What's the counterpart of the adjective 'pending'

The completion of task A cannot be achieved until task B is completed.

I can therefore say that task A is in a group of tasks whose completion is suspended 'pending' the completion of task B. I can classify them as 'Pending'

But I want an adjective for the group of tasks that task B belongs to. A group of tasks, the completion of which allows other tasks to be addressed.

Pended? Pendant? - just can't pin down a word that works for this!

Any ideas please!

Prerequisite springs to mind.

• It would be immediately intelligible to anyone who has attended an American university or played Dungeons and Dragons.

• It can be deployed as either an adjective or a noun.

• Its upstream and downstream scopes can be expressed economically (T’s prerequisites are S₁ and S₂, S₁ is prerequisite to T).

Group B tasks are independent (at least with regard to Group A tasks) and Group A tasks are dependent.

You also might characterize Group B tasks as precursor tasks. A common definition of precursor is

a predecessor or forerunner

While that meaning does not describe the contingent relationship, the term also has a meaning in chemistry and biology

a chemical substance that gives rise to another more important substance

The overall sense of the term does convey that the first, independent element must precede and influences the latter, dependent element.