Production build emits invalid `ssr_exports` reference in bundled SSR chunk (TanStack Start, any preset)

Summary

Building a TanStack Start app for production with any recent nitro beta produces a bundled SSR chunk that references an export (ssr_exports) which is never declared or imported in that module, causing a SyntaxError the moment the module is loaded at runtime.

Environment

• nitro: reproduced on 3.0.260311-beta, 3.0.260603-beta, and 3.0.260610-beta (the three most recent date-stamped betas at time of writing)
• vite: 8.2.1
• @tanstack/react-start: 1.168.46
• @tanstack/start-client-core: 1.170.24
• Node: 22.22.2
• Reproduced with both the default (node-server) preset and the vercel preset — not preset-specific.

Steps to reproduce

1. A standard TanStack Start app using createServerFn (any number of server functions is enough — this is not specific to CSRF middleware; removing createCsrfMiddleware from src/start.ts does not avoid the bug).
2. npm run build
3. Inspect .output/server/_ssr/ssr.mjs (or the equivalent chunk under .vercel/output/functions/__server.func/_ssr/ when building with NITRO_PRESET=vercel).

Actual result

The generated chunk contains an export statement like:

export { getResponseHeaders as a, ssr_exports as c, createServerEntry, server_default as default, getCookies as i, createCsrfMiddleware as l, TSS_SERVER_FUNCTION as n, setCookie$1 as o, getServerFnById as r, setResponseHeader as s, createServerFn as t, createMiddleware as u };

Run npm run build with a standard TanStack Start app using createServerFn, then inspect .output/server/_ssr/ssr.mjs or the equivalent Vercel SSR chunk. Trace the generated export list and its source through the Nitro bundling path; done means the production SSR module loads without an undeclared ssr_exports reference for both node-server and vercel presets.