fix: retry refused HTTP/2 streams

[mcollina]

This relates to...

HTTP/2 peers can reject an unprocessed stream with RST_STREAM(REFUSED_STREAM). Node.js surfaces this as the generic ERR_HTTP2_STREAM_ERROR, and Undici previously failed the request without considering the retry-safe HTTP/2 reset code.

Rationale

RFC 9113 section 8.7 permits clients to retry a request rejected with REFUSED_STREAM, including non-idempotent requests, because the peer asserts that no application processing occurred. It also says clients should not automatically retry the same request more than once.

Changes

Features

N/A

Bug Fixes

• Detect NGHTTP2_REFUSED_STREAM using stream.rstCode before response headers are exposed.
• Retry the request once on the existing HTTP/2 session.
• Restrict transparent retries to replayable bodies: no body, Buffer, or Blob.
• Preserve the numeric reset code as error.http2ErrorCode when an error is ultimately exposed.
• Add regression coverage for concurrent streams, buffered POST bodies, the one-retry limit, streaming bodies, and other reset codes.

Breaking Changes and Deprecations

None.

Status

• I have read and agreed to the Developer's Certificate of Origin
• Tested
• Benchmarked (optional)
• Documented
• Review ready
• In review
• Merge ready

Validation:

• npm run test:h2:core — 96 passed
• npm run test:h2:fetch — 11 passed
• npx eslint lib/dispatcher/client-h2.js test/http2-refused-stream.js
• Commit hook npm run lint

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.49%. Comparing base (21a8e1e) to head (b87e26f).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5598      +/-   ##
==========================================
+ Coverage   93.47%   93.49%   +0.01%     
==========================================
  Files         110      110              
  Lines       38238    38327      +89     
==========================================
+ Hits        35744    35833      +89     
  Misses       2494     2494              

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