refactor(architecture): eliminate internal package and complete cordis single-owner model and repository migration

- Physically purged all legacy internal/ packages, centralized pkg/model/ and pkg/repository/
- Migrated domain models and database repositories into self-contained owner plugins (user, auth, message_gateway, admin, upload, risk_control)
- Decoupled cross-plugin interactions via pure core/contracts and typed EventBus
- Ensured 100% test coverage pass, zero data races (-race clean), and 0 lint issues in make code-check

pkg/persistence/batchwriter/config.go

@@ -0,0 +1,69 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package batchwriter
+
+import (
+	"fmt"
+	"time"
+)
+
+const (
+	defaultQueueSize    = 10_000
+	defaultMaxBatchSize = 1_000
+	defaultMinBatchSize = 50
+	defaultFlushEvery   = time.Second
+)
+
+// Config controls queue capacity and flush thresholds for a Writer instance.
+type Config struct {
+	// Name identifies the writer in logs and diagnostics. Optional.
+	Name string
+
+	// QueueSize is the buffered channel capacity.
+	QueueSize int
+
+	// MaxBatchSize triggers a flush when the in-memory batch reaches this count.
+	MaxBatchSize int
+
+	// MinBatchSize is the minimum in-memory batch size for time-based flushes.
+	// Zero disables the threshold and preserves legacy interval flush behavior.
+	// When set, interval flushes below this size are skipped unless MaxFlushWait elapses.
+	MinBatchSize int
+
+	// FlushInterval is how often the worker checks whether a time-based flush should run.
+	FlushInterval time.Duration
+
+	// MaxFlushWait forces a flush of any non-empty batch once the oldest item has waited
+	// this long, even if MinBatchSize has not been reached. Zero disables the force path.
+	MaxFlushWait time.Duration
+}
+
+// DefaultConfig returns production-friendly defaults aligned with audit log batching.
+func DefaultConfig() Config {
+	return Config{
+		QueueSize:     defaultQueueSize,
+		MaxBatchSize:  defaultMaxBatchSize,
+		MinBatchSize:  defaultMinBatchSize,
+		FlushInterval: defaultFlushEvery,
+	}
+}
+
+func (c Config) validate() error {
+	if c.QueueSize <= 0 {
+		return fmt.Errorf("batchwriter: queue size must be positive")
+	}
+	if c.MaxBatchSize <= 0 {
+		return fmt.Errorf("batchwriter: max batch size must be positive")
+	}
+	if c.MinBatchSize < 0 {
+		return fmt.Errorf("batchwriter: min batch size must be non-negative")
+	}
+	if c.FlushInterval <= 0 {
+		return fmt.Errorf("batchwriter: flush interval must be positive")
+	}
+	if c.MaxFlushWait < 0 {
+		return fmt.Errorf("batchwriter: max flush wait must be non-negative")
+	}
+	return nil
+}

pkg/persistence/batchwriter/errs.go

@@ -0,0 +1,8 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package batchwriter
+
+import "errors"
+
+var errNilFlushFunc = errors.New("batchwriter: flush func is required")

pkg/persistence/batchwriter/writer.go

@@ -0,0 +1,264 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+// Package batchwriter provides a reusable buffered batch writer for high-throughput
+// append-only sinks such as ClickHouse. Each business domain should own an independent
+// Writer instance with its own queue, flush callback, and tuning parameters.
+package batchwriter
+
+import (
+	"context"
+	"sync"
+	"sync/atomic"
+	"time"
+)
+
+// FlushFunc persists a batch of queued items. It is invoked from the worker goroutine.
+type FlushFunc[T any] func(ctx context.Context, items []T) error
+
+// FlushErrorHandler is called when FlushFunc returns an error after optional retries.
+// The batch is discarded after the handler returns; the worker continues processing.
+// Handlers receive the failed items so callers can release dedup keys or re-queue.
+type FlushErrorHandler[T any] func(ctx context.Context, items []T, err error)
+
+// Stats is a point-in-time snapshot of Writer queue and failure counters.
+type Stats struct {
+	Name        string
+	Depth       int
+	Cap         int
+	Drops       int64
+	FlushErrors int64
+	Running     bool
+}
+
+// Writer buffers items and flushes them by size or interval.
