Type Alias TuiEpoch 

pub type TuiEpoch = u64;

Which registration of a tui_id an entry is.

A reconnecting client re-registers its OWN id, so the id alone cannot distinguish the live registration from one that has been superseded. A connection whose teardown is still draining can therefore run AFTER its successor has been adopted, and a key-only removal would evict the live entry — taking the connected TUI’s captured environment with it. This is the fact that makes the two distinguishable: a teardown quotes the epoch it registered under, so it can only ever remove its own registration.