Co-construction

In linguistics, a co-construction is a grammatical or semantic entity which has been uttered by more than one speaker. It is a technical term for the notion of one person finishing another person's thought. For example:

In learning, co-construction is a distinctive approach, where the emphasis is on collaborative, or partnership working. Creative Partnerships refer to 'Co-construction of learning' as the partnership between teaching staff, pupils and creative professionals to develop and deliver creative learning in schools.

...
Wikipedia