowIfNull(registry);
+        registry.Register(DriverTypeName, (id, json) => CreateInstance(id, json, loggerFactory, scriptRoot));
+    }
+
+    /// <summary>Public overload for the Server-side bootstrapper + test consumers.</summary>
+    /// <param name="driverInstanceId">The unique identifier for the driver instance.</param>
+    /// <param name="driverConfigJson">The merged driver config JSON (carries the <c>RawTags</c> array).</param>
+    /// <returns>The constructed <see cref="CalculationDriver"/>.</returns>
+    public static CalculationDriver CreateInstance(string driverInstanceId, string driverConfigJson)
+        => CreateInstance(driverInstanceId, driverConfigJson, loggerFactory: null, scriptRoot: null);
+
+    /// <summary>Logger/script-logger-aware overload — used by <see cref="Register"/>'s closure via DI.</summary>
+    /// <param name="driverInstanceId">The unique identifier for the driver instance.</param>
+    /// <param name="driverConfigJson">The merged driver config JSON (carries the <c>RawTags</c> array).</param>
+    /// <param name="loggerFactory">Optional logger factory for per-instance diagnostics loggers.</param>
+    /// <param name="scriptRoot">Optional root script logger for failure fan-out.</param>
+    /// <returns>The constructed <see cref="CalculationDriver"/>.</returns>
+    public static CalculationDriver CreateInstance(
+        string driverInstanceId, string driverConfigJson,
+        ILoggerFactory? loggerFactory, ScriptRootLogger? scriptRoot)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(driverInstanceId);
+        ArgumentException.ThrowIfNullOrWhiteSpace(driverConfigJson);
+
+        var dto = JsonSerializer.Deserialize<CalculationDriverConfigDto>(driverConfigJson, JsonOptions)
+            ?? throw new InvalidOperationException(
+                $"Calculation driver config for '{driverInstanceId}' deserialised to null");
+
+        var options = new CalculationDriverOptions
+        {
+            RawTags = dto.RawTags is { Count: > 0 } ? [.. dto.RawTags] : [],
+            RunTimeout = dto.RunTimeoutMs is { } ms && ms > 0
+                ? TimeSpan.FromMilliseconds(ms) : TimeSpan.FromSeconds(2),
+        };
+
+        return new CalculationDriver(
+            options, driverInstanceId, scriptRoot,
+            logger: loggerFactory?.CreateLogger<CalculationDriver>());
+    }
+
+    /// <summary>The merged-config DTO the calc factory binds from. The Calculation driver has no
+    /// backend/endpoint config — only the injected raw tags (+ an optional evaluation-timeout override).</summary>
+    internal sealed class CalculationDriverConfigDto
+    {
+        /// <summary>The driver's authored raw calc tags (RawPath + TagConfig blob + WriteIdempotent + DeviceName).</summary>
+        public List<RawTagEntry>? RawTags { get; init; }
+
+        /// <summary>Optional per-script evaluation wall-clock budget override, in milliseconds (default 2000).</summary>
+        public int? RunTimeoutMs { get; init; }
+    }
+}
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationDriverOptions.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationDriverOptions.cs
new file mode 100644
index 00000000..b6642c09
--- /dev/null
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationDriverOptions.cs
@@ -0,0 +1,20 @@
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Calculation;
+
+/// <summary>
+///     Bound options for a <see cref="CalculationDriver"/> instance. The Calculation pseudo-driver has
+///     no backend/endpoint config — its only input is the authored raw calc tags the deploy artifact
+///     injects as the <see cref="RawTags"/> list (each carrying the tag's <c>scriptId</c> + resolved
+///     <c>scriptSource</c> + trigger config inside its <see cref="RawTagEntry.TagConfig"/> blob).
+/// </summary>
+public sealed class CalculationDriverOptions
+{
+    /// <summary>The driver's authored raw calc tags (RawPath + TagConfig blob + WriteIdempotent), from
+    /// the deploy artifact. Each is mapped to a <see cref="CalculationTagDefinition"/> at construction.</summary>
+    public IReadOnlyList<RawTagEntry> RawTags { get; init; } = Array.Empty<RawTagEntry>();
+
+    /// <summary>Per-script wall-clock evaluation budget handed to the <see cref="CalculationEvaluator"/>.
+    /// Defaults to 2 seconds (parity with the VirtualTag evaluator).</summary>
+    public TimeSpan RunTimeout { get; init; } = TimeSpan.FromSeconds(2);
+}
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationDriverProbe.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationDriverProbe.cs
new file mode 100644
index 00000000..060cf5bd
--- /dev/null
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationDriverProbe.cs
@@ -0,0 +1,45 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Calculation;
+
+/// <summary>
+///     Test-connect probe for the <c>Calculation</c> pseudo-driver. There is no backend to connect to —
+///     the driver computes tags from other tags' values — so the probe just confirms the driver config
+///     parses (mini-design §7). Per-script compile verification belongs to the editor diagnostics + the
+///     tag editor's inline panel, not the probe (which receives only the driver config). Never throws;
+///     returns Ok with negligible latency.
+/// </summary>
+public sealed class CalculationDriverProbe : IDriverProbe
+{
+    private static readonly JsonSerializerOptions Opts = new()
+    {
+        PropertyNameCaseInsensitive = true,
+        UnmappedMemberHandling = JsonUnmappedMemberHandling.Skip,
+        Converters = { new JsonStringEnumConverter() },
+    };
+
+    /// <inheritdoc />
+    public string DriverType => CalculationDriverFactoryExtensions.DriverTypeName;
+
+    /// <inheritdoc />
+    public Task<DriverProbeResult> ProbeAsync(string configJson, TimeSpan timeout, CancellationToken ct)
+    {
+        if (string.IsNullOrWhiteSpace(configJson))
+            return Task.FromResult(new DriverProbeResult(false, "Config JSON is empty.", null));
+
+        try
+        {
+            // Parse-only: a Calculation driver's config is well-formed as long as it deserialises to an
+            // object (the RawTags array is optional — a driver with no calc tags is still valid).
+            _ = JsonSerializer.Deserialize<CalculationDriverFactoryExtensions.CalculationDriverConfigDto>(configJson, Opts);
+        }
+        catch (Exception ex)
+        {
+            return Task.FromResult(new DriverProbeResult(false, $"Config JSON is invalid: {ex.Message}", null));
+        }
+
+        return Task.FromResult(new DriverProbeResult(true, null, TimeSpan.Zero));
+    }
+}
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationTagDefinition.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationTagDefinition.cs
new file mode 100644
index 00000000..416f3ba2
--- /dev/null
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationTagDefinition.cs
@@ -0,0 +1,85 @@
+using System.Text.Json;
+using ZB.MOM.WW.OtOpcUa.Commons.Types;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Calculation;
+
+
+/// <summary>
+///     A single authored calc tag as the driver runs it: its <see cref="RawPath"/> identity, the script
+///     that computes it (<see cref="ScriptId"/> for attribution, <see cref="ScriptSource"/> for
+///     evaluation), its trigger config (<see cref="ChangeTriggered"/> / <see cref="TimerInterval"/>), and
+///     the static <see cref="DependencyRefs"/> extracted from the script's literal
+///     <c>ctx.GetTag("…")</c> reads.
+/// </summary>
+/// <param name="RawPath">The tag's cluster-scoped RawPath — its identity + the calc-tag id passed to the evaluator.</param>
+/// <param name="ScriptId">Logical FK to the shared <c>Script</c> entity — bound to the failure script-log for attribution.</param>
+/// <param name="ScriptSource">The resolved C# script source that produces the tag's value; empty when unresolved.</param>
+/// <param name="ChangeTriggered">Re-evaluate whenever a declared dependency changes.</param>
+/// <param name="TimerInterval">Optional periodic re-evaluation cadence; null ⇒ change-trigger only.</param>
+/// <param name="DependencyRefs">Distinct literal <c>ctx.GetTag</c> RawPaths this tag reads (first-seen order).</param>
+public sealed record CalculationTagDefinition(
+    string RawPath,
+    string ScriptId,
+    string ScriptSource,
+    bool ChangeTriggered,
+    TimeSpan? TimerInterval,
+    IReadOnlyList<string> DependencyRefs)
+{
+    /// <summary>
+    ///     Map a calc tag's <c>TagConfig</c> blob (<c>{ "scriptId", "scriptSource", "changeTriggered",
+    ///     "timerIntervalMs" }</c>) + its RawPath into a <see cref="CalculationTagDefinition"/>. Returns
+    ///     <see langword="false"/> (and leaves <paramref name="def"/> null) only when the blob has no
+    ///     <c>scriptId</c> — a tag with no identifiable script cannot be a calc tag. A present
+    ///     <c>scriptId</c> with an empty/absent <c>scriptSource</c> still maps (the driver logs it and the
+    ///     tag never computes). Never throws — malformed JSON yields a miss.
