test(opcua): cover missing-script fallback; rename composer local for clarity

src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/Phase7Composer.cs

@@ -190,7 +190,7 @@ public static class Phase7Composer
         IReadOnlyList<Script>? scripts = null)
     {
         var vtags = virtualTags ?? Array.Empty<VirtualTag>();
-        var scripts2 = scripts ?? Array.Empty<Script>();
+        var resolvedScripts = scripts ?? Array.Empty<Script>();
         var areas = unsAreas
             .OrderBy(a => a.UnsAreaId, StringComparer.Ordinal)
             .Select(a => new UnsAreaProjection(a.UnsAreaId, a.Name))
@@ -267,7 +267,7 @@ public static class Phase7Composer
         // Equipment VirtualTags = each VirtualTag joined to its Script (by ScriptId) for the
         // expression source. DependencyRefs = the distinct ctx.GetTag("…") literals the
         // VirtualTagActor subscribes to. VirtualTag has no FolderPath today → "".
-        var scriptsById = scripts2.ToDictionary(s => s.ScriptId, StringComparer.Ordinal);
+        var scriptsById = resolvedScripts.ToDictionary(s => s.ScriptId, StringComparer.Ordinal);
         var equipmentVirtualTags = vtags
             .OrderBy(v => v.EquipmentId, StringComparer.Ordinal)
             .ThenBy(v => v.Name, StringComparer.Ordinal)

tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/Phase7ComposerPurityTests.cs

@@ -182,6 +182,34 @@ public sealed class Phase7ComposerPurityTests
         plan.DependencyRefs.ShouldBe(new[] { "A.X", "B.Y" });
     }
 
+    /// <summary>A <see cref="VirtualTag"/> whose <c>ScriptId</c> has no matching <see cref="Script"/>
+    /// in the supplied list falls back to an empty Expression and an empty DependencyRefs —
+    /// the plan is always emitted (never dropped) and never carries a null Expression.</summary>
+    [Fact]
+    public void Compose_virtualtag_with_missing_script_yields_empty_expression_and_deps()
+    {
+        var vt = new VirtualTag
+        {
+            VirtualTagId = "vt-missing",
+            EquipmentId = "eq-1",
+            Name = "mystery-tag",
+            DataType = "Float64",
+            ScriptId = "s-does-not-exist",
+        };
+
+        var result = Phase7Composer.Compose(
+            Array.Empty<UnsArea>(), Array.Empty<UnsLine>(), Array.Empty<Equipment>(),
+            Array.Empty<DriverInstance>(), Array.Empty<ScriptedAlarm>(),
+            Array.Empty<Tag>(), Array.Empty<Namespace>(),
+            virtualTags: new[] { vt },
+            scripts: Array.Empty<Script>());
+
+        var plan = result.EquipmentVirtualTags.ShouldHaveSingleItem();
+        plan.VirtualTagId.ShouldBe("vt-missing");
+        plan.Expression.ShouldBe(string.Empty);
+        plan.DependencyRefs.ShouldBeEmpty();
+    }
+
     private static Equipment NewEquipment(string id) => new()
     {
         EquipmentId = id,