+type Writer[T any] struct {
+	cfg   Config
+	flush FlushFunc[T]
+
+	onFlushError FlushErrorHandler[T]
+	onDrop       func(T)
+
+	startOnce sync.Once
+	stopOnce  sync.Once
+
+	mu        sync.RWMutex
+	ch        chan T
+	workerCtx context.Context
+	done      chan struct{}
+
+	drops       atomic.Int64
+	flushErrors atomic.Int64
+}
+
+// Option configures optional Writer callbacks.
+type Option[T any] func(*Writer[T])
+
+// WithFlushErrorHandler registers a callback for flush failures.
+func WithFlushErrorHandler[T any](handler FlushErrorHandler[T]) Option[T] {
+	return func(w *Writer[T]) {
+		w.onFlushError = handler
+	}
+}
+
+// WithDropHandler registers a callback when TryEnqueue cannot accept an item.
+func WithDropHandler[T any](handler func(T)) Option[T] {
+	return func(w *Writer[T]) {
+		w.onDrop = handler
+	}
+}
+
+// New creates a Writer. Call Start before enqueueing items.
+func New[T any](cfg Config, flush FlushFunc[T], opts ...Option[T]) (*Writer[T], error) {
+	if flush == nil {
+		return nil, errNilFlushFunc
+	}
+	if err := cfg.validate(); err != nil {
+		return nil, err
+	}
+
+	w := &Writer[T]{
+		cfg:   cfg,
+		flush: flush,
+		done:  make(chan struct{}),
+	}
+	for _, opt := range opts {
+		opt(w)
+	}
+	return w, nil
+}
+
+// Start launches the background worker. It is safe to call at most once.
+func (w *Writer[T]) Start(parent context.Context) {
+	w.startOnce.Do(func() {
+		w.mu.Lock()
+		defer w.mu.Unlock()
+
+		w.ch = make(chan T, w.cfg.QueueSize)
+		w.workerCtx = context.WithoutCancel(parent)
+		go w.run()
+	})
+}
+
+// Stop closes the queue and waits until the worker drains pending items and exits.
+func (w *Writer[T]) Stop(ctx context.Context) error {
+	w.mu.RLock()
+	ch := w.ch
+	done := w.done
+	w.mu.RUnlock()
+
+	if ch == nil {
+		return nil
+	}
+
+	w.stopOnce.Do(func() {
+		close(ch)
+	})
+
+	select {
+	case <-done:
+		return nil
+	case <-ctx.Done():
+		return ctx.Err()
+	}
+}
+
+// Running reports whether Start has been called and Stop has not completed.
+func (w *Writer[T]) Running() bool {
+	w.mu.RLock()
+	defer w.mu.RUnlock()
+	if w.ch == nil {
+		return false
+	}
+	select {
+	case <-w.done:
+		return false
+	default:
+		return true
+	}
+}
+
+// TryEnqueue adds one item without blocking. It returns false when the writer is not
+// running or the queue is full.
+func (w *Writer[T]) TryEnqueue(item T) bool {
+	w.mu.RLock()
+	ch := w.ch
+	w.mu.RUnlock()
+	if ch == nil {
+		w.notifyDrop(item)
+		return false
+	}
+
+	select {
+	case ch <- item:
+		return true
+	default:
+		w.notifyDrop(item)
+		return false
+	}
+}
+
+// IsFull reports whether the queue has no remaining capacity.
+func (w *Writer[T]) IsFull() bool {
+	w.mu.RLock()
+	defer w.mu.RUnlock()
+	if w.ch == nil {
+		return false
+	}
+	return len(w.ch) >= cap(w.ch)
+}
+
+// Len returns the current queue depth.
+func (w *Writer[T]) Len() int {
+	w.mu.RLock()
+	defer w.mu.RUnlock()
+	if w.ch == nil {
+		return 0
+	}
+	return len(w.ch)
+}
+
+// Cap returns the queue capacity.
+func (w *Writer[T]) Cap() int {
+	return w.cfg.QueueSize
+}
+
+// Stats returns a point-in-time snapshot of queue depth and failure counters.
