Coverage priorities 1-5: test pure functions, extract interfaces, mock-based handler tests

- Priority 1: Test NewSendEmailTask + NewSendPushTask (5 tests)
- Priority 2: Test customHTTPErrorHandler — all 15+ branches (21 tests)
- Priority 3: Extract Enqueuer interface + payload builders in worker pkg (5 tests)
- Priority 4: Extract ClassifyFile/ComputeRelPath in migrate-encrypt (6 tests)
- Priority 5: Define Handler interfaces, refactor to accept them, mock-based tests (14 tests)
- Fix .gitignore: /worker instead of worker to stop ignoring internal/worker/

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/worker/jobs/handler.go

@@ -30,38 +30,43 @@ const (
 
 // Handler handles background job processing
 type Handler struct {
-	db                   *gorm.DB
-	taskRepo             *repositories.TaskRepository
-	residenceRepo        *repositories.ResidenceRepository
-	reminderRepo         *repositories.ReminderRepository
-	notificationRepo     *repositories.NotificationRepository
-	pushClient           *push.Client
-	emailService         *services.EmailService
-	notificationService  *services.NotificationService
-	onboardingService    *services.OnboardingEmailService
-	config               *config.Config
+	db                  *gorm.DB
+	taskRepo            TaskRepo
+	residenceRepo       ResidenceRepo
+	reminderRepo        ReminderRepo
+	notificationRepo    NotificationRepo
+	pushClient          PushSender
+	emailService        EmailSender
+	notificationService NotificationSender
+	onboardingService   OnboardingEmailSender
+	config              *config.Config
 }
 
 // NewHandler creates a new job handler
 func NewHandler(db *gorm.DB, pushClient *push.Client, emailService *services.EmailService, notificationService *services.NotificationService, cfg *config.Config) *Handler {
-	// Create onboarding email service
-	var onboardingService *services.OnboardingEmailService
-	if emailService != nil {
-		onboardingService = services.NewOnboardingEmailService(db, emailService, cfg.Server.BaseURL)
+	h := &Handler{
+		db:               db,
+		taskRepo:         repositories.NewTaskRepository(db),
+		residenceRepo:    repositories.NewResidenceRepository(db),
+		reminderRepo:     repositories.NewReminderRepository(db),
+		notificationRepo: repositories.NewNotificationRepository(db),
+		config:           cfg,
 	}
 
-	return &Handler{
-		db:                  db,
-		taskRepo:            repositories.NewTaskRepository(db),
-		residenceRepo:       repositories.NewResidenceRepository(db),
-		reminderRepo:        repositories.NewReminderRepository(db),
-		notificationRepo:    repositories.NewNotificationRepository(db),
-		pushClient:          pushClient,
-		emailService:        emailService,
-		notificationService: notificationService,
-		onboardingService:   onboardingService,
-		config:              cfg,
+	// Assign interface fields only when concrete values are non-nil
+	// to preserve correct nil checks on the interface values.
+	if pushClient != nil {
+		h.pushClient = pushClient
 	}
+	if emailService != nil {
+		h.emailService = emailService
+		h.onboardingService = services.NewOnboardingEmailService(db, emailService, cfg.Server.BaseURL)
+	}
+	if notificationService != nil {
+		h.notificationService = notificationService
+	}
+
+	return h
 }
 
 // HandleDailyDigest processes daily digest notifications with task statistics