A few days after accepting the offer, I realized that I don't have an official offer letter, just an email.
I assume that the process is pro forma, but I have to apply to the school and they writing up the offer letter now. I just finished submitting an online application to the school together with a Statement of Interest, an official transcript, and a set of recommendations. I also had to list my GRE scores and college courses in various required categories: I have 20 semesters in an area where they require 2 semesters, but only 1 semester in an area where they require 3. That would kind-of be funny if I had to take summer school in order to qualify for a postdoc.
My statement of purpose was one sentence: "I enjoyed my visit to the research center, and look forward to joining all of you in the fall." This short statement of purpose was not just out of chutzpah and protest at the procedure, but when I sat in front of my computer to type something, anything, relevant, I was wrung out and burnt out. Producing another cover letter feels harder than running a marathon.
Nonetheless, until I have the letter in hand, I suppose I shouldn't withdraw myself from anything. And so it drags out.
Update: I asked, and it turns out that it's pro forma and it's just what the school does for their paperwork. Whew.
It is a topic for a different post how administratively (e.g., health plan) some postdocs are treated as students and others are treated like employees.