Next.js Body Cloning Bug Reproduction

Issue

Next.js v15.5.2 fails with "Response body object should not be disturbed or locked" when using Node.js middleware with large request bodies (>350MB).

Quick Reproduction

npm install
npm run dev

# Test with large file (triggers bug)
chmod +x test.sh
./test.sh 500

Expected vs Actual

• ✅ Small files (<350MB): Work fine
• ❌ Large files (>350MB): 500 error with undici exception

Key Files

• middleware.ts - Node.js runtime middleware (required to trigger bug)
• app/api/upload/route.ts - API endpoint that reads request body
• test.sh - Script to test with different file sizes

Environment

• Next.js: 15.5.2
• Runtime: Node.js middleware (bug does not occur with edge runtime)