|any valid path to a .octsol solution file
This is the path to a solution file to be used for warm starting the engine.
If common coupling is if you e.g. produce a solution using
LOCAL_SEARCH, or simply a previous run, and seed it into the a new solve to see if the solver will now be able to find a better solution, or make proving global optimality easier since the solver starts with a good primal already known.