The union that represents on-air personalities at Boston’s WHDH-TV (Channel 7) has reached an agreement with the station after 2 1/2 years of contentious negotiations. The union and station management were fighting over salary provisions for anchors and reporters, and the sensitive issue of age discrimination. That lead to broken off contract negotiations last summer. The new contract, which will run through 2014, will phase out the on-air appearances that anchors and reporters receive over a three-year period in exchange for an annual salary rate increase. On-air talent salaries are based on a combination of a base salary and those on-air fees which can account to 25 to 50 percent of their overall pay.