docs/architecture/adr-payment-boundary.md

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+# Architectural Decision Record for Payment Boundary
+
+## Context
+In order to ensure the integrity and separation of concerns within the payment processing system, we need to define firm boundaries between various components: Controller, Service, Repository, Domain, and Integration. This helps in minimizing unintended dependencies that may arise during development.
+
+## Decision
+The payment boundary will be strictly defined such that:
+- Controllers interact only with Services.
+- Services interact only with Repositories and Domains (no direct interaction between Services and Controllers).
+- Repositories handle data access and business logic is encapsulated within Services.
+- Integration with external systems is managed separately and will not cross into the Service layer.
+
+## Alternatives
+1. Allow Services to directly interact with Repositories for data retrieval.  
+   **Consequences:** Increases coupling and can lead to issues with data integrity and business logic being bypassed.
+2. Utilize an Event-Driven Architecture for communications between Services and Integrations.  
+   **Consequences:** Increased complexity and potential performance hits.
+
+## Consequences
+By setting these boundaries, we are ensuring that changes in one component do not inadvertently affect others, thus maintaining a clean architecture that adheres to SOLID principles. Scalability and maintainability of the system are expected to improve as team members can work more independently without overlapping concerns.