+    /// </summary>
+    /// <param name="tagConfig">The calc tag's schemaless <c>TagConfig</c> JSON.</param>
+    /// <param name="rawPath">The tag's RawPath identity.</param>
+    /// <param name="def">The mapped definition when this returns <see langword="true"/>.</param>
+    /// <returns><see langword="true"/> when a definition (with a scriptId) was mapped.</returns>
+    public static bool TryFromTagConfig(string tagConfig, string rawPath, out CalculationTagDefinition def)
+    {
+        def = null!;
+        if (string.IsNullOrWhiteSpace(tagConfig)) return false;
+
+        string? scriptId;
+        string scriptSource;
+        bool changeTriggered;
+        int? timerMs;
+        try
+        {
+            using var doc = JsonDocument.Parse(tagConfig);
+            var root = doc.RootElement;
+            if (root.ValueKind != JsonValueKind.Object) return false;
+
+            scriptId = root.TryGetProperty("scriptId", out var sidEl) && sidEl.ValueKind == JsonValueKind.String
+                ? sidEl.GetString() : null;
+            if (string.IsNullOrWhiteSpace(scriptId)) return false;
+
+            scriptSource = root.TryGetProperty("scriptSource", out var srcEl) && srcEl.ValueKind == JsonValueKind.String
+                ? srcEl.GetString() ?? string.Empty : string.Empty;
+
+            // changeTriggered defaults to true (mini-design §2) — only an explicit false disables it.
+            changeTriggered = !(root.TryGetProperty("changeTriggered", out var ctEl)
+                && ctEl.ValueKind == JsonValueKind.False);
+
+            timerMs = root.TryGetProperty("timerIntervalMs", out var tEl)
+                && tEl.ValueKind == JsonValueKind.Number && tEl.TryGetInt32(out var ms) && ms > 0
+                ? ms : null;
+        }
+        catch (JsonException)
+        {
+            return false;
+        }
+
+        var deps = EquipmentScriptPaths.ExtractDependencyRefs(scriptSource);
+        def = new CalculationTagDefinition(
+            RawPath: rawPath,
+            ScriptId: scriptId!,
+            ScriptSource: scriptSource,
+            ChangeTriggered: changeTriggered,
+            TimerInterval: timerMs is { } m ? TimeSpan.FromMilliseconds(m) : null,
+            DependencyRefs: deps);
+        return true;
+    }
+}
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationTimerScheduler.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationTimerScheduler.cs
new file mode 100644
index 00000000..bf0bf55d
--- /dev/null
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/CalculationTimerScheduler.cs
@@ -0,0 +1,110 @@
+using Microsoft.Extensions.Logging;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Calculation;
+
+/// <summary>
+///     Periodic re-evaluation scheduler for calc tags carrying a <c>timerIntervalMs</c>. A deliberate
+///     mirror of the VirtualTag <c>TimerTriggerScheduler</c> (<c>Core.VirtualTags</c>): one
+///     <see cref="System.Threading.Timer"/> per distinct interval group (so the wire count stays low
+///     regardless of tag count) with a per-group in-flight flag that skips a tick when the prior tick for
+///     the same group is still running. Revived <b>inside the driver</b> because the VT scheduler is welded
+///     to <c>VirtualTagEngine.EvaluateOneAsync</c>; here each tick invokes the driver's own evaluate
+///     callback per tag in the group.
+/// </summary>
+internal sealed class CalculationTimerScheduler : IDisposable
+{
+    private readonly Action<string> _evaluate;
+    private readonly ILogger _logger;
+    private readonly List<Timer> _timers = [];
+    private readonly List<TickGroup> _groups = [];
+    private readonly CancellationTokenSource _cts = new();
+    private long _skippedTickCount;
+    private bool _disposed;
+
+    /// <summary>Initializes a new instance of the <see cref="CalculationTimerScheduler"/> class.</summary>
+    /// <param name="evaluate">Callback invoked with a calc tag's RawPath when its timer group ticks.</param>
+    /// <param name="logger">Logger for diagnostics.</param>
+    public CalculationTimerScheduler(Action<string> evaluate, ILogger logger)
+    {
+        _evaluate = evaluate ?? throw new ArgumentNullException(nameof(evaluate));
+        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+    }
+
+    /// <summary>Number of timer callbacks that skipped their work because the prior tick for the same
+    /// group was still running. Monotonic; exposed for tests + operational metrics.</summary>
+    public long SkippedTickCount => Interlocked.Read(ref _skippedTickCount);
+
+    /// <summary>Stand up one <see cref="Timer"/> per distinct interval. All tags sharing an interval share
+    /// a timer; each tick re-evaluates every tag in the group.</summary>
+    /// <param name="tags">The calc tags to schedule (only those with a positive <see cref="CalculationTagDefinition.TimerInterval"/> are scheduled).</param>
+    public void Start(IEnumerable<CalculationTagDefinition> tags)
+    {
+        ArgumentNullException.ThrowIfNull(tags);
+        if (_disposed) throw new ObjectDisposedException(nameof(CalculationTimerScheduler));
+
+        var byInterval = tags
+            .Where(t => t.TimerInterval is { } iv && iv > TimeSpan.Zero)
+            .GroupBy(t => t.TimerInterval!.Value);
+
+        foreach (var group in byInterval)
+        {
+            var paths = group.Select(t => t.RawPath).ToArray();
+            var interval = group.Key;
+            var ctx = new TickGroup(paths);
+            _groups.Add(ctx);
+            var timer = new Timer(_ => OnTimer(ctx), null, interval, interval);
+            _timers.Add(timer);
+            _logger.LogInformation("CalculationTimerScheduler: {TagCount} tag(s) on {Interval} cadence",
+                paths.Length, interval);
+        }
+    }
+
+    private void OnTimer(TickGroup ctx)
+    {
+        if (_cts.IsCancellationRequested) return;
+
+        // Skip the tick when the prior one for this group is still running — bounds the outstanding
+        // work to one tick per group regardless of how long an evaluation takes.
+        if (Interlocked.CompareExchange(ref ctx.InFlight, 1, 0) != 0)
+        {
+            Interlocked.Increment(ref _skippedTickCount);
+            return;
+        }
+
+        try
+        {
+            foreach (var path in ctx.Paths)
+            {
+                if (_cts.IsCancellationRequested) return;
+                try { _evaluate(path); }
+                catch (Exception ex) { _logger.LogError(ex, "CalculationTimerScheduler evaluate failed for {Path}", path); }
+            }
+        }
+        finally
+        {
+            Interlocked.Exchange(ref ctx.InFlight, 0);
+        }
+    }
+
+    /// <summary>Releases all timers and disposes the scheduler's resources.</summary>
+    public void Dispose()
+    {
+        if (_disposed) return;
+        _disposed = true;
+        _cts.Cancel();
+        foreach (var t in _timers)
+        {
+            try { t.Dispose(); } catch { /* best-effort teardown */ }
+        }
+        _timers.Clear();
+        _groups.Clear();
+        _cts.Dispose();
+    }
+
+    private sealed class TickGroup(IReadOnlyList<string> paths)
+    {
+        // 0 = idle, 1 = a tick is currently running for this group.
