After struggling for six years, legislators, labor advocates and municipal leaders will announce a long-awaited compromise Monday on post-traumatic stress disorder benefits for police and firefighters. Though they declined to provide details of the agreement, Sen. Cathy Osten, D-Sprague — who’s spearheaded the push to expand coverage for first responders — and Connecticut Conference of Municipalities Executive Director Joe DeLong, both predicted Friday it would draw bipartisan support. Connecticut has been struggling with its workers’ compensation system since the December 2012 shooting deaths of 26 children and staff at Sandy Hook Elementary School demonstrated significant shortcomings in the system’s ability to address the emotional strains placed on emergency personnel.