DropToken

The exactly-once gate for Deinit hooks (ADR 0060). Implicit sharing duplicates values by retain, and a hook runs once per copy; a hook that must act exactly once per LOGICAL value carries a token and gates on is_last() — the copy that sees owner count 1 is the last one standing, wherever it drops. A fresh token is a fresh logical identity: clone-like operations construct a new one, compiler-made copies share it.