start-plugin-core: instanceof RunnableDevEnvironment fails with vite-plus alias (dual-package hazard)

[CETE0]

Problem

@tanstack/start-plugin-core's dev server plugin uses isRunnableDevEnvironment(serverEnv) (which calls instanceof) to guard SSR middleware registration at src/dev-server-plugin/plugin.ts line ~147.

When vite is aliased to another package via pnpm overrides (e.g. vite: npm:@voidzero-dev/vite-plus-core@latest), two different RunnableDevEnvironment class references exist in memory — instanceof returns false, SSR middleware is never registered, and all routes return 404.

This is a dual-package hazard.

Reproduction

1. Create a TanStack Start project
2. Add pnpm override: "vite": "npm:@voidzero-dev/vite-plus-core@latest"
3. Run pnpm dev
4. All routes return 404 "Cannot GET /"

Suggested Fix

Replace instanceof with duck-typing in plugin.ts:

- if (!isRunnableDevEnvironment(serverEnv) || "dispatchFetch" in serverEnv) {
+ if (!("runner" in serverEnv) || "dispatchFetch" in serverEnv) {

The runner property (a public getter) is unique to RunnableDevEnvironment — FetchableDevEnvironment and DevEnvironment don't have it. The existing "dispatchFetch" in serverEnv guard correctly handles Nitro.

Versions

• @tanstack/start-plugin-core: 1.166.8
• vite-plus / @voidzero-dev/vite-plus-core: 0.1.12 (Vite 8.0.0)

Workaround

pnpm patch @tanstack/start-plugin-core with the diff above.

[schiller-manuel]

please provide a complete minimal reproducer project