Rhode Island's Supreme Court has dealt a legal setback to Providence in disputes with retired city workers that could prove costly. The city violated the U.S. and state constitutions in 2012 when it suspended cost-of-living adjustments on retiree pensions for an indefinite amount of time, the court ruled Tuesday. The high court handed down three decisions in cases brought by employees and unions over how the city sought to fix its finances. The court overturned all or part of lower court decisions that found in favor of the city and dismissed the lawsuits. The biggest decision found that if the pension plan for city employees and retirees is changed by the courts, it can’t be changed again by the City Council, unless the workers agree. That means the city’s 2012 pension reform does not apply to several dozen retired firefighters and police officers.