fix: add null and undefined to RemoteFormInput type

[PranavAgarkar07]

closes #15249

Goal

Remote form schemas using .nullable() (Zod) or equivalent null-producing validators fail TypeScript because RemoteFormInput's index signature does not include null or undefined in its value union. This means any schema whose inferred input type contains null (e.g. z.string().nullable() → string | null) cannot satisfy the StandardSchemaV1<RemoteFormInput, ...> constraint on form().

What was changed

• Added null and undefined to the MaybeArray<...> union inside the RemoteFormInput index signature in packages/kit/src/exports/public.d.ts
• Regenerated packages/kit/types/index.d.ts via pnpm generate:types
• Added a type-level regression test in packages/kit/test/types/remote.test.ts covering nullable fields (string | null, number | null)

Why this is the best fix

Minimal. One union member added to one line — the runtime already handles null (unchecked checkboxes produce null at form.svelte.js:494, proxy getters use ?? throughout). Both null and undefined are included because ZodNullish (.nullish()) produces both, and ZodOptional (.optional()) produces undefined — the same class of issue.

No runtime risk. The RemoteFormInput type is a compile-time constraint on generic parameters. It never appears in emitted code. Adding null | undefined widens the accepted schema types without changing any runtime behavior.

Community-validated. The issue reporter independently asked: "Would it be enough to allow null in the RemoteFormInput?" — confirming this approach before implementation.

Verification

• pnpm check — TypeScript passes for both main types and test types
• pnpm -F @sveltejs/kit test:unit — 537/537 tests pass
• pnpm prepublishOnly — types regenerate cleanly (no unexpected diffs)
• pnpm run lint — linting clean

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🦋 Changeset detected

Latest commit: 0649017

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@sveltejs/kit	Patch

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-kit-15859-svelte.vercel.app/