🔧 Implementing UUID v7 by hand: time-sortable primary keys (and the same-millisecond trap)

Random UUID v4 makes a poor primary key: values land all over the index, so B-tree inserts scatter across pages and page splits go up. UUID v7 puts a millisecond timestamp in the leading bits (standardized in RFC 9562), so generation order equals sort order and you get locality back.

I needed a UUID generator that runs entirely in the browser,...