fix(historian): page by the backend's timestamp resolution; QuestDB AtTime stamps the requested time

IHistorianDataSource.TimestampResolutionTicks (default 1; QuestDB 10). A drained tie
cluster now steps off T by the resolution, so a forward one-value-per-page read on a
microsecond backend no longer re-reads the same sample forever (C1). QuestDB AtTime
results carry the client's original request time (M3); regression for the NEXT seek
skipping a tombstone (M1). Conformance backend wires the real writer and updater.

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

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

@@ -212,25 +212,34 @@ internal static class HistoryPaging
     ///     after <paramref name="endUtc"/> (the reverse window excludes <c>end</c>; a resume at exactly <c>end</c>
     ///     would turn into a <c>start == end</c> point read and return the excluded sample). Forward is unchanged.
     /// </param>
+    /// <param name="resolutionTicks">
+    ///     The backend's storage timestamp resolution (<c>IHistorianDataSource.TimestampResolutionTicks</c>, &gt;= 1). A
+    ///     drained cluster steps off <paramref name="boundaryT"/> by this many ticks rather than by one: a backend that
+    ///     truncates its inputs to its resolution (QuestDB, 10 ticks) would otherwise truncate <c>T + 1 tick</c> back
+    ///     to <c>T</c> and return the drained sample again, forever. Lossless for the same reason one tick is at tick
+    ///     precision: no stored timestamp lies strictly between <c>T</c> and <c>T ± resolution</c>. The default
+    ///     <c>1</c> keeps the tick-precision behaviour exactly.
+    /// </param>
     public static void SliceTieCluster(
         int clusterCount, int skip, uint cap, DateTime boundaryT, DateTime endUtc,
         out int sliceStart, out int sliceCount, out DateTime? nextStartUtc, out int nextSkip,
-        bool reverse = false)
+        bool reverse = false, long resolutionTicks = 1)
     {
+        ArgumentOutOfRangeException.ThrowIfLessThan(resolutionTicks, 1L);
         sliceStart = Math.Min(skip, clusterCount);
         sliceCount = Math.Min((int)cap, clusterCount - sliceStart);
         var emitted = sliceStart + sliceCount;
         if (emitted < clusterCount) { nextStartUtc = boundaryT; nextSkip = emitted; }
         else if (reverse)
         {
-            // DateTime.MinValue cannot step down; nothing can lie below it anyway.
-            var more = boundaryT > DateTime.MinValue && boundaryT.AddTicks(-1) > endUtc;
-            nextStartUtc = more ? boundaryT.AddTicks(-1) : null;
+            // Nothing can lie below DateTime.MinValue, so a boundary within one resolution step of it cannot step down.
+            var more = boundaryT.Ticks >= resolutionTicks && boundaryT.AddTicks(-resolutionTicks) > endUtc;
+            nextStartUtc = more ? boundaryT.AddTicks(-resolutionTicks) : null;
             nextSkip = 0;
         }
         else
         {
-            var next = boundaryT.AddTicks(1);
+            var next = boundaryT.AddTicks(resolutionTicks);
             if (next <= endUtc) { nextStartUtc = next; nextSkip = 0; }
             else { nextStartUtc = null; nextSkip = 0; }
         }

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

@@ -5931,7 +5931,7 @@ public sealed class OtOpcUaNodeManager : CustomNodeManager2
                 HistoryPaging.SliceTieCluster(
                     cluster.Count, boundarySkip, numValuesPerNode, startUtc, endUtc,
                     out var sliceStart, out var sliceCount, out var nextStartUtc, out var nextSkip,
-                    reverse: reverse);
+                    reverse: reverse, resolutionTicks: Math.Max(1L, HistorianDataSource.TimestampResolutionTicks));
 
                 var slice = new List<DataValueSnapshot>(sliceCount);
                 for (var i = sliceStart; i < sliceStart + sliceCount; i++) slice.Add(cluster[i]);