refactor(app): 优化后台任务退出与外部 IMAP 认证

- 统一用 `WaitGroup` 管理后台 worker，关闭时等待任务结束后再释放数据库连接。
- 将外部 IMAP 的 OAuth 认证切换为 `XOAUTH2` 客户端实现，并补充对应格式测试。
- 调整发送队列的故障恢复逻辑，超时中断后恢复为排队状态以便重新投递。

apps/api/internal/app/app.go

@@ -15,6 +15,7 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+	"sync"
 	"time"
 
 	"golang.org/x/crypto/bcrypt"
@@ -28,6 +29,7 @@ type App struct {
 	now           func() time.Time
 	policy        *HTMLPolicy
 	workerCancel  context.CancelFunc
+	workerWG      sync.WaitGroup
 	maildirHealth *maildirSyncHealthTracker
 	externalIMAP  externalIMAPClientFactory
 }
@@ -73,16 +75,24 @@ func New(cfg Config, logger *slog.Logger) (*App, error) {
 	}
 	workerCtx, cancel := context.WithCancel(context.Background())
 	a.workerCancel = cancel
-	go a.scheduledSendWorker(workerCtx)
+	a.startWorker(func() { a.scheduledSendWorker(workerCtx) })
 	if strings.TrimSpace(a.cfg.MaildirRoot) != "" {
-		go a.maildirWorker(workerCtx)
+		a.startWorker(func() { a.maildirWorker(workerCtx) })
 	}
-	go a.sendQueueWorker(workerCtx)
+	a.startWorker(func() { a.sendQueueWorker(workerCtx) })
-	go a.externalIMAPWorker(workerCtx)
+	a.startWorker(func() { a.externalIMAPWorker(workerCtx) })
-	go a.smtpEventsCleanupWorker(workerCtx)
+	a.startWorker(func() { a.smtpEventsCleanupWorker(workerCtx) })
 	return a, nil
 }
 
+func (a *App) startWorker(fn func()) {
+	a.workerWG.Add(1)
+	go func() {
+		defer a.workerWG.Done()
+		fn()
+	}()
+}
+
 func (a *App) Close() error {
 	if a == nil || a.db == nil {
 		return nil
@@ -90,6 +100,7 @@ func (a *App) Close() error {
 	if a.workerCancel != nil {
 		a.workerCancel()
 	}
+	a.workerWG.Wait()
 	return a.db.Close()
 }
 

apps/api/internal/app/app_test.go

@@ -62,6 +62,13 @@ func newTestAppWithConfig(t *testing.T, cfg Config) *App {
 	return a
 }
 
+func stopTestWorkers(a *App) {
+	if a != nil && a.workerCancel != nil {
+		a.workerCancel()
+		a.workerWG.Wait()
+	}
+}
+
 func defaultAdminUserAndMailbox(t *testing.T, a *App) (*User, *Mailbox) {
 	t.Helper()
 	ctx := context.Background()
@@ -581,6 +588,21 @@ func TestExternalIMAPOAuthEmailFromIDToken(t *testing.T) {
 	}
 }
 
+func TestExternalIMAPXOAUTH2ClientFormat(t *testing.T) {
+	client := newExternalIMAPXOAUTH2Client("user@example.com", "access-token")
+	mech, initialResponse, err := client.Start()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if mech != "XOAUTH2" {
+		t.Fatalf("mechanism=%q, want XOAUTH2", mech)
+	}
+	want := "user=user@example.com\x01auth=Bearer access-token\x01\x01"
+	if string(initialResponse) != want {
+		t.Fatalf("initial response=%q, want %q", string(initialResponse), want)
+	}
+}
+
 func mustOAuthStateFromURL(t *testing.T, rawURL string) string {
 	t.Helper()
 	u, err := url.Parse(rawURL)
@@ -1588,6 +1610,7 @@ func TestMailSendRollsBackSentCopyWhenQueueInsertFails(t *testing.T) {
 
 func TestSendQueueRecoversStaleSendingItems(t *testing.T) {
 	a := newTestApp(t)
+	stopTestWorkers(a)
 	host, port, received := startCapturingSMTP(t, 1)
 	a.cfg.SMTPHost = host
 	a.cfg.SMTPPort = port
@@ -1637,6 +1660,7 @@ func TestSendQueueRecoversStaleSendingItems(t *testing.T) {
 
