Merge fix/693-gateway-attime: Gateway AtTime from raw reads + shared evaluator, node type hint (#693)

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

@@ -3399,6 +3399,36 @@ public sealed class OtOpcUaNodeManager : CustomNodeManager2
         return NodeId.Null;
     }
 
+    /// <summary>
+    ///     Gitea #693: the AtTime value-type hint of a historized variable — its DataType's built-in type as a
+    ///     <see cref="TypeCode"/> when the node is a scalar of a type the historian evaluates (Boolean, the integers, Float,
+    ///     Double, String, DateTime); <c>null</c> for an array, an unknown node, or any other type. A UNS mirror carries its
+    ///     backing raw tag's DataType, so either NodeId gives the same hint.
+    /// </summary>
+    /// <param name="nodeId">The HistoryRead request's node id.</param>
+    /// <returns>The hint, or null.</returns>
+    internal TypeCode? AtTimeValueType(NodeId nodeId)
+    {
+        if (!_variables.TryGetValue(MapKey(nodeId), out var variable) || variable.ValueRank != ValueRanks.Scalar) return null;
+        return TypeInfo.GetBuiltInType(variable.DataType) switch
+        {
+            BuiltInType.Boolean => TypeCode.Boolean,
+            BuiltInType.SByte => TypeCode.SByte,
+            BuiltInType.Byte => TypeCode.Byte,
+            BuiltInType.Int16 => TypeCode.Int16,
+            BuiltInType.UInt16 => TypeCode.UInt16,
+            BuiltInType.Int32 => TypeCode.Int32,
+            BuiltInType.UInt32 => TypeCode.UInt32,
+            BuiltInType.Int64 => TypeCode.Int64,
+            BuiltInType.UInt64 => TypeCode.UInt64,
+            BuiltInType.Float => TypeCode.Single,
+            BuiltInType.Double => TypeCode.Double,
+            BuiltInType.String => TypeCode.String,
+            BuiltInType.DateTime => TypeCode.DateTime,
+            _ => null,
+        };
+    }
+
     /// <summary>Map a Tag.DataType string ("Boolean", "Int32", "Float", "Double", "String",
     /// "DateTime") to the OPC UA built-in NodeId. Unknown names fall back to BaseDataType
     /// (matches CreateVariable's default for lazy-created nodes).</summary>
@@ -5177,9 +5207,12 @@ public sealed class OtOpcUaNodeManager : CustomNodeManager2
             var work = new List<Func<Task>>(nodesToProcess.Count);
             foreach (var handle in nodesToProcess)
             {
+                // #693: the node's scalar value type, for a backend whose stored values carry none (the Gateway).
+                var valueType = AtTimeValueType(handle.NodeId);
                 work.Add(() => ServeNodeAsync(handle, results, errors, (source, tagname, token) => source.ReadAtTimeAsync(
                     tagname,
                     timestamps,
+                    valueType,
                     token), ct));
             }