Go Error Handling

Idiomatic Go error handling with explicit error returns

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Rules

Go Error Handling · balanced balanced

- Always check returned errors immediately with `if err != nil` — never discard errors with `_`.

- Use `fmt.Errorf("context: %w", err)` to wrap errors with context while preserving the error chain.

- Use sentinel errors (`var ErrNotFound = errors.New("not found")`) for expected error conditions that callers check with `errors.Is`.

- Return `(value, error)` pairs from functions — never use panics for expected error conditions.

- Use `errors.Is(err, target)` to check for specific errors in the chain, not `err == target`.

- Use `errors.As(err, &target)` to extract typed errors from wrapped chains.

- Create custom error types implementing the `error` interface for errors that carry structured data (status codes, fields).

- Use `defer` for cleanup in error paths — ensures resources are released even when returning early.

- Wrap errors at each layer boundary with additional context: `fmt.Errorf("repository.GetUser: %w", err)`.