ContextBuilder._build_user_content now only handles images (its original
responsibility). Document text extraction (PDF, DOCX, XLSX, PPTX) is
performed by the new _extract_documents() helper in server.py, called
before process_direct(). This keeps the core context builder free of
format-specific dependencies and makes the API boundary the single place
where uploaded files are pre-processed.
Tests updated to reflect the new responsibility boundary.
Made-with: Cursor
Xubin Ren
47f5795708