The point about direction surviving sanitization is the one most guides skip — stripping attributes feels safe until an Arabic note with an English equipment code and parentheses renders backwards and the meaning changes. Treating paste as an import into a document model, rather than a clipboard dump, is also the right framing; the contenteditable default of keeping formatting is exactly how stray styles and direction markup leak in. I liked the fixture set at the end, especially reopening saved fixtures after a sanitizer or parser update — that is the check teams forget, and it is where a previously safe note quietly starts rendering differently. One thing I would add: the renderer inventory is worth extending to exported views too, like PDFs or emailed copies, since those often bypass the sanitized path entirely.