/cc @mcollina

With The Virtual File System PR getting close to landing, there are a number of areas / issues to follow-up on. Flagging here in a new issue to prevent overloading the PR discussion.

Code Review: PR #61478 — Virtual File System for Node.js

1. Security & Permission Model
2. API Compatibility Gaps
3. Correctness Bugs
4. Windows Path Handling
5. Performance Concerns
6. Architecture & Design
7. Test Runner Mock Integration
8. Provider-Specific Issues
9. Test Coverage Gaps
10. Code Quality & Cleanup

1. Security & Permission Model

We need to decide if VFS should participate in the permissions model and how.

1.1 VFS interception bypasses the Node.js permission model — CRITICAL

Disposition: follow-up

In lib/fs.js, VFS interception happens before the permission model check in every intercepted function. Pattern (repeated 96+ times):

function readFileSync(path, options) {
  const h = vfsState.handlers;
  if (h !== null) {
    const result = h.readFileSync(path, options);
    if (result !== undefined) return result;  // ← returns BEFORE permission check
  }
  // permission check is down here
  if (permission.isEnabled() && !permission.has('fs.read', path)) { ... }
}

When --experimental-permission is active, a VFS mount can serve content for any path without triggering the permission gate. This is the most significant security issue in the PR.

Recommendation: At minimum, when permission.isEnabled(), the VFS handler path should still check permission.has('fs.read', ...) / permission.has('fs.write', ...) as appropriate. Alternatively, disable VFS mounting entirely when the permissi