more robust command options;

performance tuning: avoid redundant db access;

clarified signature: proper treatment of implicit state (amending d0c9d277620e);

performance tuning: avoid redundant db access;

performance tuning: avoid multiple db roundtrips;

clarified signature: more robust treatment of implicit state;

proper sync_database for Database_Progress consumer; more efficient (but less reactive) Database_Progress.stopped;

tuned message;

tuned;

tuned messages;