* Core: typing: return type of `fill_slot_data` to `Mapping`
type checker be like:
"Wait a minute! If you give this mutable dict to those sussy sketchbags, they might mutate it and invalidate your more specific typing!"
Note that this doesn't mean the return value needs to be immutable. It just means the caller won't mutate it (which matches current `Main.py` implementation).
I've seen some talk of introducing ownership to the type system.
https://discuss.python.org/t/we-may-need-better-specification-for-existing-and-future-refinement-types-in-the-type-system/43955/5
Then maybe I could say: "Do whatever you want with it, because I'm giving up ownership."
But that doesn't exist in the type system currently.
* in docs too
* docs talk less about type and more about json
* keep `dict` to be safe with .net client and json
5e06a75bf2