+func (w *Writer[T]) Stats() Stats {
+	return Stats{
+		Name:        w.cfg.Name,
+		Depth:       w.Len(),
+		Cap:         w.Cap(),
+		Drops:       w.drops.Load(),
+		FlushErrors: w.flushErrors.Load(),
+		Running:     w.Running(),
+	}
+}
+
+func (w *Writer[T]) run() {
+	ticker := time.NewTicker(w.cfg.FlushInterval)
+	defer ticker.Stop()
+
+	batch := make([]T, 0, w.cfg.MaxBatchSize)
+	var batchStartedAt time.Time
+	flush := func() {
+		if len(batch) == 0 {
+			return
+		}
+		items := append([]T(nil), batch...)
+		if err := w.flush(w.workerCtx, items); err != nil {
+			w.flushErrors.Add(1)
+			if w.onFlushError != nil {
+				w.onFlushError(w.workerCtx, items, err)
+			}
+		}
+		batch = batch[:0]
+		batchStartedAt = time.Time{}
+	}
+
+	defer func() {
+		flush()
+		close(w.done)
+	}()
+
+	for {
+		select {
+		case item, ok := <-w.ch:
+			if !ok {
+				return
+			}
+			if len(batch) == 0 {
+				batchStartedAt = time.Now()
+			}
+			batch = append(batch, item)
+			if len(batch) >= w.cfg.MaxBatchSize {
+				flush()
+			}
+		case <-ticker.C:
+			if w.shouldFlushOnInterval(len(batch), batchStartedAt, time.Now()) {
+				flush()
+			}
+		}
+	}
+}
+
+func (w *Writer[T]) shouldFlushOnInterval(batchLen int, batchStartedAt time.Time, now time.Time) bool {
+	if batchLen == 0 {
+		return false
+	}
+	if w.cfg.MinBatchSize == 0 || batchLen >= w.cfg.MinBatchSize {
+		return true
+	}
+	if w.cfg.MaxFlushWait <= 0 || batchStartedAt.IsZero() {
+		return false
+	}
+	return !now.Before(batchStartedAt.Add(w.cfg.MaxFlushWait))
+}
+
+func (w *Writer[T]) notifyDrop(item T) {
+	w.drops.Add(1)
+	if w.onDrop == nil {
+		return
+	}
+	w.onDrop(item)
+}

pkg/persistence/batchwriter/writer_test.go

@@ -0,0 +1,491 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package batchwriter
+
+import (
+	"context"
+	"errors"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+func TestNewRejectsInvalidConfig(t *testing.T) {
+	t.Parallel()
+
+	_, err := New[int](Config{}, func(context.Context, []int) error { return nil })
+	if err == nil {
+		t.Fatal("New() = nil, want validation error")
+	}
+}
+
+func TestNewRejectsNilFlushFunc(t *testing.T) {
+	t.Parallel()
+
+	cfg := DefaultConfig()
+	_, err := New[int](cfg, nil)
+	if !errors.Is(err, errNilFlushFunc) {
+		t.Fatalf("New() error = %v, want %v", err, errNilFlushFunc)
+	}
+}
+
+func TestWriterFlushesOnMaxBatchSize(t *testing.T) {
+	t.Parallel()
+
+	var (
+		mu      sync.Mutex
+		batches [][]int
+	)
+	cfg := DefaultConfig()
+	cfg.MaxBatchSize = 3
+	cfg.FlushInterval = time.Hour
+
+	writer, err := New[int](cfg, func(_ context.Context, items []int) error {
+		mu.Lock()
+		defer mu.Unlock()
+		batches = append(batches, append([]int(nil), items...))
+		return nil
+	})
+	if err != nil {
+		t.Fatalf("New() error = %v", err)
+	}
+
+	writer.Start(context.Background())
+	t.Cleanup(func() {
+		stopCtx, cancel := context.WithTimeout(context.Background(), time.Second)
+		defer cancel()
+		if err := writer.Stop(stopCtx); err != nil {
+			t.Fatalf("Stop() error = %v", err)
+		}
+	})
+
+	for i := range 3 {
+		if !writer.TryEnqueue(i + 1) {
+			t.Fatalf("TryEnqueue(%d) = false, want true", i+1)
+		}
+	}
+
+	deadline := time.Now().Add(time.Second)
+	for {
+		mu.Lock()
+		ready := len(batches) == 1
+		mu.Unlock()
+		if ready || time.Now().After(deadline) {
+			break
+		}
+		time.Sleep(10 * time.Millisecond)
+	}
+
+	mu.Lock()
+	got := batches
+	mu.Unlock()
+
+	want := [][]int{{1, 2, 3}}
+	if diff := cmp.Diff(want, got); diff != "" {
+		t.Fatalf("flush batches mismatch (-want +got):\n%s", diff)
+	}
+}
+
+func TestWriterFlushesOnInterval(t *testing.T) {
+	t.Parallel()
+
+	var (
+		mu    sync.Mutex
+		batch []int
+	)
+	cfg := DefaultConfig()
+	cfg.MaxBatchSize = 100
+	cfg.MinBatchSize = 0
+	cfg.FlushInterval = 20 * time.Millisecond
+
+	writer, err := New[int](cfg, func(_ context.Context, items []int) error {
+		mu.Lock()
+		defer mu.Unlock()
+		batch = append([]int(nil), items...)
