The chat transcript re-laid-out every message twice per paint and again
on every mouse move; the layer panel re-walked the whole tree per frame;
the icon, markdown, and font panels re-filtered per frame while open.
Each now resolves from an owner-scoped cache: the transcript builds once
per frame/event (value-hash key, last-resolver-owns slots, forced owner
rotation at every session mutation), layer rows key on document revision
plus page with rotation at every document replacement, and panel filters
recompute only when their query/content/generation inputs change,
returning shared Rc results.
