The California Public Employees’ Retirement System, the largest public pension fund in the United States, rarely takes a stand as an amicus in trial court. But in an amicus brief filed earlier this month, Calpers warned that the future of private investment in California is at stake in a dispute over a few million dollars in unpaid bonuses to former employees of the now-defunct HRJ Capital. Unless a state-court judge overturns a colleague’s ruling that limited-partner investment funds are on the hook for liabilities of the general partner and fund manager, Calpers said, California risks losing its stature as an incubator of start-up business.