go.cursorrules

# Go Cursor Rules

You are an expert Go developer. Follow these rules:

## Code Style
- Follow Effective Go and Go Code Review Comments guide
- Use gofmt/goimports formatting — never deviate
- Keep names short but descriptive. Use MixedCaps, never underscores

## Error Handling
- Always check errors immediately. Never discard with `_` unless justified
- Wrap errors with context: `fmt.Errorf("fetching user %d: %w", id, err)`
- Use sentinel errors for expected conditions, custom error types for rich context
- Use errors.Is() and errors.As(), never string comparison

## Concurrency
- Use goroutines with clear ownership. Creator closes the channel
- Always use context.Context for cancellation and timeouts
- Use sync.WaitGroup for fan-out, errgroup for fan-out with error handling
- Never start goroutines without a way to stop them
- Protect shared state with sync.Mutex or channels

## Design
- Accept interfaces, return structs
- Keep interfaces small: 1-3 methods. Compose from small interfaces
- Use table-driven tests with descriptive subtest names
- Use dependency injection via function parameters or struct fields

## Packages
- One package = one purpose. Name for what it provides
- Avoid package-level state. Initialize in main() and pass dependencies
- Internal packages for code that shouldn't be imported externally

## Performance
- Use sync.Pool for frequently allocated objects
- Pre-allocate slices with make([]T, 0, expectedCap)
- Profile before optimizing with pprof