I forgot to add the .meta/design.md to a recent PR. The documentation says that this file is required for concept exercises (to prevent future feature creep), but configlet lint didn’t flag it as a problem.
I’m sure this is nobody’s most urgent priority, but would it be worth adding this check in a future release of configlet? Or is the file only sort-of-required?
IIRC, it is only sorta required (not every concept exercise on every track has them). That being said, they are really important for clarifying what is in and not in a given concept/concept exercise.
I’m for adding in a check in configlet when there’s time/energy. 
Fortunately, no rush - it could take a while to get to this state!
Incidentally, I realized since my original post that configlet create --concept-exercise does not create this file, nor .docs/hints.md.
I know a few people are working on a learning syllabus at the moment, so we all need to remember to add these manually if we think they’re a good idea. At least this only affects maintainers, not the vast majority of students.
I think the hints.md file was considered not required originally for concept exercises. The theory being that a concept exercise is very constrained, and should have everything a student needs to solve the problem written out in either the introduction.md or instructions.md file.
In practice, hints.md is useful for students working on an exercise, irrespective of it being a concept or practice one.
My personal rule is to try and add a hints.md file for any “complicated” exercise - practice or concept - and for any concept exercise that’s had repeated asks for help or clarification.
When I PR’d a concept exercise a few weeks ago, @BNAndras leaned on me pretty firmly to fill in the hints file. I guess experienced mentors understand the value of it.
I also think that the hints file is a pretty useful resource for students. At the very least I reiterate the things from the introduction.md, as some might have missed it.
Please create an issue in the configlet repo for this! I agree that the design.md document should be included.