fix(h2): keep the connection ref'd while requests are outstanding

[mcollina]

resumeH2() unreffed the socket and the session whenever the peer advertised SETTINGS_MAX_CONCURRENT_STREAMS = 0, regardless of whether anything was still queued:

if (client[kSize] === 0 || client[kMaxConcurrentStreams] === 0) {
  socket.unref()
  client[kHTTP2Session].unref()
}

A peer may legitimately advertise 0 to refuse new streams for a while (RFC 9113 §6.5.2) — graceful drain, overload shedding, a load balancer draining a backend. A request queued behind that owns no handle and arms no timer of its own, so once the connection was unreffed there was nothing left holding the event loop open.

The result is a process that exits with status 0 while an awaited request never settles:

warm-up request OK; server now advertises maxConcurrentStreams: 0
issuing the second request … (this await never returns)
>>> process exiting with code 0 — reached line: warm-up done

No error, no warning, no non-zero exit code — the code after the await simply never runs. For a job or a CLI that means silently skipped work reported as success.

Unref only when there is genuinely nothing outstanding.

Test

test/http2-max-concurrent-streams-zero-unref.js drives a child process whose only live work is the queued request, against a server that drains to maxConcurrentStreams: 0. Staying alive is the pass condition; exiting 0 is the bug. Verified to fail before this change (the process exited cleanly with a request still outstanding) and pass after.

test/+(http2|h2)*.js: 51 pass. Full unit suite: 1304 pass, 0 fail.

Note

This makes the failure visible rather than silent — the request itself is still stuck until a stream timeout fires. #5604 (fix(h2): honour headersTimeout) is what bounds that wait properly; the two are independent but complementary.

🤖 Generated with Claude Code

https://claude.ai/code/session_01A49JamgF2TkZHu5h58ChUM

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.15%. Comparing base (8d347dd) to head (c56333a).

Additional details and impacted files

@@            Coverage Diff             @@
##             v7.x    #5605      +/-   ##
==========================================
- Coverage   93.17%   93.15%   -0.02%     
==========================================
  Files         112      112              
  Lines       36751    36755       +4     
==========================================
- Hits        34241    34240       -1     
- Misses       2510     2515       +5     

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