Feature summary (what you would like to be able to do and where):
On Commons, Template:Search inside category is a neat template that can be manually added to category pages to add a search box where users (even unexperienced ones) can search the category contents. including all its often many subcategories. The problem is that there doesn't seem to be any way to make it use the MediaSearch – it only uses the old outdated SpecialSearch. Please enable using it with MediaSearch by making the InputBox extension compatible with MediaSearch (this probably needs a parameter for whether or not MediaSearch is to be used and some parameter(s) for the tab that should be opened which is "Images" by default).
Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):
Searching categories to see a wall of images (see also this) conveniently from category pages (+ enabling users who don't know about advanced features like the deepcategory search operator to search categories trees like that). More details here (the other issue is T376440, the namespaces thing is fixed).
Benefits (why should this be implemented?):
See above