In acclaimed playwright Bekah Brunstetter’s “The Cake,” a baker, congenial and accommodating in just about every other respect, refuses to create a wedding cake for a same-sex couple. Sound familiar? The play was inspired in part by a run of similar rebuffs across the country, by vendors who felt that it would compromise their religious beliefs to help commemorate such a union. In most cases, the bakers and spouses-to-be are strangers. But what if they weren’t? What if the baker were the best friend of the bride’s mom, a lifelong friend, practically kin?