SweepPolicy

The "sweep" half of the mark-and-sweep collector: given a proposition and its marks, decides what should actually happen to it as a SweepAction.

Implementations decide per-proposition and should be stateless. Applying the decision (transitioning status, deleting, or skipping) is the runner's job, not the policy's.

Implement this to encode domain-specific sweep behavior without touching DICE core.

Inheritors