Flat while authoring, nested once published

A draft is { roots, elements } keyed by id; an artifact is a resolved tree. Editing wants random access — selection, patching, undo, and reordering all key on id — while rendering wants a self-contained structure with no lookups.

Compile is the denormalization, which is also where reference integrity, cycle-freedom, and reachability get checked. A cyclic graph cannot flatten into a tree, so it fails at publish rather than looping at render.