+        public int InFlight;
+        public IReadOnlyList<string> Paths { get; } = paths;
+    }
+}
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/ZB.MOM.WW.OtOpcUa.Driver.Calculation.csproj b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/ZB.MOM.WW.OtOpcUa.Driver.Calculation.csproj
index c3aa6ec4..606fd3e9 100644
--- a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/ZB.MOM.WW.OtOpcUa.Driver.Calculation.csproj
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation/ZB.MOM.WW.OtOpcUa.Driver.Calculation.csproj
@@ -21,6 +21,7 @@
              owns DataValueSnapshot. -->
         <ProjectReference Include="..\..\Core\ZB.MOM.WW.OtOpcUa.Core.Abstractions\ZB.MOM.WW.OtOpcUa.Core.Abstractions.csproj"/>
         <ProjectReference Include="..\..\Core\ZB.MOM.WW.OtOpcUa.Commons\ZB.MOM.WW.OtOpcUa.Commons.csproj"/>
+        <ProjectReference Include="..\..\Core\ZB.MOM.WW.OtOpcUa.Core\ZB.MOM.WW.OtOpcUa.Core.csproj"/>
         <ProjectReference Include="..\..\Core\ZB.MOM.WW.OtOpcUa.Core.Scripting.Abstractions\ZB.MOM.WW.OtOpcUa.Core.Scripting.Abstractions.csproj"/>
         <ProjectReference Include="..\..\Core\ZB.MOM.WW.OtOpcUa.Core.Scripting\ZB.MOM.WW.OtOpcUa.Core.Scripting.csproj"/>
     </ItemGroup>
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.Host/Drivers/DriverFactoryBootstrap.cs b/src/Server/ZB.MOM.WW.OtOpcUa.Host/Drivers/DriverFactoryBootstrap.cs
index 1d4fd573..669822f3 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.Host/Drivers/DriverFactoryBootstrap.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.Host/Drivers/DriverFactoryBootstrap.cs
@@ -16,6 +16,7 @@ using TwinCATProbe   = Driver.TwinCAT.TwinCATDriverProbe;
 using FocasProbe     = Driver.FOCAS.FocasDriverProbe;
 using OpcUaProbe     = Driver.OpcUaClient.OpcUaClientDriverProbe;
 using GalaxyProbe    = Driver.Galaxy.GalaxyDriverProbe;
+using CalculationProbe = Driver.Calculation.CalculationDriverProbe;
 
 /// <summary>
 ///     Wires every cross-platform driver assembly's <c>Register(registry, loggerFactory)</c>
@@ -44,7 +45,10 @@ public static class DriverFactoryBootstrap
         {
             var registry = new DriverFactoryRegistry();
             var loggerFactory = sp.GetService<ILoggerFactory>();
-            Register(registry, loggerFactory);
+            // The calc driver needs the root script logger so a script failure fans out onto the
+            // script-logs topic; resolve it here (null on nodes without the script pipeline wired).
+            var scriptRoot = sp.GetService<ZB.MOM.WW.OtOpcUa.Core.Scripting.ScriptRootLogger>();
+            Register(registry, loggerFactory, scriptRoot);
             return registry;
         });
         services.AddSingleton<IDriverFactory>(sp =>
@@ -113,6 +117,7 @@ public static class DriverFactoryBootstrap
         services.TryAddEnumerable(ServiceDescriptor.Singleton<IDriverProbe, FocasProbe>());
         services.TryAddEnumerable(ServiceDescriptor.Singleton<IDriverProbe, OpcUaProbe>());
         services.TryAddEnumerable(ServiceDescriptor.Singleton<IDriverProbe, GalaxyProbe>());
+        services.TryAddEnumerable(ServiceDescriptor.Singleton<IDriverProbe, CalculationProbe>());
 
         return services;
     }
@@ -123,10 +128,14 @@ public static class DriverFactoryBootstrap
     ///     handles platform/role-dependent stubbing (e.g. Galaxy on macOS), so registering a
     ///     factory here doesn't mean it always runs in production.
     /// </summary>
-    private static void Register(DriverFactoryRegistry registry, ILoggerFactory? loggerFactory)
+    private static void Register(
+        DriverFactoryRegistry registry,
+        ILoggerFactory? loggerFactory,
+        ZB.MOM.WW.OtOpcUa.Core.Scripting.ScriptRootLogger? scriptRoot = null)
     {
         Driver.AbCip.AbCipDriverFactoryExtensions.Register(registry);
         Driver.AbLegacy.AbLegacyDriverFactoryExtensions.Register(registry, loggerFactory);
+        Driver.Calculation.CalculationDriverFactoryExtensions.Register(registry, loggerFactory, scriptRoot);
         Driver.FOCAS.FocasDriverFactoryExtensions.Register(registry);
         Driver.Galaxy.GalaxyDriverFactoryExtensions.Register(registry, loggerFactory);
         Driver.Modbus.ModbusDriverFactoryExtensions.Register(registry, loggerFactory);
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.Host/ZB.MOM.WW.OtOpcUa.Host.csproj b/src/Server/ZB.MOM.WW.OtOpcUa.Host/ZB.MOM.WW.OtOpcUa.Host.csproj
index e4898588..a27a1054 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.Host/ZB.MOM.WW.OtOpcUa.Host.csproj
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.Host/ZB.MOM.WW.OtOpcUa.Host.csproj
@@ -59,6 +59,7 @@
     <ItemGroup>
         <ProjectReference Include="..\..\Drivers\ZB.MOM.WW.OtOpcUa.Driver.AbCip\ZB.MOM.WW.OtOpcUa.Driver.AbCip.csproj"/>
         <ProjectReference Include="..\..\Drivers\ZB.MOM.WW.OtOpcUa.Driver.AbLegacy\ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.csproj"/>
+        <ProjectReference Include="..\..\Drivers\ZB.MOM.WW.OtOpcUa.Driver.Calculation\ZB.MOM.WW.OtOpcUa.Driver.Calculation.csproj"/>
         <ProjectReference Include="..\..\Drivers\ZB.MOM.WW.OtOpcUa.Driver.FOCAS\ZB.MOM.WW.OtOpcUa.Driver.FOCAS.csproj"/>
         <ProjectReference Include="..\..\Drivers\ZB.MOM.WW.OtOpcUa.Driver.Galaxy\ZB.MOM.WW.OtOpcUa.Driver.Galaxy.csproj"/>
         <ProjectReference Include="..\..\Drivers\ZB.MOM.WW.OtOpcUa.Driver.Historian.Gateway\ZB.MOM.WW.OtOpcUa.Driver.Historian.Gateway.csproj"/>
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/DeploymentArtifact.cs b/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/DeploymentArtifact.cs
index 33548200..573df6a7 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/DeploymentArtifact.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/DeploymentArtifact.cs
@@ -1,4 +1,5 @@
 using System.Text.Json;
+using System.Text.Json.Nodes;
 using ZB.MOM.WW.OtOpcUa.Commons.Types;
 using ZB.MOM.WW.OtOpcUa.Configuration.Enums;
 using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
@@ -141,6 +142,13 @@ public static class DeploymentArtifact
 
         var resolver = new RawPathResolver(folders, drivers, devices, groups);
 
+        // scriptId → SourceCode, from the artifact's Scripts array — the same join the VirtualTag plan
+        // builder uses. A calc tag's TagConfig carries a scriptId (not the source); the calc driver is
+        // host-blind and can't resolve it, so we inject the resolved `scriptSource` into the delivered
+        // TagConfig here (the deploy-side counterpart of the Calculation driver). Tags with no scriptId
+        // are untouched.
