fix(opcua): raw open-ended/end-only reads per Part 11; extreme-bound conformance (#669)

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

@@ -5174,7 +5174,8 @@ public sealed class OtOpcUaNodeManager : CustomNodeManager2
             // to an open upper bound, or the cursor would store MinValue and a backend would swap the reversed
             // resume window. A resumed read is always forward (the cursor is only ever stored for a forward read),
             // so its direction comes from the cursor, not from the resume request's details.
-            if (!resumed && endUtc == DateTime.MinValue && startUtc != DateTime.MinValue) endUtc = DateTime.MaxValue;
+            if (!resumed && endUtc == DateTime.MinValue && startUtc != DateTime.MinValue)
+                endUtc = new DateTime(DateTime.MaxValue.Ticks, DateTimeKind.Utc); // Utc kind: a proto Timestamp conversion rejects Unspecified
             // Reverse event reads (start > end) are not paged: the cursor below is forward-only.
             var forward = resumed || startUtc <= endUtc;
 
@@ -5966,6 +5967,17 @@ public sealed class OtOpcUaNodeManager : CustomNodeManager2
 
                 tagname = resolved;
                 startUtc = startTimeUtc;
+
+                // Part 11: with NumValuesPerNode > 0 one bound may be left unset. Only a StartTime ⇒ page FORWARD from
+                // it to an open upper bound; only an EndTime ⇒ page BACKWARD from it (a reverse read, start > end).
+                // Without this an unset EndTime (MinValue) looked like a reverse read to a lower bound of "now".
+                if (numValuesPerNode > 0)
+                {
+                    if (endUtc == DateTime.MinValue && startUtc != DateTime.MinValue)
+                        endUtc = new DateTime(DateTime.MaxValue.Ticks, DateTimeKind.Utc);
+                    else if (startUtc == DateTime.MinValue && endUtc != DateTime.MinValue)
+                        (startUtc, endUtc) = (endUtc, new DateTime(0, DateTimeKind.Utc));
+                }
             }
 
             // HistoryRead is NOT under the node-manager Lock — awaiting the async source is safe.