FilterSelect fully replaces it: delete SelectableFilter and its _selectable_*
helpers, the now-unused _get_filter_options, selectable_filter.js, and the .sf-*
rules in input.css (rebuilt base.css). The three list views load search_select.js
instead of selectable_filter.js. Drop the SelectableFilter export and refresh
docs/comments that referenced it.
https://claude.ai/code/session_01XzhXvMvw42CQGc9kmin3GS