docs : add inline comment

Signed-off-by: Su Ko <rhtn1128@gmail.com>

Author: bandalgomsu

spring-kafka/src/main/java/org/springframework/kafka/listener/KafkaMessageListenerContainer.java

@@ -844,6 +844,7 @@ private final class ListenerConsumer implements SchedulingAwareRunnable, Consume
 
 		private @Nullable ConsumerRecords<K, V> remainingRecords;
 
+		// use to fix tx marker
 		private @Nullable ConsumerRecords<K, V> lastRecords;
 
 		private boolean pauseForPending;
@@ -1613,6 +1614,15 @@ private void saveLastRecordsIfNeeded(ConsumerRecords<K, V> records) {
 			}
 		}
 
+		/**
+		 * Fix transactional offsets using ConsumerRecords#nextOffsets() API.
+		 * This method addresses the issue where Kafka transaction markers can cause
+		 * incorrect offset tracking. By using nextOffsets() instead of position(),
+		 * we ensure:
+		 * - Transaction markers are automatically filtered out
+		 * - Partition-leader epoch information is correctly captured
+		 * - Empty poll() cases are properly handled
+		 */
 		private void fixTxOffsetsIfNeeded() {
 			if (!this.fixTxOffsets) {
 				return;
@@ -1627,6 +1637,7 @@ private void fixTxOffsetsIfNeeded() {
 				Map<TopicPartition, OffsetAndMetadata> nextOffsets = this.lastRecords.nextOffsets();
 				Map<TopicPartition, OffsetAndMetadata> toFix = new HashMap<>();
 
+				// Fix offset only if records were actually processed
 				nextOffsets.forEach((tp, nextOffset) -> {
 					OffsetAndMetadata committed = this.lastCommits.get(tp);
 
@@ -1635,6 +1646,7 @@ private void fixTxOffsetsIfNeeded() {
 						return;
 					}
 
+					// Only fix if we have processed records and the next offset is greater than committed
 					if (!this.lastRecords.records(tp).isEmpty() && nextOffset.offset() > committed.offset()) {
 						toFix.put(tp, nextOffset);
 					}