State and federal lawmakers, with the support of unions, are looking to survivor registries created after 9/11 as a model for helping potentially millions of people with often-debilitating long-term symptoms of Covid-19. The efforts would center on creating data troves that so-called “long-haulers” could access to make informed decisions about their care, allow medical providers to study the coronavirus’ still-mysterious long-term effects on the body, and help them qualify for state or federal benefits.