 func TestSendQueueStaleDeliveredMarkerDoesNotRedeliver(t *testing.T) {
 	a := newTestApp(t)
+	stopTestWorkers(a)
 	host, port, received := startCapturingSMTP(t, 1)
 	a.cfg.SMTPHost = host
 	a.cfg.SMTPPort = port

apps/api/internal/app/external_imap.go

@@ -24,7 +24,6 @@ import (
 
 	"github.com/emersion/go-imap/v2"
 	"github.com/emersion/go-imap/v2/imapclient"
-	"github.com/emersion/go-sasl"
 	"github.com/go-chi/chi/v5"
 	"golang.org/x/oauth2"
 )
@@ -1498,7 +1497,7 @@ func (a *App) openExternalIMAPClient(ctx context.Context, account externalIMAPAc
 			c.Close()
 			return nil, err
 		}
-		if err := c.Authenticate(sasl.NewOAuthBearerClient(&sasl.OAuthBearerOptions{Username: account.Username, Token: token, Host: account.Host, Port: account.Port})); err != nil {
+		if err := c.Authenticate(newExternalIMAPXOAUTH2Client(account.Username, token)); err != nil {
 			c.Close()
 			return nil, err
 		}
@@ -1516,6 +1515,23 @@ func (a *App) openExternalIMAPClient(ctx context.Context, account externalIMAPAc
 	return &goExternalIMAPClient{client: c}, nil
 }
 
+type externalIMAPXOAUTH2Client struct {
+	username string
+	token    string
+}
+
+func newExternalIMAPXOAUTH2Client(username, token string) externalIMAPXOAUTH2Client {
+	return externalIMAPXOAUTH2Client{username: username, token: token}
+}
+
+func (c externalIMAPXOAUTH2Client) Start() (string, []byte, error) {
+	return "XOAUTH2", []byte("user=" + c.username + "\x01auth=Bearer " + c.token + "\x01\x01"), nil
+}
+
+func (c externalIMAPXOAUTH2Client) Next(challenge []byte) ([]byte, error) {
+	return []byte{}, nil
+}
+
 func (a *App) externalIMAPOAuthAccessToken(ctx context.Context, account externalIMAPAccountRecord) (string, error) {
 	access, err := a.decryptExternalIMAPPassword(account.OAuthAccessTokenCiphertext)
 	if err != nil {

apps/api/internal/app/send_queue.go

@@ -126,6 +126,12 @@ func (a *App) sendQueueWorker(ctx context.Context) {
 	ticker := time.NewTicker(10 * time.Second)
 	defer ticker.Stop()
 	for {
+		select {
+		case <-ctx.Done():
+			a.log.Info("send queue worker stopped")
+			return
+		default:
+		}
 		if err := a.processDueSendQueue(ctx); err != nil {
 			a.log.Warn("send queue worker failed", "error", err)
 		}
@@ -232,12 +238,12 @@ func (a *App) recoverStaleSendQueueItems(ctx context.Context) error {
 			}
 			continue
 		}
-		res, err := a.db.ExecContext(ctx, `UPDATE send_queue SET status=?,next_attempt_at=?,last_error=?,updated_at=? WHERE id=? AND status=?`, sendQueueStatusFailed, now, "send attempt interrupted", now, item.ID, sendQueueStatusSending)
+		res, err := a.db.ExecContext(ctx, `UPDATE send_queue SET status=?,next_attempt_at=?,last_error=?,updated_at=? WHERE id=? AND status=?`, sendQueueStatusQueued, now, "send attempt interrupted", now, item.ID, sendQueueStatusSending)
 		if err != nil {
 			return err
 		}
 		if n, _ := res.RowsAffected(); n > 0 {
-			a.recordSendAudit(ctx, sendAuditRetry, sendQueueStatusFailed, sendAuditInputFromQueue(item, "send attempt interrupted"))
+			a.recordSendAudit(ctx, sendAuditRetry, sendQueueStatusQueued, sendAuditInputFromQueue(item, "send attempt interrupted"))
 		}
 	}
 	return nil