feat(vtag): passthrough fast-path skips Roslyn for mirror scripts (A)

src/Core/ZB.MOM.WW.OtOpcUa.Core.Scripting.Abstractions/PassthroughScript.cs

@@ -0,0 +1,29 @@
+namespace ZB.MOM.WW.OtOpcUa.Core.Scripting;
+
+using System.Text.RegularExpressions;
+
+/// <summary>
+/// Classifies the trivial "mirror" VirtualTag script shape <c>return ctx.GetTag("X").Value;</c>,
+/// which can be evaluated by returning the dependency value directly — no Roslyn compilation.
+/// Narrow, exact pattern: any near-miss returns false and falls through to the Roslyn path.
+/// </summary>
+public static partial class PassthroughScript
+{
+    // ^ \s* return \s+ ctx . GetTag ( "X" ) . Value ; \s* $  (whitespace-tolerant around tokens)
+    [GeneratedRegex(@"^\s*return\s+ctx\s*\.\s*GetTag\s*\(\s*""([^""]+)""\s*\)\s*\.\s*Value\s*;\s*$")]
+    private static partial Regex MirrorRegex();
+
+    /// <summary>True if <paramref name="source"/> is the mirror passthrough shape; outputs the referenced tag.</summary>
+    /// <param name="source">The VirtualTag script source to classify.</param>
+    /// <param name="tagRef">On success, the tag reference captured from the mirror shape; otherwise empty.</param>
+    /// <returns><see langword="true"/> if the source is the mirror passthrough shape; otherwise <see langword="false"/>.</returns>
+    public static bool TryMatch(string? source, out string tagRef)
+    {
+        tagRef = string.Empty;
+        if (string.IsNullOrEmpty(source)) return false;
+        var m = MirrorRegex().Match(source);
+        if (!m.Success) return false;
+        tagRef = m.Groups[1].Value;
+        return true;
+    }
+}

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

@@ -50,6 +50,18 @@ public sealed class RoslynVirtualTagEvaluator : IVirtualTagEvaluator, IDisposabl
         if (_disposed) return VirtualTagEvalResult.Failure("evaluator disposed");
         if (string.IsNullOrWhiteSpace(expression)) return VirtualTagEvalResult.Failure("empty expression");
 
+        // A — passthrough fast-path: the mirror shape `return ctx.GetTag("X").Value;` needs no
+        // Roslyn. Narrow exact pattern; near-misses fall through to the compiled path below.
+        // Semantics are byte-identical to the compiled mirror: a present dependency returns its
+        // value (Ok), and an absent one makes GetTag yield a Bad snapshot whose .Value is null,
+        // so the script returns null — Ok(null) here too.
+        if (PassthroughScript.TryMatch(expression, out var passthroughRef))
+        {
+            return dependencies.TryGetValue(passthroughRef, out var ptValue)
+                ? VirtualTagEvalResult.Ok(ptValue)
+                : VirtualTagEvalResult.Ok(null);
+        }
+
         ScriptEvaluator<VirtualTagContext, object?> evaluator;
         try
         {