+        var scriptSourceById = BuildScriptSourceMap(root);
+
         foreach (var el in EnumerateArray(root, "Tags"))
         {
             var deviceId = ReadString(el, "DeviceId");
@@ -152,6 +160,7 @@ public static class DeploymentArtifact
             if (rawPath is null) continue; // broken chain — dropped (deploy gate rejects invalid names)
             var tagConfig = el.TryGetProperty("TagConfig", out var tcEl) && tcEl.ValueKind == JsonValueKind.String
                 ? tcEl.GetString() ?? "{}" : "{}";
+            tagConfig = InjectScriptSource(tagConfig, scriptSourceById);
             // WriteIdempotent (bool; non-bool/absent ⇒ false — the safe R2 default: writes are non-idempotent).
             var writeIdempotent = el.TryGetProperty("WriteIdempotent", out var wiEl)
                 && wiEl.ValueKind is JsonValueKind.True or JsonValueKind.False && wiEl.GetBoolean();
@@ -168,6 +177,47 @@ public static class DeploymentArtifact
         return byDriver;
     }
 
+    /// <summary>Build the <c>scriptId → SourceCode</c> map from the artifact's <c>Scripts</c> array (mirrors
+    /// the VirtualTag plan builder's join). Empty when the artifact carries no Scripts.</summary>
+    private static Dictionary<string, string> BuildScriptSourceMap(JsonElement root)
+    {
+        var byId = new Dictionary<string, string>(StringComparer.Ordinal);
+        foreach (var el in EnumerateArray(root, "Scripts"))
+        {
+            var sid = ReadString(el, "ScriptId");
+            if (string.IsNullOrWhiteSpace(sid)) continue;
+            byId[sid!] = el.TryGetProperty("SourceCode", out var srcEl) && srcEl.ValueKind == JsonValueKind.String
+                ? srcEl.GetString() ?? string.Empty : string.Empty;
+        }
+        return byId;
+    }
+
+    /// <summary>
+    ///     When <paramref name="tagConfig"/> carries a <c>scriptId</c> (a calc tag), inject the resolved
+    ///     <c>scriptSource</c> so the host-blind Calculation driver can compile + evaluate it. Identity for
+    ///     tags with no <c>scriptId</c> (every other driver's tags), an unresolvable id, or malformed JSON —
+    ///     so no existing tag's blob changes. The pre-existing <c>scriptId</c>/trigger fields are preserved.
+    /// </summary>
+    /// <param name="tagConfig">The tag's raw <c>TagConfig</c> JSON.</param>
+    /// <param name="scriptSourceById">The <c>scriptId → SourceCode</c> map from the artifact.</param>
+    /// <returns>The TagConfig with <c>scriptSource</c> injected, or the original when nothing to inject.</returns>
+    private static string InjectScriptSource(string tagConfig, IReadOnlyDictionary<string, string> scriptSourceById)
+    {
+        if (scriptSourceById.Count == 0 || string.IsNullOrWhiteSpace(tagConfig)) return tagConfig;
+        JsonNode? node;
+        try { node = JsonNode.Parse(tagConfig); }
+        catch (JsonException) { return tagConfig; }
+        if (node is not JsonObject obj) return tagConfig;
+
+        var scriptId = obj.TryGetPropertyValue("scriptId", out var sidNode) && sidNode is JsonValue sv
+            && sv.TryGetValue<string>(out var sid) ? sid : null;
+        if (string.IsNullOrWhiteSpace(scriptId) || !scriptSourceById.TryGetValue(scriptId!, out var source))
+            return tagConfig;
+
+        obj["scriptSource"] = source;
+        return obj.ToJsonString();
+    }
+
     /// <summary>Group the artifact's Devices into per-driver <see cref="DriverDeviceConfigMerger.DeviceRow"/>
     /// lists (entity Name + schemaless DeviceConfig), ordered by DeviceId for a stable merge.</summary>
     /// <param name="root">The artifact root element.</param>
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/DriverHostActor.cs b/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/DriverHostActor.cs
index 4d588c8c..b7fe7ba0 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/DriverHostActor.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/DriverHostActor.cs
@@ -98,6 +98,14 @@ public sealed class DriverHostActor : ReceiveActor, IWithTimers
 
     private readonly Dictionary<string, ChildEntry> _children = new(StringComparer.Ordinal);
 
+    /// <summary>Per-driver <see cref="DependencyConsumerMuxAdapter"/> children — one for each spawned driver
+    /// that implements <see cref="IDependencyConsumer"/> (e.g. the Calculation pseudo-driver). Each registers
+    /// the driver's declared dependency refs on the per-node <see cref="_dependencyMux"/> and forwards value
+    /// changes into the driver. Spawned in <see cref="SpawnChild"/>, torn down with the driver in
+    /// <see cref="StopDependencyAdapter"/>, and re-registered on every apply (refs change when tags/scripts
+    /// change). Empty when no mux is wired (the dev/None path) or no dependency-consuming driver is hosted.</summary>
+    private readonly Dictionary<string, IActorRef> _depConsumerAdapters = new(StringComparer.Ordinal);
+
     // Monotonic counter feeding the child actor-name suffix (see ActorNameFor / SpawnChild). Single-
     // threaded actor, so a plain increment is safe; it only ever grows, guaranteeing a unique name per
     // spawn so a restart's respawn never collides with the still-terminating old child.
@@ -1372,6 +1380,12 @@ public sealed class DriverHostActor : ReceiveActor, IWithTimers
         foreach (var id in plan.ToStop) StopChild(id);
         foreach (var spec in plan.ToApplyDelta) ApplyChildDelta(spec);
         foreach (var spec in plan.ToSpawn) SpawnChild(spec);
+
+        // v3 (WP7): re-register every dependency-consumer adapter's interest on each apply — a driver's
+        // declared dependency refs change when its tags/scripts change. Newly-spawned adapters already
+        // registered in PreStart; this refreshes the ones an ApplyDelta kept in place. A Tell (no blocking).
+        foreach (var adapter in _depConsumerAdapters.Values)
+            adapter.Tell(new ZB.MOM.WW.OtOpcUa.Runtime.VirtualTags.DependencyConsumerMuxAdapter.ReRegister());
     }
 
     /// <summary>
@@ -1736,10 +1750,33 @@ public sealed class DriverHostActor : ReceiveActor, IWithTimers
         }
 
         _children[spec.DriverInstanceId] = new ChildEntry(child, spec, stub);
+
+        // v3 (WP7): if the (real, non-stub) driver consumes other tags' live values, spawn a mux-adapter
+        // child that registers its dependency refs on the per-node dependency mux and forwards changes
+        // into the driver. Requires a wired mux (dev/None deployments have none — then calc inputs simply
+        // can't flow, matching the VirtualTag dev path).
+        if (!stub && driver is IDependencyConsumer consumer && _dependencyMux is not null)
+        {
+            var adapter = Context.ActorOf(
+                ZB.MOM.WW.OtOpcUa.Runtime.VirtualTags.DependencyConsumerMuxAdapter.Props(consumer, _dependencyMux),
+                "depmux-" + actorName);
+            _depConsumerAdapters[spec.DriverInstanceId] = adapter;
+            _log.Info("DriverHost {Node}: wired dependency-consumer mux adapter for {Id} ({Count} ref(s))",
+                _localNode, spec.DriverInstanceId, consumer.DependencyRefs.Count);
+        }
+
         _log.Info("DriverHost {Node}: spawned {Type} driver {Id} (stub={Stub})",
             _localNode, spec.DriverType, spec.DriverInstanceId, stub);
     }
 
+    /// <summary>Stops + forgets the dependency-consumer mux adapter for a driver (if any). Called wherever a
+    /// driver child is stopped/respawned so a stale adapter never keeps a dead driver's refs registered.</summary>
+    private void StopDependencyAdapter(string driverInstanceId)
+    {
+        if (_depConsumerAdapters.Remove(driverInstanceId, out var adapter))
+            Context.Stop(adapter);
+    }
+
     private void ApplyChildDelta(DriverInstanceSpec spec)
     {
         if (!_children.TryGetValue(spec.DriverInstanceId, out var entry)) return;
@@ -1752,6 +1789,7 @@ public sealed class DriverHostActor : ReceiveActor, IWithTimers
     private void StopChild(string driverInstanceId)
     {
         if (!_children.TryGetValue(driverInstanceId, out var entry)) return;
+        StopDependencyAdapter(driverInstanceId);
         Context.Stop(entry.Actor);
         _children.Remove(driverInstanceId);
         _log.Info("DriverHost {Node}: stopped driver child {Id}", _localNode, driverInstanceId);
@@ -1805,6 +1843,7 @@ public sealed class DriverHostActor : ReceiveActor, IWithTimers
             _localNode, msg.DriverInstanceId, msg.ActorByUserName);
 
         // Stop the existing child actor — DriverInstanceActor.PostStop calls ShutdownAsync.
