When extraction of a binary document format (.pdf, .docx, .xlsx, Office,
EPUB…) fails for a specific reason — the anydoc size cap, an encrypted or
malformed file — read_file previously swallowed the ExtractionError at
debug level and fell through to the generic 'Cannot read binary file'
guard, so the agent never saw the actionable reason (e.g. 'Document too
large to convert (N bytes, limit is 52,428,800)').
read_file now returns the specific extraction failure for binary document
formats. Fallthrough behavior is preserved where a raw read is still
useful: .ipynb (plain JSON) and converter-unavailable PDFs keep their
historical raw-read path, and the 'Unsupported document type' shape (no
extra information) keeps the generic guard.
Follow-up to #80004, where the size-cap message was being generated but
never reached the agent.
