The Request constructor extracts and locks the ReadableStream passed as body, so calling cancel() on the original reference rejects with a TypeError per spec. This PR cancels the transferred stream via request.body instead, which achieves the same goal without producing an unhandled rejection.

Related #7515
Fixes expo/expo#44382

Summary by cubic

Cancel the transferred request body (request.body) in the fetch adapter’s request stream probe to avoid TypeErrors from cancelling the original source stream. This removes unhandled rejections while keeping the probe behavior the same.

Description

• Summary of changes
  • In lib/adapters/fetch.js, create the Request with a new ReadableStream, then cancel request.body (if present) instead of the original stream.
  • Keeps duplex access check and Content-Type header probe unchanged.
• Reasoning
  • The Request constructor locks the passed stream; cancelling the original throws a TypeError.
  • Cancelling request.body achieves the same effect without errors.
• Additional context
  • Improves compatibility in environments like Expo.
  • Related: fix(fetch): cancel ReadableStream body after request stream capability probe #7515. Fixes: [jest-expo] jest tests fail with axios@^1.14.0 expo/expo#44382.

Docs

• No user-facing or API changes. No docs updates needed.

Testing

• No tests added or modified.
• Suggested: add a regression test to ensure the probe does not produce unhandled rejections and still returns the expected result when the body is locked by Request.

^{Written for commit eec1e42. Summary will update on new commits.}