fix(orchestrator): prevent concurrent double-run duplicating messages; reflect errors in status

internal/store/tasks.go

@@ -55,3 +55,14 @@ func (s *Store) SetTaskStatus(ctx context.Context, id int64, status string) erro
 	_, err := s.Pool.Exec(ctx, `UPDATE tasks SET status=$2 WHERE id=$1`, id, status)
 	return err
 }
+
+// TryMarkTaskRunning atomically sets status='running' only if the task is not already running.
+// Returns true if this call acquired the run (status was not 'running' before), false otherwise.
+func (s *Store) TryMarkTaskRunning(ctx context.Context, id int64) (bool, error) {
+	ct, err := s.Pool.Exec(ctx,
+		`UPDATE tasks SET status='running' WHERE id=$1 AND status<>'running'`, id)
+	if err != nil {
+		return false, err
+	}
+	return ct.RowsAffected() == 1, nil
+}