[mcollina]

The pipeTo() pump re-enters from two places that are not promise reactions:

• the destination's ready hook (parkOnReady, stream: cut promise churn in webstreams hot paths #65138), which writableStreamUpdateBackpressure invokes synchronously from whatever code cleared the backpressure;
• the chunk steps of its read request, which run in the context of whoever enqueued the chunk.

So once the pipe resumes, the source's pull() and the writes it issues observe that context instead of the one of the pipeTo() call, which is what the promise-based pump (v24.20 and earlier, v26.9 and earlier) gave them:

const pending = [];
const rs = new ReadableStream({ pull(c) { console.log(als.getStore()); c.enqueue(1); } }, { highWaterMark: 0 });
const ws = new WritableStream({
  write() { return new Promise((resolve) => pending.push(resolve)); },
}, { highWaterMark: 1 });
als.run('piper', () => rs.pipeTo(ws));
// Resolving the writes from another context leaks it into pull():
// logs undefined (the creator's context) instead of 'piper' after the first chunk.

This captures the async context frame when the pipe starts and runs the pump in it when it is entered from another context. The frame check uses the intrinsics directly: the AsyncContextFrame wrappers put it behind one more inlining level and cost 3-4% on pipe-to.js highWaterMarkW=1.

The new test covers a sink whose writes resolve from another context, a push source under backpressure, pipeThrough() with pulls resolved from another context, and a chain into a slow sink. Expectations match v24.18.0 (with and without --no-async-context-frame) and v26.5.1; the first three cases fail on main. It checks only the pulls and writes the pump drives: the close()/flush() contexts come from the pipe's close watcher, which #67052 fixes separately, so this PR does not depend on it.

Benchmarks (pipe-to, pipe-through, lifecycle, adapters, tee; 20 runs) are within ±2% in both directions (pipe-through transform +2.2% *, pipe-to 4096/1024 -2.0% *** which measured -0.1% in the previous run of the same code).

The leak shipped with #65138 in v24.21.0 and v26.10.0, so this should be backported to both lines.

Refs: #66906
Refs: #65138
Refs: #67052

——

Ai generated, reviewed by me

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.67%. Comparing base (ee982db) to head (bf07616).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #67054      +/-   ##
==========================================
- Coverage   90.67%   90.67%   -0.01%     
==========================================
  Files         797      797              
  Lines      278791   278819      +28     
  Branches    53616    53619       +3     
==========================================
+ Hits       252807   252823      +16     
- Misses      16334    16344      +10     
- Partials     9650     9652       +2     

Files with missing lines	Coverage Δ
lib/internal/webstreams/readablestream.js	98.37% <100.00%> (+0.01%)	⬆️

... and 38 files with indirect coverage changes

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----------------------------------- PR info ------------------------------------
Title      stream: keep async context of the pipeTo pump (#67054)
Author     Matteo Collina <matteo.collina@gmail.com> (@mcollina)
Branch     mcollina:webstreams-pipeto-async-context -> nodejs:main
Labels     author ready, needs-ci, commit-queue, web streams
Commits    1
 - stream: keep async context of the pipeTo pump
Committers 1
 - Matteo Collina <hello@matteocollina.com>
PR-URL: https://github.com/nodejs/node/pull/67054
Refs: https://github.com/nodejs/node/issues/66906
Refs: https://github.com/nodejs/node/pull/65138
Refs: https://github.com/nodejs/node/pull/67052
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Paolo Insogna <paolo@cowtech.it>
------------------------------ Generated metadata ------------------------------
PR-URL: https://github.com/nodejs/node/pull/67054
Refs: https://github.com/nodejs/node/issues/66906
Refs: https://github.com/nodejs/node/pull/65138
Refs: https://github.com/nodejs/node/pull/67052
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Paolo Insogna <paolo@cowtech.it>
--------------------------------------------------------------------------------
   ℹ  This PR was created on Tue, 27 Oct 2026 12:25:59 GMT
   ✔  Approvals: 2
   ✔  - Antoine du Hamel (@aduh95) (TSC): https://github.com/nodejs/node/pull/67054#pullrequestreview-5671219316
   ✔  - Paolo Insogna (@ShogunPanda) (TSC): https://github.com/nodejs/node/pull/67054#pullrequestreview-5681138663
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