The trivial reference Fief.Vnode implementation (implementation.md §6.1): a cache-shaped vnode backed by one ETS table per vnode. It doubles as the behaviour's documentation example — and it is genuinely trivial:

• handoff_out → Fief.Vnode.report_drained/1 immediately. A cache holds nothing worth shipping; the transfer settles as soon as the planner sees the report.
• handoff_in → start empty. Whether the assignment is fresh, a planned transfer, or a donor-return, dropping cache entries is always safe — the durable source of truth is elsewhere by definition.

No key callbacks, no residual enumeration, no migration: incremental migration is opt-in via Fief.Transfer, not contract surface.

The ETS table is created in init/2, which runs in the agent process, so the agent owns it: it lives in the agent's link tree and dies with the agent — exactly what makes the fencing kill complete (implementation.md §2).

Message format (the impl-defined payload vocabulary):

• {:put, key, value} → replies :ok
• {:get, key} → replies {:ok, value} or :error
• {:delete, key} → replies :ok

This module is also the runtime half of the first-class Fief.Cache surface: Fief.Cache hashes keys to a vnode caller-side (Fief.Hasher) and calls straight through the router, so this impl never sees a raw key needing routing — only the already-targeted {:put, ...} / {:get, ...} / {:delete, ...} payload. Caller-side hashing is exactly why config_fingerprint/1 exists here: key→vnode agreement between every node is now contractual (a joiner computing a different vnode for the same key would silently split the keyspace), so the fingerprint gates the join on the hasher module agreeing everywhere, the same rationale as Fief.Key.VnodeImpl.