content-directory-override / shader options don't work on subfolders

Example:

I have a DOS games launched with the dosbox core and also windows 3.1 games that are launched with the dosbox core. I want to use different shader presets for dos games and windows 3.1 games. Both platforms have their games stored in individual folders.

The folder structure is as follows:

MS DOS
-- game folder 1
-- game folder 2
-- ...

Windows 3.1
-- game folder 1
-- game folder 2
-- ...

So since both platforms use the same core, I cannot use the save shaders for the whole core option. But I cannot use the "content directory" option either, because that does not work for subfolders.

What I'd like to see is an option in RetroArch that allows me to apply teh "content directory" option for all the subfolders of the content directory folder as well.

Is this possible?

Thx!

No files, tests, or entry points are named in the issue. Start by locating RetroArch's content-directory and shader-option handling, then trace how paths are matched when content is inside nested folders. Done means content-directory shader settings apply consistently to the requested subfolders without changing core-wide behavior.