feat(media): 作品保存恢复 - 按原任务重试交付并避免重复生成计费

backend/internal/repository/repository.go

@@ -110,7 +110,7 @@ func (r *Repository) UserStorageUsage(userID string) (UserStorageUsage, error) {
 			(SELECT COUNT(*) FROM canvas_projects WHERE user_id = ?) AS canvas_count,
 			(SELECT COALESCE(SUM(length(CAST(COALESCE(payload_json, '') AS BLOB))), 0) FROM canvas_projects WHERE user_id = ?) AS canvas_bytes,
 			(SELECT COUNT(*) FROM tasks WHERE user_id = ?) AS task_count,
-			(SELECT COALESCE(SUM(length(CAST(COALESCE(prompt, '') AS BLOB)) + length(CAST(COALESCE(input_json, '') AS BLOB)) + length(CAST(COALESCE(result_json, '') AS BLOB)) + length(CAST(COALESCE(text_draft, '') AS BLOB)) + length(CAST(COALESCE(error, '') AS BLOB))), 0) FROM tasks WHERE user_id = ?)
+			(SELECT COALESCE(SUM(length(CAST(COALESCE(prompt, '') AS BLOB)) + length(CAST(COALESCE(input_json, '') AS BLOB)) + length(CAST(COALESCE(result_json, '') AS BLOB)) + length(CAST(COALESCE(media_recovery_json, '') AS BLOB)) + length(CAST(COALESCE(text_draft, '') AS BLOB)) + length(CAST(COALESCE(error, '') AS BLOB))), 0) FROM tasks WHERE user_id = ?)
 			+ (SELECT COALESCE(SUM(length(CAST(COALESCE(message, '') AS BLOB)) + length(CAST(COALESCE(payload, '') AS BLOB))), 0) FROM task_logs WHERE user_id = ?)
 			+ (SELECT COALESCE(SUM(length(CAST(COALESCE(url, '') AS BLOB)) + length(CAST(COALESCE(payload, '') AS BLOB))), 0) FROM results WHERE user_id = ?)
 			+ (SELECT COALESCE(SUM(byte_count), 0) FROM task_text_delta WHERE user_id = ?)
@@ -536,6 +536,12 @@ func (r *Repository) UpdateTaskProviderProgress(id string, progress int) error {
 }
 
 func (r *Repository) SaveTaskCompletion(task *model.Task, expected model.TaskStatus, results []model.Result) error {
+	return r.SaveTaskCompletionWithRegistration(task, expected, results, nil)
+}
+
+// Registration and terminal success commit together; a failed asset write leaves
+// the task recoverable and never exposes a false success to the canvas.
+func (r *Repository) SaveTaskCompletionWithRegistration(task *model.Task, expected model.TaskStatus, results []model.Result, register func(*Repository) error) error {
 	return r.db.Transaction(func(tx *gorm.DB) error {
 		updated := taskLeaseWriter(tx.Model(&model.Task{}), task.LeaseOwner).
 			Where("id = ? AND status = ?", task.ID, expected).
@@ -551,6 +557,9 @@ func (r *Repository) SaveTaskCompletion(task *model.Task, expected model.TaskSta
 				return err
 			}
 		}
+		if register != nil {
+			return register(New(tx))
+		}
 		return nil
 	})
 }
@@ -696,7 +705,7 @@ func (r *Repository) Tasks(userID string, limit int, projectID string, activeOnl
 	if limit <= 0 || limit > 100 {
 		limit = 50
 	}
-	query := r.db.Select("id", "project_id", "type", "status", "stage", "progress", "prompt", "operation", "provider", "model", "input_json", "result_json", "billing_order_id", "provider_request_id", "provider_cancel_status", "provider_cancel_error", "provider_cancel_attempts", "provider_cancel_requested_at", "provider_cancelled_at", "provider_cancel_next_check_at", "attempts", "started_at", "completed_at", "created_at", "updated_at", "agent_run_id", "generation_id", "approval_id", "authorized_charge_microcredits", "execution_diagnostic_json", "cancellation_source", "cancellation_actor_id", "cancellation_requested_at").
+	query := r.db.Select("id", "project_id", "type", "status", "stage", "media_stage", "media_recovery_json", "progress", "prompt", "operation", "provider", "model", "input_json", "result_json", "billing_order_id", "provider_request_id", "provider_cancel_status", "provider_cancel_error", "provider_cancel_attempts", "provider_cancel_requested_at", "provider_cancelled_at", "provider_cancel_next_check_at", "attempts", "started_at", "completed_at", "created_at", "updated_at", "agent_run_id", "generation_id", "approval_id", "authorized_charge_microcredits", "execution_diagnostic_json", "cancellation_source", "cancellation_actor_id", "cancellation_requested_at").
 		Where("user_id = ?", userID)
 	if strings.TrimSpace(projectID) != "" {
 		query = query.Where("project_id = ?", strings.TrimSpace(projectID))