+        StopDependencyAdapter(msg.DriverInstanceId);
         Context.Stop(entry.Actor);
         _children.Remove(msg.DriverInstanceId);
 
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/VirtualTags/DependencyConsumerMuxAdapter.cs b/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/VirtualTags/DependencyConsumerMuxAdapter.cs
new file mode 100644
index 00000000..a6bee640
--- /dev/null
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/VirtualTags/DependencyConsumerMuxAdapter.cs
@@ -0,0 +1,71 @@
+using Akka.Actor;
+using Akka.Event;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Runtime.VirtualTags;
+
+/// <summary>
+///     Bridges a driver that implements <see cref="IDependencyConsumer"/> onto the per-node
+///     <see cref="DependencyMuxActor"/>. Spawned as a child of <c>DriverHostActor</c> for each such
+///     driver: on start (and on every apply via <see cref="ReRegister"/>) it registers the driver's
+///     declared <see cref="IDependencyConsumer.DependencyRefs"/> with the mux, and forwards each
+///     <see cref="VirtualTagActor.DependencyValueChanged"/> the mux fans out into
+///     <see cref="IDependencyConsumer.OnDependencyValue"/>.
+///
+///     <para>
+///         This is the exact seam a <c>VirtualTagActor</c> uses to receive its inputs, generalised so a
+///         host-blind driver (the <c>Calculation</c> pseudo-driver) can read other tags' live values with
+///         no cross-driver plumbing. The mux fans out value + timestamp only (quality is stripped at the
+///         mux boundary, same as for virtual tags), so the forwarded status code is <c>Good</c> (0).
+///     </para>
+/// </summary>
+public sealed class DependencyConsumerMuxAdapter : ReceiveActor
+{
+    /// <summary>Sent by the host after an apply so the adapter re-reads the driver's (possibly changed)
+    /// dependency refs and re-registers them with the mux.</summary>
+    public sealed record ReRegister;
+
+    private readonly IDependencyConsumer _consumer;
+    private readonly IActorRef _mux;
+    private readonly ILoggingAdapter _log = Context.GetLogger();
+
+    /// <summary>Creates props for a <see cref="DependencyConsumerMuxAdapter"/>.</summary>
+    /// <param name="consumer">The dependency-consuming driver to feed.</param>
+    /// <param name="mux">The per-node dependency mux to register interest with.</param>
+    /// <returns>Props for the adapter.</returns>
+    public static Props Props(IDependencyConsumer consumer, IActorRef mux) =>
+        Akka.Actor.Props.Create(() => new DependencyConsumerMuxAdapter(consumer, mux));
+
+    /// <summary>Initializes a new <see cref="DependencyConsumerMuxAdapter"/>.</summary>
+    /// <param name="consumer">The dependency-consuming driver to feed.</param>
+    /// <param name="mux">The per-node dependency mux to register interest with.</param>
+    public DependencyConsumerMuxAdapter(IDependencyConsumer consumer, IActorRef mux)
+    {
+        _consumer = consumer ?? throw new ArgumentNullException(nameof(consumer));
+        _mux = mux ?? throw new ArgumentNullException(nameof(mux));
+
+        Receive<VirtualTagActor.DependencyValueChanged>(OnDependencyValueChanged);
+        Receive<ReRegister>(_ => RegisterInterest());
+    }
+
+    /// <inheritdoc />
+    protected override void PreStart() => RegisterInterest();
+
+    /// <inheritdoc />
+    protected override void PostStop() => _mux.Tell(new DependencyMuxActor.UnregisterInterest(Self));
+
+    private void RegisterInterest()
+    {
+        var refs = _consumer.DependencyRefs.ToList();
+        // A RegisterInterest replaces the prior interest set for this subscriber (mux is idempotent on
+        // re-register), so re-registering after an apply cleanly adopts an added/removed ref.
+        _mux.Tell(new DependencyMuxActor.RegisterInterest(refs, Self));
+        _log.Debug("DependencyConsumerMuxAdapter: registered {Count} dependency ref(s)", refs.Count);
+    }
+
+    private void OnDependencyValueChanged(VirtualTagActor.DependencyValueChanged msg)
+    {
+        // Quality is stripped at the mux boundary (value + timestamp only), so forward Good (0).
+        _consumer.OnDependencyValue(msg.TagId, msg.Value, statusCode: 0u, msg.TimestampUtc);
+    }
+}
diff --git a/tests/Core/ZB.MOM.WW.OtOpcUa.Configuration.Tests/DraftValidatorCalculationTests.cs b/tests/Core/ZB.MOM.WW.OtOpcUa.Configuration.Tests/DraftValidatorCalculationTests.cs
new file mode 100644
index 00000000..0b20f490
--- /dev/null
+++ b/tests/Core/ZB.MOM.WW.OtOpcUa.Configuration.Tests/DraftValidatorCalculationTests.cs
@@ -0,0 +1,156 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Configuration.Entities;
+using ZB.MOM.WW.OtOpcUa.Configuration.Enums;
+using ZB.MOM.WW.OtOpcUa.Configuration.Validation;
+
+namespace ZB.MOM.WW.OtOpcUa.Configuration.Tests;
+
+/// <summary>
+///     WP7 Calculation deploy gates in <see cref="DraftValidator"/>: <c>scriptId</c> existence and the
+///     calc→calc dependency-cycle gate (self-cycle, 2-cycle, and the cross-driver-terminal negative case).
+/// </summary>
+[Trait("Category", "Unit")]
+public sealed class DraftValidatorCalculationTests
+{
+    // A calc DriverInstance "calc" + one Device "engine" → calc tags get RawPath "calc/engine/<name>".
+    private static DriverInstance CalcDriver() => new()
+    {
+        DriverInstanceId = "di-calc", ClusterId = "c", Name = "calc",
+        DriverType = "Calculation", DriverConfig = "{}",
+    };
+
+    private static DriverInstance ModbusDriver() => new()
+    {
+        DriverInstanceId = "di-mb", ClusterId = "c", Name = "mb",
+        DriverType = "Modbus", DriverConfig = "{}",
+    };
+
+    private static Device Device(string id, string driverInstanceId, string name) => new()
+    {
+        DeviceId = id, DriverInstanceId = driverInstanceId, Name = name, DeviceConfig = "{}",
+    };
+
+    private static Tag CalcTagRow(string tagId, string deviceId, string name, string tagConfig) => new()
+    {
+        TagId = tagId, DeviceId = deviceId, Name = name, DataType = "Double",
+        AccessLevel = TagAccessLevel.Read, TagConfig = tagConfig,
+    };
+
+    private static Script ScriptRow(string id, string source) => new()
+    {
+        ScriptId = id, Name = id, SourceCode = source, SourceHash = "h-" + id,
+    };
+
+    private static string Cfg(string scriptId) => $"{{\"scriptId\":\"{scriptId}\",\"changeTriggered\":true}}";
+
+    [Fact]
+    public void Missing_scriptId_is_a_deploy_error()
+    {
+        var draft = new DraftSnapshot
+        {
+            GenerationId = 1, ClusterId = "c",
+            DriverInstances = [CalcDriver()],
+            Devices = [Device("dev-1", "di-calc", "engine")],
+            Tags = [CalcTagRow("t-1", "dev-1", "a", "{\"changeTriggered\":true}")],
+        };
+
+        DraftValidator.Validate(draft).ShouldContain(e => e.Code == "CalculationScriptMissing" && e.Context == "t-1");
+    }
+
+    [Fact]
+    public void Unknown_scriptId_is_a_deploy_error()
+    {
+        var draft = new DraftSnapshot
+        {
+            GenerationId = 1, ClusterId = "c",
+            DriverInstances = [CalcDriver()],
+            Devices = [Device("dev-1", "di-calc", "engine")],
+            Tags = [CalcTagRow("t-1", "dev-1", "a", Cfg("s-nope"))],
+            Scripts = [],
+        };
+
+        DraftValidator.Validate(draft).ShouldContain(e => e.Code == "CalculationScriptNotFound" && e.Context == "t-1");
+    }
+
+    [Fact]
+    public void Existing_scriptId_with_no_cycle_is_accepted()
+    {
+        var draft = new DraftSnapshot
+        {
+            GenerationId = 1, ClusterId = "c",
+            DriverInstances = [CalcDriver()],
+            Devices = [Device("dev-1", "di-calc", "engine")],
+            Tags = [CalcTagRow("t-1", "dev-1", "a", Cfg("s1"))],
+            Scripts = [ScriptRow("s1", "return 42.0;")],
+        };
+
+        DraftValidator.Validate(draft).ShouldNotContain(e => e.Code.StartsWith("Calculation"));
+    }
+
+    [Fact]
+    public void Self_cycle_is_rejected()
+    {
+        // calc/engine/a reads itself.
