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skills/software-architecture/SKILL.md

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+---
+name: software-architecture
+description: Expert software architecture covering architectural patterns (microservices, monolith, event-driven, CQRS), scalability, distributed systems, CAP theorem, database architecture, API design, system design, domain-driven design (DDD), hexagonal architecture, and architecture decision records (ADRs). Activates for software architecture, system design, microservices, monolith, event-driven, CQRS, scalability, distributed systems, CAP theorem, DDD, hexagonal architecture, ADR.
+allowed-tools: Read, Grep, Glob
+---
+
+# Software Architecture Expert
+
+Master of architectural patterns, system design, and scalability.
+
+## Architectural Patterns
+
+**Layered Architecture**:
+```
+Presentation Layer (UI)
+  ↓
+Business Logic Layer (Services)
+  ↓
+Data Access Layer (Repositories)
+  ↓
+Database
+```
+
+**Hexagonal Architecture (Ports & Adapters)**:
+```typescript
+// Core Domain (business logic, no dependencies)
+interface PaymentPort {
+  process(amount: number): Promise<void>;
+}
+
+// Adapter (infrastructure)
+class StripeAdapter implements PaymentPort {
+  async process(amount: number) { /* Stripe API */ }
+}
+
+// Application uses port, not concrete implementation
+class CheckoutService {
+  constructor(private payment: PaymentPort) {}
+}
+```
+
+**Event-Driven Architecture**:
+```typescript
+// Producer
+eventBus.publish({ type: 'OrderPlaced', orderId: '123' });
+
+// Consumers (decoupled)
+eventBus.subscribe('OrderPlaced', inventoryService.reserve);
+eventBus.subscribe('OrderPlaced', emailService.notify);
+```
+
+**CQRS** (Command Query Responsibility Segregation):
+- Commands: Write operations, change state
+- Queries: Read operations, no side effects
+- Separate models for read/write optimization
+
+## Scalability Patterns
+
+**Horizontal Scaling**: Add more servers
+**Vertical Scaling**: Bigger server
+**Caching**: Redis, CDN, application cache
+**Database Sharding**: Partition by key (user_id, region)
+**Read Replicas**: Offload read traffic
+**Load Balancing**: Distribute traffic evenly
+
+## CAP Theorem
+
+**Consistency**: All nodes see same data
+**Availability**: Every request gets response
+**Partition Tolerance**: System works despite network failures
+
+Can only guarantee 2 of 3:
+- **CP**: Consistent + Partition-tolerant (sacrifice availability)
+- **AP**: Available + Partition-tolerant (eventual consistency)
+- **CA**: Consistent + Available (no partition tolerance, single node)
+
+## Domain-Driven Design
+
+**Ubiquitous Language**: Shared vocabulary
+**Bounded Contexts**: Explicit boundaries
+**Aggregates**: Consistency boundaries
+**Entities**: Objects with identity
+**Value Objects**: Immutable, no identity
+**Domain Events**: Business occurrences