The modern bookend to the Xanadu/ZigZag dives: where those are unbuilt
ideals, Roam shipped fine-grained addressing (:block/uid), live
transclusion (block embeds), bidirectional links, and a queryable
structured space (DataScript datoms + Datalog). Studied as a candidate
DB-backed/API-attached shard (XWiki family) and as a concrete
engine-hosts-adapter surface (Roam Depot onload/onunload over
window.roamAlphaAPI). Added UC-50 (attach block-graph DB shard, block<->page
mapping), UC-51 (adopt native span IDs as portable span addresses), UC-52
(delegate derived views to a shard's native query engine); enriched
UC-32/34/35/38. Boundary: Roam is one candidate shard mapped into the
Markdown-first page model, not a substrate and not the federation layer.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
