Scan text for content a reader cannot see: zero-width and tag characters, bidirectional controls, hidden markup and comments, and base64 blobs (decoded and re-scanned one level; undecodable blobs reported as opaque). Deterministic findings carry exact codepoint positions and visibly rendered excerpts, plus a sanitized copy; two labeled heuristic classes are never presented as certain. A clean scan is not a finding that text is safe.