+		return nil
+	})
+	if err != nil {
+		t.Fatalf("New() error = %v", err)
+	}
+
+	writer.Start(context.Background())
+	t.Cleanup(func() {
+		stopCtx, cancel := context.WithTimeout(context.Background(), time.Second)
+		defer cancel()
+		if err := writer.Stop(stopCtx); err != nil {
+			t.Fatalf("Stop() error = %v", err)
+		}
+	})
+
+	if !writer.TryEnqueue(42) {
+		t.Fatal("TryEnqueue() = false, want true")
+	}
+
+	deadline := time.Now().Add(time.Second)
+	for {
+		mu.Lock()
+		ready := len(batch) == 1
+		mu.Unlock()
+		if ready || time.Now().After(deadline) {
+			break
+		}
+		time.Sleep(5 * time.Millisecond)
+	}
+
+	mu.Lock()
+	got := batch
+	mu.Unlock()
+
+	want := []int{42}
+	if diff := cmp.Diff(want, got); diff != "" {
+		t.Fatalf("interval flush mismatch (-want +got):\n%s", diff)
+	}
+}
+
+func TestWriterTryEnqueueDropsWhenFull(t *testing.T) {
+	t.Parallel()
+
+	cfg := DefaultConfig()
+	cfg.QueueSize = 1
+	cfg.MaxBatchSize = 10
+	cfg.FlushInterval = time.Hour
+
+	var dropped int
+	writer, err := New[int](cfg, func(context.Context, []int) error { return nil }, WithDropHandler[int](func(int) {
+		dropped++
+	}))
+	if err != nil {
+		t.Fatalf("New() error = %v", err)
+	}
+
+	writer.Start(context.Background())
+	t.Cleanup(func() {
+		stopCtx, cancel := context.WithTimeout(context.Background(), time.Second)
+		defer cancel()
+		_ = writer.Stop(stopCtx)
+	})
+
+	if !writer.TryEnqueue(1) {
+		t.Fatal("TryEnqueue(1) = false, want true")
+	}
+	if writer.TryEnqueue(2) {
+		t.Fatal("TryEnqueue(2) = true, want false")
+	}
+	if !writer.IsFull() {
+		t.Fatal("IsFull() = false, want true")
+	}
+	if dropped != 1 {
+		t.Fatalf("dropped = %d, want 1", dropped)
+	}
+}
+
+func TestWriterStopDrainsQueuedItems(t *testing.T) {
+	t.Parallel()
+
+	cfg := DefaultConfig()
+	cfg.MaxBatchSize = 10
+	cfg.FlushInterval = time.Hour
+
+	var flushed []int
+	writer, err := New[int](cfg, func(_ context.Context, items []int) error {
+		flushed = append(flushed, items...)
