Keeps a store's ext in step with reactive inputs — the Svelte twin of the
ext-sync half of React's useForm. (Creation needs no helper here: a
component script runs once.) Stateless on purpose: it pushes at setup —
catching ext that changed between store creation and mount, the SvelteKit
load/remount shape — and on every change of the getter's dependencies.
setExt itself no-ops on a deep-equal ext, so unconditional pushes cost
nothing and there is no shadow copy to fall out of sync.
Keeps a store's ext in step with reactive inputs — the Svelte twin of the ext-sync half of React's
useForm. (Creation needs no helper here: a component script runs once.) Stateless on purpose: it pushes at setup — catching ext that changed between store creation and mount, the SvelteKit load/remount shape — and on every change of the getter's dependencies.setExtitself no-ops on a deep-equal ext, so unconditional pushes cost nothing and there is no shadow copy to fall out of sync.