  Inspired by a Chern-Simons description of 2+1D gravity coupled to point
particles we propose a new Lagrangian of a multiparticle system living in
$\kappa$-Minkowski/$\kappa$-Poincar\'e spacetime. We derive the dynamics of
interacting particles with $\kappa$-momentum space, alternative to the one
proposed in the "principle of relative locality" literature. The model that we
obtain takes into account of the nonlocal topological interactions between the
particles, so that the effective multi-particle action is not a sum of their
free actions. In this construction the locality of particle processes is
naturally implemented, even for distant observers. In particular a particle
process is characterized by a local deformed energy-momentum conservation law.
The spacetime transformations are generated by total charges/generators for the
composite particle system, and leave unaffected the locality of individual
particle processes.