+		return nil
+	})
+	if err != nil {
+		t.Fatalf("New() error = %v", err)
+	}
+
+	writer.Start(context.Background())
+	for i := range 2 {
+		if !writer.TryEnqueue(i + 1) {
+			t.Fatalf("TryEnqueue(%d) = false, want true", i+1)
+		}
+	}
+
+	stopCtx, cancel := context.WithTimeout(context.Background(), time.Second)
+	defer cancel()
+	if err := writer.Stop(stopCtx); err != nil {
+		t.Fatalf("Stop() error = %v", err)
+	}
+
+	want := []int{1, 2}
+	if diff := cmp.Diff(want, flushed); diff != "" {
+		t.Fatalf("Stop() drain mismatch (-want +got):\n%s", diff)
+	}
+	if writer.Running() {
+		t.Fatal("Running() = true after Stop(), want false")
+	}
+}
+
+func TestWriterInvokesFlushErrorHandler(t *testing.T) {
+	t.Parallel()
+
+	cfg := DefaultConfig()
+	cfg.MaxBatchSize = 1
+	cfg.FlushInterval = time.Hour
+
+	flushErr := errors.New("flush failed")
+	var (
+		mu       sync.Mutex
+		errCount int
+		gotItems []int
+	)
+
+	writer, err := New[int](cfg, func(context.Context, []int) error {
+		return flushErr
+	}, WithFlushErrorHandler[int](func(_ context.Context, items []int, err error) {
+		mu.Lock()
+		defer mu.Unlock()
+		errCount++
+		gotItems = append([]int(nil), items...)
+		if !errors.Is(err, flushErr) {
+			t.Errorf("flush error = %v, want %v", err, flushErr)
+		}
+	}))
+	if err != nil {
+		t.Fatalf("New() error = %v", err)
+	}
+
+	writer.Start(context.Background())
+	t.Cleanup(func() {
+		stopCtx, cancel := context.WithTimeout(context.Background(), time.Second)
+		defer cancel()
+		_ = writer.Stop(stopCtx)
+	})
+
+	if !writer.TryEnqueue(7) {
+		t.Fatal("TryEnqueue() = false, want true")
+	}
+
+	deadline := time.Now().Add(time.Second)
+	for {
+		mu.Lock()
+		ready := errCount == 1
+		mu.Unlock()
+		if ready || time.Now().After(deadline) {
+			break
+		}
+		time.Sleep(5 * time.Millisecond)
+	}
+
+	mu.Lock()
+	gotCount := errCount
+	items := gotItems
+	mu.Unlock()
+
+	if gotCount != 1 {
+		t.Fatalf("flush error handler count = %d, want 1", gotCount)
+	}
+	if diff := cmp.Diff([]int{7}, items); diff != "" {
+		t.Fatalf("flush error handler items mismatch (-want +got):\n%s", diff)
+	}
+
+	stats := writer.Stats()
+	if stats.FlushErrors != 1 {
+		t.Fatalf("Stats().FlushErrors = %d, want 1", stats.FlushErrors)
+	}
+}
+
+func TestWriterSkipsIntervalFlushBelowMinBatchSize(t *testing.T) {
+	t.Parallel()
+
+	var (
+		mu    sync.Mutex
+		batch []int
+	)
+	cfg := DefaultConfig()
+	cfg.MaxBatchSize = 100
+	cfg.MinBatchSize = 5
+	cfg.FlushInterval = 20 * time.Millisecond
+
+	writer, err := New[int](cfg, func(_ context.Context, items []int) error {
+		mu.Lock()
+		defer mu.Unlock()
+		batch = append([]int(nil), items...)
+		return nil
+	})
+	if err != nil {
+		t.Fatalf("New() error = %v", err)
+	}
+
+	writer.Start(context.Background())
+	t.Cleanup(func() {
+		stopCtx, cancel := context.WithTimeout(context.Background(), time.Second)
+		defer cancel()
+		if err := writer.Stop(stopCtx); err != nil {
+			t.Fatalf("Stop() error = %v", err)
+		}
+	})
+
+	for i := range 3 {
+		if !writer.TryEnqueue(i + 1) {
+			t.Fatalf("TryEnqueue(%d) = false, want true", i+1)
+		}
+	}
+
+	time.Sleep(100 * time.Millisecond)
+
+	mu.Lock()
+	got := batch
+	mu.Unlock()
+
+	if len(got) != 0 {
+		t.Fatalf("interval flush with below-min batch = %v, want no flush", got)
+	}
+}
+
+func TestWriterFlushesOnIntervalWhenMinBatchSizeReached(t *testing.T) {
+	t.Parallel()
+
+	var (
+		mu    sync.Mutex
+		batch []int
+	)
+	cfg := DefaultConfig()
+	cfg.MaxBatchSize = 100
+	cfg.MinBatchSize = 3
+	cfg.FlushInterval = 20 * time.Millisecond
+
+	writer, err := New[int](cfg, func(_ context.Context, items []int) error {
+		mu.Lock()
+		defer mu.Unlock()
+		batch = append([]int(nil), items...)
