Loader stalls MessagePort since v24

Version

v24.15.0

Platform

Linux lab178 6.18.19-1.qubes.fc37.x86_64 #1 SMP PREEMPT_DYNAMIC Tue Mar 24 01:20:46 GMT 2026 x86_64 GNU/Linux

Subsystem

module

What steps will reproduce the bug?

In an async resolve hook of a custom loader, await a message from a MessagePort. The message never arrives and the promise never resolves.

This repository has a reproduction. It does a simple pong exchange with the main thread. On v23 and before it works. On v24 and later it hangs forever.

https://github.com/cinderflash/loader-stall

$ nvm use v23
Now using node v23.11.1 (npm v10.9.2)
$ node index.mjs
ping
PONG
ping
PONG
ping
PONG
$ nvm use v24
Now using node v24.15.0 (npm v11.12.1)
$ node index.mjs
(STALL FOREVER)
$ nvm use v25
Now using node v25.9.0 (npm v11.12.1)
$ node index.mjs
(STALL FOREVER)

How often does it reproduce? Is there a required condition?

On v24 and v25, 100% of the time.

On prior versions, this never happens.

What is the expected behavior? Why is that the expected behavior?

Ability to perform exchanges with the main thread within a loader hook.

I'd like to use this to acquire information available on the main thread to use in determining how to resolve the specifier.

What do you see instead?

Awaiting a message in a loader hook stalls forever. The message never arrives and the engine never detects an unresolved promise.

Additional information

No response

Start by running the linked loader-stall reproduction, index.mjs, on Node.js v23 and v24 to confirm the regression. Investigate the module loader's async resolve hook and its MessagePort exchange behavior, then add a regression test showing that the message arrives and the promise resolves on current versions.