Concurrent task scheduler

Problem Implement a concurrent task scheduler that runs tasks across a worker pool while respecting inter-task dependencies and avoiding race conditions.

Requirements

• submit(task, dependsOn[]); a task may run only after all its dependencies complete.
• Execute ready tasks in parallel across a fixed worker pool.
• Support graceful shutdown and surface task failures.

Areas to design

• The dependency model and how a task becomes "ready".
• Thread-safe hand-off of ready tasks to workers.
• Failure policy, backpressure, cycle detection, and graceful shutdown.