code: Delta newMoveRestart(Storage src, Storage dest) {
          // If the destination used to be the initial primary for the group, it's consistent and ready to promote
          // but lacking the MIRROR_CONSISTENT marker attribute which is the prereq for promotion.  Add one.
          Delta consistentMarker = dest.isConsistent() ?
                  Deltas.conditional(Conditions.isUndefined(), Deltas.literal(now())) :
                  Deltas.noop();
          return Deltas.mapBuilder()
                  .update(STORAGE.key(), Deltas.mapBuilder()
                          .update(src.getUuidString(), Deltas.mapBuilder()
                                  .put(Storage.MOVE_TO.key(), dest.getUuidString())
                                  .build())
                          .update(dest.getUuidString(), Deltas.mapBuilder()
                                  // Clean slate: clear 'moveTo' plus all markers for promotion states and later.
                                  .update(StorageState.MIRROR_CONSISTENT.getMarkerAttribute().key(), consistentMarker)
                                  .remove(Storage.MOVE_TO.key())
                                  .remove(Storage.PROMOTION_ID.key())
                                  .remove(StorageState.PRIMARY.getMarkerAttribute().key())
                                  .remove(StorageState.MIRROR_EXPIRING.getMarkerAttribute().key())
                                  .remove(StorageState.MIRROR_EXPIRED.getMarkerAttribute().key())
                                  .build())
                          .build())
                  .build();
      }
docs: Start a move to an existing mirror that may or may not have once been primary.