Design a dependency-aware job scheduler

Design a backend job scheduler where each submitted job consists of multiple tasks with dependency relationships. A task may run only after all of its prerequisite tasks have completed successfully. Your design should cover: - How clients submit a job and its task dependency graph - Validation of the job definition, including invalid dependencies and cycles - How the scheduler finds runnable tasks - How tasks are dispatched to workers - Task and job state management - Retries, timeouts, and failure handling - How the system recovers from crashes or restarts - Observability, debugging, and operational concerns Assume this is a production service that may run many jobs concurrently.