+        var draft = new DraftSnapshot
+        {
+            GenerationId = 1, ClusterId = "c",
+            DriverInstances = [CalcDriver()],
+            Devices = [Device("dev-1", "di-calc", "engine")],
+            Tags = [CalcTagRow("t-a", "dev-1", "a", Cfg("s-a"))],
+            Scripts = [ScriptRow("s-a", "return (double)ctx.GetTag(\"calc/engine/a\").Value;")],
+        };
+
+        DraftValidator.Validate(draft).ShouldContain(e =>
+            e.Code == "CalculationDependencyCycle" && e.Message.Contains("calc/engine/a"));
+    }
+
+    [Fact]
+    public void Two_node_cycle_names_both_members()
+    {
+        // a → b and b → a.
+        var draft = new DraftSnapshot
+        {
+            GenerationId = 1, ClusterId = "c",
+            DriverInstances = [CalcDriver()],
+            Devices = [Device("dev-1", "di-calc", "engine")],
+            Tags =
+            [
+                CalcTagRow("t-a", "dev-1", "a", Cfg("s-a")),
+                CalcTagRow("t-b", "dev-1", "b", Cfg("s-b")),
+            ],
+            Scripts =
+            [
+                ScriptRow("s-a", "return (double)ctx.GetTag(\"calc/engine/b\").Value;"),
+                ScriptRow("s-b", "return (double)ctx.GetTag(\"calc/engine/a\").Value;"),
+            ],
+        };
+
+        DraftValidator.Validate(draft).ShouldContain(e => e.Code == "CalculationDependencyCycle");
+        var msg = DraftValidator.Validate(draft).First(e => e.Code == "CalculationDependencyCycle").Message;
+        msg.ShouldContain("calc/engine/a");
+        msg.ShouldContain("calc/engine/b");
+    }
+
+    [Fact]
+    public void Cross_driver_ref_is_terminal_not_an_edge()
+    {
+        // A calc tag reads a Modbus tag's RawPath ("mb/plc/reg"); that is a terminal node, never an edge,
+        // so it can never form a cycle — even if the Modbus tag existed.
+        var draft = new DraftSnapshot
+        {
+            GenerationId = 1, ClusterId = "c",
+            DriverInstances = [CalcDriver(), ModbusDriver()],
+            Devices = [Device("dev-1", "di-calc", "engine"), Device("dev-2", "di-mb", "plc")],
+            Tags =
+            [
+                CalcTagRow("t-a", "dev-1", "a", Cfg("s-a")),
+                new Tag { TagId = "t-reg", DeviceId = "dev-2", Name = "reg", DataType = "Int32",
+                          AccessLevel = TagAccessLevel.Read, TagConfig = "{}" },
+            ],
+            Scripts = [ScriptRow("s-a", "return (double)ctx.GetTag(\"mb/plc/reg\").Value;")],
+        };
+
+        DraftValidator.Validate(draft).ShouldNotContain(e => e.Code == "CalculationDependencyCycle");
+    }
+}
diff --git a/tests/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions.Tests/ZB.MOM.WW.OtOpcUa.Core.Abstractions.Tests.csproj b/tests/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions.Tests/ZB.MOM.WW.OtOpcUa.Core.Abstractions.Tests.csproj
index f11c7282..b89bfe91 100644
--- a/tests/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions.Tests/ZB.MOM.WW.OtOpcUa.Core.Abstractions.Tests.csproj
+++ b/tests/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions.Tests/ZB.MOM.WW.OtOpcUa.Core.Abstractions.Tests.csproj
@@ -33,6 +33,7 @@
         <ProjectReference Include="..\..\..\src\Drivers\ZB.MOM.WW.OtOpcUa.Driver.FOCAS\ZB.MOM.WW.OtOpcUa.Driver.FOCAS.csproj"/>
         <ProjectReference Include="..\..\..\src\Drivers\ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient\ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.csproj"/>
         <ProjectReference Include="..\..\..\src\Drivers\ZB.MOM.WW.OtOpcUa.Driver.Galaxy\ZB.MOM.WW.OtOpcUa.Driver.Galaxy.csproj"/>
+        <ProjectReference Include="..\..\..\src\Drivers\ZB.MOM.WW.OtOpcUa.Driver.Calculation\ZB.MOM.WW.OtOpcUa.Driver.Calculation.csproj"/>
     </ItemGroup>
 
 </Project>
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation.Tests/CalculationDriverTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation.Tests/CalculationDriverTests.cs
new file mode 100644
index 00000000..8deca370
--- /dev/null
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation.Tests/CalculationDriverTests.cs
@@ -0,0 +1,187 @@
+using System.Collections.Concurrent;
+using Serilog;
+using Serilog.Events;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Commons.Messages.Logging;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Calculation.Tests;
+
+/// <summary>
+///     WP7 unit tests for <see cref="CalculationDriver"/>: dependency-ref extraction from the authored
+///     tags, the change-gate (no publish until every declared dep has arrived), value dedup, the
+///     Good→Bad transition + <c>ScriptLogEntry</c> emission + Good recovery, and timer-trigger recompute.
+/// </summary>
+public sealed class CalculationDriverTests
+{
+    private const uint StatusGood = 0u;
+    private const uint StatusBadInternalError = 0x80020000u;
+    private const uint StatusBadWaitingForInitialData = 0x80320000u;
+
+    private static RawTagEntry CalcTag(string rawPath, string source, bool changeTriggered = true, int? timerMs = null)
+    {
+        var timer = timerMs is { } ms ? $",\"timerIntervalMs\":{ms}" : "";
+        var json = $"{{\"scriptId\":\"s-{rawPath}\",\"changeTriggered\":{(changeTriggered ? "true" : "false")}{timer}," +
+                   $"\"scriptSource\":{System.Text.Json.JsonSerializer.Serialize(source)}}}";
+        return new RawTagEntry(rawPath, json, WriteIdempotent: false);
+    }
+
+    private static (CalculationDriver Driver, ConcurrentQueue<DataChangeEventArgs> Published, List<ScriptLogEntry> Logs)
+        Build(params RawTagEntry[] tags)
+    {
+        var logs = new List<ScriptLogEntry>();
+        var sink = new ScriptLogTopicSink(new CapturingPublisher(logs), LogEventLevel.Information);
+        var scriptRoot = new ScriptRootLogger(new LoggerConfiguration().WriteTo.Sink(sink).CreateLogger());
+        var driver = new CalculationDriver(new CalculationDriverOptions { RawTags = tags }, "calc-drv", scriptRoot);
+        var published = new ConcurrentQueue<DataChangeEventArgs>();
+        driver.OnDataChange += (_, e) => published.Enqueue(e);
+        return (driver, published, logs);
+    }
+
+    // ── dependency-ref extraction ─────────────────────────────────────────────────────────────
+
+    [Fact]
+    public void DependencyRefs_are_the_union_of_authored_tag_scripts()
+    {
+        var (driver, _, _) = Build(
+            CalcTag("calc/e/x", "return (double)ctx.GetTag(\"src/a\").Value + (double)ctx.GetTag(\"src/b\").Value;"),
+            CalcTag("calc/e/y", "return (double)ctx.GetTag(\"src/b\").Value + (double)ctx.GetTag(\"src/c\").Value;"));
+
+        driver.DependencyRefs.OrderBy(r => r).ShouldBe(new[] { "src/a", "src/b", "src/c" });
+    }
+
+    // ── change-gate ───────────────────────────────────────────────────────────────────────────
+
+    [Fact]
+    public async Task No_publish_until_every_declared_dep_has_arrived()
+    {
+        var (driver, published, _) = Build(
+            CalcTag("calc/e/sum", "return (double)ctx.GetTag(\"src/a\").Value + (double)ctx.GetTag(\"src/b\").Value;"));
+        await driver.InitializeAsync("{}", default);
+
+        // Only one of two deps arrived → the change-gate holds.
