fix(vite): forward duplex fetch option in dispatcher

[phryneas]

🔗 Linked issue

No issue found.

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

I encountered this when returning an AsyncIterable instance as the body of a Response in a TanStack Start api route handler using the nitro/vite plugin from nitro-nightly@3.0.0-20250902-103829-4daac97b.

That resulted in an unhandled error:

TypeError: RequestInit: duplex option is required when sending a body.
    at new Request (node:internal/deps/undici/undici:9813:19)
    ... 8 lines matching cause stack trace ...
    at next (file:///Users/tronic/tmp/apollo-next/integration-test/tanstack-start/.output/server/index.mjs:1740:18) {
  cause: TypeError: RequestInit: duplex option is required when sending a body.
      at new Request (node:internal/deps/undici/undici:9813:19)
      at globalThis.fetch (file:///Users/tronic/tmp/apollo-next/integration-test/tanstack-start/.output/server/index.mjs:19:15)
      at globalThis.fetch (file:///Users/tronic/tmp/apollo-next/integration-test/tanstack-start/.output/server/chunks/_/server.mjs:18205:16)
      at Object.handler (file:///Users/tronic/tmp/apollo-next/integration-test/tanstack-start/.output/server/index.mjs:4975:10)
      at file:///Users/tronic/tmp/apollo-next/integration-test/tanstack-start/.output/server/index.mjs:1871:35
      at callMiddleware (file:///Users/tronic/tmp/apollo-next/integration-test/tanstack-start/.output/server/index.mjs:1733:43)
      at next (file:///Users/tronic/tmp/apollo-next/integration-test/tanstack-start/.output/server/index.mjs:1740:18)
      at file:///Users/tronic/tmp/apollo-next/integration-test/tanstack-start/.output/server/index.mjs:1711:50
      at callMiddleware (file:///Users/tronic/tmp/apollo-next/integration-test/tanstack-start/.output/server/index.mjs:1743:15)
      at next (file:///Users/tronic/tmp/apollo-next/integration-test/tanstack-start/.output/server/index.mjs:1740:18),
  status: 500,
  statusText: undefined,
  headers: undefined,
  data: undefined,
  body: undefined,
  unhandled: true
}

It seems that when the body of a fetch request is a ReadableStream, the duplex option must be set.

I tested this locally by making the same change manually to the .output/server/chunks/_/server.mjs file, and that resolved the issue.

I also have this on Vercel. You can try this API call without this PR and see it fail:

curl 'https://apolloclient-integration-tanstack-start-q2iw66ycl.vercel.app/api/graphql' \
  -X POST \
  -H 'Accept: application/graphql-response+json,application/json;q=0.9' \
  --data-raw '{"operationName":"dynamicProducts","variables":{},"extensions":{"clientLibrary":{"name":"@apollo/client","version":"4.0.0"}},"query":"query dynamicProducts($someArgument: String) {\n  products(someArgument: $someArgument) {\n    id\n    title\n    __typename\n  }\n  env\n}"}'

This is the same deployment after apollographql/apollo-client-integrations@1a9930f, which patches the changes from this PR:

curl 'https://apolloclient-integration-tanstack-start-lqr4wphz3.vercel.app/api/graphql' \
  -X POST \
  -H 'Accept: application/graphql-response+json,application/json;q=0.9' \
  --data-raw '{"operationName":"dynamicProducts","variables":{},"extensions":{"clientLibrary":{"name":"@apollo/client","version":"4.0.0"}},"query":"query dynamicProducts($someArgument: String) {\n  products(someArgument: $someArgument) {\n    id\n    title\n    __typename\n  }\n  env\n}"}'

📝 Checklist

• I have linked an issue or discussion. (no existing issue)
• I have updated the documentation accordingly. (no docs changes needed)

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