The senior housing sector in Massachusetts has become a hot target for real estate developers as millions of baby boomers reach retirement age, but it faces a critical issue: not enough staffers to meet the soaring demand for new facilities. As the demand for senior housing continues to grow, the need for capable workers is also rising. However, construction has slowed, with 16,423 senior housing units under construction, the smallest pipeline since 2012. Nonprofit senior housing operator Hebrew SeniorLife has had to place 35 employees who are TPS holders on administrative leave, WGBH reported. Bay Cove Human Services, which supports 25,000 people across Massachusetts, laid off nine workers, including nursing assistants and a medications specialist, WGBH reported.