Permission Model bypass with fs.realpathSync

Summary

A flaw in Node.js Permission Model filesystem enforcement leaves fs.realpathSync() without the required read permission checks. This is an incomplete fix of CVE-2026-21715, which only covered fs.realpathSync.native().

As a result, code running under --permission with restricted --allow-fs-read can still use fs.realpathSync() to check file existence, resolve symlink targets, and enumerate filesystem paths outside of permitted directories.