http2: invoke pending write callback on stream destroy

[mcollina]

Summary

• Track the pending write callback on Http2Stream via kPendingWriteCb and invoke it in _destroy() before calling handle.destroy(), ensuring the Writable stream can clean up properly when a stream is destroyed mid-write
• Make the write callback idempotent so duplicate invocations from the C++ side are harmless no-ops

When an HTTP/2 stream is destroyed while a write is in progress, the pending write callback may never be called if the write data has already been consumed by nghttp2 and moved to the session's outgoing_buffers_. This leaves the Writable stream's kWriting flag set permanently, preventing errorBuffer from cleaning up remaining buffered writes and keeping references alive that block event loop exit.

Fixes: #58252
Refs: #58253

Test plan

• test-http2-close-while-writing passes consistently
• Stress tested with 500 repetitions — zero failures
• Full HTTP/2 test suite (test-http2-*) passes with no regressions

[nodejs-github-bot]

Review requested:

• @nodejs/http2
• @nodejs/net

[lpinca]

Is it possible to add a dedicated test? This allows us to clean up test-http2-close-while-writing.

[lpinca]

It does not fix the issue:

$ python3 tools/test.py --repeat=10000 parallel/test-http2-close-while-writing
=== release test-http2-close-while-writing === Path: parallel/test-http2-close-while-writing
Command: out/Release/node /Users/luigi/code/node/test/parallel/test-http2-close-while-writing.js
--- TIMEOUT ---
=== release test-http2-close-while-writing === Path: parallel/test-http2-close-while-writing
Command: out/Release/node /Users/luigi/code/node/test/parallel/test-http2-close-while-writing.js
--- TIMEOUT ---
=== release test-http2-close-while-writing === Path: parallel/test-http2-close-while-writing
Command: out/Release/node /Users/luigi/code/node/test/parallel/test-http2-close-while-writing.js
--- TIMEOUT ---
=== release test-http2-close-while-writing === Path: parallel/test-http2-close-while-writing
Command: out/Release/node /Users/luigi/code/node/test/parallel/test-http2-close-while-writing.js
--- TIMEOUT ---
=== release test-http2-close-while-writing === Path: parallel/test-http2-close-while-writing
Command: out/Release/node /Users/luigi/code/node/test/parallel/test-http2-close-while-writing.js
--- TIMEOUT ---
[05:03|% 100|+ 9995|- 5]: Done Failed tests:
out/Release/node /Users/luigi/code/node/test/parallel/test-http2-close-while-writing.js
out/Release/node /Users/luigi/code/node/test/parallel/test-http2-close-while-writing.js
out/Release/node /Users/luigi/code/node/test/parallel/test-http2-close-while-writing.js
out/Release/node /Users/luigi/code/node/test/parallel/test-http2-close-while-writing.js
out/Release/node /Users/luigi/code/node/test/parallel/test-http2-close-while-writing.js

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.72%. Comparing base (ae2ffce) to head (c16f526).
⚠️ Report is 406 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #61821 +/- ##
==========================================
- Coverage 89.75% 89.72% -0.03% 
==========================================
Files 674 675 +1 Lines 204416 204807 +391 Branches 39285 39351 +66 ==========================================
+ Hits 183472 183766 +294 - Misses 13227 13331 +104 + Partials 7717 7710 -7 

Files with missing lines	Coverage Δ
lib/internal/http2/core.js	95.20% <100.00%> (-0.03%)	⬇️

... and 73 files with indirect coverage changes

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[amyssnippet]

i think this partially addresses the issue, but there are a few tests which are still flaking as @lpinca mentioned.
i suspect the done() barrier in lib/internal/http2/core.js is the remaining culprit. Even with pendingWriteCb being invoked, done() still gates on both waitingForWriteCallback and waitingForEndCheck like

if(!waitingForWriteCallback&&!waitingForEndCheck){constcallback=cb;cb=nop;callback(err);}