Go Error Handling

Go's explicit error handling is a feature, not a limitation. These patterns ensure errors are informative, actionable, and properly propagated.

1. Error Decision Tree

When creating or returning an error, follow this tree:

1. Simple, no extra context needed? → errors.New("message")
2. Need to add context to existing error? → fmt.Errorf("doing X: %w", err)
3. Caller needs to detect this error? → Sentinel var or custom type
4. Error carries structured data? → Custom type implementing error
5. Propagating from downstream? → Wrap with %w and add context

2. Sentinel Errors

Use package-level var for errors that callers need to check: