Invalid

Every Form handler receives an invalid proxy next to the validated data. Calling a path on the proxy produces an Effect that fails with a typed FormError addressed to that exact field, which SvelteKit routes back to the form as a field issue.

Reject a field

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import { Form } from "svelte-effect-runtime";
import { Effect, Schema } from "effect";

export const CreateItem = Form(ItemSchema, ({ data, invalid }) =>
	Effect.gen(function* () {
		if (data.items[0]?.label === "blocked") {
			return yield* invalid.items[0]!.label("Blocked labels are rejected.");
		}

		return { message: `saved:${data.name}` };
	}),
);

The proxy mirrors the shape of the validated input, so paths are fully typed: invalid.email("Use an email address.") for a flat field, invalid.items[0]!.label("...") for nested collections. The produced failure lands on the Form's error channel as a FormError, and the message appears on the matching field in the browser.