Middleware exceptions escape the generated handleRequest and bypass configureServerErrors #382

Problem

In Start mode, the generated handleRequest runs the start.middleware chain without a catch:

When a middleware throws or rejects in a production build, the exception leaves handleRequest and each host deals with it in its own way:

• Nitro (h3) logs the original error with console.error and answers 500 with {"error":true,"status":500,"unhandled":true} as JSON. The headers and cookies the chain already wrote to the response stub are lost.
• start.node logs it and answers a plain-text 500 (src/node-entry/index.ts#L154-L161).
• The examples/start-ssr server sends e.message back to the client (examples/start-ssr/server.js#L78-L81).

Two consequences go beyond the inconsistent response:

1. The hook registered with configureServerErrors({ onError }) never sees these failures, although its docs describe it as seeing "the failure that fails a request". Apps that rely on it to keep original errors out of logs, or to forward them to an APM (as start.instrument in feat: start.instrument — a server module awaited to completion before the handler graph loads #365 suggests), lose that for middleware, API handlers mounted in middleware, and start.setup / start.renderMode failures.
2. A thrown control response turns into a 500. return redirect('/login') from a middleware works, but throw redirect('/login') reaches h3 as a non-Error rejection and becomes an unhandled 500. The server-function endpoint, served by the same handler, already treats a thrown Response as the response.

Reproduction

With @solidjs/vite-plugin 3.0.0-next.46, @solidjs/web 2.0.0-rc.11 and Nitro 3 beta:

// the module passed to start.middleware
export default async function middleware(request: Request, next: () => Promise<Response>) {
  if (new URL(request.url).pathname === '/boom') throw new Error('token=abc123')
  return next()
}

Build for production, serve it and request /boom: the response is Nitro's JSON 500, the server log shows Error: token=abc123 with its stack, and a hook registered with configureServerErrors is not called.

Expected

In production builds, the generated handler contains request failures the way the server-function endpoint does:

• a thrown Response (except Response.error()) or response envelope becomes the response;
• anything else goes through the configured server error policy and yields a generic 500 that still carries the stub's headers and cookies;
• dev keeps the current behavior, so the Vite overlay still shows the original error.

Notes

• There is no public API today to run a value through the configured policy outside a render, so the handler would have to call the hook registered under the configureServerErrors symbol. A public entry point in @solidjs/web for request failures, with its own kind in ServerErrorSite, would remove that coupling.
• A later step could render the app's error boundary when the chain fails before the page render, so a failed navigation gets an HTML error page instead of an empty 500. Apps can do that in userland today, but it depends on the single-render rule and on excluding the server-function endpoint.
• Related: Define the portable application deployment adapter contract #328, since a deploy adapter would benefit from a handler that does not reject for application failures.

I'll follow up with a PR for the containment part.