Design a Task Dependency (DAG) Tracker

Problem Design a system to track and display task dependencies within a project (Asana's domain).

Requirements

• addTask, addDependency(a, b) (a blocks b).
• Detect cycles (an invalid dependency).
• Compute ready tasks (those with no incomplete blockers).
• Mark a task complete, unblocking its dependents.

Areas to design

• The DAG model and cycle detection at add time.
• Querying ready vs blocked tasks (a topological view).
• Separation of the model from the query layer.