The Writers Guild of America West has reached a tentative deal with its staff union to end a lengthy strike, which became an unwanted distraction during negotiations with the major studios. “After nearly three months of strength, unity, and resolve, WGSU members were able to secure seniority provisions in layoffs and a no-strike clause that both parties agree protects concerted activity,” the Writers Guild Staff Union said in a statement. The WGSU went on strike on Feb. 17, accusing union management of failing to bargain in good faith. Popular on Variety The staff union — which represents about 110 WGA West employees — was seeking higher wages and “just cause” protections in the employee discipline process. Staffers picketed for weeks outside the union’s headquarters at Fairfax Avenue and 3rd Street.…