  We measure $C\!P$ asymmetries and branching-fraction ratios for $B^\pm \to
DK^\pm$ and $D\pi^\pm$ decays with $D\to K^0_{\rm S} K^\pm\pi^\mp$, where $D$
is a superposition of $D^0$ and $\bar{D}^0$. We use the full data set of the
Belle experiment, containing $772\times 10^6~B\bar{B}$ pairs, and data from the
Belle~II experiment, containing $387\times 10^6~B\bar{B}$ pairs, both collected
in electron-positron collisions at the $\Upsilon(4S)$ resonance. Our results
provide model-independent information on the unitarity triangle angle $\phi_3$.
