feat: microservice architecture

docs/content/adr/0029-microservices-architecture.md

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+# ADR-0029: Microservices Architecture
+
+## Status
+Accepted
+
+## Context
+The platform needs to scale independently, support team autonomy, and enable flexible deployment. A microservices architecture provides these benefits from day one, and the complexity of supporting both monolith and microservices modes is unnecessary.
+
+## Decision
+Design the platform as **microservices architecture from day one**:
+
+1. **Service-Based Architecture**: All modules are independent services:
+   - Each module is a separate service with its own process
+   - Services communicate via gRPC (primary) or HTTP (fallback)
+   - Service client interfaces for all inter-service communication
+   - No direct in-process calls between services
+
+2. **Service Registry**: Central registry for service discovery:
+   - All services register on startup
+   - Service discovery via registry
+   - Health checking and automatic deregistration
+   - Support for Consul, etcd, or Kubernetes service discovery
+
+3. **Communication Patterns**:
+   - **Synchronous**: gRPC service calls (primary), HTTP/REST (fallback)
+   - **Asynchronous**: Event bus via Kafka
+   - **Shared State**: Cache (Redis) and Database (PostgreSQL)
+
+4. **Service Boundaries**: Each module is an independent service:
+   - Independent Go modules (`go.mod`)
+   - Own database schema (via Ent)
+   - Own API routes
+   - Own process and deployment
+   - Can be scaled independently
+
+5. **Development Simplification**: For local development, multiple services can run in the same process, but they still communicate via service clients (no direct calls)
+
+## Consequences
+
+### Positive
+- **Simplified Architecture**: Single architecture pattern, no dual-mode complexity
+- **Independent Scaling**: Scale individual services based on load
+- **Team Autonomy**: Teams can own and deploy their services independently
+- **Technology Diversity**: Different services can use different tech stacks (future)
+- **Fault Isolation**: Failure in one service doesn't bring down entire platform
+- **Deployment Flexibility**: Deploy services independently
+- **Clear Boundaries**: Service boundaries are explicit from the start
+
+### Negative
+- **Network Latency**: Inter-service calls have network overhead
+- **Distributed System Challenges**: Need to handle network failures, retries, timeouts
+- **Service Discovery Overhead**: Additional infrastructure needed
+- **Debugging Complexity**: Distributed tracing becomes essential
+- **Data Consistency**: Cross-service transactions become challenging
+- **Development Setup**: More complex local development (multiple services)
+
+### Mitigations
+- **Service Mesh**: Use service mesh (Istio, Linkerd) for advanced microservices features
+- **API Gateway**: Central gateway for routing and cross-cutting concerns
+- **Event Sourcing**: Use events for eventual consistency
+- **Circuit Breakers**: Implement circuit breakers for resilience
+- **Comprehensive Observability**: OpenTelemetry, metrics, logging essential
+- **Docker Compose**: Simplify local development with docker-compose
+- **Development Mode**: Run multiple services in same process for local dev (still use service clients)
+
+## Implementation Strategy
+
+### Phase 1: Service Client Interfaces (Phase 1)
+- Define service client interfaces for all core services
+- All inter-service communication goes through interfaces
+
+### Phase 2: Service Registry (Phase 3)
+- Create service registry interface
+- Implement service discovery
+- Support for Consul, Kubernetes service discovery
+
+### Phase 3: gRPC Services (Phase 5)
+- Implement gRPC service definitions
+- Create gRPC servers for all services
+- Create gRPC clients for service communication
+- HTTP clients as fallback option
+
+## References
+- [Service Abstraction Pattern](https://microservices.io/patterns/data/service-per-database.html)
+- [Service Discovery Patterns](https://microservices.io/patterns/service-registry.html)
+- [gRPC Documentation](https://grpc.io/docs/)
+