CCR: Use single global checkpoint to normalize range (#33545)

We may use different global checkpoints to validate/normalize the range
of a change request if the global checkpoint is advanced between these
calls. If this is the case, then we generate an invalid request range.

x-pack/plugin/ccr/src/main/java/org/elasticsearch/xpack/ccr/action/ShardChangesAction.java

@@ -297,12 +297,13 @@ public class ShardChangesAction extends Action<ShardChangesAction.Response> {
         if (indexShard.state() != IndexShardState.STARTED) {
             throw new IndexShardNotStartedException(indexShard.shardId(), indexShard.state());
         }
-        if (fromSeqNo > indexShard.getGlobalCheckpoint()) {
+        if (fromSeqNo > globalCheckpoint) {
             return EMPTY_OPERATIONS_ARRAY;
         }
         int seenBytes = 0;
         // - 1 is needed, because toSeqNo is inclusive
         long toSeqNo = Math.min(globalCheckpoint, (fromSeqNo + maxOperationCount) - 1);
+        assert fromSeqNo <= toSeqNo : "invalid range from_seqno[" + fromSeqNo + "] > to_seqno[" + toSeqNo + "]";
         final List<Translog.Operation> operations = new ArrayList<>();
         try (Translog.Snapshot snapshot = indexShard.newChangesSnapshot("ccr", fromSeqNo, toSeqNo, true)) {
             Translog.Operation op;