Is your feature request related to a problem? Please describe.
Right now there's no way to tell if an item is in the reagent bag or not.

Describe the solution you'd like
Add an option for the 4 icon corners for a "in reagent bag" indicator. The reagent bag slots already have the leaf icon, those could be used in the corners.

Describe alternatives you've considered
A different icon border. Separation of regular bag and reagent bag.

Additional context
I use category, not single bag. Not sure if this is also an issue in single bag or not.

Is there a problem that you're trying to solve with this extra bit of information? I think one of the goals of category view is that you don't need to worry as much about which items are in which bags.

If my reagent bag fills up either in my regular inventory or bank it would be handy to have an indicator which items are actually in the reagent bag and not. Since they take up different types of slots I'd like an optional indicator what type of slot they're in. Category view in general removes the need to know what's in what bag, but since the reagent bag stores a very specific thing compared to every other bag it would be nice to know at a glance if an item is in it or not. I'm coming from Adibags, and that addon had a very similar category view, but indicated which items were in my reagent bag in a similar way to the corner indicators of Baganator.

So is it about identifying items that aren't in a reagent bag, but should be, because the reagent bag is full? Maybe to help you know you need to put stuff in the bank?

That's the main use case, yes