  We consider an optomechanical quantum system composed of a single cavity mode
interacting with N mechanical resonators. We propose a scheme for generating
continuous-variable graph states of arbitrary size and shape, including the
so-called cluster states for universal quantum computation. The main feature of
this scheme is that, differently from previous approaches, the graph states are
hosted in the mechanical degrees of freedom rather than in the radiative ones.
Specifically, via a 2N-tone laser drive, we engineer a linear Hamiltonian which
is instrumental to dissipatively drive the system to the desired target state.
The robustness of this scheme is assessed against finite interaction times and
mechanical noise, confirming it as a valuable approach towards quantum state
engineering for continuous-variable computation in a solid-state platform.
