offtopic question:
as a recent dabbling reader of introductory popsci content in cryptography, I've been wondering about what are the different segmentation of expert roles in the field?
e.g. in Filippo's blogpost about Age he clarified that he's not a cryptographer but rather a cryptography engineer, is that also what your role is, what are the concrete divisions of labor, and what other related but separate positions exists in the overall landscape?
where is the cutoff point of "don't roll your own crypto" in the different levels of expertise?
There isn't one, but the modal professional cryptography engineer probably has a graduate degree in cryptography.
My job title is in the Security Engineer family.
I do not have a Ph.D in Cryptography (not even an honorary one), so I do not call myself a Cryptographer. (Though I sometimes use "Cryptografur" in informal contexts for the sake of the pun.)
You did not ask me, but you should do your due diligence because there are way too many armchair cryptographers around here.
There's no clear segmentation. There's symmetric and asymmetric primitives (and stuff that doesn't fit into these like ZKP), algorithms, protocols, research in many different types of attacks against each of these, research in design and defenses, and plenty of people will cover completely different subsets.
"don't" roll your own cover everything from "don't design your own primitive" to "don't make your own encryption algorithm/mode" to "don't make your own encryption protocol", to "don't reimplement an existing version of any of the above and just use an encryption library"
(and it's mostly "don't deploy your own", if you want to experiment that's fine)