Gate r2 (reuse Low): the long-request test rebuilt the fixture by
overwriting the request and appending groups 10..39, which
_oversized_active_turn(request, groups) already does. The
"user text after the last summary boundary" join was copied at three
sites; fold it into a test-local _actionable_user_text(). Behaviour is
unchanged: the long-request test is still red with 97183e2be1's
production change reverted (cut 2 > 3 fails) and green on HEAD.
81e1ce7867