Lazy JSON renderer (lazy/react/)

The React layer over the lazy JSON seam (../rowModel.ts). Built once against the async RowModel, so it renders an in-memory value today and a Worker-backed ~1 GB stream tomorrow with no change. See ../../LAZY_TREE_DESIGN.md for the full engine→source→model→renderer picture.

Owner map

File	Role
rowModelStore.ts	Per-mount vanilla Zustand store. Owns the RowModel lifecycle and all async actions (init, ensureRange, toggle, loadMore, materialize, dispose). A generation token abandons work from a previous document or after teardown. This is where logic lives.
LazyJsonViewer.tsx	Controller / in-memory entry. Creates the store, builds the model over value in the feature's one effect (an external-engine lifecycle boundary), and gates render (spinner → list).
LazyJsonList.tsx	Virtualized body (@tanstack/react-virtual). Positions row shells, reads rows from the store's per-revision cache, and reports the visible range back via the virtualizer's onChange — the external event that drives windowed loading. Owns no document state.
LazyJsonRow.tsx	View-only row. Receives one JsonRow + stable callbacks; no state, no effects, no fetching. Memoized so scrolling never re-renders unchanged rows.
rowModelStore.clienttest.ts	Pins the store contract: laziness, expand/collapse counts, pagination + load-more, revision bumps, materialize, async-race + error capture.

No Storybook story: LazyJsonViewer is a full-height, value-driven viewer, so it can't render "as it is" in a canvas without a layout decorator (which the Storybook guide forbids), and a scale demo needs large fixtures (also discouraged). Correctness is covered by the store client tests and the integrated trace-view flow (JSON Beta over a large seeded trace).

Rules that keep it honest

• The RowModel is the only thing the renderer knows; it never sees bytes/tree.
• Cost is proportional to what is expanded/visible — never to total size. A row carries only a bounded preview; the full value is fetched on demand.
• Within one revision a visible row is immutable, so the store merges only missing indices and scroll re-fetches never churn stable row objects.
• Async responses are revision-stamped; a window resolved against a since-mutated model is dropped.