-`Options` struct — `Level slog.Level` (minimum log level; default `slog.LevelInfo`), `JSON bool` (JSON vs text output; default text), `StaticArgs []any` (key-value pairs attached to every record); zero value is valid
-`New(opts Options) Logger` — constructs a `Logger` backed by `log/slog`, writing to `os.Stdout`; returns the `Logger` interface, never the concrete type
-`WithRequestID(ctx context.Context, id string) context.Context` — stores a request correlation ID in the context under a private unexported key owned by this package
-`GetRequestID(ctx context.Context) string` — retrieves the correlation ID; returns `""` if absent or if ctx is nil
-`WithField(ctx context.Context, key string, value any) context.Context` — adds a single key-value logging field to the context
-`WithFields(ctx context.Context, fields map[string]any) context.Context` — merges multiple key-value fields into the context without overwriting existing fields
-`Logger.WithContext(ctx context.Context) Logger` — returns a child logger pre-enriched with `request_id` and any extra fields stored in the context via `WithRequestID` / `WithField` / `WithFields`; returns the same logger unchanged if ctx is nil or carries no relevant values
-`Logger.With(args ...any) Logger` — returns a child logger with the given key-value attributes permanently attached to every subsequent record
- Automatic `error_code` field enrichment in `Logger.Error` when `err` satisfies the private `errorWithCode` duck-type interface (`ErrorCode() string`)
- Automatic context-field enrichment in `Logger.Error` when `err` satisfies the private `errorWithContext` duck-type interface (`ErrorContext() map[string]any`)
### Design Notes
-`New` returns the `Logger` interface (not `*slogLogger`), and `With` likewise returns `Logger`; the concrete type is never exported, making the interface the only public surface and enabling safe local re-declaration in downstream libraries without importing this package.
- This package owns the context keys `ctxRequestIDKey{}` and `ctxExtraFieldsKey{}` as unexported struct types, preventing collisions; any module that needs to attach a request ID to logs imports only `logz`.
- The xerrors integration is zero-import: `Logger.Error` uses `errors.As` against two private interfaces (`errorWithCode`, `errorWithContext`) that `xerrors.Err` satisfies — no import between the two packages is required in either direction.
