KAFKA-19250 : txnProducer.abortTransaction() API should not return abortable exception (#19656)

## Problem
When an `txnProducer.abortTransaction()`operation encounters a
`TRANSACTION_ABORTABLE` error, it currently tries to transition to
`ABORTABLE_ERROR` state. This can create an infinite retry loop since:
1. The abort operation fails with `TRANSACTION_ABORTABLE`
2. We transition to `ABORTABLE_ERROR` state
3. The application recieves instance of TransactionAbortableException
and it retries the abort
4. The cycle repeats

## Solution
For `txnProducer.abortTransaction()`API,  convert
`TRANSACTION_ABORTABLE` errors to fatal errors (`KafkaException`) during
abort operations to ensure clean transaction termination. This prevents
retry loops by:
1. Treating abort failures as fatal errors at application layer
2. Ensuring the transaction can be cleanly terminated
3. Providing clear error messages to the application

## Changes
- Modified `EndTxnHandler.handleResponse()` to convert
`TRANSACTION_ABORTABLE` errors to `KafkaException` during abort
operations
- Set TransactionManager state to FATAL
- Updated test `testAbortableErrorIsConvertedToFatalErrorDuringAbort` to
verify this behavior

## Testing
- Added test case verifying that abort operations convert
`TRANSACTION_ABORTABLE` errors to `KafkaException`
    - Verified that Commit API with TRANSACTION_ABORTABLE error should
set TM to Abortable state
    - Verified that Abort API with TRANSACTION_ABORTABLE error should
convert to Fatal error i.e. KafkaException

## Impact
At application layer, this change improves transaction reliability by
preventing infinite retry loops during abort operations.

Reviewers: Justine Olshan <jolshan@confluent.io>

clients/src/main/java/org/apache/kafka/clients/producer/internals/TransactionManager.java

@@ -1738,7 +1738,7 @@ public class TransactionManager {
         public void handleResponse(AbstractResponse response) {
             EndTxnResponse endTxnResponse = (EndTxnResponse) response;
             Errors error = endTxnResponse.error();
-
+            boolean isAbort = !builder.data.committed();
             if (error == Errors.NONE) {
                 // For End Txn version 5+, the broker includes the producerId and producerEpoch in the EndTxnResponse.
                 // For versions lower than 5, the producer Id and epoch are set to -1 by default.
@@ -1771,6 +1771,11 @@ public class TransactionManager {
                 fatalError(error.exception());
             } else if (error == Errors.UNKNOWN_PRODUCER_ID) {
                 abortableErrorIfPossible(error.exception());
+            } else if (isAbort && error.exception() instanceof TransactionAbortableException) {
+                // When aborting a transaction, we must convert TRANSACTION_ABORTABLE errors to KafkaException
+                // because if an abort operation itself encounters an abortable error, retrying the abort would create a cycle.
+                // Instead, we treat this as fatal error at the application layer to ensure the transaction can be cleanly terminated.
+                fatalError(new KafkaException("Failed to abort transaction", error.exception()));
             } else if (error == Errors.TRANSACTION_ABORTABLE) {
                 abortableError(error.exception());
             } else {

clients/src/test/java/org/apache/kafka/clients/producer/internals/SenderTest.java

@@ -3236,6 +3236,61 @@ public class SenderTest {
 
         txnManager.beginTransaction();
     }
+
+    @Test
+    public void testAbortableErrorIsConvertedToFatalErrorDuringAbort() throws Exception {
+
+        // Initialize and begin transaction
+        TransactionManager transactionManager = new TransactionManager(logContext, "testAbortableErrorIsConvertedToFatalErrorDuringAbort", 60000, 100, apiVersions, false);
+        setupWithTransactionState(transactionManager);
+        doInitTransactions(transactionManager, new ProducerIdAndEpoch(1L, (short) 0));
+        transactionManager.beginTransaction();
+
+        // Add partition and send record
+        TopicPartition tp = new TopicPartition("test", 0);
+        addPartitionToTxn(sender, transactionManager, tp);
+        appendToAccumulator(tp);
+
+        // Send record and get response
+        sender.runOnce();
+        sendIdempotentProducerResponse(0, tp, Errors.NONE, 0);
+        sender.runOnce();
+
+        // Commit API with TRANSACTION_ABORTABLE error should set TM to Abortable state
+        client.prepareResponse(new EndTxnResponse(new EndTxnResponseData()
+                .setErrorCode(Errors.TRANSACTION_ABORTABLE.code())));
+
+        // Attempt to commit transaction
+        TransactionalRequestResult commitResult = transactionManager.beginCommit();
+        sender.runOnce();
+        try {
+            commitResult.await(1000, TimeUnit.MILLISECONDS);
+            fail("Expected abortable error to be thrown for commit");
+        } catch (KafkaException e) {
+            assertTrue(transactionManager.hasAbortableError());
+            assertEquals(commitResult.error().getClass(), TransactionAbortableException.class);
+        }
+
+        // Abort API with TRANSACTION_ABORTABLE error should convert to Fatal error i.e. KafkaException
+        client.prepareResponse(new EndTxnResponse(new EndTxnResponseData()
+                .setErrorCode(Errors.TRANSACTION_ABORTABLE.code())));
+
+        // Attempt to abort transaction
+        TransactionalRequestResult abortResult = transactionManager.beginAbort();
+        sender.runOnce();
+
+        // Verify the error is converted to KafkaException (not TransactionAbortableException)
+        try {
+            abortResult.await(1000, TimeUnit.MILLISECONDS);
+            fail("Expected KafkaException to be thrown");
+        } catch (KafkaException e) {
+            // Verify TM is in FATAL_ERROR state
+            assertTrue(transactionManager.hasFatalError());
+            assertFalse(e instanceof TransactionAbortableException);
+            assertEquals(abortResult.error().getClass(), KafkaException.class);
+        }
+    }
+
     @Test
     public void testProducerBatchRetriesWhenPartitionLeaderChanges() throws Exception {
         Metrics m = new Metrics();