**Affected version:** 8.2 - 8.5.2
**Fixed in:** 8.5.3

### Problem Description

The problem applies to transforms that use more than 1 CCS cluster or 1 local and 1 CCS as source. A typical source could look like this (the important part: `remotes*`):

```
        "index" : [
          "remotes*:filebeat*"
        ],

```

If 2 indices share the same name the transform might fail with an error similar to this:

```
 Failed to retrieve checkpoint due to: Duplicate key logs-2022-11-14 (attempted merging values [... and ...]
```

Similar to the above the `_stats` call is broken for such a transform, it can fail with an error message starting with:

```
Failure during checkpoint retrieval
```

This can happen even if the transform is in state `STOPPED` or `FAILED`.

### Mitigation

Choose _one_ of the following mitigations:

 - split your transforms to use max 1 CCS/local indices

_or_

 - avoid upgrading to 8.2, until the issue got resolved (this is a regression of #80984)

_or_

 - avoid duplicate names for your indices even on remote cluster, e.g. name the index: `remote1-filebeat...`, `remote2-filebeat...`


### Solution

This is a regression of #80984 which introduced a new way of check-pointing. The remote needs to be prefixed to the index name.
x-pack/plugin/transform/src/main/java/org/elasticsearch/xpack/transform/checkpoint/DefaultCheckpointProvider.java
if (userIndices.contains(indexName)) {
                
                long globalCheckpoint = shard.getSeqNoStats() == null ? -1L : shard.getSeqNoStats().getGlobalCheckpoint();
                String fullIndexName = cluster.isEmpty()
                    ? indexName
                    : cluster + RemoteClusterService.REMOTE_CLUSTER_INDEX_SEPARATOR + indexName;
                if (checkpointsByIndex.containsKey(fullIndexName)) {
                    
                    TreeMap<Integer, Long> checkpoints = checkpointsByIndex.get(fullIndexName);
                    
                    
                    
                    
                    if (checkpoints.containsKey(shard.getShardRouting().getId()) == false
                        || checkpoints.get(shard.getShardRouting().getId()) < globalCheckpoint) {
                        checkpoints.put(shard.getShardRouting().getId(), globalCheckpoint);
                    }
                } else {
                    
                    checkpointsByIndex.put(fullIndexName, new TreeMap<>());
                    checkpointsByIndex.get(fullIndexName).put(shard.getShardRouting().getId(), globalCheckpoint);
                }
            }
        }
        
        
        
        
        if (logger.isDebugEnabled()) {
            Set<String> userIndicesClone = new HashSet<>(userIndices);