78953cf775
mdrt-2 (markdown export): add lossless turndown rules for the custom nodes that had no rule — transclusionReference, pageBreak, mention, status. Each re-emits the node as inert raw HTML carrying every data-* attribute instead of being silently dropped (childless atom divs) or collapsed to bare text (mention/status losing data-id/data-color). Empty atom blocks are made non-blank before turndown's blank-rule strips them (mirrors the footnote-ref fix). markdownToHtml passes the raw HTML through and each node's parseHTML rebuilds it, so the form round-trips. Flips the it.fails cases to passing and adds export + import round-trip coverage. persist-6 (collab store): add a store-side empty-guard in onStoreDocument. Before updatePage, if the serialized live doc is an empty paragraph doc AND the persisted page is non-empty, skip the write and log — unless an explicit context.intentionalClear signal is present (deliberate select-all+delete). New/empty pages and unchanged docs are unaffected. Flips the it.failing case to passing and adds escape-hatch + empty-over-empty coverage. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>