Function is_keyword_at 

fn is_keyword_at(s: &str, i: usize, keyword: &str) -> bool

True if keyword starts at byte i preceded by a keyword boundary. In addition to valid libpq whitespace separators, ; and & are treated as conservative boundaries so malformed DSNs cannot leak credentials. Other punctuation, such as the = in application_name=password=x, is handled by the fail-closed path.