Who placed the item. Drives the ownership chrome (chips / violet vs slate-amber).
Stable item id (e.g. sticky-3) — referenced by connectors, deltas and agent tools.
OptionalTagOptional free-form role tag ('slot', 'heading', 'step-done'). It carries no behavior:
the board lands it on the item's wrapper as a wb-tag-<slug> class (see
WhiteboardTagClass) so a host restyling the board from outside can tell two ROLES of
one kind apart — a shape used as a section head vs an empty "fill this in" slot — which the
DOM could not distinguish before (CSS cannot select on label text). Persisted with the item;
the agent's scene view carries it as tag.
Render order (higher renders on top). Assigned by the engine.
Fields shared by every board item.