Flowable framework architecture overview

Create a restrained, high-contrast 16:9 technical editorial diagram for the open-source Flowable engine. Use a light neutral background with dark graphite text, Flowable red as a limited accent, and small secondary accents in teal and amber. Do not use gradients, product screenshots, decorative cards, copied logos, mascots or invented interfaces.

Show five clearly separated architectural zones with directional flow:

1. Entry layer: Java API, Spring Boot application, REST client.
2. Engine layer: BPMN Process Engine in the center, with CMMN Case Engine, DMN Decision Engine and Event Registry around it.
3. Runtime core inside BPMN: Services to Command Interceptor Chain to CommandContext and Transaction to Agenda Operations to ActivityBehavior.
4. Shared services: Task, Variable, Identity Link, Event Subscription and Job services shared by the engines.
5. Persistence and external systems: ACT_RE definition data, ACT_RU runtime data, ACT_HI history data, relational database, business services, messages, timers and human users.

Make the two important control boundaries visually obvious: a User Task or message wait state persists execution and returns control; an async node creates a database job that is later acquired, locked, executed, retried and possibly moved to dead letter. Use solid arrows for synchronous control, dashed arrows for persisted resume paths, and a small legend. Keep labels concise and technically exact. The image is a conceptual overview only; do not include method names or pretend to show an exact sequence diagram.

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