+        driver.OnDependencyValue("src/a", 10.0, StatusGood, DateTime.UtcNow);
+        published.ShouldBeEmpty();
+
+        // Second dep arrives → now it computes + publishes 30.
+        driver.OnDependencyValue("src/b", 20.0, StatusGood, DateTime.UtcNow);
+        published.Count.ShouldBe(1);
+        published.TryDequeue(out var e).ShouldBeTrue();
+        e!.FullReference.ShouldBe("calc/e/sum");
+        e.Snapshot.Value.ShouldBe(30.0);
+        e.Snapshot.StatusCode.ShouldBe(StatusGood);
+    }
+
+    // ── dedup + recompute ─────────────────────────────────────────────────────────────────────
+
+    [Fact]
+    public async Task Equal_result_is_deduped_and_a_changed_result_republishes()
+    {
+        var (driver, published, _) = Build(
+            CalcTag("calc/e/dbl", "return (double)ctx.GetTag(\"src/a\").Value * 2.0;"));
+        await driver.InitializeAsync("{}", default);
+
+        driver.OnDependencyValue("src/a", 5.0, StatusGood, DateTime.UtcNow);   // → 10 (publish)
+        driver.OnDependencyValue("src/a", 5.0, StatusGood, DateTime.UtcNow);   // → 10 (dedup, no publish)
+        driver.OnDependencyValue("src/a", 7.0, StatusGood, DateTime.UtcNow);   // → 14 (publish)
+
+        published.Select(p => p.Snapshot.Value).ShouldBe(new object?[] { 10.0, 14.0 });
+    }
+
+    // ── Bad transition + script-log + recovery ────────────────────────────────────────────────
+
+    [Fact]
+    public async Task Failure_publishes_Bad_once_per_transition_emits_script_log_and_recovers()
+    {
+        var (driver, published, logs) = Build(
+            CalcTag("calc/e/div", "return 100 / (int)ctx.GetTag(\"src/a\").Value;"));
+        await driver.InitializeAsync("{}", default);
+
+        // a = 0 → DivideByZero → Failure → Bad (carrying last-known = null) + one script-log.
+        driver.OnDependencyValue("src/a", 0, StatusGood, DateTime.UtcNow);
+        published.Count.ShouldBe(1);
+        published.TryDequeue(out var bad).ShouldBeTrue();
+        bad!.Snapshot.StatusCode.ShouldBe(StatusBadInternalError);
+        logs.Count.ShouldBe(1);
+        logs[0].Level.ShouldBe("Warning");
+        logs[0].ScriptId.ShouldBe("s-calc/e/div");
+        logs[0].VirtualTagId.ShouldBe("calc/e/div");
+
+        // a = 0 again → still failing, but NOT a fresh transition → no second Bad publish (script-log still emits).
+        driver.OnDependencyValue("src/a", 0, StatusGood, DateTime.UtcNow);
+        published.ShouldBeEmpty();
+        logs.Count.ShouldBe(2);
+
+        // a = 5 → 20 → Good recovery is force-published.
+        driver.OnDependencyValue("src/a", 5, StatusGood, DateTime.UtcNow);
+        published.Count.ShouldBe(1);
+        published.TryDequeue(out var good).ShouldBeTrue();
+        good!.Snapshot.Value.ShouldBe(20);
+        good.Snapshot.StatusCode.ShouldBe(StatusGood);
+    }
+
+    // ── timer trigger ─────────────────────────────────────────────────────────────────────────
+
+    [Fact]
+    public async Task Timer_only_tag_computes_on_its_interval()
+    {
+        // No dependencies (constant script) so only the timer can drive it.
+        var (driver, published, _) = Build(
+            CalcTag("calc/e/const", "return 42.0;", changeTriggered: false, timerMs: 50));
+        await driver.InitializeAsync("{}", default);
+
+        var fired = await WaitUntil(() => !published.IsEmpty, TimeSpan.FromSeconds(3));
+        fired.ShouldBeTrue("the timer trigger should have computed the tag within 3s");
+        published.TryDequeue(out var e).ShouldBeTrue();
+        e!.FullReference.ShouldBe("calc/e/const");
+        e.Snapshot.Value.ShouldBe(42.0);
+
+        await driver.ShutdownAsync(default);
+    }
+
+    // ── IReadable ─────────────────────────────────────────────────────────────────────────────
+
+    [Fact]
+    public async Task Read_returns_BadWaitingForInitialData_before_first_eval_then_the_computed_value()
+    {
+        var (driver, _, _) = Build(CalcTag("calc/e/x", "return (double)ctx.GetTag(\"src/a\").Value * 2.0;"));
+        await driver.InitializeAsync("{}", default);
+
+        var before = await driver.ReadAsync(new[] { "calc/e/x" }, default);
+        before[0].StatusCode.ShouldBe(StatusBadWaitingForInitialData);
+
+        driver.OnDependencyValue("src/a", 3.0, StatusGood, DateTime.UtcNow);
+        var after = await driver.ReadAsync(new[] { "calc/e/x" }, default);
+        after[0].StatusCode.ShouldBe(StatusGood);
+        after[0].Value.ShouldBe(6.0);
+    }
+
+    [Fact]
+    public void Health_is_always_Connected()
+    {
+        var (driver, _, _) = Build(CalcTag("calc/e/x", "return 1.0;"));
+        driver.GetHealth().State.ShouldBe(DriverState.Healthy);
+    }
+
+    private static async Task<bool> WaitUntil(Func<bool> predicate, TimeSpan timeout)
+    {
+        var deadline = DateTime.UtcNow + timeout;
+        while (DateTime.UtcNow < deadline)
+        {
+            if (predicate()) return true;
+            await Task.Delay(20);
+        }
+        return predicate();
+    }
+
+    private sealed class CapturingPublisher(List<ScriptLogEntry> sink) : IScriptLogPublisher
+    {
+        private readonly object _lock = new();
+        public void Publish(ScriptLogEntry entry)
+        {
+            lock (_lock) sink.Add(entry);
+        }
+    }
+}
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation.Tests/CalculationTagDefinitionTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation.Tests/CalculationTagDefinitionTests.cs
new file mode 100644
index 00000000..d63ac218
--- /dev/null
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Calculation.Tests/CalculationTagDefinitionTests.cs
@@ -0,0 +1,55 @@
+using Shouldly;
+using Xunit;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Calculation.Tests;
+
+/// <summary>Parsing contract for <see cref="CalculationTagDefinition.TryFromTagConfig"/> — the calc tag's
+/// <c>TagConfig</c> blob (<c>scriptId</c> + resolved <c>scriptSource</c> + trigger fields) → typed def with
+/// its static dependency refs.</summary>
+public sealed class CalculationTagDefinitionTests
+{
+    [Fact]
+    public void Missing_scriptId_is_not_a_calc_tag()
+    {
+        CalculationTagDefinition.TryFromTagConfig("{\"changeTriggered\":true}", "calc/e/x", out _).ShouldBeFalse();
+    }
+
+    [Fact]
+    public void Malformed_json_is_a_miss()
+    {
+        CalculationTagDefinition.TryFromTagConfig("not json", "calc/e/x", out _).ShouldBeFalse();
+    }
+
+    [Fact]
+    public void Parses_scriptId_source_triggers_and_extracts_dependency_refs()
+    {
+        var json = "{\"scriptId\":\"s1\",\"changeTriggered\":true,\"timerIntervalMs\":5000," +
+                   "\"scriptSource\":\"return (double)ctx.GetTag(\\\"src/a\\\").Value + (double)ctx.GetTag(\\\"src/b\\\").Value;\"}";
+        CalculationTagDefinition.TryFromTagConfig(json, "calc/e/x", out var def).ShouldBeTrue();
