Permission system done right.

Permission is an ideal example of the context contract additional rules and composition.

We have a nested story with a more strict permission rule than the wrapper story.

`user` has its place in each context contract and we attach different permission validation to it in each contract.

When the `user` will be assigned in the wrapper story, we'll run all its permission validators from all nested stories. So we'll fail early.

Some nested stories will run in the `Celery` task because of the `Delegate` feature. We can fail **that** early.