A symlink anywhere under skills/ makes _safe_skills_path serve the skills
mount from a fresh mkdtemp copy per process, so hashing its host path into
hermes-environment made the label differ across processes: the persistent
container was never reused and every session started fresh, losing the
long-lived-container contract (installed packages, filesystem state).
Canonicalize tempdir-sourced mount specs to a stable placeholder that
keeps the container path; real mounts, image and HERMES_HOME still force
a fresh container on change.
Follow-up to #131895.
80aab939c8