CVE-2026-77763: Improper Limitation of a Pathname to a Restricted Directory

The filestore backend in pkg/object/file.go, used for file:// stores and as a common juicefs sync destination, derived every operation's target from pathkey, which returned either filepath.Joind.root, key or filepath.Cleand.root + key with no check that the result stayed beneath the root. Put, Ge...