feat(host): F8b RoslynVirtualTagEvaluator — production virtual-tag eval

RoslynVirtualTagEvaluator wraps Core.Scripting.ScriptEvaluator + Core
.VirtualTags.VirtualTagContext into a single-tag IVirtualTagEvaluator
adapter. Caches the compiled ScriptEvaluator per unique expression so
the second-and-onwards Evaluate is an in-process method call against the
dependency dictionary. Compile/sandbox/runtime errors all surface as
VirtualTagEvalResult.Failure rather than propagating exceptions through
the VirtualTagActor message loop.

Single-tag scope: cross-tag ctx.SetVirtualTag writes are dropped + logged
because fan-out between actors is owned by DependencyMuxActor. Cycle
detection + cascade ordering stay in Core.VirtualTags.VirtualTagEngine
where they belong (loaded fleet-wide); this adapter keeps the actor
message handler simple.

Host adds Core.Scripting + Core.VirtualTags project refs, plus a
TargetWarningsAsErrors NU1608 suppression — Microsoft.CodeAnalysis.CSharp
.Scripting 4.12.0 pins Common to 4.12.0 but ASP.NET Core transitively
brings Microsoft.CodeAnalysis.Common 5.0.0; the surface we use is stable
across the drift (verified by Core.Scripting.Tests).

Program.cs binds RoslynVirtualTagEvaluator → IVirtualTagEvaluator on
driver-role hosts, replacing the F8-default NullVirtualTagEvaluator so
VirtualTagActor evaluates real user scripts at runtime.

6 new adapter tests cover: simple expression sums, cache reuse across
calls, compile-error denial, runtime-throw denial, empty-expression
denial, post-dispose denial. Host.IntegrationTests now 10/10 green.

Closes #79. F9b + #107 next.

src/Server/ZB.MOM.WW.OtOpcUa.Host/Engines/RoslynVirtualTagEvaluator.cs

@@ -0,0 +1,116 @@
+using System.Collections.Concurrent;
+using Microsoft.Extensions.Logging;
+using ZB.MOM.WW.OtOpcUa.Commons.Engines;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Core.Scripting;
+using ZB.MOM.WW.OtOpcUa.Core.VirtualTags;
+using SerilogLogger = Serilog.ILogger;
+using SerilogLog = Serilog.Log;
+
+namespace ZB.MOM.WW.OtOpcUa.Host.Engines;
+
+/// <summary>
+/// F8b — production <see cref="IVirtualTagEvaluator"/> binding. Compiles each unique
+/// expression once via <see cref="ScriptEvaluator{TContext, TResult}"/> (Roslyn-backed
+/// sandbox) and caches the resulting evaluator keyed by source. Subsequent evaluations are
+/// in-process method invocations on the dependency dictionary — fast enough to run inline
+/// inside the actor's message handler.
+///
+/// Single-tag mode: cross-tag <c>ctx.SetVirtualTag</c> writes are dropped (logged) because
+/// fan-out between actors is owned by <c>DependencyMuxActor</c>, not by the eval engine.
+/// Cycle detection + cascade ordering live in <see cref="VirtualTagEngine"/>; this adapter
+/// stays single-tag scoped to keep <see cref="VirtualTagActor"/>'s message loop simple.
+/// </summary>
+public sealed class RoslynVirtualTagEvaluator : IVirtualTagEvaluator, IDisposable
+{
+    private static readonly SerilogLogger ScriptLogger = SerilogLog.ForContext<RoslynVirtualTagEvaluator>();
+
+    private readonly ConcurrentDictionary<string, ScriptEvaluator<VirtualTagContext, object?>> _cache
+        = new(StringComparer.Ordinal);
+    private readonly ILogger<RoslynVirtualTagEvaluator> _logger;
+    private readonly TimeSpan _runTimeout;
+    private bool _disposed;
+
+    public RoslynVirtualTagEvaluator(ILogger<RoslynVirtualTagEvaluator> logger, TimeSpan? runTimeout = null)
+    {
+        _logger = logger;
+        _runTimeout = runTimeout ?? TimeSpan.FromSeconds(2);
+    }
+
+    public VirtualTagEvalResult Evaluate(string virtualTagId, string expression, IReadOnlyDictionary<string, object?> dependencies)
+    {
+        if (_disposed) return VirtualTagEvalResult.Failure("evaluator disposed");
+        if (string.IsNullOrWhiteSpace(expression)) return VirtualTagEvalResult.Failure("empty expression");
+
+        ScriptEvaluator<VirtualTagContext, object?> evaluator;
+        try
+        {
+            evaluator = _cache.GetOrAdd(expression, ScriptEvaluator<VirtualTagContext, object?>.Compile);
+        }
+        catch (CompilationErrorException ex)
+        {
+            _logger.LogWarning(ex, "VirtualTag {Id}: Roslyn compile failed", virtualTagId);
+            return VirtualTagEvalResult.Failure($"compile error: {ex.Message}");
+        }
+        catch (ScriptSandboxViolationException ex)
+        {
+            _logger.LogWarning(ex, "VirtualTag {Id}: sandbox violation", virtualTagId);
+            return VirtualTagEvalResult.Failure($"sandbox violation: {ex.Message}");
+        }
+        catch (Exception ex)
+        {
+            _logger.LogWarning(ex, "VirtualTag {Id}: compile threw", virtualTagId);
+            return VirtualTagEvalResult.Failure($"compile failure: {ex.Message}");
+        }
+
+        var readCache = BuildReadCache(dependencies);
+        var context = new VirtualTagContext(
+            readCache,
+            setVirtualTag: (path, _) =>
+                _logger.LogDebug("VirtualTag {Id}: cross-tag write to {Path} dropped (single-tag adapter)",
+                    virtualTagId, path),
+            logger: ScriptLogger);
+
+        try
+        {
+            using var cts = new CancellationTokenSource(_runTimeout);
+            var raw = evaluator.RunAsync(context, cts.Token).GetAwaiter().GetResult();
+            return VirtualTagEvalResult.Ok(raw);
+        }
+        catch (OperationCanceledException)
+        {
+            return VirtualTagEvalResult.Failure($"script timed out after {_runTimeout.TotalSeconds:F1}s");
+        }
+        catch (Exception ex)
+        {
+            _logger.LogWarning(ex, "VirtualTag {Id}: script execution threw", virtualTagId);
+            return VirtualTagEvalResult.Failure($"script threw: {ex.Message}");
+        }
+    }
+
+    private static IReadOnlyDictionary<string, DataValueSnapshot> BuildReadCache(
+        IReadOnlyDictionary<string, object?> deps)
+    {
+        // VirtualTagContext.GetTag returns a DataValueSnapshot — we wrap each raw dep value
+        // as Good-quality so the script's `(int)ctx.GetTag("a").Value` pattern works. Null
+        // values stay null; the script can null-check via GetTag(path).Value.
+        var nowUtc = DateTime.UtcNow;
+        var cache = new Dictionary<string, DataValueSnapshot>(StringComparer.Ordinal);
+        foreach (var kv in deps)
+        {
+            cache[kv.Key] = new DataValueSnapshot(kv.Value, StatusCode: 0u, SourceTimestampUtc: nowUtc, ServerTimestampUtc: nowUtc);
+        }
+        return cache;
+    }
+
+    public void Dispose()
+    {
+        if (_disposed) return;
+        _disposed = true;
+        foreach (var ev in _cache.Values)
+        {
+            try { ev.Dispose(); } catch { /* best-effort */ }
+        }
+        _cache.Clear();
+    }
+}