The query side reads identity through transcriptRowIds, which takes
sourceRowId from every part, while the index side still filtered on
`part.type === 'text'`. Only text parts are ever stamped, so the filter
did nothing but make the two sides use different rules; drop it.
Replace the comment that restated the rowId-vs-last-part ternary with
the reason for it: a fold with a rowId is addressed by its first source
row (hydration's key); without one, its last part row is the final
reply the settled live bubble holds, so pending rows land before it.
No behaviour change.
bc3de98ed7