RuntimeTextInputFocus

Opaque identity of one committed editable-text focus interval.

The owning runtime retains only its current interval and replaces it when the logical owner or its accepting text-input targets change. Detachment and focus loss end the interval; later acquisition creates a distinct identity even for the same retained node. Tokens contain no node, session, callback, or native references and may be compared by identity on any thread. Runtime adapters read the current token only outside owner-thread frame, input, and lifecycle operations.