CountryListIndex

A lookup from a country (or an initial letter) to its row index in the flat LazyColumn that CountryList emits.

The translation is the whole point. CountryList renders a list of CountrySections, each optionally preceded by a sticky header, into one flat lazy list — so the nth country is not at lazy index n, and anything that wants to scroll to a specific country has to account for every header and every preceding section. Doing that arithmetic at each call site is how off-by-one scroll bugs get written; doing it once, here, from the same sections the list was built from, is how they do not.

Build one with rememberCountryListIndex.