The Boston Herald and most of its unions have struck a deal over the company’s contentious plan to dissolve labor contracts that had sparked an exchange of strike threats and dire warnings that the newspaper could be forced to close its doors for good, the Herald reported. The agreement filed yesterday in U.S. bankruptcy court in Delaware cools tensions as the Communication Workers of America’s News Guild of Greater Boston — representing newsroom and commercial employees — agreed to back off its opposition to the newspaper’s plan to reject their collective bargaining agreements. The union, in return, won stipulations that any bidder for the paper in the Feb. 13 auction would have to honor the accrued paid time off and years of seniority for employees — union and non-union — who are offered jobs by the bidder, and also commit to offering jobs to at least 175 of the Herald’s current employees.