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

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
         {