feat(app): validateAction() — framework-level action validation pipeline

[SisyphusZheng]

Summary

Provide a framework-level validation pipeline for route actions, inspired by Astro Actions' schema→error model. The framework owns the FormData → parse → typed result | 422 re-render plumbing without binding to a specific validation library.

Competitive context

Framework	Approach
Astro 7	Built-in Actions with input: schema (zod-like, library-agnostic)
SvelteKit	User implements (valibot/zod recipe)
Next.js	User implements (zod recipe)
Fresh	User implements
openElement	User implements — no framework helper

Astro proves that a thin framework-owned validation pipe (schema in → typed data or structured 422 errors out) is a meaningful DX differentiator without becoming an ORM.

Proposed design

// In route module
import { validateAction } from '@openelement/app';
import * as v from 'valibot'; // or zod — user's choice

const ContactSchema = v.object({
  email: v.pipe(v.string(), v.email()),
  message: v.pipe(v.string(), v.minLength(10)),
});

export const action = validateAction(ContactSchema, async (data, ctx) => {
  // data is typed: { email: string; message: string }
  // validation failures auto-return 422 with field errors
  await sendEmail(data);
  return redirect('/thanks');
});

Scope

• validateAction(schema, handler) helper in @openelement/app
• Schema protocol: { safeParse(input): { success, data?, error? } } (zod AND valibot compatible)
• On failure: auto fail(422, { fieldErrors }) with the 0.42 form re-render semantics
• On success: typed handler receives parsed data
• No dependency on zod or valibot — protocol-only

Non-goals

• No built-in validation library
• No client-side validation (stays user-owned)
• No schema generation from TypeScript types

Target version

0.43.0 (Universal WC SSR line) or 0.44.0 (Production Runtime)