We saw a case where the recovery stats reported `recovered_bytes` greater than `length_in_bytes` for one file:

```
GET /_recovery?detailed

200 OK
...
{
  "name": "_buk.fdt",
  "length_in_bytes": 26891307173,
  "reused": false,
  "recovered_in_bytes": 35324928266,
  "recovered_from_snapshot_in_bytes": 8433621093
}
...
```

NB `35324928266 == 26891307173 + 8433621093`

This causes Elasticsearch to compute a negative value for the reserved space on the target node of this recovery, which prevents stats APIs from working. This appears to be caused by a network-level failure which triggers a retry without first cancelling an ongoing download of a different file with the same name from the snapshot repository.

---

### Workaround

Restart the target node to clear these stats.
server/src/main/java/org/elasticsearch/index/shard/IndexShard.java
throw new IllegalIndexShardStateException(
                    shardId,
                    state,
                    "operation only allowed when shard state is one of " + writeAllowedStates + ", origin [" + origin + "]"
                );
            }
        }
    }
    private boolean assertPrimaryMode() {
        assert shardRouting.primary() && replicationTracker.isPrimaryMode()
            : "shard " + shardRouting + " is not a primary shard in primary mode";
        return true;
    }
    private boolean assertReplicationTarget() {
        assert replicationTracker.isPrimaryMode() == false : "shard " + shardRouting + " in primary mode cannot be a replication target";
        return true;
    }
    private void verifyNotClosed() throws IllegalIndexShardStateException {
        verifyNotClosed(null);
    }
    private void verifyNotClosed(Exception suppressed) throws IllegalIndexShardStateException {
        IndexShardState state = this.state; 
        if (state == IndexShardState.CLOSED) {
            final IllegalIndexShardStateException exc = new IndexShardClosedException(shardId, "operation only allowed when not closed");
            if (suppressed != null) {
                exc.addSuppressed(suppressed);
            }
            throw exc;
        }
    }