An observable expansion of a user's active language repertoire through AI-assisted interaction, evidenced when a lexical or expressive item first encountered via the AI later appears in the user's own unaided production.
One occurrence is coded when a word or expression introduced by the AI subsequently appears in the user's independent, non-AI output; the later unaided use is the observable marker, distinguishing uptake from mere exposure.
Proposed measurement protocol (not yet empirically validated): Uptake count: the number of AI-introduced lexical or expressive items that recur in the user's subsequent unaided writing within a follow-up window, tracked by term matching against the interaction log.