feat(logz)!: promote to v1.0.0 — configurable io.Writer output destination

Add Writer io.Writer field to Options; when nil, defaults to os.Stdout (no
breaking change). Enables log capture in tests via the public API and supports
writing to files, multi-writers, or any io.Writer implementation in production.
All remaining roadmap items validated in production (xerrors enrichment
concurrency, WithFields merge semantics, Logger interface finality). API
committed as stable.

CHANGELOG.md

@@ -5,6 +5,21 @@ All notable changes to this module will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this module adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [1.0.0] — 2026-05-12
+
+### Added
+
+- `Options.Writer io.Writer` — configurable output destination; `nil` defaults
+  to `os.Stdout` (backward-compatible). Accepts any `io.Writer` implementation:
+  `*os.File`, `bytes.Buffer`, `io.MultiWriter`, custom sinks, etc.
+
+### Unchanged
+
+All existing API (`Logger`, `New`, `WithRequestID`, `GetRequestID`, `WithField`,
+`WithFields`) is API-compatible with v0.9.0.
+
+[1.0.0]: https://code.nochebuena.dev/go/logz/releases/tag/v1.0.0
+
 ## [0.9.0] - 2026-03-18
 
 ### Added

logz.go

@@ -3,6 +3,7 @@ package logz
 import (
 	"context"
 	"errors"
+	"io"
 	"log/slog"
 	"os"
 )
@@ -20,7 +21,7 @@ type errorWithContext interface {
 }
 
 // Options configures a Logger instance.
-// The zero value is valid: INFO level, text output, no static args.
+// The zero value is valid: INFO level, text output, os.Stdout, no static args.
 type Options struct {
 	// Level is the minimum log level. Default: slog.LevelInfo (zero value).
 	Level slog.Level
@@ -28,6 +29,9 @@ type Options struct {
 	JSON bool
 	// StaticArgs are key-value pairs attached to every log record.
 	StaticArgs []any
+	// Writer is the output destination. Defaults to os.Stdout when nil.
+	// Accepts any io.Writer: *os.File, bytes.Buffer, io.MultiWriter, etc.
+	Writer io.Writer
 }
 
 // Logger is the interface for structured logging.
@@ -56,16 +60,17 @@ type slogLogger struct {
 
 // New returns a new Logger configured by opts.
 func New(opts Options) Logger {
-	handlerOpts := &slog.HandlerOptions{
+	w := opts.Writer
-		Level:     opts.Level,
+	if w == nil {
-		AddSource: false,
+		w = os.Stdout
 	}
 
+	handlerOpts := &slog.HandlerOptions{Level: opts.Level}
 	var handler slog.Handler
 	if opts.JSON {
-		handler = slog.NewJSONHandler(os.Stdout, handlerOpts)
+		handler = slog.NewJSONHandler(w, handlerOpts)
 	} else {
-		handler = slog.NewTextHandler(os.Stdout, handlerOpts)
+		handler = slog.NewTextHandler(w, handlerOpts)
 	}
 
 	base := slog.New(handler)

logz_test.go

@@ -36,9 +36,8 @@ func (e *errFull) ErrorContext() map[string]any { return e.fields }
 // Helper: logger that writes to a buffer for inspection
 // ---------------------------------------------------------------
 
-func newTestLogger(buf *bytes.Buffer, level slog.Level) *slogLogger {
+func newTestLogger(buf *bytes.Buffer, level slog.Level) Logger {
-	handler := slog.NewJSONHandler(buf, &slog.HandlerOptions{Level: level})
+	return New(Options{Writer: buf, Level: level, JSON: true})
-	return &slogLogger{logger: slog.New(handler)}
 }
 
 // ---------------------------------------------------------------
@@ -56,10 +55,8 @@ func TestNew_ZeroOptions(t *testing.T) {
 
 func TestNew_JSONFormat(t *testing.T) {
 	var buf bytes.Buffer
-	sl := &slogLogger{
+	l := New(Options{JSON: true, Writer: &buf})
-		logger: slog.New(slog.NewJSONHandler(&buf, &slog.HandlerOptions{Level: slog.LevelInfo})),
+	l.Info("json test", "key", "value")
-	}
-	sl.Info("json test", "key", "value")
 
 	var out map[string]any
 	if err := json.Unmarshal(buf.Bytes(), &out); err != nil {
@@ -70,13 +67,19 @@ func TestNew_JSONFormat(t *testing.T) {
 	}
 }
 
+func TestNew_Writer(t *testing.T) {
+	var buf bytes.Buffer
+	l := New(Options{Writer: &buf})
+	l.Info("writer test")
+	if !strings.Contains(buf.String(), "writer test") {
+		t.Errorf("output not written to provided writer: %s", buf.String())
+	}
+}
+
 func TestNew_StaticArgs(t *testing.T) {
 	var buf bytes.Buffer
-	handler := slog.NewJSONHandler(&buf, &slog.HandlerOptions{Level: slog.LevelInfo})
+	l := New(Options{Writer: &buf, JSON: true, StaticArgs: []any{"service", "test-svc"}})
-	base := slog.New(handler).With("service", "test-svc")
+	l.Info("static args test")
-	sl := &slogLogger{logger: base}
-
-	sl.Info("static args test")
 
 	if !strings.Contains(buf.String(), "test-svc") {
 		t.Errorf("static arg not found in output: %s", buf.String())