useSyncExternalStore requires getSnapshot to return an identical
reference when unchanged; @wrnexus/store's readonlySnapshot returns a
fresh clone per call. The cache lives here rather than in the store
package so existing consumers are untouched.
createSelectorCache takes an optional equality function: the Object.is
default can never stabilize a selector that allocates, which is the
usual source of infinite re-renders.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
