[mcollina]

WritableStreamDefaultControllerProcessClose clears the controller algorithms while the stream is still 'writable', before the sink close settles. A write in that window reaches the cleared size algorithm and fails the internal assertion in writableStreamDefaultControllerGetChunkSize, which crashes the process instead of rejecting the write:

const ws = new WritableStream({ close() { return new Promise(() => {}); } });
const writer = ws.getWriter();
writer.close();
setImmediate(() => writer.write('x'));
// Error [ERR_INTERNAL_ASSERTION]: This is caused by either a bug in Node.js ...

The same happens when writing to a TransformStream whose flush() is pending. This affects v26.5.1 as well as main.

#57280 handled the 'closed' case (#57272, whatwg/streams#1341). The spec still asserts that the state is not 'writable' there, so the close-in-flight window is a gap in the spec too. This also accepts that state, so the write continues to the closing check and is rejected with a TypeError, as it is once the stream has closed.

Tests are added to test-whatwg-writablestream-close.js for both cases; they fail with the assertion on main.

Refs: #57272
Refs: whatwg/streams#1341

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https://claude.ai/code/session_01Sfj4nCwaLmXB1NxA7sEJfi

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.65%. Comparing base (29bd740) to head (199d95b).
⚠️ Report is 214 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #67058      +/-   ##
==========================================
+ Coverage   90.47%   90.65%   +0.18%     
==========================================
  Files         791      797       +6     
  Lines      277245   278270    +1025     
  Branches    53310    53503     +193     
==========================================
+ Hits       250834   252277    +1443     
+ Misses      16811    16385     -426     
- Partials     9600     9608       +8     

Files with missing lines	Coverage Δ
lib/internal/webstreams/writablestream.js	99.52% <100.00%> (+<0.01%)	⬆️

... and 135 files with indirect coverage changes

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