vfs: RealFSProvider readFileSync(fd) fails after backing file is renamed

[trivikr]

Version

main

Platform

macOS 26.5.0

Subsystem

vfs

What steps will reproduce the bug?

import fs from 'node:fs';
import os from 'node:os';
import path from 'node:path';
import vfs from 'node:vfs';

const realRoot = fs.mkdtempSync(path.join(os.tmpdir(), 'vfs-real-root-'));
const mountPoint = fs.mkdtempSync(path.join(os.tmpdir(), 'vfs-mount-'));

const mounted = vfs
 .create(new vfs.RealFSProvider(realRoot), { emitExperimentalWarning: false })
 .mount(mountPoint);

try {
 fs.writeFileSync(path.join(realRoot, 'a.txt'), 'still readable');

 const fd = fs.openSync(path.join(mountPoint, 'a.txt'), 'r');
 fs.renameSync(path.join(realRoot, 'a.txt'), path.join(realRoot, 'b.txt'));

 try {
 console.log(fs.readFileSync(fd, 'utf8'));
 } finally {
 fs.closeSync(fd);
 }
} finally {
 mounted.unmount();
 fs.rmSync(realRoot, { recursive: true, force: true });
 fs.rmSync(mountPoint, { recursive: true, force: true });
}

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

Always

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

It should print still readable. An already-open fd should remain usable after the file is renamed, matching native filesystem behavior.

What do you see instead?

fs.readFileSync(fd, 'utf8') throws ENOENT after the backing file is renamed. This shows RealFSProvider is trying to read through the original path.

Additional information

No response

[trivikr]

Equivalent in fs

import fs from 'node:fs';
import os from 'node:os';
import path from 'node:path';

const dir = fs.mkdtempSync(path.join(os.tmpdir(), 'native-fd-'));

try {
 const oldPath = path.join(dir, 'a.txt');
 const newPath = path.join(dir, 'b.txt');

 fs.writeFileSync(oldPath, 'still readable');

 const fd = fs.openSync(oldPath, 'r');
 fs.renameSync(oldPath, newPath);

 try {
 console.log(fs.readFileSync(fd, 'utf8'));
 } finally {
 fs.closeSync(fd);
 }
} finally {
 fs.rmSync(dir, { recursive: true, force: true });
}

This outputs

still readable