`process.finalization` removes extra refs during cleanup

[trivikr]

Version

main

Platform

macOS 26.5.0

Subsystem

process

What steps will reproduce the bug?

import process from 'node:process';
import { setImmediate } from 'node:timers/promises';

const kept = [];

function onFinalize(ref) {
  console.log(`finalized: ${ref.name}`);
}

function setup() {
  const first = { name: 'first' };
  let collected = { name: 'collected' };
  const third = { name: 'third' };

  kept.push(first, third);

  process.finalization.register(first, onFinalize);
  process.finalization.register(collected, onFinalize);
  process.finalization.register(third, onFinalize);

  collected = null;
}

setup();

// Give V8 a few chances to collect `collected` and run the
// FinalizationRegistry cleanup before process exit.
for (let i = 0; i < 10; i++) {
  gc();
  await setImmediate();
}

console.log('expected: finalized: first');
console.log('expected: finalized: third');

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

Always

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

expected: finalized: first
expected: finalized: third
finalized: first
finalized: third

Both first and third are strongly reachable through kept, so both should remain registered and run their finalization callbacks during process exit.

What do you see instead?

expected: finalized: first
expected: finalized: third
finalized: first

After collected is garbage-collected, cleanup removes its ref and also removes third because splice(1, 2) deletes two entries. As a result, third is still alive but its exit callback is skipped.

Additional information

Noticed while working on #64085

The docs for process.finalization.register(ref, callback) say that it "registers a callback to be called when the process emits the exit event if the ref object was not garbage collected."