fix(abcip): thread CIP template-instance-id so discovered-UDT expansion works in production (review)

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/CipSymbolObjectDecoderTests.cs

@@ -98,11 +98,15 @@ public sealed class CipSymbolObjectDecoderTests
         CipSymbolObjectDecoder.MapTypeCode(0xFF).ShouldBeNull();
     }
 
-    /// <summary>Verifies that struct flag overrides type code.</summary>
+    /// <summary>
+    ///     Verifies that the struct flag overrides the type code AND that the lower 12 bits are
+    ///     surfaced as the CIP template instance id (used by discovery to fetch the UDT's Template
+    ///     Object). This is the plumbing that makes top-level discovered-UDT expansion functional.
+    /// </summary>
     [Fact]
-    public void Struct_flag_overrides_type_code_and_yields_Structure()
+    public void Struct_flag_yields_Structure_and_surfaces_template_instance_id()
     {
-        // 0x8000 (struct) + 0x1234 (template instance id in lower 12 bits; uses 0x234)
+        // 0x8000 (struct flag) | 0x0234 (template instance id in the lower 12 bits)
         var bytes = BuildEntry(
             instanceId: 5,
             symbolType: 0x8000 | 0x0234,
@@ -112,6 +116,25 @@ public sealed class CipSymbolObjectDecoderTests
 
         var tag = CipSymbolObjectDecoder.Decode(bytes).Single();
         tag.DataType.ShouldBe(AbCipDataType.Structure);
+        tag.TemplateInstanceId.ShouldBe(0x0234u);
+    }
+
+    /// <summary>
+    ///     Verifies that an atomic (non-struct) symbol carries no template instance id — only struct
+    ///     symbols repurpose the lower 12 bits as a template id.
+    /// </summary>
+    [Fact]
+    public void Atomic_symbol_has_no_template_instance_id()
+    {
+        var bytes = BuildEntry(
+            instanceId: 7,
+            symbolType: 0xC4, // DINT — atomic, not a struct
+            elementLength: 4,
+            arrayDims: (0, 0, 0),
+            name: "Counter");
+
+        var tag = CipSymbolObjectDecoder.Decode(bytes).Single();
+        tag.TemplateInstanceId.ShouldBeNull();
     }
 
     /// <summary>Verifies that system flag surfaces as IsSystemTag true.</summary>