dev-worker: `throw` in fetch handler crashes Deno.serve

[nestarz]

Bug: throw in ViteEnvRunner.fetch() crashes Deno.serve

Summary

In dev-worker.mjs:77, ViteEnvRunner.fetch() throws an error when the SSR entry hasn't finished loading:

if (!this.entry) {
  throw httpError(503, `Vite environment "${this.name}" is unavailable`);
}

This throw propagates as an unhandled rejection to Deno.serve, which expects the handler to return a Response. Deno crashes with:

Terminating Deno.serve loop due to unexpected error TypeError: Cannot read properties of undefined (reading 'status')
    at mapped (ext:deno_http/00_serve.ts:438:26)

Why this happens

The race condition:

1. initEnvRunner() starts the worker during nitro's config hook
2. The worker's onReady callback sends nitro:vite-env → creates ViteEnvRunner → calls this.reload() (async, not awaited)
3. reload() calls this.runner.import(entryPath) which compiles the entire SSR module tree (takes seconds on cold start)
4. Deno.serve is already accepting requests
5. A browser request arrives before this.entry is set → fetch() throws → Deno.serve crashes

The retry loop (lines 70-72) waits up to ~3.1s, but on cold start the SSR entry tree compilation often takes longer.

Environment

• Runtime: Deno 2.7
• Vite: 8.0.9
• Nitro: 3.0.260415-beta
• SSR config: noExternal: true (to prevent duplicate React instances)

Fix

Line 77 should return a proper Response instead of throwing:

    if (!this.entry) {
-     throw httpError(503, `Vite environment "${this.name}" is unavailable`);
+     return renderError(req, httpError(503, `Vite environment "${this.name}" is unavailable`));
    }

renderError is already defined in the same file and returns a proper Response object with the correct status code. This matches how entryError is handled on lines 67-68 and 73-74.

Workaround

Patching the file at config load time in vite.config.ts:

import { readFileSync, writeFileSync } from "node:fs";

const devWorkerPath = resolve(
  import.meta.dirname!,
  "../../node_modules/.deno/nitro@3.0.260415-beta/node_modules/nitro/dist/runtime/internal/vite/dev-worker.mjs",
);
try {
  const src = readFileSync(devWorkerPath, "utf-8");
  const bad = 'throw httpError(503, `Vite environment "${this.name}" is unavailable`)';
  if (src.includes(bad)) {
    writeFileSync(devWorkerPath, src.replace(bad, 'return renderError(req, httpError(503, `Vite environment "${this.name}" is unavailable`))'));
  }
} catch {}