Low-income Coloradans with mental illnesses are poised to receive longer hospital stays after state legislators set aside money to expand a decades-old Medicaid rule. Federal law requires that Medicaid patients hospitalized in psychiatric facilities be discharged after 15 hospital days in a month or the facility doesn’t get paid. The rule was intended to prevent hospitals from warehousing patients, but advocates and psychiatrists say that it instead pushes hundreds of vulnerable Coloradans out of the facilities prematurely and into a cycle of homelessness, incarceration and emergency room visits. That may finally change.