Add checkpoints for both parent tasks and subtasks

[kokorolx]

Currently, subtask checkpoints work well, but parent tasks do not seem to preserve their own checkpoint state.
When I return to a parent task after working on a subtask, then switch to another subtask, the parent task’s code can be lost or broken by the new subtask

Proposed Improvement:

• Have independent checkpoints for both parent tasks and subtasks.

• Allow restoring the previous code state when returning to a parent task, similar to how subtask checkpoints work.

Benefit:
This would prevent accidental code loss and make it easier to resume work exactly where it was left off.