If a search exposed form is showing facets as well as a full-text search, then the autocomplete results don't take the currently-selected facets into account.
Allow the configuration of the search_api_autocomplete_search entity to include a list of facet exposed filters (using Facets 3!).
Enhance the autocomplete JS to pass the values of those form elements to the autocomplete AJAX request.
Enhance the autocomplete route and controller to accept those parameters, and pass them to the query.
Active
1.0
General code
In core's autocomplete.js:
const options = $.extend(
{ success: sourceCallbackHandler, data: { q: term } },
autocomplete.ajax,
);
$.ajax(this.element.attr('data-autocomplete-path'), options);
We'd need to override autocomplete.ajax to include something like
data: { q: term, *something else here } },