Link to the code that reproduces this issue

https://github.com/vincent-turato/next.js

To Reproduce

1. Clone the reproduction repository:
   git clone https://github.com/vincent-turato/next.js.git
   cd next.js

2. Check out the reproduction branch:
   git checkout repro/streaming-html-suffix-bug

3. Install dependencies:
   pnpm install

4. Build the Next.js packages:
   pnpm build

5. Run the failing test:
   pnpm test packages/next/src/server/stream-utils/node-web-streams-helper.test.ts

6. Observe the failure showing incorrect handling when the closing HTML suffix spans multiple stream chunks:

   FAIL packages/next/src/server/stream-utils/node-web-streams-helper.test.ts
   createMoveSuffixStream
   ✕ duplicates closing tags when suffix spans chunks

   ● createMoveSuffixStream › duplicates closing tags when suffix spans
   Expected: "Hello"
   Received: "Hello"

Current vs. Expected behavior

Expected: "Hello"
Received: "Hello"

Provide environment information

Operating System:
  Platform: linux
  Arch: x64
  Version: #37~24.04.1-Ubuntu SMP PREEMPT_DYNAMIC Thu Nov 20 10:25:38 UTC 2
  Available memory (MB): 23956
  Available CPU cores: 16
Binaries:
  Node: 22.19.0
  npm: 10.9.3
  Yarn: N/A
  pnpm: 9.6.0
Relevant Packages:
  next: 16.1.1-canary.7 // Latest available version is detected (16.1.1-canary.7).
  eslint-config-next: N/A
  react: 19.3.0-canary-65eec428-20251218
  react-dom: 19.3.0-canary-65eec428-20251218
  typescript: 5.9.2
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

Loading UI and Streaming

Which stage(s) are affected? (Select all that apply)

Vercel (Deployed)

Additional context

Potential impacts of this issue include:

• Reliance on browser HTML error recovery during parsing, which can lead to subtle or undefined hydration behavior in SSR streaming paths (see https://nextjs.org/docs/messages/react-hydration-error).
• Emission of malformed or incomplete HTML during server-side streaming when document closing tags span multiple chunks.
• Missing </body> and/or </html> tags in the streamed response under specific chunking conditions that do not occur in fully buffered renders.