+
+        def.RawPath.ShouldBe("calc/e/x");
+        def.ScriptId.ShouldBe("s1");
+        def.ChangeTriggered.ShouldBeTrue();
+        def.TimerInterval.ShouldBe(TimeSpan.FromMilliseconds(5000));
+        def.DependencyRefs.ShouldBe(new[] { "src/a", "src/b" });
+    }
+
+    [Fact]
+    public void ChangeTriggered_defaults_true_and_timer_is_optional()
+    {
+        CalculationTagDefinition.TryFromTagConfig(
+            "{\"scriptId\":\"s1\",\"scriptSource\":\"return 1.0;\"}", "calc/e/x", out var def).ShouldBeTrue();
+        def.ChangeTriggered.ShouldBeTrue();
+        def.TimerInterval.ShouldBeNull();
+        def.DependencyRefs.ShouldBeEmpty();
+    }
+
+    [Fact]
+    public void Present_scriptId_with_empty_source_still_maps()
+    {
+        CalculationTagDefinition.TryFromTagConfig(
+            "{\"scriptId\":\"s1\",\"changeTriggered\":false}", "calc/e/x", out var def).ShouldBeTrue();
+        def.ScriptSource.ShouldBe("");
+        def.ChangeTriggered.ShouldBeFalse();
+    }
+}
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Drivers/CalculationDependencyFlowTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Drivers/CalculationDependencyFlowTests.cs
new file mode 100644
index 00000000..a6ed5b17
--- /dev/null
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Drivers/CalculationDependencyFlowTests.cs
@@ -0,0 +1,82 @@
+using System.Collections.Concurrent;
+using Akka.Actor;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Commons.OpcUa;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Driver.Calculation;
+using ZB.MOM.WW.OtOpcUa.Runtime.Drivers;
+using ZB.MOM.WW.OtOpcUa.Runtime.Tests.Harness;
+using ZB.MOM.WW.OtOpcUa.Runtime.VirtualTags;
+
+namespace ZB.MOM.WW.OtOpcUa.Runtime.Tests.Drivers;
+
+/// <summary>
+///     WP7 register-AND-consume proof: dependency values actually FLOW end-to-end through the REAL
+///     <see cref="DependencyMuxActor"/> → <see cref="DependencyConsumerMuxAdapter"/> →
+///     <see cref="CalculationDriver"/> path (not merely that <see cref="IDependencyConsumer"/> exists).
+///     A source value published to the mux is fed into the calc driver, which computes and publishes a
+///     value; and a calc tag reading ANOTHER calc tag's output (calc-of-calc) recomputes when the first
+///     tag's output re-enters the mux — the exact re-entry the host's <c>ForwardToMux</c> performs, mirrored
+///     here by looping the driver's <see cref="ISubscribable.OnDataChange"/> back into the mux.
+/// </summary>
+public sealed class CalculationDependencyFlowTests : RuntimeActorTestBase
+{
+    private static readonly DateTime Ts = new(2026, 7, 16, 10, 0, 0, DateTimeKind.Utc);
+
+    private static RawTagEntry CalcTag(string rawPath, string source)
+    {
+        var json = $"{{\"scriptId\":\"s-{rawPath}\",\"changeTriggered\":true," +
+                   $"\"scriptSource\":{System.Text.Json.JsonSerializer.Serialize(source)}}}";
+        return new RawTagEntry(rawPath, json, WriteIdempotent: false);
+    }
+
+    [Fact]
+    public async Task Source_value_flows_through_mux_and_adapter_into_the_calc_driver_and_propagates_calc_of_calc()
+    {
+        // A: out = src/a * 2.   B: b = A.out + 1  (calc-of-calc; B depends on A's RawPath).
+        var driver = new CalculationDriver(
+            new CalculationDriverOptions
+            {
+                RawTags =
+                [
+                    CalcTag("calc/engine/out", "return (double)ctx.GetTag(\"src/a\").Value * 2.0;"),
+                    CalcTag("calc/engine/b", "return (double)ctx.GetTag(\"calc/engine/out\").Value + 1.0;"),
+                ],
+            },
+            "calc-drv");
+        await driver.InitializeAsync("{}", CancellationToken.None);
+
+        // The driver declares interest in both the external source AND the first calc tag's output.
+        driver.DependencyRefs.OrderBy(r => r).ShouldBe(new[] { "calc/engine/out", "src/a" });
+
+        var published = new ConcurrentQueue<DataChangeEventArgs>();
+        var mux = Sys.ActorOf(DependencyMuxActor.Props(), "dep-mux");
+
+        // Loop the driver's outputs back into the mux exactly as DriverHostActor.ForwardToMux does — this
+        // is what makes calc-of-calc chains work.
+        driver.OnDataChange += (_, e) =>
+        {
+            published.Enqueue(e);
+            var quality = e.Snapshot.StatusCode == 0u ? OpcUaQuality.Good : OpcUaQuality.Bad;
+            mux.Tell(new DriverInstanceActor.AttributeValuePublished(
+                "calc-drv", e.FullReference, e.Snapshot.Value, quality, Ts));
+        };
+
+        // The REAL adapter registers the driver's dependency refs on the mux + forwards changes into it.
+        Sys.ActorOf(DependencyConsumerMuxAdapter.Props(driver, mux), "dep-adapter");
+
+        // Publish the external source into the mux. AwaitAssert re-Tells (idempotent after the first
+        // compute dedups) until the computed value has flowed all the way through.
+        AwaitAssert(() =>
+        {
+            mux.Tell(new DriverInstanceActor.AttributeValuePublished(
+                "src-drv", "src/a", 21.0, OpcUaQuality.Good, Ts));
+
+            // Leg 1 — dep flow: src/a=21 → A computes 42 and publishes on calc/engine/out.
+            published.ShouldContain(e => e.FullReference == "calc/engine/out" && Equals(e.Snapshot.Value, 42.0));
+            // Leg 2 — calc-of-calc: A's 42 re-entered the mux → B computes 43 on calc/engine/b.
+            published.ShouldContain(e => e.FullReference == "calc/engine/b" && Equals(e.Snapshot.Value, 43.0));
+        }, TimeSpan.FromSeconds(5), TimeSpan.FromMilliseconds(100));
+    }
+}
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/ZB.MOM.WW.OtOpcUa.Runtime.Tests.csproj b/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/ZB.MOM.WW.OtOpcUa.Runtime.Tests.csproj
index 14f0e0b2..0e9fb05f 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/ZB.MOM.WW.OtOpcUa.Runtime.Tests.csproj
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/ZB.MOM.WW.OtOpcUa.Runtime.Tests.csproj
@@ -28,6 +28,9 @@
         <ProjectReference Include="..\..\..\src\Core\ZB.MOM.WW.OtOpcUa.Core\ZB.MOM.WW.OtOpcUa.Core.csproj"/>
         <ProjectReference Include="..\..\..\src\Core\ZB.MOM.WW.OtOpcUa.Configuration\ZB.MOM.WW.OtOpcUa.Configuration.csproj"/>
         <ProjectReference Include="..\..\..\src\Core\ZB.MOM.WW.OtOpcUa.Commons\ZB.MOM.WW.OtOpcUa.Commons.csproj"/>
+        <!-- WP7: the real Calculation driver, so the dependency-flow integration test drives values through
+             the real DependencyMuxActor → DependencyConsumerMuxAdapter → CalculationDriver path. -->
+        <ProjectReference Include="..\..\..\src\Drivers\ZB.MOM.WW.OtOpcUa.Driver.Calculation\ZB.MOM.WW.OtOpcUa.Driver.Calculation.csproj"/>
     </ItemGroup>
 
 </Project>