Unified file identification and routing for KnowledgeSynthesizer pipeline. Detects file types via magic bytes with extension fallback, returns extractor skill to invoke. Use FIRST when processing any unknown file. Handles databases (sqlite, access), PDFs, images (png, jpg, gif, bmp, tiff), HTML, archives (zip, rar, 7z, tar), Office docs (docx, pptx, xlsx), and plain text.