What is API-led connectivity and what are its three layers?

API-led connectivity is MuleSoft's architectural approach for building reusable, composable integrations. The three layers:

1. System APIs: Expose core systems of record (Salesforce, SAP, databases) in a stable, standardised way. They shield consumers from system complexity and change. Single responsibility — one System API per backend system.
2. Process APIs: Implement business logic and orchestrate multiple System APIs to execute a business process (e.g., Order Processing API calls Inventory System API + CRM System API).
3. Experience APIs: Tailor data to specific consumer needs (mobile app, web portal, partner integration) — formatm filter, and aggregate data from Process APIs without changing underlying logic. Benefits: reusability (a System API is built once and used many times), flexibility (change a backend system by updating only its System API), speed of delivery.