Function is_binary_document 

pub fn is_binary_document(path: &Path) -> bool

Whether path is a binary document format that must be read through extract from raw bytes because it is not valid UTF-8 text. Text and structured formats (json/csv/eml/html/markdown/…) index fine as raw UTF-8; only true binary documents — currently PDF — need byte-level extraction before they can enter the text index. Grows as binary extractors (DOCX, XLSX, …) are added. Single source of truth for the indexer’s read path.