fix(sitecallaudit): UpdatedAtUtc index + per-row pull resilience + UTC-convention + first-cycle test (review)

src/ZB.MOM.WW.ScadaBridge.Communication/Grpc/SiteStreamGrpcServer.cs

@@ -457,7 +457,9 @@ public class SiteStreamGrpcServer : SiteStreamService.SiteStreamServiceBase
         // sinceUtc defaults to DateTime.MinValue when the wrapper is absent —
         // i.e. "pull from the beginning of recorded history", which is the
         // intended behaviour for the very first reconciliation cycle.
-        var since = request.SinceUtc?.ToDateTime().ToUniversalTime() ?? DateTime.MinValue;
+        var since = request.SinceUtc is not null
+            ? DateTime.SpecifyKind(request.SinceUtc.ToDateTime(), DateTimeKind.Utc)
+            : DateTime.MinValue;
 
         IReadOnlyList<AuditEvent> events;
         try
@@ -537,10 +539,10 @@ public class SiteStreamGrpcServer : SiteStreamService.SiteStreamServiceBase
 
         // since_utc defaults to DateTime.MinValue when the wrapper is absent —
         // i.e. "pull from the beginning of recorded history", the intended
-        // behaviour for the very first reconciliation cycle. ToUniversalTime
-        // is safe here (the wire value is always a real UTC Timestamp, never the
-        // unspecified-MinValue the central client guards against on its side).
-        var since = request.SinceUtc?.ToDateTime().ToUniversalTime() ?? DateTime.MinValue;
+        // behaviour for the very first reconciliation cycle.
+        var since = request.SinceUtc is not null
+            ? DateTime.SpecifyKind(request.SinceUtc.ToDateTime(), DateTimeKind.Utc)
+            : DateTime.MinValue;
 
         IReadOnlyList<SiteCallOperational> operationals;
         try