+		return nil
+	})
+	if err != nil {
+		t.Fatalf("New() error = %v", err)
+	}
+
+	writer.Start(context.Background())
+	t.Cleanup(func() {
+		stopCtx, cancel := context.WithTimeout(context.Background(), time.Second)
+		defer cancel()
+		if err := writer.Stop(stopCtx); err != nil {
+			t.Fatalf("Stop() error = %v", err)
+		}
+	})
+
+	for i := range 3 {
+		if !writer.TryEnqueue(i + 1) {
+			t.Fatalf("TryEnqueue(%d) = false, want true", i+1)
+		}
+	}
+
+	deadline := time.Now().Add(time.Second)
+	for {
+		mu.Lock()
+		ready := len(batch) == 3
+		mu.Unlock()
+		if ready || time.Now().After(deadline) {
+			break
+		}
+		time.Sleep(5 * time.Millisecond)
+	}
+
+	mu.Lock()
+	got := batch
+	mu.Unlock()
+
+	want := []int{1, 2, 3}
+	if diff := cmp.Diff(want, got); diff != "" {
+		t.Fatalf("interval flush at min batch size mismatch (-want +got):\n%s", diff)
+	}
+}
+
+func TestWriterForcesFlushAfterMaxFlushWait(t *testing.T) {
+	t.Parallel()
+
+	var (
+		mu    sync.Mutex
+		batch []int
+	)
+	cfg := DefaultConfig()
+	cfg.MaxBatchSize = 100
+	cfg.MinBatchSize = 50
+	cfg.FlushInterval = 20 * time.Millisecond
+	cfg.MaxFlushWait = 80 * time.Millisecond
+
+	writer, err := New[int](cfg, func(_ context.Context, items []int) error {
+		mu.Lock()
+		defer mu.Unlock()
+		batch = append([]int(nil), items...)
+		return nil
+	})
+	if err != nil {
+		t.Fatalf("New() error = %v", err)
+	}
+
+	writer.Start(context.Background())
+	t.Cleanup(func() {
+		stopCtx, cancel := context.WithTimeout(context.Background(), time.Second)
+		defer cancel()
+		if err := writer.Stop(stopCtx); err != nil {
+			t.Fatalf("Stop() error = %v", err)
+		}
+	})
+
+	if !writer.TryEnqueue(1) {
+		t.Fatal("TryEnqueue(1) = false, want true")
+	}
+
+	deadline := time.Now().Add(time.Second)
+	for {
+		mu.Lock()
+		ready := len(batch) == 1
+		mu.Unlock()
+		if ready || time.Now().After(deadline) {
+			break
+		}
+		time.Sleep(5 * time.Millisecond)
+	}
+
+	mu.Lock()
+	got := batch
+	mu.Unlock()
+	if diff := cmp.Diff([]int{1}, got); diff != "" {
+		t.Fatalf("max flush wait mismatch (-want +got):\n%s", diff)
+	}
+}
+
+func TestWriterStatsTracksDrops(t *testing.T) {
+	t.Parallel()
+
+	cfg := DefaultConfig()
+	cfg.Name = "test-drops"
+	cfg.QueueSize = 1
+	cfg.MaxBatchSize = 10
+	cfg.FlushInterval = time.Hour
+
+	writer, err := New[int](cfg, func(context.Context, []int) error { return nil })
+	if err != nil {
+		t.Fatalf("New() error = %v", err)
+	}
+
+	writer.Start(context.Background())
+	t.Cleanup(func() {
+		stopCtx, cancel := context.WithTimeout(context.Background(), time.Second)
+		defer cancel()
+		_ = writer.Stop(stopCtx)
+	})
+
+	if !writer.TryEnqueue(1) {
+		t.Fatal("TryEnqueue(1) = false, want true")
+	}
+	if writer.TryEnqueue(2) {
+		t.Fatal("TryEnqueue(2) = true, want false")
+	}
+
+	stats := writer.Stats()
+	if stats.Drops != 1 {
+		t.Fatalf("Stats().Drops = %d, want 1", stats.Drops)
+	}
+	if stats.Cap != 1 {
+		t.Fatalf("Stats().Cap = %d, want 1", stats.Cap)
+	}
+	if !stats.Running {
+		t.Fatal("Stats().Running = false, want true")
+	}
+}