){
    fossil_fatal("would fork.  \"update\" first or use --allow-fork.");
  }

  /*
  ** Do not allow a commit against a closed leaf on the same branch.
  */
  if( !( sCiInfo.zBranch &&
         !db_exists("SELECT 1 FROM tagxref"
                    " WHERE tagid=%d AND rid=%d AND tagtype>0"
                    "   AND value=%Q", TAG_BRANCH, vid, sCiInfo.zBranch )
      ) && db_exists("SELECT 1 FROM tagxref"
                     " WHERE tagid=%d AND rid=%d AND tagtype>0",
                     TAG_CLOSED, vid) ){
    fossil_fatal("cannot commit against a closed leaf");
  }

  if( useCksum ) vfile_aggregate_checksum_disk(vid, &cksum1);
  if( zComment ){
    blob_zero(&comment);
    blob_append(&comment, zComment, -1);