[Ethan-Arrowood]

If the stream is destroyed right after sendHeaders(), nghttp3 still has the response headers queued. On the next write it asks for the removed stream's body, the read callback fails, and the whole session closes without notifying the peer.

In an HTTP/3 session, before clearing nghttp3's pointer to a stream when the stream is destroyed, shut down nghttp3's writes for that stream so that other requests can continue to complete.

This PR adds regression tests to cover the issue.

Discovered this while reviewing #66007, which adds stream.cancel(). That PR's cancel-after-headers case depends on this fix. Calling destroy() without a code still sends no reset, which is out of scope here (continue discussion in #66007).

_{AI-assisted (Claude Opus 5.5, my setup). The words are my own, per the Human Voice policy.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.68%. Comparing base (6728a1c) to head (d51bf3e).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #67446      +/-   ##
==========================================
- Coverage   90.68%   90.68%   -0.01%     
==========================================
  Files         801      801              
  Lines      281889   281889              
  Branches    54318    54319       +1     
==========================================
- Hits       255645   255641       -4     
- Misses      16358    16360       +2     
- Partials     9886     9888       +2     

see 20 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.