export function removeAndRenumberTimelineItem<  Id,  Row extends { readonly position: number; readonly sourceItemId: Id },>(rows: ReadonlyArray<Row>, sourceItemId: Id): Array<Row> {  return rows    .filter((row) => row.sourceItemId !== sourceItemId)    .map((row, position) => ({ ...row, position }));} export function upsertTimelineItemAtStablePosition<  Id,  Row extends { readonly position: number; readonly sourceItemId: Id },>(rows: ReadonlyArray<Row>, item: Row): Array<Row> {  const existingIndex = rows.findIndex((row) => row.sourceItemId === item.sourceItemId);  if (existingIndex === -1) {    return [...rows, { ...item, position: rows.length }];  }   return rows.map((row, index) =>    index === existingIndex ? { ...item, position: row.position } : row,  );}