We present a measurement of the Cabibbo-Kobayashi-Maskawa unitarity triangle angle phi(3) (also known as gamma) using a model-independent Dalitz plot analysis of B+ -> D(K(S)(0)h(+)h(-))h(+), where D is either a D-0 or (D) over bar (0) meson and h is either a pi or K. This is the first measurement that simultaneously uses Belle and Belle II data, combining samples corresponding to integrated luminosities of 711 fb(-1) and 128 fb(-1), respectively. All data were accumulated from energy-asymmetric e(+)e(-) collisions at a centre-of-mass energy corresponding to the mass of the Upsilon(4S) resonance. We measure phi(3) = (78.4 +/- 11.4 +/- 0.5 +/- 1.0)degrees, where the first uncertainty is statistical, the second is the experimental systematic uncertainty and the third is from the uncertainties on external measurements of the D-decay strong-phase parameters.
