A tab created before profiles existed carries no profile of its own and runs
in the built-in `default` partition — the scope the browser used before
profiles. It was labelled with, and cleared against, whatever profile is
configured as the default now, so on a machine with a custom default the
active tab's data was left untouched while another profile's was wiped.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>