Nice, just a bit of nitpicking then this is good!

I also do agree that this should be a generic endpoint. I do understand that you don't want to introduce more logic, even though I fear that it won't happen if you don't do it now (that might just be a good thing if we don't ever have a need for it though 🤷)

I did think about this a bit as well and came up with a method to do this both generic and fix the "stable" randomness that we need.

I figured that we can generate a hash on the client, f.ex. using their username and the current day/hour/week (however long we want to keep the current values), and send this hash to the endpoint. We can then create a random list if ids, and store it in redis with this hash as a key. Then, we can just fetch the existing list of ids from redis the next time around, and fetch those objects

Not sure if this is needed, but if you do want to this more generic and also simplify the client code, this might be an option.

LGTM