The invitee input had no combobox semantics: assistive
technology could not tell that the widget owns a listbox with
suggestions. Mark the input as role="combobox" with
aria-autocomplete="list" and an initial aria-expanded="false",
point aria-controls at the list and give the JS-built list a
matching id so the reference resolves.
The static datalist only carried the first 50 address book
contacts, so typed fragments could not match anything beyond
that. A new read-only GET /contacts/search endpoint queries
the full address book per keystroke, and a small vanilla JS
combobox shows the results and replaces only the fragment
after the last separator, so comma-separated lists keep
working. The server-rendered datalist remains as the no-JS
fallback; the JS removes the list attribute at runtime so
the native popup does not double the custom one.
stefan.tollkuehn