Investigate if strong references between tasks can be avoided.

The following example leads to OOM because of chain of references.

```
public class RetentionExample extends AbstractExample {

private Task last = null;

public static void main(String[] args) throws Exception {
new RetentionExample2().runExample();
}

@Override
protected void doRunExample(final Engine engine) throws Exception {

for (int i = 0; i < 1000000; i++) {
Task t = null;
if (last != null) {
t = last.andThen(Task.callable(() -> ""));
engine.run(t);
t.await();
} else {
t = Task.callable(() -> "");
}
last = t;
}

System.out.println(last.getTrace());
}
}
```

Start with the RetentionExample snippet, then trace how Task.andThen, Engine.run, await, and getTrace retain references during the million-iteration chain. Reproduce the OOM and inspect the task-chain lifecycle to determine whether strong references can be avoided; done means a documented conclusion or a verified change that prevents the demonstrated retention.

Written by the indexing model from the issue text.