options_with_key_prefix

Return every option whose key sits under the dotted prefix section.

Matching is exact on segment boundaries: credentials matches credentials.openai but credential matches nothing, so config get can accept a section name without also accepting truncated guesses.

Matching is case-insensitive, and key prefixes are the only section namespace: display group titles (Credentials, Tools) are not accepted, since several headings (Models, Tools) name a different set of options than the same word as a prefix — one namespace keeps a section unambiguous.