findIndexCleanStart = (transaction, structs, clock) => {
  const index = findIndexSS(structs, clock);
  const struct = structs[index];

  if (struct.id.clock < clock && struct instanceof Item) {
    structs.splice(index + 1, 0, splitItem(transaction, struct, clock - struct.id.clock));
    return index + 1;
  }

  return index;
}
@param {Transaction} transaction
@param {Array<Item|GC>} structs
@param {number} clock