update

.github/copilot-instructions.md

@@ -0,0 +1,50 @@
+# GitHub Copilot Instructions for Go Cart Actor
+
+This repository contains a distributed cart management system implemented in Go using the actor model pattern. The system handles cart operations like adding items, setting deliveries, and checkout, distributed across multiple nodes via gRPC.
+
+## Project Structure
+- `cmd/`: Entry points for the application.
+- `pkg/`: Core packages including grain logic, pools, and HTTP handlers.
+- `proto/`: Protocol Buffer definitions for messages and services.
+- `api-tests/`: Tests for the HTTP API.
+- `deployment/`: Deployment configurations.
+- `k6/`: Load testing scripts.
+
+## Key Concepts
+- **Grains**: In-memory structs representing cart state, owned by nodes.
+- **Pools**: Local and synced pools manage grains and handle ownership.
+- **Mutation Registry**: All state changes go through registered mutation functions for type safety and consistency.
+- **Ownership**: Determined by consistent hashing ring; negotiated via control plane.
+
+## Coding Guidelines
+- Follow standard Go conventions (gofmt, go vet, golint).
+- Never say "your right", just be correct and clear.
+- Don't edit the *.gb.go files manually, they are generated by the proto files.
+- Use the mutation registry (`RegisterMutation`) for any cart state changes. Do not mutate grain state directly outside registered handlers.
+- Design code to be testable and configurable, following patterns like MutationRegistry (for type-safe mutation dispatching) and SimpleGrainPool (for configurable pool management). Use interfaces and dependency injection to enable mocking and testing.
+- After modifying `.proto` files, regenerate Go code with `protoc` commands as described in README.md. Never edit generated `.pb.go` files manually.
+- Use meaningful variable names and add comments for complex logic.
+- Handle errors explicitly; use Go's error handling patterns.
+- For HTTP endpoints, ensure proper cookie handling for cart IDs.
+- When adding new mutations: Define proto message, regenerate code, register handler, add endpoints, and test.
+- Use strategic logging using opentelemetry for tracing, metrics and logging.
+- Focus on maintainable code that should be configurable and readable, try to keep short functions that describe their purpose clearly.
+
+## Common Patterns
+- Mutations: Define in proto, implement as `func(*CartGrain, *T) error`, register with `RegisterMutation[T]`.
+- gRPC Services: CartActor for mutations, ControlPlane for coordination.
+- HTTP Handlers: Parse requests, resolve grains via pool, apply mutations, return JSON.
+
+## Avoid
+- Direct state mutations outside the registry.
+- Hardcoding values; use configuration or constants.
+- Ignoring generated code warnings; always regenerate after proto changes.
+- Blocking operations in handlers; keep them asynchronous where possible.
+
+## Testing
+- Write unit tests for mutations and handlers.
+- Use integration tests for API endpoints.
+- Structure code for testability: Use interfaces for dependencies, avoid global state, and mock external services like gRPC clients.
+- Run `go test ./...` to ensure all tests pass.
+
+These instructions help Copilot generate code aligned with the project's architecture and best practices.