fix: serve loader responses as CJS for ?platform=native requests

[clayrisser]

Symptom

In dev, useLoader on native fetches route loaders with ?platform=native (the comment in useLoader.ts even says "?platform=native tells vite plugin to return CJS") and evaluates the response body as CJS on Hermes. But two gates in the request pipeline only recognize platform=ios|android, so platform=native requests can receive the Vite-transformed web ESM module instead. Hermes then throws while compiling the loader body:

[one] native loader error for /pokemon: 1:21:import declaration must be at top level of module

The error is caught and swallowed (data: {}), so the route silently loses its server-side loader data — including __oneRedirect / __oneError signals, meaning server redirects thrown from loaders never reach the native client.

Root cause (two spots)

1. createHandleRequest.ts → resolveLoaderRoute: isNativeRequest misses platform=native, so the CJS conversion (toCjsLoader) and the redirect (302) / auth (401/403) fallback loader bodies are emitted as web ESM for those requests. (The dispatch-level check in handleRequest already recognizes native; this inner one didn't.)

2. fileSystemRouterPlugin.tsx → handleLoader: the export function loader() stub-regex gate early-returns the raw Vite-transformed web ESM (HMR preamble included) above the platform check that would have produced the native CJS body. Any route whose loader the client tree-shake plugin doesn't rewrite to the literal stub — e.g. a re-export like export { pokemonListLoader as loader } from './loaders' — fails the regex and sends web ESM to native. The regex is irrelevant for native responses: the native branch never uses transformedJS at all — it imports the route through the module runner (which resolves re-exports fine) and returns the JSON-embedding CJS body.

Fix

• include native in resolveLoaderRoute's isNativeRequest
• hoist the platform check in handleLoader above the stub-regex gate so native requests always take the module-runner path; web requests keep the existing shortcut (including the skip-SSR-import optimization for routes without loader stubs)

Verification

• 3 new unit tests in createHandleRequest.test.ts. The two platform=native ones fail before the fix (body arrives as export function loader(){...} web ESM) and pass after; the web test guards against regressions on the ESM path. Full file: 23/23 pass.
• Downstream: we've been carrying the dist-level equivalent of this diff as a pnpm patch in multiplatform.one against one@1.16.5. With routes written as plain re-exports:

curl 'http://localhost:3000/assets/pokemon_<cachekey>_vxrn_loader.js?platform=native'
# before: import { createHotContext as __vite__createHotContext } from "/@vite/client";...  (Hermes parse error)
# after:  exports.loader = () => ({"pokemon":[{"name":"bulbasaur",...}]});

On device (Expo Go SDK 55 / Hermes): the [one] native loader error toast is gone and the route receives the server-prefetched loader data.

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