Two hours at the CAF desk and one very kind woman
Bring three copies of everything. Bring a book. Bring the lease. And thank the person who is not the system, even when the system is slow.
I queued for two hours at the CAF desk with a folder that I was sure was complete, and then it was not complete, and then a woman behind the counter looked at my face and decided to be the kind of civil servant you remember.
She told me which photocopy was actually missing — not the one the website listed, the other one — and she wrote the name of the form on a sticky note so I would not have to translate it later on the tram. I went to the copy shop downstairs, came back, and she called me forward as if we had an appointment.
The paperwork in France is rarely personal. The people sometimes are. That is the part nobody puts on the form.
If you are heading in: print more than you think you need, arrive when they open, and say bonjour first. The rest is waiting, and then one small administrative victory.