Process Orders Through a DAG with Completion and Timeout Refunds

Design and implement the core of an order-processing workflow represented as a DAG. Support order submission and status queries. An order that completes in time is finalized; an order that times out follows a refund path. ### Constraints & Assumptions The source describes microservices and an example timeout/refund branch but gives no exact DAG or payment API. State the workflow and terminal-state rules before coding. A shared in-memory store can demonstrate one-process behavior; it does not by itself provide durable coordination across independent services. ### Clarifying Questions When does the timeout start? What counts as completion? Can a late completion race with a refund? Are tasks and external effects idempotent? How is a failed workflow resumed after restart? ### What a Strong Answer Covers Validated DAG definitions, per-order task state, prerequisite scheduling, an atomic terminal decision, effect identities, status reads, and recovery. ### Follow-up Questions What happens if the completion and timeout handlers run concurrently? Can refunding fail? How do status queries distinguish refund requested from refund confirmed?