Frontier

The set of nodes whose prerequisites are all satisfied — the edge of what is takeable now. On a tracker that is items which are ready-labelled, unassigned, and blocked neither by a dependency edge nor by a label. In an interview it is every decision whose prerequisites are already settled. Same word, same meaning, two surfaces. An empty frontier is a fact that needs a reason attached — all claimed, triage stalled, or everything blocked — because an empty answer with no breakdown sends people guessing.