Detect a file's true MIME type from its magic-number byte signature — not from a declared extension or Content-Type. Send the raw bytes (≤10 MB) as the body, or JSON { bytes: base64 }. Returns {mime, extension, confidence, description, category, executable}. Covers images, documents (incl. OOXML/OpenDocument), archives, audio/video, fonts and executables (which are flagged). Security check for file pipelines. Not a barcode/QR reader.